Simple Variable Power Supply 1.5 – 30V, 5A

The power supply is based on two chips and in addition they contain only a few discrete components. In this regard, it is easy to manufacture and configuration. At the same time, the power supply provides a high level indicators, such as the smooth adjustment of the voltage in the large range, low coefficient of fluctuation, the output current up to 5A with the ability to stabilize the current, high reliability. Also, the power supply has short circuit protection.

The transformer uses the secondary winding of 25-35 volts and at a current of 5 A the output voltage is reduced not by much. Two capacitors connected in parallel 4700mkf provide a low ripple factor before the integral voltage regulator on the LM338. Potentiometer P1 can change the power supply from 1.5V to 25V. It is convenient to establish two potentiometers for coarse and consistently smooth adjustment of the tension. Double switch SW2 connects or disconnects a current executed on the chip LM317. Current regulator can limit the output current power supply in the range 0 … 1.5 A.

The potentiometer P2 is best to use the switch to 8-10 as a fixed value potentiometer is difficult to establish the desired current. The following table shows the approximate maximum value of the output current as a function of the resistor connected between pins and Out Adj chip LM317.

Current	Resistor
20 mA	62 Ohm
30 mA	43 Ohm
40 mA	33 Ohm
80 mA	16 Ohm
350 mA	3.9 Ohm
750 mA	1.8 Ohm
1000 mA	1.3 Ohm

Power supply current stabilization mode is useful for charging batteries up to 15AH.
The instrument used a voltmeter to 30V and the ammeter to 5A.
Both devices are equipped with a heatsink that tend to heat up, especially for large values ​​of output current, it is desirable to use thernal grease. Using a different heatsink and no contact with each other. Good Thermal ensure reliable operation. Boards, transformers and all the controls and displays are placed in a large case and has holes for air circulation.

Author: Andrey Veselov