The power supply is made on the basis of two circuits, and in addition they contain only a few discrete elements. In this regard, it is simple to manufacture and set up. At the same time, the power supply has a high rate, such as a stepless voltage within a wide range, low coefficient ripple, output current up to 5A with the possibility of constant current, high reliability. Also, the power supply is protected against short circuit.
The transformer used is the one which produces the secondary winding of 25-35 Volts and at a current of 5 And its output voltage is reduced not by much. 2 capacitors on MC connected in parallel provide low pulsation factor before the integral of the voltage regulator on LM338. The potentiometer P1 is possible to change the output voltage of the power supply from 1.5 V to 25V. Convenient to install the two potentiometers in series for rough and smooth adjustment of the voltage. Double switch SW2 connects or disconnects the current stabilizer is made on the LM317 chip. The current stabilizer allows you to limit the output current of the power supply in the range 0...1.5 A
Instead of the potentiometer P2 is better to use the switch on 8-10 fixed values as the potentiometer is difficult to set the desired current. In the table gives the approximate maximum value of the output current depending on the value of the resistor connected between the legs Adj and Out of the LM317 chip
Current
The resistance of the resistor
20 mA
62 Ohms
30 mA
43 Ohms
40 mA
33 Ohm
80 mA
16 Ohms
350 mA
3,9 Ohm
750 mA
the 1.8 Ohm
1000 mA
the 1.3 Ohm
The power supply in constant current mode, useful for charging batteries with a capacity of up to AC.
The instrument used a voltmeter to 30V and an ammeter 5A.
Both devices are equipped with radiators as tend to heat up especially for large values of output current, it is desirable to use the thermal paste. Naturally the radiators are different and do not contact each other. A good heat will ensure the reliable operation of the device. Board, transformer and all the controls and display are placed in spacious housing, the housing has openings for air circulation.
LM338 Case - out LM317
The method of winding transformer: first wrap of the first winding turn to turn. Then, in the same manner of winding the secondary winding until it fills the entire ring.
Author: Andrey Veselov; Publication: www.cxem.net