In this review of the channel “Reviews of parcels and homemade products from jakson” about a simple circuit of a bipolar power supply with an output voltage of 15 volts at the output. The circuit that we will assemble does not require many details. The main thing is to find that 2 regulators 7815 and 7915. They can be ordered in China.
Radio components, boards can be bought with free shipping in this Chinese store.
As a result, the output should be plus 15 and minus 15 volts of bipolar power. To do this, we need a special transformer, at the output of which we can get a bipolar power supply with a midpoint.
This can be achieved in two ways. For example, if the transformer is built so that between its two contacts (in our case +15 and -15) there is a midpoint, which is the contact of the middle of the secondary winding. The voltage between the middle and first contact will be 15 volts, and between the middle and last, also 15. Between the first and last - 30 volts.
If the design of the transformer does not provide for the point we need, we can take two secondary windings with the same voltage. The midpoint between them will be the midpoint of our 2-polar supply. So let's do it. There will be not 2 windings, but 4, since there are many secondary windings in this transformer, we will connect several to get the required voltage.
An old Soviet military transformer, which is over 30 years old, will be used. Despite this, it works great and in fact there is nothing to break, since it is completely flooded, it is airtight. Perhaps its quality will be even better than that of modern Chinese transformers. But its power is only 60 watts.
The assembly of the block will be implemented on a good quality breadboard. There are IN 5408 diodes in the diode bridge. They are enough with a margin. We also need four electrolytic capacitors. Two of them are at 2200 microfarads, 25 volts and the others are at 100 microfarads, 35 volts. Two 0.1 microfarad capacitors. Also the regulators mentioned above. When soldering the regulators, be careful, as they have different pinouts.
There are two LEDs in the circuit - indicators that are not particularly needed, they can be omitted.
Discussion
How to assemble a simple power supply and a powerful voltage source yourself.
Sometimes you have to connect various electronic devices, including homemade ones, to a 12 volt DC source. The power supply is easy to assemble on your own during half a day off. Therefore, there is no need to purchase a ready-made block, when it is more interesting to make the necessary thing for your laboratory yourself. 
Anyone who wants to be able to make a 12-volt unit on their own, without much difficulty.
Someone needs a source to power the amplifier, and someone needs to power a small TV or radio ...
Step 1: What parts are needed to assemble the power supply...
To assemble the block, prepare in advance the electronic components, parts and accessories from which the block itself will be assembled....
-Circuit board.
- Four diodes 1N4001, or similar. The bridge is diode.
- Voltage stabilizer LM7812.
- Low-power step-down transformer for 220 V, the secondary winding should have 14V - 35V AC voltage, with a load current of 100 mA to 1A, depending on how much power you need to get at the output.
- Electrolytic capacitor with a capacity of 1000uF - 4700uF.
- 1uF capacitor.
-Two 100nF capacitors.
- Cut wires.
-Radiator, if needed.
If you need to get the maximum power from the power supply, you need to prepare the appropriate transformer, diodes and heatsink for the chip.
Step 2: Tools....
For the manufacture of the block, tools for installation are required:
-Soldering iron or soldering station
-Nippers
- Mounting tweezers
-Wire strippers
- Solder suction device.
-Screwdriver.
And other tools that you might find useful.
Step 3: Schematic and more... 
To get a 5 volt stabilized power supply, you can replace the LM7812 stabilizer with the LM7805.
To increase the load capacity by more than 0.5 amperes, you will need a heatsink for the microcircuit, otherwise it will fail from overheating.
However, if you need to get a few hundred milliamps (less than 500 mA) from the source, then you can do without a heatsink, heating will be negligible.
In addition, an LED is added to the circuit to visually verify that the power supply is working, but you can do without it.
Power supply circuit 12v 30A.
When using one 7812 stabilizer as a voltage regulator and several powerful transistors, this power supply is capable of providing an output load current of up to 30 amperes.
Perhaps the most expensive part of this circuit is the power step-down transformer. The voltage of the secondary winding of the transformer must be a few volts more than the stabilized voltage of 12V in order to ensure the operation of the microcircuit. It must be borne in mind that one should not strive for a larger difference between the input and output voltage values, since at such a current the heat sink of the output transistors increases significantly in size.
In the transformer circuit, the diodes used must be designed for a large maximum forward current, approximately 100A. The maximum current flowing through the 7812 chip in the circuit will not exceed 1A.
Six composite Darlington type TIP2955 transistors connected in parallel provide a load current of 30A (each transistor is rated for a current of 5A), such a large current requires an appropriate size of the radiator, each transistor passes through itself one sixth of the load current.
A small fan can be used to cool the radiator.
Checking the power supply
When you first turn it on, it is not recommended to connect the load. We check the operation of the circuit: we connect a voltmeter to the output terminals and measure the voltage, it should be 12 volts, or the value is very close to it. Next, we connect a load resistor of 100 ohms, with a dissipation power of 3 W, or a similar load - such as an incandescent lamp from a car. In this case, the voltmeter reading should not change. If there is no 12 volt voltage at the output, turn off the power and check the correct installation and serviceability of the elements.
Before installation, check the serviceability of the power transistors, since with a broken transistor, the voltage from the rectifier goes directly to the output of the circuit. To avoid this, check the power transistors for a short circuit, to do this, measure the resistance between the collector and emitter of the transistors separately with a multimeter. This check must be carried out before installing them in the circuit.
The power supply circuit produces an adjustable voltage in the range from 3 to 25 volts, with a maximum load current of up to 2A, if you reduce the current-limiting resistor of 0.3 ohms, the current can be increased to 3 amperes or more.
Transistors 2N3055 and 2N3053 are installed on the corresponding heatsinks, the power of the limiting resistor must be at least 3 watts. Voltage regulation is controlled by the LM1558 or 1458 op amp. When using the 1458 op amp, it is necessary to replace the stabilizer elements that supply voltage from pin 8 to 3 op amps from a divider with 5.1 K resistors.
The maximum constant voltage for supplying the op-amps 1458 and 1558 is 36 V and 44 V, respectively. The power transformer must deliver at least 4 volts more than the stabilized output voltage. The power transformer in the circuit has an output voltage of 25.2 volts AC with a tap in the middle. When switching the windings, the output voltage decreases to 15 volts.
The power supply circuit for obtaining a voltage of 1.5 volts uses a step-down transformer, a bridge rectifier with a smoothing filter and an LM317 chip.
A power supply circuit with output voltage regulation to obtain a voltage from 1.5 volts to 12.5 volts, the LM317 microcircuit is used as a regulatory element. It must be installed on the radiator, on an insulating gasket to prevent a short circuit to the case.
Power supply circuit with a fixed output voltage of 5 volts or 12 volts. The LM 7805 microcircuit is used as an active element, LM7812 is installed on a radiator to cool the heating of the case. The choice of transformer is shown on the left side of the plate. By analogy, you can make a power supply for other output voltages.
The circuit is for a small homemade transceiver by DL6GL. When developing the unit, the task was to have an efficiency of at least 50%, a nominal supply voltage of 13.8V, a maximum of 15V, for a load current of 2.7A.
According to what scheme: switching power supply or linear?
Switching power supplies turn out to be small-sized and the efficiency is good, but it is not known how it will behave in a critical situation, output voltage surges ...
Despite the shortcomings, a linear control scheme was chosen: a sufficiently large transformer, not high efficiency, cooling is necessary, etc.
Used parts from a homemade power supply from the 1980s: a heatsink with two 2N3055s. The only thing missing was the µA723/LM723 voltage regulator and a few small parts.
The voltage regulator is assembled on a microcircuit µA723/LM723 in standard inclusion. Output transistors T2, T3 type 2N3055 are mounted on radiators for cooling. Using the potentiometer R1, the output voltage is set within 12-15V. Using the variable resistor R2, the maximum voltage drop across the resistor R7 is set, which is 0.7V (between pins 2 and 3 of the microcircuit).
A toroidal transformer is used for the power supply (it can be any at your discretion).
On the MC3423 chip, a circuit is assembled that is triggered when the voltage (emissions) at the output of the power supply is exceeded, by adjusting R3, the threshold for the voltage operation on leg 2 is set from the divider R3 / R8 / R9 (2.6V reference voltage), voltage is supplied from output 8 to open the thyristor BT145, causing a short circuit leading to the operation of the fuse 6.3a.
To prepare the power supply for operation (fuse 6.3a is not involved yet), set the output voltage, for example, 12.0V. Load the unit with a load, for this you can connect a 12V / 20W halogen lamp. Set R2 so that the voltage drop is 0.7V (the current must be within 3.8A 0.7 = 0.185Ωx3.8).
We configure the operation of overvoltage protection, for this we smoothly set the output voltage to 16V and adjust R3 to actuate the protection. Next, we set the output voltage to normal and install the fuse (before that, we put a jumper).
The described power supply can be reconstructed for more powerful loads, for this, install a more powerful transformer, additional transistors, strapping elements, a rectifier at your discretion.
If you need a powerful power supply, 3.3 volts, then it can be made by redoing the old power supply from the PC or using the above diagrams. For example, in a 1.5 V power supply circuit, replace a 47 ohm resistor of a higher rating, or put a potentiometer for convenience, adjusting it to the desired voltage.
Many radio amateurs still have old Soviet radio components that are lying around idle, but which can be successfully applied and they will serve you faithfully for a long time, one of the well-known UA1ZH circuits that walks around the Internet. Many spears and arrows have been broken on the forums when discussing what is better than a field-effect transistor or an ordinary silicon or germanium one, what temperature of crystal heating they can withstand and which one is more reliable?
Each side has its own arguments, but you can get the parts and make another simple and reliable power supply. The circuit is very simple, it is protected from current overload and, when three KT808s are connected in parallel, it can deliver a current of 20A, the author used such a block with 7 parallel transistors and gave 50A to the load, while the capacitance of the filter capacitor was 120,000 microfarads, the voltage of the secondary winding was 19v. It must be taken into account that the relay contacts must switch such a large current.
With proper installation, the output voltage drawdown does not exceed 0.1 volts
If we need to have a high voltage constant voltage source to power the lamp of the transmitter output stage, what should we use for this? There are many different power supply circuits for 600v, 1000v, 2000v, 3000v on the Internet.
First: for high voltage, circuits are used from transformers for both one phase and three phases (if there is a three-phase voltage source in the house).
Second: to reduce the size and weight, a transformerless power supply circuit is used, directly a 220 volt network with voltage multiplication. The biggest drawback of this circuit is that there is no galvanic isolation between the network and the load, as the output is connected to this voltage source, observing the phase and zero.
The circuit has a step-up anode transformer T1 (for the required power, for example, 2500 VA, 2400V, current 0.8 A) and a step-down incandescent transformer T2 - TN-46, TN-36, etc. To eliminate current surges when switching on and protecting diodes when charging capacitors, switching on through quenching resistors R21 and R22 is used.
The diodes in the high-voltage circuit are shunted by resistors in order to evenly distribute Uobr. Calculation of the nominal value according to the formula R (Ohm) \u003d PIVx500. C1-C20 to eliminate white noise and reduce surges. Bridges of the KBU-810 type can also be used as diodes by connecting them according to the indicated scheme and, accordingly, taking the right amount, not forgetting about shunting.
R23-R26 for discharging capacitors after a power outage. To equalize the voltage on series-connected capacitors, equalizing resistors are placed in parallel, which are calculated from the ratio for every 1 volt there are 100 ohms, but at a high voltage, the resistors turn out to be of sufficiently high power and you have to maneuver here, given that the open circuit voltage is 1 more, 41.
Do-it-yourself transformer power supply 13.8 volts 25 a for a HF transceiver.
Repair and refinement of the Chinese power supply to power the adapter.
I have two multimeters, and both have the same drawback - they are powered by a 9-volt battery of the Krona type.
I always tried to have a fresh 9-volt battery in stock, but, for some reason, when it was necessary to measure something with an accuracy higher than that of a pointer device, the Krona turned out to be either inoperative, or it was only enough for a few hours of work.
It is very difficult to wind a gasket on a ring core of such small dimensions, and winding a wire on a bare core is inconvenient and dangerous. The wire insulation can be damaged by the sharp edges of the ring. To prevent damage to the insulation, blunt the sharp edges of the magnetic core as described.
So that during the laying of the wire, the turns do not “scatter”, it is useful to cover the core with a thin layer of “88N” glue and dry it before winding.
First, the secondary windings III and IV are wound (see the converter diagram). They need to be wound in two wires at once. The turns can be fixed with glue, for example, "BF-2" or "BF-4".
I did not find a suitable wire, and instead of a wire with a calculated diameter of 0.16 mm, I used a wire with a diameter of 0.18 mm, which led to the formation of a second layer in several turns.
Then, also in two wires, the primary windings I and II are wound. The turns of the primary windings can also be fixed with glue.
I assembled the converter using the surface mounting method, having previously connected transistors, capacitors and a transformer with a cotton thread.
The input, output and common bus of the converter was brought out by a flexible stranded wire.
Adjustment may be required to set the desired output voltage level.
I chose the number of turns so that with a battery voltage of 1.0 volts, the output of the converter was about 7 volts. At this voltage, the low battery indicator lights up in the multimeter. In this way, too deep discharge of the battery can be prevented.
If, instead of the proposed KT209K transistors, others are used, then the number of turns of the secondary winding of the transformer will have to be selected. This is due to the different magnitude of the voltage drop across p-n junctions for different types of transistors.
I tested this circuit on KT502 transistors with unchanged transformer parameters. The output voltage dropped by a volt or so.
You also need to keep in mind that the base-emitter junctions of transistors are also output voltage rectifiers. Therefore, when choosing transistors, you need to pay attention to this parameter. That is, the maximum allowable base-emitter voltage must exceed the required output voltage of the converter.
If generation does not occur, check the phasing of all coils. The dots on the converter diagram (see above) mark the beginning of each winding.
To avoid confusion when phasing the coils of the annular magnetic circuit, take as the beginning of all windings, For example, all conclusions coming out from below, and at the end of all windings, all conclusions coming out from above.
Before final assembly, all elements of the circuit were connected with a stranded wire, and the ability of the circuit to receive and give energy was checked.
To prevent a short circuit, the pulse voltage converter was insulated from the side of the contacts with silicone sealant.
Then all structural elements were placed in the case from the "Krona". In order to prevent the front cover with the connector from sinking inward, a celluloid plate was inserted between the front and back walls. After that, the back cover was fixed with 88H glue.
To charge the upgraded "Krona" I had to make an additional cable with a 3.5mm Jack plug at one end. At the other end of the cable, to reduce the likelihood of a short circuit, standard instrument sockets were installed instead of similar plugs.
The DT-830B multimeter immediately started working from the upgraded Krona. But the M890C + tester had to be slightly modified.
The fact is that most modern multimeters have an automatic power off function. The picture shows the part of the multimeter control panel where this function is indicated.
The Auto Power Off circuit works as follows. When the battery is connected, the capacitor C10 will be charged. When the power is turned on, while the capacitor C10 is discharged through the resistor R36, the output of the comparator IC1 is held high, which leads to the firing of transistors VT2 and VT3. Through the open transistor VT3, the supply voltage enters the multimeter circuit.
As you can see, for the normal operation of the circuit, it is necessary to supply power to C10 even before the main load turns on, which is impossible, since our modernized Krona, on the contrary, will turn on only when the load appears.
In general, the whole refinement consisted in installing an additional jumper. For her, I chose the place where it was most convenient to do it.
Unfortunately, the designations of the elements on the electrical circuit did not match the designations on the printed circuit board of my multimeter, so I found the points for setting the jumper like this. The dialer identified the desired switch output, and identified the + 9V power bus by the 8th leg of the operational amplifier IC1 (L358).
It was difficult to purchase just one battery. They are mostly sold, either in pairs or in fours. However, some kits, such as "Varta", come with five batteries in a blister. If you are as lucky as I am, you will be able to share such a kit with someone. I bought the battery for only $3.3, while one Krona costs from $1 to $3.75. True, there are also “Crowns” and $ 0.5 each, but those are completely stillborn.
