0 Digital-Controlled Power Supply

This circuit is a logic-controlled power supply unit. The regulator IC (like 7805, 7806, 7808, 7812, others) output is controlled by a signal  (CMOS or TTL) from microcontrollers, comparator, opamp, and other signal generators. When signal is 1 (5V) output is high (determined by IC regulator), and when signal is 0 (0V) output is low (0V). You can add fuse at the input or output for protection.

Power supply schematic

Part List:
Q1 - TIP42C, TIP32C or similar PNP transistor
Q2 - 2N2222, CS9013, or similar NPN transistor
R1 - 1.2 kilo ohms 1/4W
R2 - 120 ohms 1/4W
C1 - 100uF electrolytic capacitor rated 16V
C2 - 10uF electrolytic capacitor rated 16V
IC - 7805, 7806, 7812 and other 78XX regulator IC
DC - 15V DC supply

2n2222 pinout

7805, 7806, 78XX pinout

TIP42C, TIP32C pinout