Latching Overvoltage Protection Using Amplitude Modulated Synch
Original Publication Date: 1988-Sep-01
Included in the Prior Art Database: 2005-Feb-15
This article describes a method of latching-off the primary circuit of a switched mode power supply (SMPS) due to a secondary overvoltage fault. An existing component, the synchronizing transformer, is used to bridge the primary/secondary isolation barrier. The normal sync pulses are amplitude modulated to provide primary shutdown via a silicon controlled rectifier (SCR). In an SMPS with secondary regulators, there is the possibility of an opening of a control loop or a short circuit in the switching or regulating device which would cause excessive voltage at the load. For this reason overvoltage protection is often specified to prevent damage to the load. This protection is usually implemented by 'crowbarring' (deliberate short circuit) the secondary bulk voltage (i.e., the regulator input), Vbus, in Fig. 1.