Variable Power Supply 0 to 12 V

This Power supply circuit is powered by 12 volt AC power supply rectifier diodes form VD1 … VD4, included in a bridge circuit and the rectified voltage stabilizer – capacitors CI, C2, zener VD5 and transistors VT1 and VT2. Voltage power supply output from 0 to 12 regulate the variable resistor R2. The highest current given up power supply to the load (300 mA) is limited to permissible direct current rectifier diodes.

In the rectifier diodes can be used D226 or D7 with any letter index. Variable resistor R2 – with a power switch, it is desirable to group A, to its scale, on which set the output voltage of the power supply was equal numbered. In the stabilizer instead of transistor MP39 MP40 transistors can be used … MP42, and instead of P213 – P214 … P217 transistors, P201, P4 with any letter indices. The gain of transistors must be at least 15. Zener diode D813 can be replaced by zener diodes D811, D814D D814G or. The maximum stress on the power supply output voltage will correspond to the stabilization is used to block the zener. Scale of the resistor R2 should calibrate for exemplary voltmeter connected to the output terminals of the block.

Parts list :
R1,R2,R3 : 1K
C1,C2 : 500uF/25V
D1 : D813
Q1 : MP39
Q2 : P213
VR1 : 10K