Direct Current Dimmer

This energy saving, 12-V controller is nearly universally applicable. In addition to controlling battery powered lighting in a car, boat or caravan it is also quite able to control the speed of a model train. In essence, this circuit converts the 12-V DC voltage into a rectangular pulse train with a duty cycle that is adjustable from 0 to 100%. The circuit can be divided into four sub-circuits: the saw-tooth generator built around IC1, reference network P1/R3/C3, comparator IC2 and driver stage T1/T2. The comparator compares the generated sawtooth voltage (1) with the reference voltage (2).

The text erroneously states that the 555 oscillates at 65 Hz. This should be corrected to read "65 ms (15 Hz)". To enable the 555 to oscillate at 65 Hz, the value of capacitor C2 should be lowered to about 220 nF.