AC power supply circuit for halogen lamp LV photo enlarger - has timing circuit controlling thyristor bridge that feeds voltage stabiliser

摘要

The AC power supply circuit, is for a 12V AC lamp which is used in photographic enlargers. It has a constant voltage regulator supplying the lamp with a stabilised AC voltage. The voltage stabiliser is coupled to the output of a half-controlled bridge. The bridge has two thyristors which are triggered by a transistor switch in the timing circuit. The transistor switch is turned on and off by an AC voltage. This voltage is proportional to the mains voltage and it bears a fixed relationship to it but it is of twice the frequency.