Voltage and current regulator for KT825g. Switching voltage stabilizer on KT825. For the "Transistor voltage regulator" circuit

Hello dear readers. There are many circuits where the wonderful high-power composite transistors KT827 are used with great success and naturally sometimes there is a need to replace them. When the code for these transistors is not found at hand, we begin to think about their possible analogues.

I have not found complete analogues among foreign-made products, although there are many proposals and statements on the Internet about replacing these transistors with TIP142. But for these transistors the maximum collector current is 10A, for 827 it is 20A, although their powers are the same and equal to 125W. For 827, the maximum collector-emitter saturation voltage is two volts, for TIP142 it is 3V, which means that in pulse mode, when the transistor is in saturation, with a collector current of 10A, a power of 20 W will be released on our transistor, and in the bourgeois mode - 30 W , so you will have to increase the size of the radiator.

A good replacement could be the KT8105A transistor, see the data on the plate. With a collector current of 10A, the saturation voltage of this transistor is no more than 2V. This is good.

In the absence of all these replacements, I always assemble an approximate analogue using discrete elements. Transistor circuits and their appearance are shown in photo 1.

I usually assemble by hanging installation, one of possible options shown in photo 2.

Depending on the required parameters of the composite transistor, you can select replacement transistors. The diagram shows diodes D223A, I usually use KD521 or KD522.

In photo 3, the assembled composite transistor operates on a load at a temperature of 90 degrees. The current through the transistor in this case is 4A, and the voltage drop across it is 5 volts, which corresponds to the released thermal power of 20W. I usually perform this procedure on semiconductors within two or three hours. For silicon this is not at all scary. Of course, for such a transistor to work on this radiator inside the device case, additional airflow will be required.

To select transistors, I provide a table with parameters.

The source is convenient for powering installed electronic devices and charging batteries. The stabilizer is built according to a compensation circuit, which is characterized by a low level of output voltage ripple and, despite the low efficiency compared to switching stabilizers, it fully meets the requirements for a laboratory power source.

Fundamental electrical diagram power supply is shown in Fig. 1. The source consists of a network transformer T1, a diode rectifier VD3-VD6, a smoothing filter SZ-S6, a voltage stabilizer DA1 with an external powerful control transistor VT1, a current stabilizer assembled on the op-amp DA2 and an auxiliary bipolar power supply, an output voltage/current meter load PA1 with switch SA2 "Voltage/Current".

In voltage stabilization mode, the output of op-amp DA2 is high, LED HL1 and diode VD9 are closed. Stabilizer DA1 and transistor VT1 operate in standard mode. With a relatively small load current, transistor VT1 is closed, and all the current flows through the stabilizer DA1. As the load current increases, the voltage drop across resistor R3 increases, transistor VT1 opens and enters linear mode, turning on and unloading stabilizer DA1. The output voltage is set by the resistive divider R6R10. Rotate the knob variable resistor R10 sets the required output voltage of the source.

Signal feedback the current is removed from resistor R9 and supplied through resistor R8 to the inverting input of op-amp DA2. When the current increases above the value set by variable resistor R8, the voltage at the op-amp output decreases, diode VD9 opens, LED HL1 turns on and the stabilizer goes into load current stabilization mode, indicated by LED HL1.

The auxiliary low-power bipolar power supply op-amp DA2 is assembled on two half-wave rectifiers on VD1, VD2 with parametric stabilizers VD7R1, VD8R2. Their common point is connected to the output of the adjustable stabilizer DA1. This scheme was chosen for reasons of minimizing the number of turns of auxiliary winding III, which must be additionally wound on the network transformer T1.

Most of the parts of the block are placed on a printed circuit board made of fiberglass foil on one side with a thickness of 1 mm. Drawing printed circuit board shown in Fig. 2. Resistor R9 is made up of two resistances of 1.5 0 m each with a power of 1 W. Transistor VT1 is mounted on a pin heat sink with external dimensions of 130x80x20 mm, which is the rear wall of the source casing. Transformer T1 must have an overall power of 40...50 W. The voltage (under load) of winding II should be about 25 V, and winding III - 12 V.

With the element ratings indicated in the diagram, the unit provides an output voltage of 1.25...25 V, load current - 15...1200 mA. The upper voltage limit, if necessary, can be expanded to 30 V by selecting R6R10 divider resistors. The upper current limit can also be raised by reducing the resistance of shunt R9, but in this case you will have to install rectifier diodes on the heat sink, use more power transistor VT1 (for example, KT825A-KT825G), and possibly a more powerful transformer.

First, a rectifier with a filter and a bipolar power supply for op-amp DA2 are installed and tested, then everything else except DA2. After making sure that the adjustable voltage stabilizer is working, solder in op-amp DA2 and check it under load adjustable stabilizer current The R11 shunt is made independently (its resistance is hundredths or thousandths of an Ohm), and the additional resistor R12 is selected for the specific microammeter available. My source uses an M42305 microammeter with a full needle deflection current of 50 μA.

Capacitor C13, in accordance with the recommendations of the manufacturer of the K142EN12A stabilizer, it is advisable to use tantalum, for example, K52-2 (ETO-1). The KT837E transistor can be replaced with KT818A-KT818G or KT825A-KT825G. Instead of KR140UD1408A, KR140UD6B, K140UD14A, LF411, LM301A or another op-amp with a low input current and a suitable supply voltage will be suitable (correction of the printed circuit board conductor pattern may be required). The K142EN12A stabilizer can be replaced with the imported LM317T.

If it is necessary that the output voltage can be adjusted from zero, you need to add a galvanically isolated additional voltage stabilizer of 1.25 V to the source (it can also be assembled on K142EN12A) and connect it with a plus to the common wire, and a minus to the right terminal connected together and a variable resistor R10 motor, previously disconnected from the common wire.

Radio No. 10, 2006

List of radioelements

Due to their high efficiency, switching voltage stabilizers have recently become increasingly widespread, although they are, as a rule, more complex than traditional ones and contain a larger number of elements. For example, a simple pulse stabilizer (Fig. 5.6) with an output voltage lower than the input voltage can be assembled using only three transistors, two of which (VT1, VT2) form a key control element, and the third (VT3) is an amplifier of the mismatch signal.

The device operates in self-oscillating mode. The positive feedback voltage from the collector of transistor VT2 (it is composite) through capacitor C2 enters the base circuit of transistor VT1. Transistor VT2 periodically opens until it is saturated with the current flowing through resistor R2. Since the base current transfer coefficient of this transistor is very large, it saturates at a relatively small base current. This allows you to choose the resistance of resistor R2 quite large and, therefore, increase the transmission coefficient of the control element.

The voltage between the collector and the emitter of the saturated transistor VT1 is less than the opening voltage of the transistor VT2 (in a compound transistor, as is known, two are connected in series between the base and emitter terminals р-n junction), so when transistor VT1 is open, VT2 is securely closed.

The comparison element and mismatch signal amplifier is a cascade on transistor VT3. Its emitter is connected to the reference voltage source - zener diode VD2, and the base - to the output voltage divider R5...R7.

In pulse stabilizers, the regulating element operates in switch mode, so the output voltage is regulated by changing the duty cycle of the switch. In the device under consideration, the opening and closing of transistor VT2 is controlled by transistor VT1 based on a signal from transistor VT3. At the moments when transistor VT2 is open, electromagnetic energy is stored in inductor L1, due to the flow of load current. After the transistor closes, the stored energy is transferred to the load through the diode VD1.

Despite its simplicity, the stabilizer has a fairly high efficiency. So, with an input voltage of 24 V, output voltage of 15 V and a load current of 1 A, the measured efficiency value was 84%.

Choke L1 is wound on a ring K26x16x12' of ferrite with magnetic permeability 100 with a wire with a diameter of 0.63 mm and contains 100 turns. The inductance of the inductor at a bias current of 1 A is about 1 mH. The characteristics of the stabilizer are largely determined by the parameters of transistor VT2 and diode VD1, the speed of which should be as high as possible. The stabilizer can use transistors KT825G (VT2), KT313B, KT3107B (VT1), KT315B, (VT3), diode KD213 (VD1) and zener diode KS168A (VD2).

T That’s what Alexander Borisov called this power supply when I showed him what happened in the end))) so be it, let my power supply now bear the proud name - Cosmic)

As has already become clear, we'll talk about a power supply with adjustable output voltage, this article is not new at all, 2 years have passed since the creation of this power supply, but I still couldn’t implement the topic on the website. At that time, this power supply was the most acceptable for me in terms of availability of parts and repeatability. The power supply diagram was taken from RADIO 2006 magazine, issue No. 6.

The source is convenient for powering electronic devices being set up and charging batteries. The stabilizer is built according to a compensation circuit, which is characterized by a low level of output voltage ripple and, despite the low efficiency compared to switching stabilizers, it fully meets the requirements for a laboratory power source.

The electrical circuit diagram of the power supply is shown in Fig. 1. The source consists of a network transformer T1, a diode rectifier VD3-VD6, a smoothing filter SZ-S6, a voltage stabilizer DA1 with an external powerful control transistor VT1, a current stabilizer assembled on the op-amp DA2 and an auxiliary bipolar power supply, an output voltage/load current meter PA1 with switch SA2 "Voltage"/"Current".

In voltage stabilization mode, the output of op-amp DA2 is high, LED HL1 and diode VD9 are closed. Stabilizer DA1 and transistor VT1 operate in standard mode. With a relatively small load current, transistor VT1 is closed, and all the current flows through the stabilizer DA1. As the load current increases, the voltage drop across resistor R3 increases, transistor VT1 opens and enters linear mode, turning on and unloading stabilizer DA1. The output voltage is set by the resistive divider R6R10. Rotate the knob of the variable resistor R10 to set the required output voltage of the source.

The current feedback signal is removed from resistor R9 and supplied through resistor R8 to the inverting input of op-amp DA2. When the current increases above the value set by the variable resistor R8, the voltage at the output of the op-amp decreases, the diode VD9 opens, the HL1 LED turns on and the stabilizer goes into load current stabilization mode, indicated by the HL1 LED.

In my version, for some reason this current protection only works during a short circuit.

The idea of ​​such a joint inclusion of a three-terminal adjustable stabilizer and an operational amplifier is borrowed from technical description stabilizer LM317T.

The auxiliary low-power bipolar power supply op-amp DA2 is assembled on two half-wave rectifiers on VD1, VD2 with parametric stabilizers VD7R1, VD8R2. Their common point is connected to the output of the adjustable stabilizer DA1. This scheme was chosen for reasons of minimizing the number of turns of auxiliary winding III, which must be additionally wound on the network transformer T1.

Most of the parts of the block are placed on a printed circuit board made of fiberglass foil on one side with a thickness of 1 mm. Resistor R9 is made up of two 1.5 Ohm resistances with a power of 1 W. Transistor VT1 is mounted on a pin heat sink with external dimensions of 130x80x20 mm, which is the rear wall of the source casing. Transformer T1 must have an overall power of 40...50 W. The voltage (under load) of winding II should be about 25 V, and winding III - 12 V.

With the element ratings indicated in the diagram, the unit provides an output voltage of 1.25...25 V, load current - 15...1200 mA. The upper voltage limit, if necessary, can be expanded to 30 V by selecting R6R10 divider resistors. The upper current limit can also be raised by reducing the resistance of the shunt R9, but in this case you will have to install rectifier diodes on the heat sink, use a more powerful transistor VT1 (for example, KT825A-KT825G) and possibly a more powerful transformer.

First, a rectifier with a filter and a bipolar power supply for op-amp DA2 are installed and tested, then everything else except DA2. After making sure that the adjustable voltage stabilizer is working, solder in op-amp DA2 and check the adjustable current stabilizer under load. Shunt R11 is made independently (its resistance is hundredths or thousandths of an ohm), and the additional resistor R12 is selected for the specific microammeter available. My source uses an M42305 microammeter with a full needle deflection current of 50 μA.

Capacitor C13, in accordance with the recommendations of the manufacturer of the K142EN12A stabilizer, it is advisable to use tantalum, for example, K52-2 (ETO-1). The KT837E transistor can be replaced with KT818A-KT818G or KT825A-KT825G. Instead of KR140UD1408A, KR140UD6B, K140UD14A, LF411, LM301A or another op-amp with a low input current and a suitable supply voltage will be suitable (correction of the printed circuit board conductor pattern may be required). The K142EN12A stabilizer can be replaced with the imported LM317T.

If it is necessary that the output voltage can be adjusted from zero, you need to add a galvanically isolated additional voltage stabilizer of 1.25 V to the source (it can also be assembled on K142EN12A) and connect it with a plus to the common wire, and a minus to the right ones connected together the output and motor of the variable resistor R10, previously disconnected from the common wire.

Well, now how I implemented this power supply.

The search for radio components began:

The upper current limit was expanded to 2.5 A by using a shunt from a “C” type pointer device

To display the output parameters, I used an ICL 7107 ADC, one ADC for displaying current, another ADC for voltage.

I got a ready-made digital block for an ADC from a previous job, these blocks had already been written off due to inoperability, fortunately, only the internal measuring trans was unusable, the rest was intact.

Rice. 2. Voltmeter circuit

I assembled the circuit from scratch, the one that was in finished block didn’t fit, so I had to dig up information, look for datasheets, and in the end the diagram turned out like this, in principle no different from the one according to the datasheet.

During the setup process, it turned out that the ADC can be powered with unipolar voltage. The brightness of the LED segments can be varied by adding or removing 1N4148 diodes.

Setting up the ADC - Using a 10 kOhm trimmer resistor R5, set the voltage between the pins. 35 and 36 equal to 1 V. The given circuit is a voltmeter circuit, below is a circuit of an input divider for constructing an ammeter

(Fig. 3.)

Rice. 3. Divider

When assembling the ammeter, it is necessary to exclude resistor R3 Fig. 2 and connect a divider in its place (in the figure it is labeled “to 31 legs”)

In order to make it possible to measure currents from 20 mA to 2.5 A, a chain of resistors R5-R8 was introduced into the divider (the diagram shows frequently used ranges), but for myself, as I said above, I limited it to 2.5 A. Capacitor in the divider - 100...470nF. You can, of course, use multimeters like DT-838 to display output parameters by building them into the power supply housing.

There was no extra winding on the trans to power all the ADCs, so we had to use another small trans.

The transformer that powers the ADC feeds the cooler to cool the power transistor and the cranks, I’m already thrifty about this) It would be possible to do without a cooler.

I didn’t draw the ADC power supply, everything is simple there, a KTs407 diode bridge, a 5-volt bank and two electrolytes

The housing is used from a high-frequency millivoltmeter

So this is the result of the Space Power Supply, excuse my importunity, but I really like using LEDs as backlighting)))

OK it's all over Now. The BP is still working to this day, and it’s already 2013.

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