1.5-25V Power supply with preregulator

This circuit using KR142EN12 (analog – LM317 ) ic regulator that can handle load currents up to 2 amperes. For higher currents can be used IC LT1083/84/85 that each can handle currents 7/5/3A. 2000uF capacitor C3 is selected from the calculation of the current 1 Ampere. Resistor R9 is used as a current sensor to an ammeter.

In fact, not all of the thyristor passes the half-wave rectified voltage, and some of them, depending on the output voltage and load current. This can significantly reduce the power dissipated in the regulating element, especially at low output voltages and currents.

Parts list :
R1 : 4K3
R2 : 18K
R3 : 100
R4,R8 : 100K
R5 : 1K
R6 : 240
R7 : 4K7 ( Variable resistor )
R9 : 0.33 E
C2 : 0.1uF
C3 : 10000uF/40V
C4 : 100uF/25V
D1 : KY202
D2 : KD521
D3 : D311
D4 : KC147
T1 : KT814B
T3 : KT209
T4 : KT 3102
IC1 : KR142EN14 (LM317)