Switched-mode power supply with delay network to reduce switching losses

摘要

A switched-mode power supply circuit for converting a d.c. input voltage into a d.c. output voltage. The circuit includes a controllable power switch (Tr1) connected in series with the primary winding (L1) of a transformer (T). This winding forms part of a resonant circuit. To reduce the power losses caused by turning on the switch, the drive path of the switch incorporates a delay network (R11, C9) for each time delaying the turn-on until an instant which is substantially half a cycle of the resonance frequency later than the initial instant of the decrease of the voltage across the switch during its previous cut-off time.