PC 12-V Adapter

This circuit can replace small mains adapters in the vicinity of the computer. This is particularly handy for devices that need a 12-V supply, such as active PC loudspeakers. The necessary 12-V supply voltage is taken directly from the PC power supply. In order to protect the PC supply against possible short circuits, and especially to prevent the PC from being crashed, a current limiting circuit is connected in series with the 12-V supply.

Resistors:
R1 = 0Ω1 5W
R2 = 390 Ω
R3 = 12kΩ
R4 = 5kΩ6
Capacitors:
C1 = 100nF ceramic
Semiconductors:
T1 = BC560C
T2 = IRF9540 (see text)
Miscellaneous:
K1 = 4-way PC-supply plug, PCB mount (Farnell)
K2,K3,K4 = mains adaptor plug, PCB mount