12-V Dimmer

Designing a dimmer for 12 V is tricky business. The dimmers you find in your home are designed to operate from an AC voltage and use this AC voltage as a fundamental characteristic for their operation. Because we now have to start with 12 V DC, we have to generate the AC voltage ourselves. We also have to keep in mind that we’re dealing with battery-powered equipment and have to be frugal with energy. The circuit that we finally arrived at can easily drive 6 lamps of 10 W each. Fewer are also possible, of course.

Resistors:

R1 = 1M

R2 = 47k

R3 = 470k

R4 = 12k

R5 = 100

P1 = 1M preset

Capacitors:

C1,C3,C5 = 10nF

C2,C4 = 6nF8

C6 = 100µF 25V radial

Semiconductors:

D1,D2 = 1N4148

D3 = zener diode 15V /1.3W

T1 = IRL2203, BUZ10, BUZ11, BUZ100 or BUK455 *

IC1 = TS556CN (CMOS) or NE556N (not CMOS)

Miscellaneous:

L1 = 3µH 9A suppressor coil * (e.g., Farnell # 976-416)

K1 = 2-way PCB terminal block, lead pitch 5mm

S1 = on/off switch, 10A

PCB, ref. 030141-1

* see text