Hello everyone. This article is a companion piece to the video. We will look at a powerful laboratory power supply, which is not yet fully completed, but functions very well.

The laboratory source is single-channel, completely linear, with digital display, current protection, although there is also an output current limitation.

The power supply can provide an output voltage from zero to 20 volts and a current from zero to 7.5-8 Amps, but more is possible, at least 15, at least 20 A, and the voltage can be up to 30 Volts, but my option has a limitation due to with transformer.

Regarding stability and ripples, it is very stable, the video shows that the voltage at a current of 7 Amperes does not drop even by 0.1 V, and the ripples at currents of 6-7 Amperes are about 3-5 mV! in class it can compete with industrial professional power supplies for a couple of hundred dollars.

At a current of 5-6 Amps, the ripple is only 50-60 millivolts; budget Chinese industrial-style power supplies have the same ripples, but at currents of only 1-1.5 amperes, that is, our unit is much more stable and can compete in class with samples for a couple of hundred dollars

Despite the fact that the side is linear, it has high efficiency, it has an automatic winding switching system, which will reduce power losses on transistors at low output voltages and high current.

This system is built on the basis of two relays and a simple control circuit, but later I removed the board, since the relays, despite the declared current of more than 10 Amps, could not cope, I had to buy powerful 30 Ampere relays, but I have not yet made a board for them, but without a system The switching unit works great.

By the way, with the switching system, the unit will not need active cooling; a huge radiator at the rear will be enough.

The case is from an industrial network stabilizer, the stabilizer was bought new, from the store, just for the sake of the case.

I left only a voltmeter, a power switch, a fuse and a built-in socket.

There are two LEDs under the voltmeter, one shows that the stabilizer board is receiving power, the second, red, shows that the unit is operating in current stabilization mode.

The display is digital, designed by a good friend of mine. This is a personalized indicator, as evidenced by the greeting, you will find the firmware with the board at the end of the article, and below is the indicator diagram

But essentially this is a volt/ampere wattmeter, there are three buttons under the display that will allow you to set the protection current and save the value, the maximum current is 10 Amps. The protection is relay, the relay is again weak, and at high currents there is quite a strong heating of the contacts.

There are power terminals at the bottom and a fuse at the output. By the way, foolproof protection is implemented here; if you use the power supply as a charger and accidentally reverse the polarity of the connection, the diode will open, burning the fuse.

Now about the scheme. This is a very popular variation based on three op-amps, the Chinese are also churning them out en masse, in this source it is the Chinese board that is used, but with major changes.

Here is the diagram that I got, with what was changed highlighted in red.

Let's start with the diode bridge. The bridge is full-wave, made on 4 powerful dual Schottky diodes type SBL4030, 40 volts 30 amperes, diodes in TO-247 package.

There are two diodes in one case, I paralleled them, and as a result I got a bridge on which there is a very small voltage drop, and therefore losses, at maximum currents, “that bridge is barely warm, but despite this the diodes are installed on an aluminum heat sink, represented by a massive plate The diodes are isolated from the radiator with a mica gasket.

A separate board was created for this node.

Next is the power part. The original circuit is only 3 Amperes, but a modified one can easily give out 8 Amps in this situation. There are already two keys. These are powerful composite transistors 2SD2083 with a collector current of 25 Amps. It would be appropriate to replace it with KT827, they are cooler.
The keys are essentially parallelized; in the emitter circuit there are equalizing resistors of 0.05 Ohm 10 watts, or rather, for each transistor, 2 resistors of 5 watts 0.1 Ohm are used in parallel.

Both keys are installed on a massive radiator, their substrates are isolated from the radiator; this can not be done, since the collectors are common, but the radiator is screwed to the body, and any short circuit can have disastrous consequences.

The smoothing capacitors after the rectifier have a total capacitance of about 13,000 µF and are connected in parallel.
The current shunt and the specified capacitors are located on the same printed circuit board.

A fixed resistor was added on top (in the diagram) of the variable resistor responsible for regulating the voltage. The fact is that when power is supplied (say 20 Volts) from the transformer, we get some drop on the diode rectifier, but then the capacitors are charged to the amplitude value (about 28 Volts), that is, at the output of the power supply the maximum voltage will be greater than the voltage supplied transformer. Therefore, when connecting a load to the output of the block, there will be a large drawdown, this is unpleasant. The task of the previously indicated resistor is to limit the voltage to 20 Volts, that is, even if you turn the variable to maximum, it is impossible to set more than 20 Volts at the output.

The transformer is a converted TS-180, provides an alternating voltage of about 22 volts and a current of at least 8 A, there are 9 and 15 volt taps for the switching circuit. Unfortunately, there was no normal winding wire at hand, so the new windings were wound with mounting, stranded copper wire 2.5 sq. mm. This wire has thick insulation, so it was impossible to wind the winding at a voltage of more than 20-22V (this takes into account the fact that that I left the original filament windings at 6.8V, and connected the new one in parallel with them).

Since I resumed my amateur radio activities, the thought of quality and universality has often come to my mind. The power supply available and manufactured 20 years ago had only two output voltages - 9 and 12 volts with a current of about one Ampere. The remaining voltages necessary in practice had to be “twisted” by adding various voltage stabilizers, and to obtain voltages above 12 Volts, a transformer and various converters had to be used.

I got pretty tired of this situation and started looking for a lab diagram on the Internet to repeat. As it turned out, many of them are the same circuit on operational amplifiers, but in different variations. At the same time, on the forums, discussions of these schemes on the topic of their performance and parameters resembled the topic of dissertations. I didn’t want to repeat and spend money on dubious circuits, and during my next trip to Aliexpress I suddenly came across a linear power supply design kit with quite decent parameters: adjustable voltage from 0 to 30 Volts and current up to 3 Amps. The price of $7.5 made the process of independently purchasing components, designing and etching the board simply pointless. As a result, I received this set in the mail:

Regardless of the price of the set, I can call the quality of the board's manufacturing excellent. The kit even included two extra 0.1 uF capacitors. Bonus - they will come in handy)). All you need to do yourself is to “turn on the attention mode”, place the components in their places and solder them. The Chinese comrades took care to mix up what only a person who first learned about a battery and a light bulb could do - the board was silk-screened with the component values. The final result is a board like this:

Laboratory power supply specifications

• input voltage: 24 VAC;
• output voltage: 0 to 30 V (adjustable);
• output current: 2 mA - 3 A (adjustable);
• Output voltage ripple: less than 0.01%
• board size 84 x 85 mm;
• short circuit protection;
• protection for exceeding the set current value.
• When the set current is exceeded, the LED signals.

To obtain a complete unit, you should add only three components - a transformer with a voltage on the secondary winding of 24 volts at 220 volts at the input (an important point, which is discussed in detail below) and a current of 3.5-4 A, a radiator for the output transistor and a 24-volt cooler for cooling the radiator at high load current. By the way, I found a diagram of this power supply on the Internet:

The main components of the circuit include:

• diode bridge and filter capacitor;
• control unit on transistors VT1 and VT2;
• the protection node on transistor VT3 turns off the output until the power supply to the operational amplifiers is normal
• fan power supply stabilizer on 7824 chip;
• A unit for forming the negative pole of the power supply of operational amplifiers is built on elements R16, R19, C6, C7, VD3, VD4, VD5. The presence of this node determines the power supply of the entire circuit with alternating current from the transformer;
• output capacitor C9 and protective diode VD9.

Separately, you need to dwell on some components used in the circuit:

• rectifier diodes 1N5408, selected end-to-end - maximum rectified current 3 Amperes. And although the diodes in the bridge work alternately, it would still not be superfluous to replace them with more powerful ones, for example, 5 A Schottky diodes;
• The fan power stabilizer on the 7824 chip was, in my opinion, not very well chosen - many radio amateurs will probably have 12-volt fans from computers on hand, but 24-volt coolers are much less common. I didn’t buy one, deciding to replace the 7824 with a 7812, but during the testing process the BP abandoned this idea. The fact is that with an input alternating voltage of 24 V, after the diode bridge and filter capacitor we get 24 * 1.41 = 33.84 Volts. The 7824 chip will do an excellent job of dissipating the extra 9.84 Volts, but the 7812 has a hard time dissipating 21.84 Volts into heat.

In addition, the input voltage for microcircuits 7805-7818 is regulated by the manufacturer at 35 Volts, for 7824 at 40 Volts. Thus, in the case of simply replacing 7824 with 7812, the latter will work on the edge. Here is a link to the datasheet.

Taking into account the above, I connected the available 12 Volt cooler through the 7812 stabilizer, powering it from the output of the standard 7824 stabilizer. Thus, the cooler’s power supply circuit turned out to be, although two-stage, reliable.

Operational amplifiers TL081, according to the datasheet, require bipolar power +/- 18 Volts - a total of 36 Volts and this is the maximum value. Recommended +/- 15.

And this is where the fun begins regarding the 24 Volt variable input voltage! If we take a transformer that, at 220 V at the input, produces 24 V at the output, then again after the bridge and filter capacitor we get 24 * 1.41 = 33.84 V.

Thus, only 2.16 Volts remain until the critical value is reached. If the voltage in the network increases to 230 Volts (and this happens in our network), we will remove 39.4 Volts of DC voltage from the filter capacitor, which will lead to the death of the operational amplifiers.

There are two ways out: either replace the operational amplifiers with others, with a higher permissible supply voltage, or reduce the number of turns in the secondary winding of the transformer. I took the second path, selecting the number of turns in the secondary winding at the level of 22-23 Volts at 220 V at the input. At the output, the power supply received 27.7 Volts, which suited me quite well.

As a heatsink for the D1047 transistor, I found a processor heatsink in the bins. I also attached a 7812 voltage stabilizer to it. Additionally, I installed a fan speed control board. A donor PC power supply shared it with me. The thermistor was secured between the fins of the radiator.

When the load current is up to 2.5 A, the fan rotates at medium speed; when the current increases to 3 A for a long time, the fan turns on at full power and reduces the temperature of the radiator.

Digital indicator for the block

To visualize the voltage and current readings in the load, I used a DSN-VC288 voltammeter, which has the following characteristics:

• measuring range: 0-100V 0-10A;
• operating current: 20mA;
• measurement accuracy: 1%;
• display: 0.28 "(Two colors: blue (voltage), red (current);
• minimum voltage measurement step: 0.1 V;
• minimum current measurement step: 0.01 A;
• operating temperature: from -15 to 70 °C;
• size: 47 x 28 x 16 mm;
• operating voltage required for operation of the ampere-voltmeter electronics: 4.5 - 30 V.

Considering the operating voltage range, there are two connection methods:

• If the measured voltage source operates in the range from 4.5 to 30 Volts, then the connection diagram looks like this:

• If the measured voltage source operates in the range of 0-4.5 V or above 30 Volts, then up to 4.5 Volts the ampere-voltmeter will not start, and at a voltage of more than 30 Volts it will simply fail, to avoid which you should use the following circuit:

In the case of this power supply, there is plenty to choose from for powering the ampere-voltmeter. The power supply has two stabilizers - 7824 and 7812. Before 7824, the wire length was shorter, so I powered the device from it, soldering the wire to the output of the microcircuit.

About the wires included in the kit

• The wires of the three-pin connector are thin and made of 26AWG wire - thicker is not needed here. Colored insulation is intuitive - red is the power supply for the module electronics, black is ground, yellow is the measuring wire;
• The wires of the two-contact connector are current-measuring wires and are made of thick 18AWG wire.

When connecting and comparing the readings with the multimeter readings, the discrepancies were 0.2 Volts. The manufacturer has provided trimmers on the board to calibrate voltage and current readings, which is a big plus. In some instances, non-zero ammeter readings are observed without load. It turned out that the problem can be solved by resetting the ammeter readings, as shown below:

The picture is from the Internet, so please forgive any grammatical errors in the captions. In general, we're done with the circuitry -

We assemble a laboratory power supply 0-30V 3(5)A.

In this article we present to you a circuit of a power supply regulated from zero to 30 volts for a home radio amateur laboratory, capable of delivering a current of 3 amperes or more to the load. Let's look at the schematic diagram of the device:

The power supply circuit uses a TLC2272 microcircuit (operational amplifier), which receives power from a unipolar source assembled on elements VT1, VD2. According to the diagram, this unit produces a voltage of 6.5 volts, but a 5-volt power supply can also be used, and the value of the resistor R9 will need to be reduced to approximately 1.6 kOhm; it is marked with an asterisk in the diagram, which means that by selecting it it is necessary will set the reference voltage, which should be equal to 2.5 volts.

Resistor R11 – determines the maximum voltage level of the regulation range.

Variable resistor R14 continuously regulates the output voltage of the power supply, and resistor R7 adjusts the current limit (0...3 Amperes). In principle, the limit parameters can be expanded and adjusted, for example, from 0 to 5A. To do this, it will be necessary to recalculate the values ​​of the divider resistors R6 and R8.

The VD4 LED is used as an indicator of the presence of an overload or short circuit.

Power supply circuit board:

View of the printed circuit board from the side of the installed elements:

The printed circuit board is designed to install a socket for the DA1 chip. This will be useful when setting up the power supply after assembling it.

First turn on and how to configure the power supply:

The DA1 chip is not inserted into the socket, resistor R14 is in the lower position according to the diagram.
Turn on the power, measure the voltage at capacitor C1, it should be within 35...38 volts.
Using resistor R2 (SP5 series) we set the voltage to 6.5 volts on the 8th pin of the socket of the DA1 microcircuit.
Turn off the power, insert DA1 into the socket, turn on the power, and measure the supply voltage of the microcircuit again. If it is different from 6.5V, we make an adjustment.
We set the reference U = 2.5 volts at the top terminal of potentiometer R14 according to the diagram (as already written above, it is in the lower position according to the diagram), that is, we select the value of R9.
We unscrew the potentiometer R14 to the upper position according to the diagram, adjust the upper limit of voltage regulation by adjusting the resistor R11 (SP5 series), set it to 30 volts.
Resistor R16 is indicated by a dotted line in the diagram. If you do not install it, the minimum output U will be equal to 3.3 mV, in principle this is practically zero. When installing R16 rated at 1.3 MΩ, the minimum voltage should be 0.3 mV. The printed circuit board provides for the installation of this resistor.
The last stage of setup is checking the protection node implemented on the DA1.2 element. If necessary, select the values ​​of resistors R6 and R8.

Possible changes to the scheme.

As already written above, instead of the node that generates the 6.5 V supply voltage for the DA1 microcircuit, you can use a 5-volt source. It can be assembled on a 7805 integrated stabilizer chip according to the following scheme (don’t forget to pick up R9):

You can also convert a node that produces a reference voltage of 2.5 volts, that is, instead of VD3 (TL431) put TLE2425, whose input voltage can be from 4 to 40 volts, and its output will have a stable 2.5 volts. The circuit diagram for TLE2425 is below:

Instead of the TLC2272 operational amplifier, you can install the TLC2262 without any circuit changes.
The domestic analogue of the TL431 chip is 142EN19.
Instead of 2N2222A, you can install BC109, BSS26, ECG123A, 91L14, 2114 or similar characteristics.

You can quite easily make a power source that has a stable output voltage and is adjustable from 0 to 28V. The base is cheap, reinforced with two 2N3055 transistors. In this circuit connection it becomes more than 2 times more powerful. You can, if necessary, use this design to get 20 amperes (almost without modifications, but with an appropriate transformer and a huge radiator with a fan), you just didn’t need such a large current in your project. Once again, make sure you install the transistors on a large heatsink, the 2N3055 can get very hot under full load.

List of parts used in the diagram:

Transformer 2 x 15 volt 10 amp

D1...D4 = four MR750 (MR7510) diodes or 2 x 4 1N5401 (1N5408).

F1 = 1 ampere

F2 = 10 amperes

R1 2k2 2.5 watt

R3,R4 0.1 Ohm 10 watts

R9 47 0.5 watt

C2 two times 4700uF/50v

C3,C5 10uF/50v

D5 1N4148, 1N4448, 1N4151

D11 LED

D7, D8, D9 1N4001

Two 2N3055 transistors

P2 47 or 220 Ohm 1 watt

P3 10k trimmer

Although LM317 and has protection against short circuit, overload and overheating, fuses in the transformer mains circuit and fuse F2 at the output will not interfere. Rectified voltage: 30 x 1.41 = 42.30 volts measured at C1. So all capacitors must be rated for 50 volts. Attention: 42 volts is the voltage that can be at the output if one of the transistors is broken!

Regulator P1 allows you to change the output voltage to any value between 0 and 28 volts. Since in LM317 the minimum voltage is 1.2 volts, then to get zero voltage at the output of the power supply unit - we will put 3 diodes, D7, D8 and D9 at the output LM317 to base 2N3055 transistors. At the microcircuit LM317 the maximum output voltage is 30 volts, but with the use of diodes D7, D8 and D9, the output voltage will drop on the contrary, and it will be about 30 - (3x0.6V) = 28.2 volts. You need to calibrate the built-in voltmeter using the P3 trimmer and, of course, a good digital voltmeter.

Note . Remember to isolate the transistors from the chassis! This is done with insulating and thermally conductive pads or at least thin mica. You can use hot glue and thermal paste. When assembling a powerful regulated power supply, remember to use thick connecting wires that are suitable for carrying large currents. Thin wires will heat up and melt!

The simplest 0-30 Volt power supply for a radio amateur.

Scheme.

In this article we continue the topic of circuit design of power supplies for amateur radio laboratories. This time we will talk about the simplest device, assembled from domestically produced radio components, and with a minimum number of them.

And so, the circuit diagram of the power supply:

As you can see, everything is simple and accessible, the element base is widespread and does not contain shortages.

Let's start with the transformer. Its power should be at least 150 Watts, the voltage of the secondary winding should be 21...22 Volts, then after the diode bridge on capacitance C1 you will get about 30 Volts. Calculate so that the secondary winding can provide a current of 5 Amps.

After the step-down transformer there is a diode bridge assembled on four 10-amp D231 diodes. The current reserve is of course good, but the design is quite cumbersome. The best option would be to use an imported diode assembly of the RS602 type; with small dimensions, it is designed for a current of 6 Amps.

Electrolytic capacitors are designed for an operating voltage of 50 Volts. C1 and C3 can be set from 2000 to 6800 uF.

Zener diode D1 - it sets the upper limit for adjusting the output voltage. In the diagram we see the inscription D814D x 2, this means that D1 consists of two series-connected zener diodes D814D. The stabilization voltage of one such zener diode is 13 Volts, which means two connected in series will give us an upper limit for voltage regulation of 26 volts minus the voltage drop at the junction of transistor T1. As a result, you get smooth adjustment from zero to 25 volts.
The KT819 is used as a regulating transistor in the circuit; they are available in plastic and metal cases. The location of the pins, housing dimensions and parameters of this transistor can be seen in the next two images.