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Power supply: with and without regulation, laboratory, pulsed, device, repair. Simple power supply Do-it-yourself 5v 1a power supply

The article describes a simple and inexpensive network block power supply with an output voltage of 5 V and a load current of up to 4 A.

The power source is a single-ended flyback voltage converter with self-excitation. Distinctive feature The proposed device is the absence of specialized microcircuits, simplicity and low cost of manufacture.

Main technical characteristics

The device diagram is shown in Figure 1. The power supply contains a network rectifier VD1-VD4, a noise suppression filter L1C1-SZ, a converter based on a switching transistor VT1 and a pulse transformer T1, an output rectifier VD8 with a filter C9C10L2 and a stabilization unit made on a stabilizer DA1 and an optocoupler U1.

Fig.1. Schematic diagram devices

The device works as follows. After turning on the power source, the switching transistor VT1 opens slightly and current begins to flow through the primary winding of the pulse transformer T1. In the winding feedback II of the transformer is induced by an EMF, which through a positive feedback circuit - resistor R9, diode VD5, capacitor C5 is supplied to the gate of field-effect transistor VT1. As a result, an avalanche-like process develops, leading to the complete opening of the switching transistor. Energy accumulation begins in transformer T1. The current through the switching transistor VT1 increases linearly, and the voltage from the current sensor-resistor R10 through the diode VD6 and capacitor C7 affects the base of the phototransistor of the optocoupler U1.1, opening it slightly, which causes the voltage at the gate of the field-effect transistor to decrease. The reverse process begins, leading to the closing of the switching transistor VT1. At this moment, diode VD8 opens and the energy accumulated in transformer T1 is transferred to the output filter capacitor C9.

When the output voltage for any reason exceeds the rated value, the DA1 stabilizer opens and current begins to flow through it and the series-connected emitting diode of the optocoupler U1.2. The emission of the diode leads to an earlier opening of the optocoupler transistor, as a result of which the on-state time of the switching transistor decreases, less energy is stored in the transformer, and, consequently, the output voltage decreases.

If the output voltage decreases, the current through the optocoupler emitting diode decreases, and the optocoupler transistor closes. As a result, the open time of the switching transistor increases, more energy is stored in the transformer and the output voltage is restored.

Resistor R3 is necessary to reduce the influence of the dark current of the optocoupler transistor and improve the thermal stability of the entire device. Capacitor C7 increases the stability of the power supply. Circuit C6R8 speeds up the switching processes of transistor VT1 and increases the efficiency of the device.

According to the above scheme, several dozen power supplies with an output power of 15...25 W were manufactured.

In place of the switching transistor VT1, you can use both field-effect and bipolar transistors, for example, the 2T828, 2T839, KT872, KP707, BUZ90, etc. series. The 4N35 transistor optocoupler can be replaced with any of the AOT110, AOT126, AOT128 series, and the KR142EN19A stabilizer can be replaced with TL431 . However, the best results were obtained with imported elements (BUZ90, 4N35, TL431).

All resistors in the power supply are for surface mounting of standard size 1206 with a power of 0.25 W, capacitors C1-SZ, C8 - K10-47v for a voltage of 500 V, C5-C7 are for surface mounting of standard size 0805, the rest are any oxide ones.

Transformer T1 is wound on two folded together ring magnetic cores K19x11x6.7 made of MP 140 permalloy. The primary winding contains 180 turns of PEV-2 0.35 wire, winding II - 8 turns of PEV-2 0.2 wire, winding III for the output voltage 5V - 7 turns of five conductors PEV-2 0.56. The winding order corresponds to their numbering, and the turns of each winding must be evenly distributed along the entire perimeter of the magnetic circuit.

Chokes L1 and L2 are made on ring magnetic cores K15x7x6.7 from MP140 permalloy. The first contains two windings of 30 turns each, wound with PEV-2 0.2 wire on different halves of the magnetic core, the second is wound with PEV-2 0.8 wire in one layer along the entire length of the magnetic core as much as will fit.

To reduce output voltage ripple, the common point of capacitors C2 and SZ should first be connected to the negative terminal of capacitor C10, and then to the remaining parts - winding III of transformer T1, negative terminal of capacitor C9, resistor R12 and terminal 2 of stabilizer DA1.

The device is assembled on printed circuit board dimensions 80x60 mm. On one side of the board there are printed conductors and surface-mount elements, as well as a switching transistor VT1 and a diode VD8, which are pressed against an aluminum heat sink plate of the same dimensions, and on the other - everything else.

It is better to turn on the device for the first time from a current-limiting power source, for example, B5-50, and the operating voltage should be applied immediately, rather than increasing it gradually. Setting up the device consists of adjusting the output voltage with the divider R11R12 and, if necessary, setting the threshold for limiting the output power with the current sensor R10 (the beginning of a sharp drop in the output voltage when the load current increases).

To obtain a different output voltage, you need to proportionally change the number of turns of winding III of transformer T1 and the division coefficient of the divider R11R12.

When operating the device, you should remember that its negative terminal is galvanically connected to the network.

List of radioelements

Designation	Type	Denomination	Quantity	My notepad
DA1	Linear regulator	KR142EN19A	1	To notepad
VT1	Transistor	KP707V1	1	To notepad
VD1-VD4, VD7	Diode	KD258G	5	To notepad
VD5, VD7	Diode	KD629AS9	2	To notepad
VD8	Diode	KD238VS	1	To notepad
U1	Optocoupler	4N35M	1	To notepad
C1-C3, C7	Capacitor	3300 pF	4	To notepad
C4		10 µF 400 V	1	To notepad
C5, C8	Capacitor	0.022 µF	2	To notepad
C6	Capacitor	680 pF	1	To notepad
C9	Electrolytic capacitor	1000 µF 16 V	1	To notepad
C10	Electrolytic capacitor	100 µF 16 V	1	To notepad
R1, R2, R4-R7	Resistor	180 kOhm	6	To notepad
R3	Resistor	100 kOhm	1	To notepad
R8	Resistor	82 Ohm	1	To notepad
R9	Resistor	3.6 kOhm	1

I present a review of a micro-power voltage converter, which is of little use.

Built quite well, compact size 34x15x10mm

Stated:
Input voltage: 0.9-5V
With one AA battery, output current up to 200mA
With two AA batteries, output current 500~600mA
Efficiency up to 96%
Real converter circuit

What immediately catches your eye is the very small capacitance of the input capacitor - only 0.15 µF. Usually they set it more than once in 100, apparently they naively count on the low internal resistance of the batteries :) Well, they installed this one and God bless it, if necessary, you can change it - I immediately set it to 10 μF. Below in the photo is the original capacitor.

The dimensions of the throttle are also very small, which makes you think about the veracity of the declared characteristics
A red LED is connected to the converter input, which begins to glow when the input voltage is more than 1.8V

The test was carried out for the following stabilized input voltages:
1.25V - voltage of Ni-Cd and Ni-MH batteries
1.5V - voltage of one galvanic cell
3.0V - voltage of two galvanic cells
3.7V - Li-Ion battery voltage
At the same time, I loaded the converter until the voltage dropped to a reasonable 4.66V

Open circuit voltage 5.02V
- 0.70V - the minimum voltage at which the converter starts idling. The LED naturally does not light up - there is not enough voltage.
- 1.25V no-load current 0.025mA, maximum output current only 60mA at a voltage of 4.66V. The input current is 330mA, the efficiency is about 68%. The LED naturally does not light up at this voltage.

- 1.5V no-load current 0.018mA, maximum output current 90mA at a voltage of 4.66V. The input current is 360mA, the efficiency is about 77%. The LED naturally does not light up at this voltage.

- 3.0V no-load current 1.2mA (consumes mainly the LED), maximum output current 220mA at a voltage of 4.66V. The input current is 465mA, the efficiency is about 74%. The LED glows normally at this voltage.

- 3.7V idle current 1.9mA (consumes mainly the LED), maximum output current 480mA at a voltage of 4.66V. The input current is 840mA, the efficiency is about 72%. The LED glows normally at this voltage. The converter begins to warm up slightly.

For clarity, I summarized the results in a table.

Additionally, at an input voltage of 3.7V, I checked the dependence of the conversion efficiency on the load current
50mA - efficiency 85%
100mA - efficiency 83%
150mA - efficiency 82%
200mA - efficiency 80%
300mA - efficiency 75%
480mA - efficiency 72%
As is easy to see, the lower the load, the higher the efficiency
Falls far short of the stated 96%

Output voltage ripple at 0.2A load

Output voltage ripple at 0.48A load

As is easy to see, at maximum current the ripple amplitude is very large and exceeds 0.4V.
Most likely this is due to a small output capacitor with a high ESR (measured 1.74 Ohm)
Operating conversion frequency about 80 kHz
I additionally soldered 20 µF ceramics to the output of the converter and received a 5-fold reduction in ripple at maximum current!

Conclusion: the converter is very low-power - this should definitely be taken into account when choosing it to power your devices

I'm planning to buy +20 Add to favorites I liked the review +37 +69

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 to can make a 12-volt unit on their own, 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 should have 14V - 35V alternating 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, for this it is necessary to prepare an appropriate transformer, diodes and a radiator for the microcircuit.
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 the power transistors for short circuits; to do this, use a multimeter to separately measure the resistance between the collector and emitter of the transistors. This check must be carried out before installing them in the circuit.

Power supply 3 - 24V

The power supply circuit gives 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. The LM 7805 chip 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 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 intended for a small homemade transceiver, author 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. With help variable resistor R2 sets the maximum voltage drop across resistor R7, 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 halogen lamp 12V/20W. 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 are broken on forums when discussing which is better field-effect transistor or ordinary silicon or germanium, 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 when high voltage The resistors are quite powerful and you have to maneuver here, taking into account that the open circuit voltage is 1.41 higher.

Power supply 12V 5A on an integrated circuit LM338

The voltage from the network is supplied to the step-down transformer through the 7A fuse FU1. V1 at 240 volts, is used to protect the power supply circuit from voltage surges in the electrical network. Step-down transformer Tr1 with a voltage on the secondary winding of at least 15 volts and a load current of at least 5 amperes.

The reduced voltage from the secondary winding is supplied to a diode bridge consisting of four rectifier diodes VD1-VD4. At the output of the diode bridge, an electrolytic capacitor C1 is installed, designed to smooth out the ripples of the rectified voltage. Diodes VD5 and VD6 are used as protection devices to prevent capacitors C2 and C3 from discharging from minor leakage current in the LM338 regulator. Capacitor C4 is used to filter the high-frequency component of the power supply.

For normal operation 12V power supply, voltage stabilizer LM338 must be installed on the radiator. Instead of rectifier diodes VD1-VD4, you can use a rectifier assembly with a current of at least 5 amperes, for example, KBU810.

12 volt power supply on stabilizer 7812

The following circuit of a powerful power supply for 12 volts and 5 amperes of load is built on the integrated 7812. Since the permissible maximum load current of this stabilizer is limited to 1.5 amperes, a power transistor VT1 is added to the power supply circuit. This transistor is known as an external bypass transistor.

If the load current is less than 600 mA, then it will flow through the 7812 stabilizer. If the current exceeds 600 mA, then resistor R1 will have a voltage of more than 0.6 volts, as a result of which power transistor VT1 begins to conduct additional current through itself to the load. Resistor R2 limits excessive base current.

The power transistor in this circuit must be placed on a good heatsink. The minimum input voltage should be several volts higher than the voltage at the regulator output. Resistor R1 should be rated at 7 W. Resistor R2 can have a power of 0.5 W.

You can get stabilized 5V or 12V from a simple 1.5 volt battery by using a DC/DC converter on a microcircuit for this LT1073 — DC-DC converter with regulated output or unregulated 5V, 12V. Using it, you can get standard USB voltage from one AA element to power and recharge mobile equipment.

LT1073 - typical DC-DC converter circuit

This IC is available in three different versions, depending on the output voltage. Two with a fixed output voltage of 5V and 12V, but this value can be adjusted. The adjustment is made through a voltage divider with two resistors, which are connected to a voltage comparator, which is responsible for stabilizing the output voltage.

LT1073 - an excellent solution if you need to make a small DC/DC converter with low operating voltage and no-load current consumption.

The most critical element for many inverters is the inductor. If you do not have an inductance meter, then we use some possible ready-made solutions. On a ferrite ring from a burnt-out converter energy saving lamp we wind 7 turns of 0.3 mm wire.

It is recommended to use a tantalum capacitor. The diode must be fast, you should not try to solder ordinary ones here 1N4002 of rectifiers, Schottky is recommended, which are characterized by high response time and low internal resistance, for example 1N5818 suitable for this converter.

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