Bi-directional magnetic isolator

Abstract

A bi-directional, magnetic isolator which can pass an isolated housekeeping supply voltage from an input side to an output side and can also transfer an isolated error signal from the output side to the input side of the isolator. The dual functions of the magnetic isolator allow a power supply to operate properly during either a no-load or output short circuit condition. The magnetic isolator comprises a pair of pulse transformers each having a primary and a secondary winding. The housekeeping supply voltage is transferred through one of the pulse transformers by pulsing the supply voltage from the primary winding to a secondary winding, rectifying the pulsating voltage and storing the rectified voltage on an output capacitor. The error signal is transferred in an opposite direction through the second pulse transformer using the same technique, i.e., the error signal is chopped to create a pulsating signal that can be transferred from a primary winding to a secondary winding of the second pulse transformer where it is rectified and stored on an output capacitor as a voltage representative of the error signal. A fixed on-time clock is used to pulse both the supply voltage and the error signal.