Current stabilizer on a transistor. Current stabilizers circuits

Current stabilizer circuits for LEDs on transistors and microcircuits

It is known that the brightness of an LED depends very much on the current flowing through it. At the same time, the LED current depends very sharply on the supply voltage. This results in noticeable brightness ripples even with slight power instability.

But ripple is not scary, what’s much worse is that the slightest increase in the supply voltage can lead to such a strong increase in the current through the LEDs that they simply burn out.

To prevent this, LEDs (especially powerful ones) are usually powered through special circuits - drivers, which are essentially current stabilizers. This article will discuss circuits of simple current stabilizers for LEDs (on transistors or common microcircuits).

To stabilize the current through LEDs, you can use well-known solutions:

Figure 1 shows a diagram whose operation is based on the so-called. emitter follower. A transistor connected in this way tends to maintain the voltage at the emitter exactly the same as at the base (the only difference will be the voltage drop across the base-emitter junction). Thus, by fixing the base voltage using a zener diode, we obtain a fixed voltage on R1.

Conventional diodes have a very weak dependence of forward voltage on current, so they can be used instead of hard-to-find low-voltage zener diodes. Here are two variants of circuits for transistors of different conductivities, in which the zener diodes are replaced by two conventional diodes VD1, VD2:

The current through the LEDs is set by selecting resistor R2. Resistor R1 is selected in such a way as to reach the linear section of the I-V characteristic of the diodes (taking into account the base current of the transistor). The supply voltage of the entire circuit must be no less than the total voltage of all LEDs plus about 2-2.5 volts on top for stable operation of the transistor.

For example, if you need to get a current of 30 mA through 3 LEDs connected in series with a forward voltage of 3.1 V, then the circuit should be powered with a voltage of at least 12 Volts. In this case, the resistor resistance should be about 20 Ohms, the dissipation power should be 18 mW. The transistor should be selected with a maximum voltage Uke not lower than the supply voltage, for example, the common S9014 (n-p-n).

Resistance R1 will depend on the coefficient. gain of the transistor hfe and the current-voltage characteristics of the diodes. For S9014 and 1N4148 diodes, 10 kOhm will be enough.

Let's use the described stabilizer to improve one of the LED lamps described in this article. The improved diagram would look like this:

This modification can significantly reduce current ripple and, consequently, the brightness of the LEDs. But the main advantage of the circuit is to normalize the operating mode of the LEDs and protect them from voltage surges during switching on. This leads to a significant extension of the life of the LED lamp.

From the oscillograms it can be seen that by adding a current stabilizer for the LED on a transistor and a zener diode to the circuit, we immediately reduced the ripple amplitude several times:

With the ratings indicated in the diagram, the power dissipated by the transistor is slightly more than 0.5 W, which makes it possible to do without a radiator. If the capacitance of the ballast capacitor is increased to 1.2 μF, then the transistor will drop ~23 Volts, and the power will be about 1 W. In this case, you cannot do without a radiator, but the pulsations will drop almost to zero.

Instead of the 2CS4544 transistor indicated in the diagram, you can take 2SC2482 or a similar one with a collector current of more than 100 mA and a permissible voltage Uke of at least 300 V (for example, the old Soviet KT940, KT969 are suitable).

The desired current, as usual, is set by resistor R*. The zener diode is designed for a voltage of 5.1 V and a power of 0.5 W. Common SMD LEDs from Chinese light bulbs are used as LEDs (or better yet, take a ready-made lamp and add the missing components to it).

Now consider the diagram presented in Figure 2. Here it is separately:

The current sensor here is a resistor, the resistance of which is calculated using the formula 0.6/Iload. As the current through the LEDs increases, transistor VT2 begins to open more strongly, which leads to stronger blocking of transistor VT1. The current decreases. This way the output current is stabilized.

The advantage of the scheme is its simplicity. The disadvantage is a fairly large voltage drop (and therefore power) across transistor VT1. This is not critical at low currents (tens and hundreds of milliamps), however, a further increase in the current through the LEDs will require installing this transistor on a radiator.

You can get rid of this drawback by using a p-channel MOSFET with low drain-source resistance instead of a bipolar transistor:

The required current, as before, is set by selecting resistor R1. VT1 - any low-power. Instead of the powerful IRL3705N, you can take, for example, IRF7210 (12A, 12V) or IRLML6402 (3.7A, 20V). See for yourself what currents you need.

The simplest current stabilizer circuit for LEDs on a field-effect transistor consists of just one transistor with a short-circuited gate and source:

Instead of KP303E, for example, BF245C or a similar one with a built-in channel is suitable. The principle of operation is similar to the diagram in Figure 1, only the ground potential is used as the reference voltage. The magnitude of the output current is determined solely by the initial drain current (taken from the datasheet) and is practically independent of the drain-to-source voltage Usi. This can be clearly seen from the output characteristic graph:

In the diagram in Figure 3, a resistor R1 is added to the source circuit, which sets some reverse gate bias and thus allows you to change the drain current (and therefore the load current).

An example of the simplest current driver for an LED is presented below:

A field-effect transistor with an insulated gate and a built-in n-type channel BSS229 is used here. The exact value of the output current will depend on the characteristics of the particular instance and the resistance R1.

These are, in general, all the ways to turn a transistor into a current stabilizer. There is also a so-called current mirror, but it is not suitable for LED lamps. So let's move on to microcircuits.

Current stabilizers on microcircuits

Microcircuits allow you to achieve much higher performance than transistors. Most often, to assemble a do-it-yourself current stabilizer for LEDs, they use precision thermally stable reference voltage sources (TL431, LM317 and others).

TL431

A typical current stabilizer circuit for LEDs on the TL431 looks like this:

Since the chip behaves in such a way as to maintain a fixed voltage across resistor R2 of 2.5 V, the current through this resistor will always be equal to 2.5 / R2. And if we neglect the base current, then we can assume that IRн = IR2. And the higher the gain of the transistor hfe is, the more these currents will coincide.

R1 is calculated in such a way as to ensure the minimum operating current of the microcircuit - 1 mA.

And here is an example of the practical application of TL431 in an LED lamp:

The transistor drops about 20-30 V, the power dissipation is less than 1.5 W. In addition to the 2SC4544 indicated in the diagram, you can use the BD711 or the old Soviet KT940A. Transistors in the TO-220 package do not require installation on a radiator up to powers of 1.5-2 W inclusive.

Resistor R3 serves to limit the charging pulse of the capacitor when the power is turned on. The current through the load is set by resistor R2.

The load Rn here is 90 white chip LEDs LED2835. The maximum power at a current of 60 mA is 0.2 W (24Lm), the voltage drop is 3.2 V.

To increase the service life, the power of the diodes is specially reduced by 20% (0.16 W, current 45 mA), respectively, the total power of all LEDs is 14 W.

Of course, the above current stabilizer circuit for 220 V LEDs can be calculated for any required current and/or other number of available LEDs.

Taking into account the permissible voltage spread of 220 Volts (see GOST 29322-2014), the rectified voltage on capacitor C1 will be in the range from 293 to 358 V, so it must be designed for a voltage of at least 400 V.

Based on the range of supply voltages, the parameters of the remaining elements of the circuit are calculated.

For example, the resistor that sets the operating mode of the DA1 chip must provide a current of at least 0.5 mA at a voltage at C1 = 293 V. The maximum number of LEDs should not exceed NLED< (358 - 6) / 3.2, причем, чем их больше, тем выше яркость светильника и тем меньшая мощность будет уходить в никуда (рассеиваться в виде тепла на транзисторе VT1). Максимальное напряжение Uкэ транзистора VT1 должно быть не ниже 358 - (ULED * NLED).

LM7805, LM7812...

Any integrated voltage stabilizer can be turned into a current stabilizer by adding just one resistor in accordance with the diagram:

You just need to take into account that, with this connection, the input voltage must be greater than the stabilization voltage of the microcircuit by a certain amount (voltage drop on the stabilizer itself). Usually it's somewhere around 2-2.5 volts. Well, of course, add voltage to the load.

Here, for example, is a specific example of a current stabilizer for LEDs based on LM7812:

The circuit parameters are designed for 10 5730 SMD diodes with a forward voltage of 3.3 volts on each. Current consumption (current through LEDs) - 300 mA. Lamp power ~10 Watt.

Since when LEDs are connected in series, the total voltage will be equal to the sum of the voltages on each of the LEDs, the minimum supply voltage of the circuit should be: Upit = 2.5 + 12 + (3.3 x 10) = 47.5 Volts.

You can calculate the resistance and power of the resistor for other current values ​​using the simple Regulator Design program (download).

Obviously, the higher the output voltage of the stabilizer, the more heat will be generated at the current-setting resistor and, therefore, the worse the efficiency. Therefore, for our purposes, the LM7805 is better than the LM7812.

LM317

The linear current stabilizer for LEDs based on LM317 is no less effective. Typical connection diagram:

The simplest LM317 connection circuit for LEDs, which allows you to assemble a powerful lamp, consists of a rectifier with a capacitive filter, a current stabilizer and 93 SMD 5630 LEDs. MXL8-PW35-0000 (3500K, 31 Lm, 100 mA, 3.1 V, 400 mW, 5.3 x3 mm).

If such a large garland of LEDs is not needed, then you will have to add a ballast resistor or capacitor to the LM317 driver to power the LEDs (to suppress excess voltage). We discussed how to do this in great detail in this article.

The disadvantage of such a current driver circuit for LEDs is that when the voltage in the network increases above 235 volts, the LM317 will be outside the design operating mode, and when it drops to ~208 volts and below, the microcircuit completely ceases to stabilize and the ripple depth will entirely depend from container C1.

Therefore, such a lamp should be used where the voltage is more or less stable. And you should not skimp on the capacity of this capacitor. The diode bridge can be taken ready-made (for example, a miniature MB6S) or assembled from suitable diodes (Uarb at least 400 V, direct current >= 100 mA).

Instead of a conclusion

The disadvantages of the circuits presented in the article include low efficiency due to the waste of power on the control elements. However, this is typical of all linear current stabilizers.

Low efficiency is unacceptable for devices powered by autonomous current sources (lamps, flashlights, etc.). A significant increase in efficiency (90% or more) can be achieved by using pulsed current stabilizers.

electro-shema.ru

When the first power supply is assembled, the simplest circuit is taken - so that everything works out for sure. When you manage to start it up and get as much as 12 adjustable volts and a current of under half an ampere, the radio amateur is imbued with the meaning of the phrase “And you will be happy!” But this happiness does not last very long and soon it becomes completely obvious that the power supply must have the ability to regulate the output current. By modifying an existing power supply, this is achievable, but it is somewhat troublesome - it would be better to assemble another, more “advanced” one. There is an interesting option. For a low-power power supply, you can make an attachment to adjust the current in the range from 20 mA to the maximum that it can provide, according to this scheme:

I assembled such a device almost a year ago.

A current stabilizer is a really necessary thing. For example, it will help to charge any battery designed for voltage up to 9 volts inclusive, and I note, charge it efficiently. But it clearly lacks a measuring head. I decide to modernize and disassemble my homemade product into its component parts, where, perhaps, the most significant component is a variable resistor PPB-15E with a maximum resistance of 33 Ohms.

The new case is oriented exclusively to the dimensions of the indicator from the tape recorder, which will serve as a milliammeter.

To do this, he “draws” a new scale (I chose the current of the full deflection of the needle at 150 mA, but you can do it to the maximum).

Then a shunt is placed on the pointer device.

The shunt was made from a nichrome heating coil with a diameter of 0.5 mm. The KT818 transistor must be placed on the cooling radiator.

The connection (articulation) of the set-top box with the power supply is made using an improvised plug integrated into the body, the pins of which are taken from a regular power plug, at one end of which an M4 thread is cut, through which and two nuts each of them is screwed to the body.

Final image of what came out. Definitely a more perfect creation. The LED performs not only an indication function, but also partly illumination of the current stabilizer scale. With best wishes, Babay.

el-shema.ru

Current stabilizers. Types and device. Operation and Application

Current stabilizers are designed to stabilize the current on the load. The voltage across the load depends on its resistance. Stabilizers are necessary for the functioning of various electronic devices, such as gas-discharge lamps.

For high-quality charging of batteries, current stabilizers are also needed. They are used in microcircuits to adjust the current of the conversion and amplification stages. In microcircuits they play the role of a current generator. There are always various types of interference in electrical circuits. They negatively affect the operation of appliances and electrical devices. Current stabilizers easily cope with this problem.

A distinctive feature of current stabilizers is their significant output resistance. This makes it possible to exclude the influence of the input voltage and load resistance on the current value at the device output. Current stabilizers maintain the output current within certain limits while varying the voltage so that the current flowing through the load remains constant.

Device and principle of operation

The instability of the load current is affected by the value of resistance and input voltage. Consider an example in which the load resistance is constant and the input voltage increases. The load current also increases.

As a result, the current and voltage across resistances R1 and R2 will increase. The zener diode voltage will become equal to the sum of the voltages of the resistances R1, R2 and at the base-emitter junction VT1: Uvd1=UR1+UR2+UVT1(b/e)

The voltage at VD1 does not change when the input voltage changes. As a result, the current at the base-emitter junction will decrease and the resistance between the emitter-collector terminals will increase. The current strength at the collector-emitter junction and the load resistance will begin to decrease, that is, go to the original value. This is how the current is equalized and maintained at the same level.

Let's consider an elementary circuit using a field-effect transistor.

The load current passes through R1. The current in the circuit: “+” of the voltage source, drain-gate VT1, load resistance, negative pole of the source is very insignificant, since the drain-gate is biased in the opposite direction.

The voltage on R1 is positive: on the left “-”, on the right the voltage is equal to the voltage of the right arm of the resistance. Therefore, the gate voltage relative to the source is negative. As the load resistance decreases, the current increases. Therefore, the gate voltage compared to the source has an even greater difference. As a result, the transistor closes more strongly.

As the transistor closes more, the load current will decrease and return to its initial value.

Types of current stabilizers

There are many different types of stabilizers depending on their purpose and operating principle. Let's take a closer look at the main such devices.

Resistor stabilizers

In the elementary case, the current generator can be a circuit consisting of a power supply and resistance. A similar circuit is often used to connect an LED that functions as an indicator.

Among the disadvantages of such a scheme, one can note the need to use a high-voltage source. Only under this condition can you use a resistor with a high resistance and obtain good current stability. The resistance dissipates power P = I 2 x R.

Transistor stabilizers

Stabilizers assembled on transistors function much better.

You can adjust the voltage drop so that it is very small. This makes it possible to reduce losses with good stability of the output current. The resistance at the output of the transistor is very high. This circuit is used to connect LEDs or charge low-power batteries.

The voltage across the transistor is determined by the zener diode VD1. R2 plays the role of a current sensor and determines the current at the output of the stabilizer. As the current increases, the voltage drop across this resistor becomes larger. Voltage is supplied to the emitter of the transistor. As a result, the voltage at the base-emitter junction, which is equal to the difference between the base voltage and the emitter voltage, decreases, and the current returns to the specified value.

Current mirror circuit

Current generators function similarly. A popular circuit for such generators is the “current mirror”, in which a bipolar transistor, or more precisely, an emitter junction, is used instead of a zener diode. Instead of resistance R2, emitter resistance is used.

Stabilizers on the field

The circuit using field-effect transistors is simpler. It can use the ground potential as a voltage stabilizer.

Devices on a chip

In past schemes there are elements of comparison and adjustment. A similar circuit structure is used when designing voltage equalization devices. The difference between devices that stabilize current and voltage is that the signal in the feedback circuit comes from a current sensor, which is connected to the load current circuit. Therefore, to create current stabilizers, popular microcircuits 142 EH 5 or LM 317 are used.

Here, the role of a current sensor is played by resistance R1, on which the stabilizer maintains a constant voltage and load current. The sensor resistance value is significantly lower than the load resistance. A decrease in voltage at the sensor affects the output voltage of the stabilizer. This circuit goes well with chargers and LEDs.

Switching stabilizer

Pulse stabilizers made on the basis of switches have high efficiency. They are capable of creating a high voltage at the consumer with a low input voltage. This circuit is assembled on a MAX 771 chip.

Resistances R1 and R2 play the role of voltage dividers at the output of the microcircuit. If the voltage at the output of the microcircuit becomes higher than the reference value, then the microcircuit reduces the output voltage, and vice versa.

If the circuit is changed so that the microcircuit reacts and regulates the output current, then a stabilized current source is obtained.

When the voltage across R3 drops below 1.5 V, the circuit acts as a voltage stabilizer. As soon as the load current increases to a certain level, the voltage drop across resistor R3 becomes larger, and the circuit acts as a current stabilizer.

Resistance R8 is connected according to the circuit when the voltage rises above 16.5 V. Resistance R3 sets the current. A negative aspect of this circuit is the significant voltage drop across the current-measuring resistance R3. This problem can be solved by connecting an operational amplifier to amplify the signal from R3.

Current stabilizers for LEDs

You can make such a device yourself using the LM 317 microcircuit. To do this, all that remains is to select a resistor. It is advisable to use the following power supply for the stabilizer:

• 32 V printer block.
• 19 V laptop block.
• Any 12 V power supply.

The advantage of such a device is its low cost, simplicity of design, and increased reliability. There is no point in assembling a complex circuit yourself; it is easier to purchase it.

Related topics:

electrosam.ru

Current stabilizer circuit

1. Relay current stabilizers
2. Triac stabilizer
3. High frequency current stabilizer
4. Pulse width devices
5. Resonant current stabilizer
6. AC Stabilizer
7. Stabilizing devices for LED
8. Adjustable current stabilizer
9. DC Stabilizers
10. A simple current stabilizer made of two transistors

Operating electrical networks constantly contain various interferences that have a negative impact on the operation of devices and equipment. A current stabilizer circuit helps to effectively cope with this problem. Stabilizing devices differ in technical characteristics and depend on power sources. If current stabilization is not a priority at home, then when using measuring equipment, current indicators must be stable. Devices based on field-effect transistors are particularly accurate. The absence of interference allows you to obtain the most reliable results after measurements.

General structure and principle of operation

The main element of each stabilizer is a transformer. The simplest circuit consists of a rectifier bridge connected to capacitors and resistors. Each circuit uses elements of different types, with individual capacitance and ultimate resistance.

The principle of operation of the stabilizer is quite simple. When current enters the transformer, its limiting frequency changes. At the input, this parameter coincides with the network frequency and is 50 Hz. After performing the current conversion, the value of the limiting frequency at the output will already be 30 Hz. During the operation of high-voltage rectifiers, the voltage polarity is determined. Current stabilization is carried out through the operation of capacitors, and noise reduction occurs with the help of resistors. In the end, a constant voltage is again formed at the output, entering the transformer with a frequency not exceeding 30 Hz.

Types of current stabilizers

In accordance with their intended purpose, a large number of different types of stabilizing devices have been developed.

Relay current stabilizers. Their circuit consists of standard elements, including compensation capacitors. In this case, bridge rectifiers are installed at the beginning of the circuit. One should also take into account such a factor as the presence of two pairs of transistors in the stabilizer. The first pair is installed in front of the capacitor. Due to this, the maximum frequency rises.

In a stabilizer of this type, the output voltage will be about 5 amperes. A certain level of nominal resistance is maintained using resistors. Simple models use two-channel elements. They are distinguished by a long conversion process, but they have a low dissipation coefficient.

Triac stabilizer LM317. This model is widely used in various fields. Its main element is a triac, with the help of which the maximum voltage in the device increases significantly. This output indicator has a value of about 12 V. The system can withstand external resistance up to 3 ohms. The smoothing coefficient is increased using multichannel capacitors. Open type transistors are used only in high-voltage devices.

The position change is controlled by varying the output rated current. The LM317 current stabilizer can withstand differential resistance of up to 5 ohms. If measuring instruments are used, this value must be at least 6 ohms. A powerful transformer provides continuous inductor current. In the usual circuit, it is installed immediately after the rectifier. 12-volt receivers use ballast type resistors, which reduce oscillations in the circuit.

High frequency current stabilizer. Its main element is the KK20 transistor, characterized by an accelerated conversion process. This is facilitated by changing the polarity at the output. Capacitors that set the frequency are installed in pairs in the circuit. The pulse front in this case should not be more than 2 μs, otherwise it will lead to significant dynamic losses.

In some circuits, at least three powerful amplifiers are used to saturate resistors. To reduce heat losses, capacitive capacitors are used. The value of the speed characteristics of the key transistor completely depends on the parameters of the divider.

Pulse width stabilizers. Stabilizers of this type have a fairly significant inductance of the choke, due to the quick change of the divider. This circuit uses two-channel resistors that pass current in different directions, as well as capacitive capacitors. All these elements make it possible to maintain the maximum resistance value at the output within 4 ohms. The maximum load that such stabilizers can withstand is 3 A. These models are rarely used in measuring instruments. The maximum dissipation of power supplies in this case should be no higher than 5 volts, which allows maintaining the standard value of the dissipation coefficient.

In current stabilizers of this type, the key transistors do not have very high speed characteristics. The reason is the low ability of the resistors to block the current coming from the rectifier. As a result, high amplitude interference causes significant heat loss. Neutralization of the transformer properties is reduced and leads to pulse drops. Current conversion is carried out only through the operation of a ballast resistor installed directly behind the rectifier bridge. A pulse-width stabilizer very rarely uses semiconductor diodes, since the pulse front in the circuit is no more than 1 μs.

Resonant current stabilizer. It consists of small capacitors and resistors with different resistances. An integral part of such amplifiers are transformers. An increase in the efficiency of the device is achieved through the use of a large number of fuses. This leads to an increase in the dynamic characteristics of resistors. Low-frequency transistors are installed directly behind the rectifiers. Provided good current conductivity, operation of capacitors becomes possible at different frequencies.

AC stabilizer. As a rule, it is used in power supplies with voltages up to 15 volts and is their integral part. The maximum value of external resistance perceived by devices is 4 ohms. The average incoming AC voltage will be within 13 V. In this case, control over the level of the smoothing coefficient is carried out using open capacitors. The design of the resistors has a direct impact on the level of ripple created at the output.

The maximum linear current for such stabilizers is 5 amperes. Accordingly, the differential resistance will have a value of 5 ohms. The maximum permissible power dissipation is on average 2 W. This indicates serious problems with AC stabilizers with pulse edges. Reducing their oscillations is only possible with the help of bridge rectifiers. Fuses can significantly reduce heat losses.

Stabilizing devices for LEDs. In this case, stabilizers should not have too much power. The main task of the current stabilizer is to reduce the dissipation threshold as much as possible. To make such a stabilizer with your own hands, two main schemes are used. The first option is performed using converters. This makes it possible to achieve a maximum frequency of no more than 4 Hz at all stages, thereby significantly increasing the performance of the device.

In the second case, reinforcing elements are used. The main task is to neutralize alternating current. It is possible to reduce dynamic losses using high-voltage transistors. Excessive saturation of elements is overcome by open-type capacitors. The performance of transformers is ensured by key resistors. Their location in the circuit is standard - directly behind the rectifier bridge.

Adjustable current stabilizer. It is in demand mainly in the field of industrial production. An adjustable stabilizer makes it possible to adjust devices and equipment by changing current and voltage. Many models can be controlled remotely using special controllers mounted inside the stabilizer. For such devices, the maximum AC voltage is approximately 12 V. In this case, the stabilization level must be at least 14 W. The threshold voltage is directly related to the frequency of the device.

To change the smoothing coefficient, capacitive capacitors are installed in the adjustable stabilizer. These devices have good performance: maximum current is 4 A, differential resistance is 6 Ohms. Ensuring continuous throttle mode is carried out by key type transformers. Voltage is supplied to the primary winding through the cathode, the output current is blocked depending on the type of capacitors. Fuses most often do not participate in stabilizing the process.

DC stabilizers. Their work is based on the principle of double integration. Special converters are responsible for this process. The dynamic characteristics of stabilizers are increased with the help of two-channel transistors. The significant capacitance of the capacitors allows to minimize heat losses. Straightening indicators are determined by precise calculations. A DC output voltage of 12A corresponds to a maximum limit of 5 volts at a device frequency of 30 Hz.

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cxema.org - Three circuits of simple current regulators

Three circuits of simple current regulators

There are a lot of voltage regulator circuits on the network for a variety of purposes, but with current regulators things are different. And I want to fill this gap a little, and present to you three simple DC regulator circuits that are worth adopting, as they are universal and can be used in many homemade designs.

In theory, current regulators are not much different from voltage regulators. Please do not confuse current regulators with current stabilizers; unlike the former, they maintain a stable output current regardless of the input voltage and output load.

A current stabilizer is an integral part of any normal laboratory power supply or charger; it is designed to limit the current supplied to the load. In this article we will look at a couple of stabilizers and one regulator for general use.

In all three options, shunts, essentially low-resistance resistors, are used as a current sensor. To increase the output current of any of the listed circuits, it will be necessary to reduce the shunt resistance. The required current value is set manually, usually by rotating a variable resistor. All three circuits operate in linear mode, which means the power transistor will become very hot under heavy loads.

The first scheme is characterized by maximum simplicity and accessibility of components. There are only two transistors, one of them is the control one, the second is the power transistor, through which the main current flows.

The current sensor is a low-resistance wirewound resistor. When connecting an output load, a certain voltage drop is formed across this resistor; the more powerful the load, the greater the drop. This voltage drop is enough to trigger the control transistor; the greater the drop, the more the transistor is open. Resistor R1 sets the bias voltage for the power transistor, it is thanks to it that the main transistor is in the open state. Current limitation occurs due to the fact that the voltage at the base of the power transistor, which was formed by resistor R1, roughly speaking, is damped or shorted to the power ground through the open junction of the low-power transistor, this will close the power transistor, therefore, the current flowing through it decreases down to complete zero .

Resistor R1 is essentially an ordinary voltage divider, with which we can set the degree of opening of the control transistor, and therefore control the power transistor by limiting the current flowing through it.

The second circuit is based on an operational amplifier. It has been used several times in chargers for car batteries. Unlike the first option, this circuit is a current stabilizer.

As in the first circuit, there is also a current sensor (shunt), the operational amplifier records the voltage drop across this shunt, all according to the circuit already familiar to us. The operational amplifier compares the voltage on the shunt with the reference voltage, which is set by the zener diode. With a variable resistor we artificially change the reference voltage. The operational amplifier, in turn, will try to balance the voltage at the inputs by changing the output voltage.

The output of the op-amp drives a high-power field-effect transistor. That is, the principle of operation is not much different from the first circuit, except that there is a reference voltage source made on a zener diode.

This circuit also operates in linear mode and the power transistor will become very hot under heavy loads.

The latest circuit is based on the popular LM317 stabilizer integrated circuit. This is a linear voltage stabilizer, but it is possible to use the microcircuit as a current stabilizer.

The required current is set by a variable resistor. The disadvantage of the circuit is that the main current flows precisely through the previously indicated resistor and naturally it needs a powerful one; the use of wirewound resistors is highly desirable.

The maximum permissible current for the LM317 microcircuit is 1.5 amperes; it can be increased with an additional power transistor. In this case, the microcircuit will already act as a control chip, so it will not heat up, instead the transistor will heat up and there is no escape from it.

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Current stabilizers

1. General structure and principle of operation
2. Diode current stabilizer
3. Current stabilizer on two transistors
4. Video: DIY stabilizer on LM2576

In every electrical network, interference periodically occurs that negatively affects the standard parameters of current and voltage. This problem is successfully solved with the help of various devices, among which current stabilizers are very popular and effective. They have various technical characteristics, which makes it possible to use them in conjunction with any household electrical appliances and equipment. Special requirements apply to measuring equipment that requires stable voltage.

General structure and principle of operation of current stabilizers

Knowledge of the basic principles of operation of current stabilizers contributes to the most effective use of these devices. Electrical networks are literally saturated with various interferences that negatively affect the operation of household appliances and electrical equipment. To overcome the negative effects, a simple voltage and current stabilizer circuit is used.

Each stabilizer has a main element - a transformer, which ensures the operation of the entire system. The simplest circuit includes a rectifier bridge connected to various types of capacitors and resistors. Their main parameters are individual capacitance and ultimate resistance.

The current stabilizer itself operates according to a very simple scheme. When current enters the transformer, its limiting frequency changes. At the input it will coincide with the frequency of the electrical network and will be 50 Hz. After all current conversions have been completed, the maximum output frequency will drop to 30 Hz. The conversion circuit involves high-voltage rectifiers, with the help of which the polarity of the voltage is determined. Capacitors are directly involved in stabilizing the current, and resistors reduce interference.

Diode current stabilizer

Many luminaire designs contain diode stabilizers, better known as current stabilizers for LEDs. Like all types of diodes, LEDs have a nonlinear current-voltage characteristic. That is, when the voltage on the LED changes, a disproportionate change in current occurs.

As the voltage increases, a very slow increase in current is initially observed, as a result, the LED does not glow. Then, when the voltage reaches a threshold value, light begins to be emitted and the current increases very quickly. A further increase in voltage leads to a catastrophic increase in current and LED burnout. The threshold voltage value is reflected in the technical characteristics of LED light sources.

High-power LEDs require the installation of a heat sink, since their operation is accompanied by the release of a large amount of heat. In addition, they require a fairly powerful current stabilizer. Correct operation of LEDs is also ensured by stabilizing devices. This is due to the strong spread of threshold voltage even for light sources of the same type. If two such LEDs are connected in parallel to the same voltage source, currents of different magnitudes will pass through them. The difference can be so significant that one of the LEDs will immediately burn out.

Thus, it is not recommended to turn on LED light sources without stabilizers. These devices set the current to a set value without taking into account the voltage applied to the circuit. The most modern devices include a two-terminal stabilizer for LEDs, used to create inexpensive solutions for controlling LEDs. It consists of a field-effect transistor, strapping parts and other radio elements.

Current stabilizer circuits for ROLL

This circuit works stably using elements such as KR142EN12 or LM317. They are adjustable voltage stabilizers that operate with current up to 1.5A and input voltage up to 40V. In normal thermal conditions, these devices are capable of dissipating power up to 10W. These chips have low self-consumption of approximately 8mA. This indicator remains unchanged even with a changing current passing through the ROLL and a changed input voltage.

The LM317 element is capable of maintaining a constant voltage across the main resistor, which is regulated within certain limits using a trimming resistor. The main resistor with a constant resistance ensures the stability of the current passing through it, so it is also known as a current-setting resistor.

The ROLL stabilizer is simple and can be used as an electronic load, battery charging and other applications.

Current stabilizer on two transistors

Due to their simple design, stabilizers with two transistors are very often used in electronic circuits. Their main disadvantage is considered to be not quite stable current in loads at varying voltages. If high current characteristics are not required, then this stabilizing device is quite suitable for solving many simple problems.

In addition to two transistors, the stabilizer circuit contains a current-setting resistor. When the current increases on one of the transistors (VT2), the voltage across the current-setting resistor increases. Under the influence of this voltage (0.5-0.6V), another transistor (VT1) begins to open. When this transistor opens, another transistor - VT2 begins to close. Accordingly, the amount of current flowing through it decreases.

A bipolar transistor is used as VT2, but if necessary, it is possible to create an adjustable current stabilizer using a MOSFET field-effect transistor used as a zener diode. Its selection is based on a voltage of 8-15 volts. This element is used when the power supply voltage is too high, under the influence of which the gate in the field-effect transistor can be broken. More powerful MOSFET zener diodes are designed for higher voltages - 20 volts or more. The opening of such zener diodes occurs at a minimum gate voltage of 2 volts. Accordingly, there is an increase in voltage, ensuring normal operation of the current stabilizer circuit.

Adjustable DC Regulator

Sometimes there is a need for current stabilizers with the ability to adjust over a wide range. Some circuits may use a current-setting resistor with reduced characteristics. In this case, it is necessary to use an error amplifier, which is based on an operational amplifier.

With the help of one current-setting resistor, the voltage in the other resistor is amplified. This condition is called enhanced error voltage. Using a reference amplifier, the parameters of the reference voltage and the error voltage are compared, after which the state of the field-effect transistor is adjusted.

This circuit requires separate power, which is supplied to a separate connector. The supply voltage must ensure normal operation of all components of the circuit and not exceed a level sufficient to cause breakdown of the field-effect transistor. Proper configuration of the circuit requires setting the variable resistor slider to the highest position. Using a trimming resistor, the maximum current value is set. Thus, the variable resistor allows the current to be adjusted from zero to the maximum value set during the setup process.

Powerful pulse current stabilizer

A wide range of supply currents and loads is not always the main requirement for stabilizers. In some cases, decisive importance is given to the high efficiency of the device. This problem is successfully solved by a pulse current stabilizer microcircuit, replacing compensation stabilizers. Devices of this type allow you to create high voltage across the load even in the presence of a low input voltage.

In addition, there is a pulse-type boost current stabilizer. They are used together with loads whose supply voltage exceeds the input voltage of the stabilizing device. Two resistors used in the microcircuit are used as output voltage dividers, with the help of which the input and output voltage alternately decreases or increases.

Stabilizer on LM2576

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Current stabilizer on a transistor

1. Assembling a current stabilizer from two transistors

During the operation of electrical networks, the need for current stabilization constantly arises. This procedure is carried out using special devices, which include a current stabilizer on a transistor. They are widely used in various electronic devices, as well as in charging batteries of all types. Stabilizers are used in integrated circuits as current generators, creating conversion and amplification stages.

Conventional current stabilizers have a high output resistance, thereby eliminating the influence of load resistance and input voltage factors on the output current. The main disadvantage of these devices is the need to use a high voltage power supply. In this case, current stability is achieved by using resistors with high resistance. Therefore, the power generated by the resistor (P = I2 x R) at high current values ​​may become unacceptable for normal operation of the system. Current stabilizers based on transistors, which perform their functions regardless of the input voltage, have proven themselves much better.

A simple current stabilizer on a transistor

The simplest devices are considered to be diode stabilizers. Thanks to them, electrical circuits are significantly simplified, which leads to a reduction in the overall cost of devices. The operation of the circuits becomes more stable and reliable. These qualities have made diode stabilizers simply indispensable in providing power to LEDs. The voltage range in which they can function normally is 1.8-100 volts. This makes it possible to overcome pulsed and continuous voltage changes.

Therefore, the glow of LEDs can be of different brightness and shades, depending on the current flowing in the circuit. Several of these lamps, connected in series, operate in normal mode with the participation of just one diode stabilizer. This circuit can be easily converted, depending on the number of LEDs and supply voltage. The required current is set by stabilizers connected in parallel to the LED circuit.

Such stabilizers are installed in many designs of LED lamps, including a current stabilizer based on a bipolar transistor. This is due to the properties of LEDs, which have a nonlinear current-voltage characteristic. That is, when the voltage changes across the LED, the current changes disproportionately. With a gradual increase in voltage, at first a very slow increase in current is observed and the LED does not glow. After the voltage reaches a threshold value, light appears and at the same time a very rapid increase in current is observed.

If the voltage continues to increase, a critical increase in current occurs, which leads to the LED burning out. Therefore, the threshold voltage value is always indicated among the characteristics of LED light sources. High power LEDs generate a lot of heat and must be connected to special heat sinks.

Due to the wide variation in threshold voltage, all LEDs must be connected to the power source through a stabilizer. Even LEDs of the same type can have different forward voltages. Therefore, when two light sources are connected in parallel, different currents will pass through them. The difference can be so great that one of the LEDs will fail prematurely or burn out immediately.

Using a stabilizer, the LED is set to a given current value, regardless of the voltage applied to the circuit. When the voltage exceeds the threshold level, the current, having reached the desired value, does not change further. With a further increase in voltage, it remains unchanged on the LED, but increases only on the stabilizer.

Current stabilizer on a field-effect transistor circuit

Power surges very often lead to failure of electrical appliances, devices and other equipment. In order to prevent the occurrence of such situations, various stabilizing devices are used. Among them, current stabilizers based on field-effect transistors are widely popular, ensuring stable operation of electrical equipment. In everyday life, a do-it-yourself DC stabilizer is often used, the circuit of which allows you to solve basic problems.

The main function of these devices is to compensate for voltage drops and surges in the network. Stabilizers automatically maintain precisely specified current parameters. In addition to current surges, changes in load power and ambient temperature are compensated. For example, if the power consumed by the equipment increases, then the current consumption will correspondingly increase. As a rule, this leads to a voltage drop across the resistance of the wires and the current source.

Among many stabilizing devices, the most reliable is considered to be a field current stabilizer circuit, in which the transistor is connected in series with the load resistance. This causes only minor changes in the load current, while the value of the input voltage is constantly changing.

In order to know how such stabilizers work, you need to know the structure and principle of operation of field-effect transistors. These elements are controlled by an electric field, which is why their name arose. The electric field itself arises under the influence of an applied voltage, therefore, all field-effect transistors are semiconductor devices operating under the control of a voltage that opens the channels of these devices.

A field-effect transistor consists of three electrodes - source, drain and gate. Charged particles enter through the source, and exit through the drain. Closing or opening the flow of particles is carried out using a shutter that acts as a tap. Charged particles will flow only if the voltage must be applied between the drain and source. If there is no voltage, then there will be no current in the channel. Therefore, the higher the applied voltage, the more the tap opens. Due to this, the current in the channel between drain and source increases, and the resistance of the channel decreases. For power supplies, field-effect transistors operate in switch mode, ensuring full opening or closing of the channel.

These properties make it possible to calculate a current stabilizer on a transistor, which ensures that current parameters are maintained at a certain level. The use of field-effect transistors also determines the operating principle of such a stabilizer. Everyone knows that every ideal current source has an EMF tending to infinity and also an infinitely large internal resistance. This allows you to obtain a current with the required parameters, regardless of the load resistance.

In such an ideal source, a current arises that remains at the same level despite changes in load resistance. Maintaining the current at a constant level requires a constant change in the magnitude of the EMF in the range above zero and to infinity. That is, the load resistance and EMF must change in such a way that the current remains stably at the same level.

However, in practice, such an ideal current stabilizer microcircuit will not be able to provide all the necessary qualities. This is due to the fact that the voltage range across the load is very limited and does not support the required current level. In real conditions, current and voltage sources are used together. An example is a regular network with a voltage of 220 volts, as well as other sources in the form of batteries, generators, power supplies and other devices that generate electricity. Current stabilizers using field-effect transistors can be connected in series to each of them. The outputs of these devices are essentially current sources with the required parameters.

Do-it-yourself electrical wiring diagrams in the house

The main electrical parameter of light emitting diodes (LEDs) is their operating current. When we see operating voltage in the table of LED characteristics, we need to understand that we are talking about the voltage drop across the LED when operating current flows. That is, the operating current determines the operating voltage of the LED. Therefore, only a current stabilizer for LEDs can ensure their reliable operation.

Purpose and principle of operation

Stabilizers must provide a constant operating current for the LEDs when the power supply has problems with voltage deviations from the norm (you will be interested to know). A stable operating current is primarily necessary to protect the LED from overheating. After all, if the maximum permissible current is exceeded, the LEDs fail. Also, the stability of the operating current ensures the constancy of the luminous flux of the device, for example, when batteries are discharged or voltage fluctuations in the supply network.

Current stabilizers for LEDs have different types of designs, and the abundance of design options is pleasing to the eye. The figure shows the three most popular semiconductor stabilizer circuits.

1. Scheme a) - Parametric stabilizer. In this circuit, the zener diode sets a constant voltage at the base of the transistor, which is connected according to the emitter follower circuit. Due to the stability of the voltage at the base of the transistor, the voltage across the resistor R is also constant. By virtue of Ohm's law, the current across the resistor also does not change. Since the resistor current is equal to the emitter current, the emitter and collector currents of the transistor are stable. By including the load in the collector circuit, we obtain a stabilized current.
2. Scheme b). In the circuit, the voltage across resistor R is stabilized as follows. As the voltage drop across R increases, the first transistor opens more. This leads to a decrease in the base current of the second transistor. The second transistor closes slightly and the voltage on R stabilizes.
3. Scheme c). In the third circuit, the stabilization current is determined by the initial current of the field-effect transistor. It is independent of the voltage applied between drain and source.

In circuits a) and b), the stabilization current is determined by the value of the resistor R. By using a subline resistor instead of a constant resistor, you can regulate the output current of the stabilizers.

Electronic component manufacturers produce many LED regulator chips. Therefore, at present, integrated stabilizers are more often used in industrial products and amateur radio designs. You can read about all the possible ways to connect LEDs.

Review of famous models

Most microcircuits for powering LEDs are made in the form of pulse voltage converters. Converters in which the role of an electrical energy storage device is played by an inductor (choke) are called boosters. In boosters, voltage conversion occurs due to the phenomenon of self-induction. One of the typical booster circuits is shown in the figure.

The current stabilizer circuit works as follows. A transistor switch located inside the microcircuit periodically closes the inductor to the common wire. At the moment the switch opens, a self-induction EMF arises in the inductor, which is rectified by a diode. It is characteristic that the self-induction EMF can significantly exceed the voltage of the power source.

As you can see from the diagram, very few components are required to make a booster on the TPS61160 manufactured by Texas Instruments. The main attachments are inductor L1, Schottky diode D1, which rectifies the pulse voltage at the output of the converter, and R set.

The resistor performs two functions. Firstly, the resistor limits the current flowing through the LEDs, and secondly, the resistor serves as a feedback element (a kind of sensor). The measuring voltage is removed from it, and the internal circuits of the chip stabilize the current flowing through the LED at a given level. By changing the resistor value you can change the current of the LEDs.

The TPS61160 converter operates at a frequency of 1.2 MHz, the maximum output current can be 1.2 A. Using the microcircuit, you can power up to ten LEDs connected in series. The brightness of the LEDs can be changed by applying a variable duty cycle PWM signal to the “brightness control” input. The efficiency of the above circuit is about 80%.

It should be noted that boosters are usually used when the voltage across the LEDs is higher than the voltage of the power supply. In cases where it is necessary to reduce the voltage, linear stabilizers are often used. A whole line of such MAX16xxx stabilizers is offered by MAXIM. A typical connection diagram and internal structure of such microcircuits is shown in the figure.

As can be seen from the block diagram, the LED current is stabilized by a P-channel field-effect transistor. The error voltage is removed from the resistor R sens and supplied to the field control circuit. Since the field-effect transistor operates in linear mode, the efficiency of such circuits is noticeably lower than that of pulse converter circuits.

The MAX16xxx line of ICs are often used in automotive applications. The maximum input voltage of the chips is 40 V, output current is 350 mA. They, like switching stabilizers, allow PWM dimming.

Stabilizer on LM317

Not only specialized microcircuits can be used as a current stabilizer for LEDs. The LM317 circuit is very popular among radio amateurs.

LM317 is a classic linear voltage regulator with many analogs. In our country, this microcircuit is known as KR142EN12A. A typical circuit for connecting LM317 as a voltage stabilizer is shown in the figure.

To turn this circuit into a current stabilizer, it is enough to exclude resistor R1 from the circuit. The inclusion of LM317 as a linear current stabilizer is as follows.

Calculating this stabilizer is quite simple. It is enough to calculate the value of resistor R1 by substituting the current value into the following formula:

The power dissipated by the resistor is equal to:

Adjustable stabilizer

The previous circuit can be easily converted into an adjustable stabilizer. To do this, you need to replace the constant resistor R1 with a potentiometer. The diagram will look like this:

How to make a stabilizer for an LED with your own hands

All of the above stabilizer schemes use a minimum number of parts. Therefore, even a novice radio amateur who has mastered the skills of working with a soldering iron can independently assemble such structures. The designs on the LM317 are especially simple. You don't even need to design a printed circuit board to make them. It is enough to solder a suitable resistor between the reference pin of the microcircuit and its output.

Also, two flexible conductors need to be soldered to the input and output of the microcircuit and the design will be ready. If it is intended to power a powerful LED using the current stabilizer on LM317, the microcircuit must be equipped with a radiator that will ensure heat removal. As a radiator, you can use a small aluminum plate with an area of ​​15-20 square centimeters.

When making booster designs, you can use filter coils from various power supplies as chokes. For example, ferrite rings from computer power supplies are well suited for these purposes; several dozen turns of enameled wire with a diameter of 0.3 mm should be wound around them.

Which stabilizer to use in a car

Nowadays, car enthusiasts are often engaged in upgrading the lighting technology of their cars, using LEDs or LED strips for these purposes (read). It is known that the voltage of a car’s on-board network can vary greatly depending on the operating mode of the engine and generator. Therefore, in the case of a car, it is especially important to use not a 12-volt stabilizer, but one designed for a specific type of LED.

For a car, we can recommend designs based on LM317. You can also use one of the modifications of a linear stabilizer with two transistors, in which a powerful N-channel field-effect transistor is used as a power element. Below are options for such schemes, including the scheme.

Conclusion

To summarize, we can say that for reliable operation of LED structures, they must be powered using current stabilizers. Many stabilizer circuits are simple and easy to make yourself. We hope that the information provided in the material will be useful to everyone who is interested in this topic.

There is a misconception that the supply voltage is an important indicator for an LED. However, it is not. For its proper operation, direct current consumption (Iconsumption) is essential, which is usually around 20 milliamps. The rated current is determined by the LED design and heat dissipation efficiency.

But the magnitude of the voltage drop, mostly determined by the semiconductor material from which the LED is made, can range from 1.8 to 3.5V.

It follows that for normal operation of the LED, it is the current stabilizer that is needed, not the voltage stabilizer. In this article we will look at current stabilizer on lm317 for LEDs.

Current stabilizer for LEDs - description

Of course, the easiest way to limit Iconsumption. for LED is . But it should be noted that this method is ineffective due to large energy losses, and is only suitable for low-current LEDs.

Formula for calculating the required resistance: Rd= (Upit.-Ufall.)/Ipot.

Example: Upit. = 12V; Upd. on LED = 1.5V; Iconsumption LED = 0.02A. It is necessary to calculate the additional resistance Rd.

In our case, Rd = (12.5V-1.5V)/0.02A = 550 Ohm.

But again, I repeat, this stabilization method is only suitable for low-power LEDs.

Next option current stabilizer on more practical. In the diagram below, LM317 limits Iinput. LED, which is set by resistance R.

For stable operation on LM317, the input voltage must exceed the LED supply voltage by 2-4 volts. The output current limitation range is 0.01A...1.5A and with an output voltage of up to 35 volts.

Formula for calculating the resistance of the resistor R: R=1.25/Iconst.

Example: for LED with Ipot. at 200mA, R= 1.25/0, 2A=6.25 Ohm.

Current stabilizer calculator for LM317

To calculate the resistance and power of the resistor, simply enter the required current:

Don't forget that the maximum continuous current the LM317 can handle is 1.5 amps with a good heatsink. For higher currents, use one, which is rated at 5 amperes, and with a good radiator up to 8 amperes.

If you need to adjust the brightness of the LED, then the article provides an example of a circuit using the LM2941 voltage stabilizer.

The most important power parameter for any LED is current. When connecting an LED to a car, the required current can be set using a resistor. In this case, the resistor is calculated based on the maximum voltage of the on-board network (14.5V). The negative side of this connection is that the LED does not glow at full brightness when the voltage in the vehicle's on-board network is below the maximum value.

A more correct way is to connect the LED through a current stabilizer (driver). Compared to a current-limiting resistor, a current stabilizer has a higher efficiency and is able to provide the LED with the necessary current both at maximum and at reduced voltage in the vehicle’s on-board network. The most reliable and easiest to assemble are stabilizers based on specialized integrated circuits (ICs).

Stabilizer on LM317

The three-terminal adjustable stabilizer lm317 is ideal for designing simple power supplies that are used in a wide variety of devices. The simplest circuit for connecting lm317 as a current stabilizer has high reliability and small wiring. A typical lm317 current driver circuit for a car is shown in the figure below and contains only two electronic components: a microcircuit and a resistor. In addition to this circuit, there are many other, more complex circuit solutions for building drivers using a variety of electronic components. A detailed description, principle of operation, calculations and selection of elements of the two most popular circuits on lm317 can be found.

The main advantages of linear stabilizers built on the basis of lm317 are ease of assembly and low cost of components used in wiring. The retail price of the IC itself is no more than $1, and the finished driver circuit does not require adjustment. It is enough to measure the output current with a multimeter to ensure that it corresponds to the calculated data.

The disadvantages of the lm317 MM include strong heating of the case with an output power of more than 1 W and, as a consequence, the need for heat removal. For this purpose, the TO-220 type housing has a hole for a bolted connection to the radiator. Also, a disadvantage of the above circuit can be considered the maximum output current, no more than 1.5 A, which sets a limit on the number of LEDs in the load. However, this can be avoided by connecting several current stabilizers in parallel or using the lm338 or lm350 microcircuit instead of lm317, which are designed for higher load currents.

Stabilizer on PT4115

PT4115 is a unified chip developed by PowTech specifically for building drivers for high-power LEDs, which can also be used in cars. A typical PT4115 connection circuit and the formula for calculating the output current are shown in the figure below.

It is worth emphasizing the importance of having a capacitor at the input, without which the PT4115 MI will fail the first time it is turned on.

You can understand why this happens, as well as get acquainted with a more detailed calculation and selection of the remaining elements of the circuit. The microcircuit gained fame due to its versatility and a minimal set of parts in the harness. To light an LED with a power from 1 to 10 W, the car enthusiast only needs to calculate the resistor and select the inductance from the standard list.

The PT4115 has a DIM input that greatly expands its capabilities. In the simplest version, when you just need to light the LED at a given brightness, it is not used. But if it is necessary to adjust the brightness of the LED, then either the signal from the output of the frequency converter or the voltage from the output of the potentiometer is supplied to the DIM input. There are options for setting a specific potential at the DIM pin using a MOSFET. In this case, when power is applied, the LED glows at full brightness, and when the MOSFET starts up, the LED dims the brightness by half.

The disadvantages of an LED driver for cars based on PT4115 include the difficulty of selecting the current-setting resistor Rs due to its very low resistance. The service life of the LED directly depends on the accuracy of its rating.

Both microcircuits discussed have proven themselves to be excellent in constructing drivers for LEDs in a car with their own hands. LM317 is a long-known, proven linear stabilizer, the reliability of which is beyond doubt. A driver based on it is suitable for organizing interior and dashboard lighting, turns and other elements of LED tuning in a car.

PT4115 is a newer integrated stabilizer with a powerful MOSFET transistor at the output, high efficiency and dimming capability.

Read also

It's no secret that LED lamps periodically burn out, despite the long warranty periods established by manufacturers. Many people simply do not know the real reasons why they fail. However, there are no special difficulties here, it’s just that such lamps have certain parameters that require mandatory stabilization. This is the current strength in the lamp itself and the voltage drop in the supply network.

To solve this problem, a current stabilizer for LEDs is used. However, not all stabilizers can effectively solve the problem. Therefore, in some cases it is recommended to make a stabilizer yourself. Before starting this process, you should carefully understand the purpose, structure and operating principle of the stabilizer in order to avoid mistakes when assembling the circuit.

Purpose of the stabilizer

The main function of the stabilizer is to equalize the current, regardless of voltage drops in the electrical network. There are two types of stabilizing devices - linear and pulsed. In the first case, all output parameters are adjusted by distributing power between the load and its own resistance. The second option is much more efficient, since in this case only the required amount of power is supplied to the LEDs. The operation of such stabilizers is based on the principle of pulse width modulation.

It has a higher efficiency of at least 90%. However, they have a rather complex circuit and, accordingly, a high cost compared to linear type devices. It should be noted that the use of LM317 stabilizers is only permissible for linear circuits. They cannot be connected to circuits with high current values. That is why these devices are best suited for use with LEDs.

The need to use stabilizers is explained by the characteristics of LED parameters. They are distinguished by a nonlinear current-voltage characteristic, when a change in voltage on the LED leads to a disproportionate change in current. As the voltage increases, the current increases very slowly at the very beginning, so no glow is observed. Further, when the voltage reaches a threshold value, light emission begins with a simultaneous rapid increase in current. If the voltage continues to increase, then the current increases even more, causing the LED to burn out.

LED characteristics reflect the threshold voltage value as forward voltage at rated current. The current rating for most low power LEDs is 20 mA. High-power LEDs require higher current ratings, reaching 350 mA or higher. They generate a large amount of heat and are installed on special heat sinks.

In order to ensure normal operation of the LEDs, power must be connected to them through a current stabilizer. This is due to the spread of the threshold voltage. That is, different types of LEDs have different forward voltages. Even lamps of the same type may not have the same forward voltage, and not only its minimum, but also its maximum value.

Thus, if to the same source, then they will pass completely different currents through themselves. The difference in currents leads to their premature failure or instant burnout. To avoid such situations, it is recommended to turn on LEDs together with stabilizing devices designed to equalize the current and bring it to a certain, specified value.

Linear type stabilizing devices

Using a stabilizer, the current passing through the LED is set to a specified value, independent of the voltage applied to the circuit. If the voltage exceeds the threshold level, the current will still remain the same and will not change. In the future, when the total voltage increases, its increase will occur only at the current stabilizer, and at the LED it will remain unchanged.

Thus, with unchanged LED parameters, the current stabilizer can be called a power stabilizer. The distribution of active power generated by the device in the form of heat occurs between the stabilizer and the LED in proportion to the voltage on each of them. This type of stabilizer is called linear.

The heating of the linear current stabilizer increases with the increase in voltage applied to it. This is its main disadvantage. However, this device has several advantages. There is no electromagnetic interference during operation. The design is very simple, which makes the product quite cheap in most schemes.

There are applications where a linear current regulator for 12V LEDs becomes more efficient than a switching converter, especially when the input voltage is only slightly higher than the LED voltage. If the power is supplied from the network, the circuit can use a transformer, to the output of which a linear stabilizer is connected.

Thus, first the voltage is reduced to the same level as in the LED, after which the linear stabilizer sets the required current value. Another option involves bringing the LED voltage closer to the supply voltage. For this purpose, the LEDs are connected in series into a common chain. As a result, the total voltage in the circuit will be the sum of the voltages of each LED.

Some current stabilizers can be made on a field-effect transistor using a pn junction. The drain current is set using the gate-source voltage. The current passing through the transistor is the same as the initial drain current specified in the technical documentation. The minimum operating voltage of such a device depends on the transistor and is about 3 V.

Pulse current stabilizers

More economical devices include current stabilizers, which are based on a pulse converter. This element is also known as a key converter or converter. Inside the converter, power is pumped in certain portions in the form of pulses, which determined its name. In a normally operating device, power consumption occurs continuously. It is continuously transmitted between the input and output circuits and is also continuously supplied to the load.

In electrical circuits, a current and voltage stabilizer based on pulse converters has almost the same operating principle. The only difference is that the current through the load is controlled instead of the voltage across the load. If the current in the load decreases, the stabilizer pumps up power. In case of increase, the power is reduced. This allows you to create current stabilizers for high-power LEDs.

The most common circuits additionally have a reactive element called a choke. Energy is supplied to it in certain portions from the input circuit, which is subsequently transferred to the load. Such transmission occurs through a switch or key, which is in two main states - off and on. In the first case, no current passes and no power is released. In the second case, the key conducts current while having very low resistance. Therefore, the released power is also close to zero. Thus, energy transfer occurs with virtually no power loss. However, the pulse current is considered unstable and special filters are used to stabilize it.

Along with obvious advantages, the pulse converter has serious disadvantages, the elimination of which requires specific design and technical solutions. These devices are complex in design and create electromagnetic and electrical interference. They expend a certain amount of energy for their own work and, as a result, heat up. Their cost is significantly higher than that of linear stabilizers and transformer devices. However, most of the shortcomings are successfully overcome, which is why switching stabilizers are widely popular among consumers.

LED power driver