dissipation limiter - for variable power supplies

PE july/august 1984 for variable power supplies Most mains power supplies nowadays make use of a voltage regulator IC. These circuits un- doubtedly simplify the design and result in a more compact unit. This applies to fixed output as well as to variable output devices. The latter have, however, one unfortunate characteristic: at high input voltage, low output voltage, and low load current, the dissipation in the regulator is maximum. This loss can be minimized with little additional effort and cost as can be seen from the circuit diagram. In this, the additional components are connected between the bridge rec- tifier and capacitor C1. Immediately after switch. on, a zener voltage, Uz, develops across D5 which causes T1 to conduct. The current through T1 then flows to the gate of silicdn-controlled rectifier (SCR) Th1. The SCR then conducts and the consequent current charges C1 via R4. It is only when C1 is charged that the regulator, IC1, pro- vides an output voltage, Uo, whose l...