Powerful switching current regulator for LEDs. Voltage stabilizer and current stabilizer

Almost all motorists are familiar with such a problem as the rapid failure of LED lamps. Which are often placed in side lights, daytime running lights (DRLs) or other lights.
As a rule, these LED lamps have low power and current consumption. What exactly is the reason for their choice.
By itself, the LED easily serves in optimal conditions for more than 50,000 hours, but in a car, especially in a domestic one, it is sometimes not enough for a month. First, the LED starts to flicker, and then it burns out altogether.

What explains this?

The lamp manufacturer writes the marking "12V". This is the optimal voltage at which the LEDs in the lamp operate almost at maximum. And if you apply 12 V to this lamp, then it will last at maximum brightness for a very long time.
So why does it burn out in the car? Initially, the voltage of the car’s on-board network is 12.6 V. An overestimation of 12 is already visible. And the voltage of the network of a running car can reach up to 14.5 V. Let’s add to all this various jumps from switching powerful high-beam or low-beam lamps, powerful voltage pulses and magnetic interference when starting the engine from the starter. And we get not the best network for powering LEDs, which, unlike incandescent lamps, are very sensitive to all drops.
Since often in simple Chinese lamps there are no limiting elements, except for a resistor, the lamp fails due to overvoltage.
During my practice, I have changed dozens of such lamps. Most of them did not serve even a year. In the end, I got tired and decided to look for a simpler way out.

A simple voltage regulator for LEDs

To ensure comfortable operation for LEDs, I decided to make a simple stabilizer. Absolutely not difficult, any motorist can repeat it.
All we need:

• - a piece of textolite for the board,

Look like that's it. All equipment costs a penny on Ali Express - links in the list.

Stabilizer circuit

The circuit is taken from the datasheet for the L7805 chip.

It's simple - on the left is the entrance, on the right is the exit. Such a stabilizer can withstand up to 1.5 A of load, provided that it is installed on a radiator. Naturally, for small bulbs, no radiator is needed.

Assembling a stabilizer for LEDs

All that is needed is to cut out the desired piece from the textolite. There is no need to etch the tracks - I cut out simple lines with a regular screwdriver.
Solder all the elements and you're done. Does not need setting.

In the role of the body is a thermal blower.
Another advantage of the scheme is that it is fashionable to use the body of a car as a radiator, since the central terminal of the microcircuit housing is connected to a minus.

That's all, the LEDs no longer burn out. I have been driving for more than a year and forgot about this problem, which I advise you too.

The main electrical parameter of light-emitting diodes (LED) is their operating current. When we meet the operating voltage in the LED characteristics table, we need to understand that we are talking about the voltage drop across the LED when the 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 should provide a constant operating current of the LEDs when the power supply has problems with voltage deviation from the norm (you will be interested to know). A stable operating current is primarily needed to protect the LED from overheating. After all, if the maximum allowable 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 execution, and the abundance of options for execution schemes pleases 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 through 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 a load in the collector circuit, we get a stabilized current.
2. Scheme b). In the circuit, the voltage across the 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 a little and the voltage across R stabilizes.
3. Scheme c). In the third scheme, 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. Using a subscript instead of a constant resistor, you can adjust the output current of the stabilizers.

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

Overview 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 performed 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. The transistor key located inside the microcircuit periodically closes the inductor to a common wire. At the moment of opening the key, an EMF of self-induction occurs in the inductor, which is rectified by a diode. It is characteristic that the EMF of self-induction can significantly exceed the voltage of the power source.

As can be seen from the diagram, for the manufacture of a booster on the TPS61160 manufactured by Texas Instruments, very few components are required. The main attachments are the inductor L1, the Schottky diode D1, which rectifies the pulsed voltage at the output of the converter, and Rset.

The resistor has 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 value of the resistor, you can change the current of the LEDs.

The converter on the TPS61160 operates at a frequency of 1.2 MHz, the maximum output current can be 1.2 A. Using a 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 scheme is about 80%.

It should be noted that boosters are usually used when the LED voltage is higher than the power supply voltage. In cases where it is required to lower the voltage, linear stabilizers are more often used. A whole line of such MAX16xxx stabilizers is offered by MAXIM. A typical switching circuit and the internal structure of such microcircuits are shown in the figure.

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

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

Stabilizer on LM317

As a current stabilizer for LEDs, you can use not only specialized microcircuits. The LM317 circuit is very popular with radio amateurs.

The LM317 is a classic linear voltage regulator with many analogues. In our country, this chip is known as KR142EN12A. A typical circuit for switching on the LM317 as a voltage regulator is shown in the figure.

To turn this circuit into a current stabilizer, it is enough to exclude the resistor R1 from the circuit. Turning on the LM317 as a linear current regulator is as follows.

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

The power dissipated in the resistor is:

Adjustable stabilizer

The previous circuit is easy to turn into an adjustable stabilizer. To do this, you need to replace the constant resistor R1 with a potentiometer. The schema will look like this:

How to make a do-it-yourself LED stabilizer

In all the given schemes of stabilizers, the minimum number of parts is used. 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. For their manufacture, you do not even need to develop printed circuit board. It is enough to solder a suitable resistor between the reference pin of the microcircuit and its output.

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

When making booster designs, filter coils of various power supplies can be used as chokes. For example, ferrite rings from computer power supplies are well suited for these purposes, on which several tens of turns of enameled wire with a diameter of 0.3 mm should be wound.

What kind of stabilizer to use in a car

Now motorists are often engaged in upgrading the lighting equipment of their cars, using LEDs or LED strips for this purpose (read,). It is known that the voltage of the vehicle'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, designs based on LM317 can be advised. You can also use one of the modifications of the linear stabilizer on 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

Summing up, we can say that for reliable operation of LED structures, they must be powered by current stabilizers. Many stabilizer circuits are simple and affordable for DIY. We hope that the information provided in the material will be useful to everyone who is interested in this topic.

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, for example.

You can adjust the voltage drop so that it is very small. This makes it possible to reduce losses with good current stability at the output. At the output of the transistor, the resistance 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. The voltage is applied 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 set value.

Schematic of the current mirror

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

Current stabilizers on the field

The circuit using field effect transistors is simpler.

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

The voltage on R1 is positive: on the left is "-", 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 minus. As the load resistance decreases, the current increases. Therefore, the gate voltage compared to the source has more big difference. As a result, the transistor closes more strongly.

With a greater closing of the transistor, the load current will decrease and return to the initial value.

Devices on a chip

In past schemes, there are elements of comparison and adjustment. A similar circuit structure is used in the design of voltage equalization devices. The difference between devices that stabilize current and voltage is that the signal comes to the feedback circuit from the 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 the current sensor is played by the resistance R1, on which the stabilizer maintains a constant voltage and load current. The resistance value of the sensor is much lower than the load resistance. Reducing the voltage on the sensor affects the output voltage of the stabilizer. A similar scheme goes well with chargers, LEDs.

Switching stabilizer

Switching stabilizers made on the basis of keys have high efficiency. They are capable of creating a high voltage at the consumer at a low input voltage. Such a circuit is assembled on a microcircuit MAX 771.

Resistors 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 in such a way that the microcircuit reacts and regulates the current at the output, then a stabilized current source will be obtained.

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

Resistor R8 is connected according to the circuit when the voltage becomes higher than 16.5 V. Resistor R3 sets the current. The negative point of this circuit is a significant voltage drop across the current-measuring resistance R3. This problem can be solved by connecting operational amplifier to amplify the signal from the resistance R3.

Current stabilizers for LEDs

You can make such a device yourself using the LM 317 chip. To do this, you just have to pick up a resistor. It is advisable to use the following power supply for the stabilizer:

• 32V printer block.
• Block from a laptop for 19 V.
• Any 12V power supply.

The advantage of such a device is low cost, simple design, increased reliability. It makes no sense to assemble a complex scheme on your own, it is easier to purchase it.

LED lighting is becoming more and more a part of our lives. Capricious light bulbs fail and beauty immediately fades. And all because LEDs cannot work simply by being plugged into the mains. They must be connected through stabilizers (drivers). The latter prevent voltage surges, component failure, overheating, etc. About this and how to assemble a simple circuit with their own hands, and will be discussed in the article.

Stabilizer selection

In the on-board network of a car, the working power is approximately 13 V, while most LEDs are suitable for 12 V. Therefore, a voltage stabilizer is usually installed, the output of which is 12 V. Thus, normal conditions are provided for the operation of lighting equipment without emergency and premature failure.

At this stage, amateurs are faced with the problem of choice: there are many designs published, but not all work well. You need to choose the one that is worthy of your favorite vehicle and, in addition:

• will really work;
• ensure the safety and security of lighting equipment.

The simplest DIY voltage stabilizer

If you have no desire to buy a ready-made device, then you should learn how to make a simple stabilizer yourself. It is difficult to make a switching stabilizer in a car with your own hands. That is why it is worth taking a closer look at the selection of amateur schemes and designs. linear stabilizers voltage. The simplest and most common version of a stabilizer consists of a finished microcircuit and a resistor (resistance).

It is easiest to make a current stabilizer for LEDs with your own hands on a microcircuit. Assembly of parts (see figure below) is carried out on a perforated panel or a universal printed circuit board.

Scheme of a 5 amp power supply with a voltage regulator from 1.5 to 12 V.

For self-assembly of such a device, you will need the following parts:

• plateau size 35*20 mm ;
• chip LD1084;
• diode bridge RS407 or any small diode for reverse current;
• power supply, consisting of a transistor and two resistances. Designed to turn off the rings when you turn on the high or low beam.

In this case, the LEDs (in the amount of 3 pcs.) Are connected in series with a current-limiting resistor that equalizes the current. Such a set, in turn, is connected in parallel with the next same set of LEDs.

Stabilizer for LEDs on the L7812 chip in a car

The current stabilizer for LEDs can be assembled on the basis of a 3-pin DC voltage regulator (L7812 series). The wall-mounted device is great for powering both LED strips and individual light bulbs in a car.

Necessary components for assembling such a circuit:

• chip L7812;
• capacitor 330 microfarad 16 V;
• capacitor 100 microfarad 16 V;
• 1 amp rectifier diode (1N4001, for example, or a similar Schottky diode);
• wires;
• heat shrink 3 mm.

There are actually many options.

Wiring diagram based on LM2940CT-12.0

The body of the stabilizer can be made from almost any material except wood. When using more than ten LEDs, it is recommended to attach an aluminum heatsink to the stabilizer.

Maybe someone has tried it and will say that you can easily do without unnecessary troubles by directly connecting the LEDs. But in this case, the latter will most of the time be in adverse conditions, therefore, they will not last long or even burn out. But tuning expensive cars results in a fairly large amount.

And about the described schemes, their main advantage is simplicity. It does not require special skills and abilities to make. However, if the circuit is too complicated, then it becomes not rational to assemble it with your own hands.

Conclusion

The ideal option for connecting LEDs is through. The device balances the fluctuations of the network, with its use current surges will no longer be terrible. In this case, the requirements for the power supply must be observed. This will allow you to adjust your stabilizer to the network.

The device should provide maximum reliability, stability and stability, preferably for many years. The cost of assembled devices depends on where all the necessary parts will be bought.

In the video - for LEDs.

Current stabilizers, unlike voltage stabilizers, stabilize the current. In this case, the voltage on the load will depend on its resistance. Current stabilizers are required to power electronic devices such as LEDs or gas discharge lamps, they can be used in soldering stations or thermostats to set the operating temperature. In addition, current stabilizers are required to charge batteries. various types. Current stabilizers are widely used as part of integrated circuits for setting the current of amplifying and converting stages. There they are usually called current generators.

A feature of current stabilizers is their high output impedance. This eliminates the influence of the input voltage and load resistance on the output current. Of course, in the simplest case, a voltage source and a resistor can serve as a current generator. Such a scheme is often used to power the indicator LED. A similar scheme is shown in Figure 1.

Figure 1. Scheme of a current stabilizer on a resistor

The disadvantage of this scheme is the need to use a high voltage power supply. Only in this case it is possible to use a sufficiently high-resistance resistor and achieve acceptable current stability. In this case, the power is dissipated in the resistor P=I 2× R, which may be unacceptable at high currents.

Current stabilizers on transistors have proven themselves much better. Here we take advantage of the fact that the output resistance of the transistor is very high. This is clearly seen in the output characteristics of the transistor. For illustration, Figure 2 shows how to determine the output impedance of a transistor from its output characteristics.

Figure 2. Determining the output resistance of a transistor by its output characteristics

In this case, the voltage drop can be set small, which makes it possible to obtain small losses with a high stability of the output current. This allows you to use this circuit to power backlight LEDs or to charge low-power batteries. The current stabilizer circuit on a bipolar transistor is shown in Figure 3.

Figure 3. Scheme of a current stabilizer on a transistor

In this circuit, the voltage at the base of the transistor is set by the zener diode VD1, the resistor R2 serves as a current sensor. It is its resistance that determines the output current of the stabilizer. As the current increases, the voltage drop across it increases. It is applied to the emitter of the transistor. As a result, the base-emitter voltage, defined as the difference between the constant voltage at the base and the voltage at the emitter, decreases and the current returns to the set value.

Current generators work in a similar way, the most famous of which is the "current mirror" circuit. Instead of a zener diode, it uses the emitter junction of a bipolar transistor, and the internal resistance of the emitter of the transistor is used as a resistor R2. The diagram of the current mirror is shown in Figure 4.

Figure 4. Scheme of the "current mirror"

Current stabilizers, operating on the principle of operation of the circuit shown in Figure 3, assembled on field-effect transistors are even simpler. In them, instead of a voltage stabilizer, you can use the ground potential. The current stabilizer circuit, made on a field-effect transistor, is shown in Figure 5.

Figure 5. Scheme of a current stabilizer on a field-effect transistor

All considered schemes combine a control element and a comparison scheme. A similar situation was observed in the development of compensation voltage stabilizers. Current stabilizers differ from voltage stabilizers in that the signal to the feedback circuit comes from a current sensor included in the load current circuit. Therefore, to implement current stabilizers, such common microcircuits as 142EN5 (LM7805) or LM317 are used. Figure 6 shows a current stabilizer circuit on the LM317 chip.

Figure 6. Scheme of the current stabilizer on the LM317 chip

The current sensor is the resistor R1 and on it the stabilizer maintains the voltage unchanged and, therefore, the current in the load. The current sensor resistance is much less than the load resistance. The voltage drop across the sensor corresponds to the output voltage of the compensation regulator. The circuit shown in Figure 6 is perfect for both powering lighting LEDs and battery chargers.

And are perfect as current stabilizers. They provide greater efficiency. compared to compensation stabilizers. It is these circuits that are commonly used as drivers inside LED lamps.

Literature:

1. Sazhnev A.M., Rogulina L.G., Abramov S.S. “Power supply of devices and communication systems”: Tutorial/ GOU VPO SibGUTI. Novosibirsk, 2008 - 112 p.
2. Aliev I.I. Electrotechnical reference book. - 4th ed. correct - M.: IP Radio Soft, 2006. - 384 p.
3. Geytenko E.N. Sources of secondary power supply. Circuitry and calculation. Tutorial. - M., 2008. - 448 p.
4. Power supply of devices and telecommunications systems: Textbook for universities / V.M. Bushuev, V.A. Deminsky, L.F. Zakharov and others - M., 2009. – 384 p.