Power unit. How to make a switching power supply with your own hands Do-it-yourself 30-volt switching power supply

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 yourself within half a weekend. Therefore, there is no need to purchase a ready-made unit, when it is more interesting to independently make the necessary thing for your laboratory.

Anyone who wants can make 12 volt block independently, without much difficulty.
Some people need a source to power an amplifier, while others need a source 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 1N4001 diodes, or similar. Diode bridge.
- Voltage stabilizer LM7812.
-Low-power step-down transformer for 220 V, the secondary winding must have 14V - 35V AC voltage, with a load current from 100 mA to 1A, depending on how much power is needed at the output.
-Electrolytic capacitor with a capacity of 1000 µF - 4700 µF.
-Capacitor with a capacity of 1uF.
-Two 100nF capacitors.
-Cuttings of installation wire.
-Radiator, if necessary.
If you need to get maximum power from the power source, you need to prepare an appropriate transformer, diodes and a heatsink for the chip.
Step 2: Tools....
To make a block, you need the following installation tools:
-Soldering iron or soldering station
-Pliers
-Installation tweezers
- Wire strippers
-Device for solder suction.
-Screwdriver.
And other tools that may be useful.
Step 3: Diagram and others...

To obtain 5 volt stabilized power, you can replace the LM7812 stabilizer with an LM7805.
To increase the load capacity to more than 0.5 amperes, you will need a heatsink for the microcircuit, otherwise it will fail due to overheating.
However, if you need to get several hundred milliamps (less than 500 mA) from the source, then you can do without a radiator, the heating will be negligible.
In addition, an LED has been 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 several volts higher than the stabilized voltage of 12V to ensure the operation of the microcircuit. It must be borne in mind that you 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 high maximum forward current, approximately 100A. The maximum current flowing through the 7812 chip in the circuit will not be more than 1A.
Six composite Darlington transistors of the TIP2955 type connected in parallel provide a load current of 30A (each transistor is designed for a current of 5A), such a large current requires an appropriate size of the radiator, each transistor passes through one sixth of the load current.
A small fan can be used to cool the radiator.
Checking the power supply
When you turn it on for the first time, it is not recommended to connect a load. We check the functionality of the circuit: 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 100 Ohm load resistor 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 if the transistor is broken, the voltage from the rectifier goes directly to the output of the circuit. To avoid this, check for short circuit power transistors, 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.

Power supply 3 - 24V

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 to 0.3 ohms, the current can be increased to 3 amperes or more.
Transistors 2N3055 and 2N3053 are installed on the corresponding radiators; the power of the limiting resistor must be at least 3 W. Voltage regulation is controlled by an LM1558 or 1458 op amp. When using a 1458 op amp, it is necessary to replace the stabilizer elements that supply voltage from pin 8 to 3 of the op amp from a divider on resistors rated 5.1 K.
The maximum DC voltage for powering op-amps 1458 and 1558 is 36 V and 44 V, respectively. The power transformer must produce a voltage at least 4 volts higher 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 windings, the output voltage decreases to 15 volts.

1.5 V power supply circuit

The power supply circuit to obtain a voltage of 1.5 volts uses a step-down transformer, a bridge rectifier with a smoothing filter and an LM317 chip.

Diagram of an adjustable power supply from 1.5 to 12.5 V

Power supply circuit with output voltage regulation to obtain voltage from 1.5 volts to 12.5 volts; the LM317 microcircuit is used as a regulating element. It must be installed on the radiator, on an insulating gasket to prevent a short circuit to the housing.

Power supply circuit with fixed output voltage

Power supply circuit with a fixed output voltage of 5 volts or 12 volts. As active element The LM 7805, LM7812 microcircuit is used; it is installed on the radiator to cool the heating of the case. The choice of transformer is shown on the left on the plate. By analogy, you can make a power supply for other output voltages.

20 Watt power supply circuit with protection

The circuit is designed for a small transceiver homemade, by DL6GL. When developing the unit, the goal was to have an efficiency of at least 50%, a nominal supply voltage of 13.8V, maximum 15V, for a load current of 2.7A.
Which scheme: switching power supply or linear?
Switching power supplies are small-sized and have good efficiency, but it is unknown how they will behave in a critical situation, surges in the output voltage...
Despite the shortcomings, a linear control scheme was chosen: a fairly large transformer, not high efficiency, cooling required, etc.
Parts from a homemade power supply from the 1980s were used: a radiator with two 2N3055. The only thing missing was a µA723/LM723 voltage regulator and a few small parts.
The voltage regulator is assembled on a µA723/LM723 microcircuit with standard inclusion. Output transistors T2, T3 type 2N3055 are installed on radiators for cooling. Using potentiometer R1, the output voltage is set within 12-15V. Using variable resistor R2, the maximum voltage drop across 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 (can be any at your discretion).
On the MC3423 chip, a circuit is assembled that is triggered when the voltage (surge) at the output of the power supply is exceeded, by adjusting R3 the voltage threshold is set on leg 2 from the divider R3/R8/R9 (2.6V reference voltage), the voltage that opens the thyristor BT145 is supplied from output 8, causing a short circuit leading to tripping of fuse 6.3a.

To prepare the power supply for operation (the 6.3A fuse is not yet involved), set the output voltage to, 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 should be within 3.8A 0.7=0.185Ωx3.8).
We configure the operation of the overvoltage protection; to do this, we smoothly set the output voltage to 16V and adjust R3 to trigger the protection. Next, we set the output voltage to normal and install the fuse (before that we installed a jumper).
The described power supply can be reconstructed for more powerful loads; to do this, install a more powerful transformer, additional transistors, wiring elements, and a rectifier at your discretion.

Homemade 3.3v power supply

If you need a powerful power supply of 3.3 volts, then it can be made by converting an old power supply from a PC or using the above circuits. For example, replace a 47 ohm resistor of a higher value in the 1.5 V power supply circuit, or install a potentiometer for convenience, adjusting it to the desired voltage.

Transformer power supply on KT808

Many radio amateurs still have old Soviet radio components that are lying around idle, but which can be successfully used and they will serve you faithfully for a long time, one of the well-known UA1ZH circuits that is floating around the Internet. Many spears and arrows have been broken on forums when discussing what is better, a field-effect transistor or a regular silicon or germanium one, what temperature of crystal heating will they 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, protected from overcurrent, and when three KT808 are connected in parallel, it can produce a current of 20A; the author used such a unit with 7 parallel transistors and delivered 50A to the load, while the filter capacitor capacity was 120,000 uF, the voltage of the secondary winding was 19V. It must be taken into account that the relay contacts must switch such a large current.

If installed correctly, the output voltage drop does not exceed 0.1 volt

Power supply for 1000V, 2000V, 3000V

If we need to have a high voltage DC source to power the transmitter output stage lamp, what should we use for this? On the Internet there are many different power supply circuits for 600V, 1000V, 2000V, 3000V.
First: for high voltage, circuits with transformers for both one phase and three phases are used (if there is a three-phase voltage source in the house).
Second: to reduce size and weight, they use a transformerless power supply circuit, 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 a given voltage source, observing 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 filament transformer T2 - TN-46, TN-36, etc. To eliminate current surges during switching on and protection diodes when charging capacitors, switching is used through quenching resistors R21 and R22.
The diodes in the high-voltage circuit are shunted by resistors in order to uniformly distribute Urev. Calculation of the nominal value using the formula R(Ohm) = PIVx500. C1-C20 to eliminate white noise and reduce surge voltages. You can also use bridges like KBU-810 as diodes by connecting them according to the specified circuit and, accordingly, taking the required 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 high voltage the resistors turn out to be quite powerful and here you have to maneuver, taking into account that the open-circuit voltage is higher by 1, 41.

Step-by-step instruction

circuit diagram

structural scheme

Assembly is carried out according to the drawn circuit diagram. The microcircuit was selected according to the characteristics of the circuit.

Assembly is carried out as follows:

At the entrance install a PTC thermistor and diode bridges.
Then, a pair of capacitors is installed.
Drivers necessary to regulate the operation of the gates of field-effect transistors. If drivers have a D index at the end of the marking, there is no need to install FR107.
Field effect transistors installed without shorting the flanges. When attaching to the radiator, use special insulating gaskets and washers.
Transformers installed with shorted leads.
The output is diodes.

All elements are installed in the designated places on the board and soldered on the reverse side.

Examination

In order to correctly assemble the power supply, you need to be careful about installing the polar elements, and you should also be careful when working with mains voltage. After disconnecting the unit from the power source, there should be no dangerous voltage remaining in the circuit. If assembled correctly, no further adjustment is required.

You can check the correct operation of the power supply as follows:

We include in the circuit, at the output of the light bulb, for example, 12 volts. At the first short-term start, the light should be on. In addition, you should pay attention to the fact that all elements should not heat up. If something gets hot, it means the circuit is assembled incorrectly.
On the second start We measure the current value using a tester. Let the unit operate for a sufficient amount of time to ensure that there are no heating elements.

In addition, it would be useful to check all elements using a tester for the presence of high current after turning off the power.

As previously noted, the operation of a switching power supply is based on feedback. The considered circuit does not require a special organization of feedback and various power filters.
Particular attention should be paid to the selection of field-effect transistors. In this case, it is recommended field effect transistors IR, which are famous for their thermal resolution resistance. According to the manufacturer, they can operate stably up to 150 degrees Celsius. However, in this circuit they do not heat up very much, which can be called a very important feature.
If the transistors heat up constantly, active cooling should be installed. As a rule, it is represented by a fan.

Advantages and disadvantages

The pulse converter has the following advantages:

High rate stabilization coefficient allows you to provide power conditions that will not harm sensitive electronics.
Designs considered have a high efficiency rate. Modern options executions have this indicator at 98%. This is due to the fact that losses are reduced to a minimum, as evidenced by the low heating of the block.
Large input voltage range- one of the qualities due to which such a design has spread. At the same time, the efficiency does not depend on the input current indicators. It is the immunity to the current voltage indicator that allows you to extend the service life of electronics, since jumps in the voltage indicator are a common occurrence in the domestic power supply network.
Input frequency affects the operation of only the input elements of the structure.
Small dimensions and weight, are also responsible for their popularity due to the proliferation of portable and portable equipment. After all, when using a linear block, the weight and dimensions increase several times.
Organization of remote control.
Lower cost.

There are also disadvantages:

Availability pulse interference.
Necessity inclusion in the circuit of power factor compensators.
Complexity self-regulation.
Less reliability due to the complexity of the chain.
Severe consequences when one or more circuit elements fail.

When creating such a design yourself, you should take into account that mistakes made can lead to failure of the electrical consumer. Therefore, it is necessary to provide protection in the system.

Design and operating features

When considering the operating features of the pulse unit, the following can be noted:

At first The input voltage is rectified.
Rectified voltage depending on the purpose and features of the entire structure, it is redirected in the form of a rectangular pulse high frequency and is fed to an installed transformer or filter operating at low frequencies.
Transformers are small in size and weight when using a pulse unit due to the fact that increasing the frequency makes it possible to increase the efficiency of their operation, as well as reduce the thickness of the core. In addition, ferromagnetic material can be used in the manufacture of the core. At low frequency, only electrical steel can be used.
Voltage stabilization occurs through negative feedback. Thanks to the use this method, the voltage supplied to the consumer remains unchanged, despite fluctuations in the incoming voltage and the generated load.

Feedback can be organized as follows:

With galvanic isolation, an optocoupler or transformer winding output is used.
If you don't need to create a junction, a resistor voltage divider is used.

Using similar methods, the output voltage is maintained with the required parameters.

Standard blocks switching power supply, which can be used, for example, to regulate the output voltage when powering , consists of the following elements:

Input part, high voltage. It is usually represented by a pulse generator. Pulse width is the main indicator that affects the output current: the wider the indicator, the greater the voltage, and vice versa. The pulse transformer stands at the section between the input and output parts and separates the pulse.
There is a PTC thermistor at the output part. It is made of semiconductor and has a positive temperature coefficient. This feature means that as the temperature of the element increases above certain value, the resistance indicator rises significantly. Used as a key security mechanism.
Low voltage part. The pulse is removed from the low-voltage winding, rectification occurs using a diode, and the capacitor acts as a filter element. The diode assembly can rectify current up to 10A. It should be taken into account that capacitors can be designed for different loads. The capacitor removes the remaining pulse peaks.
Drivers they suppress the resistance that arises in the power circuit. During operation, drivers alternately open the gates of installed transistors. Work occurs at a certain frequency
Field effect transistors selected taking into account resistance indicators and maximum voltage when open. At minimum value, resistance significantly increases efficiency and reduces heating during operation.
Transformer standard for downgrade.

Taking into account the chosen circuit, you can begin to create a power supply of the type in question.

In this article we continue the topic of circuit design of power supplies for amateur radio laboratories. This time we will talk about the simple 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 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 will use an imported diode assembly of the RS602 type; with small dimensions, it is designed for a current of 6 Amperes.

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.