1V-27V 3A Variable DC Power Supply Circuit Diagram

Above diagram is the scheme of variable DC power supply with output range of 1V to 17V. This power supply is used very few components, the power supply will be so easy to build. Serial power transistor which will be known and popular 2N3055, power supply has a voltage control and current. The source of alternating voltage is 24V transformer.

This circuit used Integrated Circuit / IC LM723, also known as UA723 which is a dedicated integrated circuit design and manufacture a wide range of stabilized power supplies. If you have little hold on the label of the integrated circuit 723, then you would find between different manufacturers may find some other designation, all of the total number of 723 in the middle of the whole label.

723 can be used independently, without external power transistor, in this case, the output current up to 150mA max and total dissipation from the chip to the max 1W. Of course, such a power supply rather weak, so it is necessary to use external transistors, also known as serial element. The power supply operates in a linear mode, completely analogously, so the dissipation can be very large. As a serial element can be used NPN or PNP transistor or transistors in different weaves.

723 has an integrated reference voltage source (PIN 6) with a typical output voltage of 7.15 V, which may be loaded up to 15mA . The output voltage is dependent on the stability of the reference source , which is amateurish use more than enough accurate and stable.

Current limit is very simple, because it is only an integrated NPN transistor, which begins to open up somewhere at 0.4 V, and thus lowers the base voltage on the integrated output serial transistor.

Serial transistor is routed to the output terminals, all three electrodes, such as the transistor for current limitation.

In the above scheme diagram, the power transformer is not inscribed to 3A of output current is used 75W power transformer with a secondary voltage of 24V .

On the left side of the scheme are 4 diodes in Bridge junction, right behind them are three electrolytic capacitors (elco) of 4700UF that used to smooth the electric current. To 3A of output current would otherwise be enough 2x elcos of 4700uF, but 3x elcos of 4700uF will give you better output. The voltage on the capacitors will be unloaded at the power supply of about 35V when used 24V transformer, and therefore must be used electrolytic capacitors voltage is 35V or more.

Power supply 723 is connected directly to the C1-C3, whereas 35V is still within the limits permitted for the 40V power supply 723 of the hybrid.

The output of the reference source is connected via a resistor divider to the error amplifier to the input IN + and contains the voltage is about 1V, the voltage represents the minimum output voltage of the power supply. According to the manufacturers, to make this voltage 2V or more, but in practice it works also slightly lower. In this power-supply voltage of the divider resistors ( R1 and R3 ), is reduced to approximately 1V .

Output voltage is adjustable via potentiometer P2 ( 10K ), current limit is adjustable with P1 (500ohm, or 470ohm if you have difficulty to find 500ohm pot on market). Current limitation acting through resistor R5 ( 0.15 Ohms ), in that the value of the maximum output current of about 3.5 A. Resistor R5 is 2.5 A output current 0.22 ohm for greater output current, the resistance R5 is lower. For starters it would be good to draw power from 0.22 ohm, then by trying to find an appropriate maximum output current by changing resistors. Suggested values ​​are therefore 0.22 ohm, 0.18 ohm and 0.15 ohm.

Output power section is simple, it is used only one output transistor. Gain exit 723 is made by PNP transistor Q1 medium power, proposed the BD712 or BD912, of course, will be replaced by the proposed fine also similar transistors withstand at least 2A flow and have allowed at least dissipation of 20W and a maximum voltage of at least 40V. Output power transistor Q2 is a 2N3055 or higher.

The printed circuit board is one-sided, printed circuit board to the plate, all the elements except for the output of the transistor Q2, which is mounted on the heat profile of the plate and connected by wires. A potentiometer for adjusting the voltage and current are at the plate, if necessary, they can also be connected by wires. View of the template is from the side of the copper.

Mounting scheme is viewed by the components. Resistor R5 to the tile away from a few millimeters, diodes D1 to D4 also because at higher current warm.