Switched mode power supply with additional supply voltage has switch element current input coupled to d.c. voltage produced by transformer, control input coupled to a.c. voltage

摘要

The switched mode power supply has a transformer (TR1) with a primary winding (W1) and secondary windings (W2,W3) for producing supply voltages and a switching transistor (T1) in series with the primary winding. A switch element (T2) has a current input (2) coupled to a direct voltage produced by the transformer and a control input (1) coupled to a transformer alternating voltage.