Protection circuit for a switched-mode power supply

摘要

The invention relates to a protection circuit for a switched mode power supply comprising a transformer with a primary winding (W1) and secondary windings (W2 - W6), a switching transistor (TP20) in series with the primary winding (W1) and a driver stage (TP22, TP23) and/or a control capacitor (CP22) for the switching transistor (TP20). The protection circuit comprises a storage capacitor (CP37) which is coupled with a terminal (6) of a secondary winding (W3) which charges said storage capacitor (CP37) during the on-interval of the switching transistor (TP20). During the off-interval of the switching transistor the charge of the storage capacitor (TP37) is fed to the driver stage or the control capacitor (CP22) for closing or keeping closed the switching transistor when one of the secondary windings (W2 - W6) has a short circuit. <IMAGE>