Simple power supply. How a simple and powerful switching power supply works Making an adjustable power supply

This power supply, based on the LM317 chip, does not require any special knowledge for assembly, and after proper installation from serviceable parts, does not require adjustment. Despite its apparent simplicity, this unit is a reliable power source for digital devices and has built-in protection against overheating and overcurrent. The microcircuit inside itself has over twenty transistors and is a high-tech device, although from the outside it looks like an ordinary transistor.

The power supply of the circuit is designed for voltages up to 40 volts alternating current, and the output can be obtained from 1.2 to 30 volts of constant, stabilized voltage. Adjustment from minimum to maximum with a potentiometer occurs very smoothly, without jumps or dips. Output current up to 1.5 amperes. If the current consumption is not planned to exceed 250 milliamps, then a radiator is not needed. When consuming a larger load, place the microcircuit on a heat-conducting paste to a radiator with a total dissipation area of ​​350 - 400 or more square millimeters. The selection of a power transformer must be calculated based on the fact that the voltage at the input to the power supply should be 10 - 15% greater than what you plan to receive at the output. It is better to take the power of the supply transformer with a good margin, in order to avoid excessive overheating, and be sure to install a fuse at its input, selected according to the power, to protect against possible troubles.
To make this necessary device, we will need the following parts:

• Chip LM317 or LM317T.
• Almost any rectifier assembly or four separate diodes with a current of at least 1 ampere each.
• Capacitor C1 from 1000 μF and higher with a voltage of 50 volts, it serves to smooth out voltage surges in the supply network and the larger its capacitance, the more stable the output voltage will be.
• C2 and C4 – 0.047 uF. There is a number 104 on the capacitor cap.
• C3 – 1 µF or more with a voltage of 50 volts. This capacitor can also be used with a larger capacity to increase the stability of the output voltage.
• D5 and D6 - diodes, for example 1N4007, or any others with a current of 1 ampere or more.
• R1 – potentiometer for 10 Kom. Any type, but always a good one, otherwise the output voltage will “jump”.
• R2 – 220 Ohm, power 0.25 – 0.5 watts.

Before connecting the supply voltage to the circuit, be sure to check the correct installation and soldering of the circuit elements.

Assembling an adjustable stabilized power supply

I assembled it on a regular breadboard without any etching. I like this method because of its simplicity. Thanks to it, the circuit can be assembled in a matter of minutes.

Checking the power supply

By rotating the variable resistor you can set the desired output voltage, which is very convenient.

Lithium-Ion (Li-Io), charge voltage of one can: 4.2 - 4.25V. Further by the number of cells: 4.2, 8.4, 12.6, 16.8.... Charge current: for ordinary batteries is equal to 0.5 of the capacity in amperes or less. High-current ones can be safely charged with a current equal to the capacity in amperes (high-current 2800 mAh, charge 2.8 A or less).
Lithium polymer (Li-Po), charge voltage per can: 4.2V. Further by the number of cells: 4.2, 8.4, 12.6, 16.8.... Charge current: for ordinary batteries is equal to the capacity in amperes (battery 3300 mAh, charge 3.3 A or less).
Nickel-metal hydride (NiMH), charge voltage per can: 1.4 - 1.5V. Further by the number of cells: 2.8, 4.2, 5.6, 7, 8.4, 9.8, 11.2, 12.6... Charge current: 0.1-0.3 capacity in amperes (battery 2700 mAh, charge 0.27 A or less). Charging takes no more than 15-16 hours.
Lead-acid (Lead Acid), charge voltage per can: 2.3V. Further by number of cells: 4.6, 6.9, 9.2, 11.5, 13.8 (automotive). Charge current: 0.1-0.3 capacity in amperes (battery 80 Ah, charge 16A or less).

How to make a full-fledged power supply yourself with an adjustable voltage range of 2.5-24 volts is very simple; anyone can repeat it without any amateur radio experience.

We will make it from an old computer power supply, TX or ATX, it doesn’t matter, fortunately, over the years of the PC Era, every home has already accumulated a sufficient amount of old computer hardware and a power supply unit is probably also there, so the cost of homemade products will be insignificant, and for some masters it will be zero rubles .

I got this AT block for modification.

The more powerful you use the power supply, the better the result, my donor is only 250W with 10 amperes on the +12v bus, but in fact, with a load of only 4 A, it can no longer cope, the output voltage drops completely.

Look what is written on the case.

Therefore, see for yourself what kind of current you plan to receive from your regulated power supply, this potential of the donor and lay it in right away.

There are many options for modifying a standard computer power supply, but they are all based on a change in the wiring of the IC chip - TL494CN (its analogues DBL494, KA7500, IR3M02, A494, MV3759, M1114EU, MPC494C, etc.).

Fig No. 0 Pinout of the TL494CN microcircuit and analogues.

Let's look at several options execution of computer power supply circuits, perhaps one of them will be yours and dealing with the wiring will become much easier.

Scheme No. 1.

Let's get to work.
First you need to disassemble the power supply housing, unscrew the four bolts, remove the cover and look inside.

We are looking for a chip on the board from the list above, if there is none, then you can look for a modification option on the Internet for your IC.

In my case, a KA7500 chip was found on the board, which means we can begin to study the wiring and the location of unnecessary parts that need to be removed.

For ease of operation, first completely unscrew the entire board and remove it from the case.

In the photo the power connector is 220v.

Let's disconnect the power and fan, solder or cut out the output wires so that they don't interfere with our understanding of the circuit, leave only the necessary ones, one yellow (+12v), black (common) and green* (start ON) if there is one.

My AT unit does not have a green wire, so it starts immediately when plugged into the outlet. If the unit is ATX, then it must have a green wire, it must be soldered to the “common” one, and if you want to make a separate power button on the case, then just put a switch in the gap of this wire.

Now you need to look at how many volts the large output capacitors cost, if they say less than 30v, then you need to replace them with similar ones, only with an operating voltage of at least 30 volts.

In the photo there are black capacitors as a replacement option for the blue one.

This is done because our modified unit will produce not +12 volts, but up to +24 volts, and without replacement, the capacitors will simply explode during the first test at 24v, after a few minutes of operation. When selecting a new electrolyte, it is not advisable to reduce the capacity; increasing it is always recommended.

The most important part of the job.
We will remove all unnecessary parts in the IC494 harness and solder other nominal parts so that the result is a harness like this (Fig. No. 1).

Rice. No. 1 Change in the wiring of the IC 494 microcircuit (revision scheme).

We will only need these legs of the microcircuit No. 1, 2, 3, 4, 15 and 16, do not pay attention to the rest.

Rice. No. 2 Option for improvement based on the example of scheme No. 1

Explanation of symbols.

You should do something like this, we find leg No. 1 (where the dot is on the body) of the microcircuit and study what is connected to it, all circuits must be removed and disconnected. Depending on how the tracks will be located and the parts soldered in your specific modification of the board, the optimal modification option is selected; this may be desoldering and lifting one leg of the part (breaking the chain) or it will be easier to cut the track with a knife. Having decided on the action plan, we begin the remodeling process according to the revision scheme.

The photo shows replacing resistors with the required value.

In the photo - by lifting the legs of unnecessary parts, we break the chains.

Some resistors that are already soldered into the wiring diagram can be suitable without replacing them, for example, we need to put a resistor at R=2.7k connected to the “common”, but there is already R=3k connected to the “common”, this suits us quite well and we leave it there unchanged (example in Fig. No. 2, green resistors do not change).

On the picture- cut tracks and added new jumpers, write down the old values ​​​​with a marker, you may need to restore everything back.

Thus, we review and redo all the circuits on the six legs of the microcircuit.

This was the most difficult point in the rework.

We make voltage and current regulators.

We take variable resistors of 22k (voltage regulator) and 330Ohm (current regulator), solder two 15cm wires to them, solder the other ends to the board according to the diagram (Fig. No. 1). Install on the front panel.

Voltage and current control.
To control we need a voltmeter (0-30v) and an ammeter (0-6A).

These devices can be purchased in Chinese online stores at the best price; my voltmeter cost me only 60 rubles with delivery. (Voltmeter: )

I used my own ammeter, from old USSR stocks.

IMPORTANT- inside the device there is a Current resistor (Current sensor), which we need according to the diagram (Fig. No. 1), therefore, if you use an ammeter, then you do not need to install an additional Current resistor; you need to install it without an ammeter. Usually a homemade RC is made, a wire D = 0.5-0.6 mm is wound around a 2-watt MLT resistance, turn to turn for the entire length, solder the ends to the resistance terminals, that's all.

Everyone will make the body of the device for themselves.
You can leave it completely metal by cutting holes for regulators and control devices. I used laminate scraps, they are easier to drill and cut.

So the next device has been assembled, now the question arises: what to power it from? Batteries? Batteries? No! The power supply is what we will talk about.

Its circuit is very simple and reliable, it has short-circuit protection and smooth adjustment of the output voltage.
A rectifier is assembled on the diode bridge and capacitor C2, circuit C1 VD1 R3 is a reference voltage stabilizer, circuit R4 VT1 VT2 is a current amplifier for power transistor VT3, protection is assembled on transistor VT4 and R2, and resistor R1 is used for adjustment.

I took the transformer from an old charger from a screwdriver, at the output I got 16V 2A
As for the diode bridge (at least 3 amperes), I took it from an old ATX block as well as electrolytes, a zener diode, and resistors.

I used a 13V zener diode, but the Soviet D814D is also suitable.
The transistors were taken from an old Soviet TV; transistors VT2, VT3 can be replaced with one component, for example KT827.

Resistor R2 is a wirewound with a power of 7 Watts and R1 (variable) I took nichrome for adjustment without jumps, but in its absence you can use a regular one.

It consists of two parts: the first one contains the stabilizer and protection, and the second one contains the power part.
All parts are mounted on the main board (except for power transistors), transistors VT2, VT3 are soldered onto the second board, we attach them to the radiator using thermal paste, there is no need to insulate the housing (collectors). The circuit was repeated many times and does not need adjustment. Photos of two blocks are shown below with a large 2A radiator and a small 0.6A.

Indication
Voltmeter: for it we need a 10k resistor and a 4.7k variable resistor and I took an indicator m68501, but you can use another one. From resistors we will assemble a divider, a 10k resistor will prevent the head from burning out, and with a 4.7k resistor we will set the maximum deviation of the needle.

After the divider is assembled and the indication is working, you need to calibrate it; to do this, open the indicator and glue clean paper onto the old scale and cut it along the contour; it is most convenient to cut the paper with a blade.

When everything is glued and dry, we connect the multimeter in parallel to our indicator, and all this to the power supply, mark 0 and increase the voltage to volts, mark, etc.

Ammeter: for it we take a resistor of 0.27 ohm!!! and variable at 50k, The connection diagram is below, using a 50k resistor we will set the maximum deviation of the arrow.

The graduation is the same, only the connection changes, see below; a 12 V halogen light bulb is ideal as a load.

List of radioelements

Designation	Type	Denomination	Quantity	Note	Shop	My notepad
VT1	Bipolar transistor	KT315B	1			To notepad
VT2, VT4	Bipolar transistor	KT815B	2			To notepad
VT3	Bipolar transistor	KT805BM	1			To notepad
VD1	Zener diode	D814D	1			To notepad
VDS1	Diode bridge		1			To notepad
C1		100uF 25V	1			To notepad
C2, C4	Electrolytic capacitor	2200uF 25V	2			To notepad
R2	Resistor	0.45 Ohm	1			To notepad
R3	Resistor	1 kOhm	1			To notepad
R4	Resistor