Patent ID: 6600239
Filing Date: 2003-07-29
Classification: H02J,H03K

Abstract:
An active protection circuit for a MOSFET isolated switched power supply system, said system comprising a first power supply operatively connected to a node via a first isolation switch and a second power supply operatively connected to said node via a second isolation switch, said active protection circuit comprising:a first power supply monitoring circuit which monitors a first power supply output voltage of said first power supply and generates a first output indicating whether said first power supply output voltage deviates from a first pre-selected voltage level by a first pre-selected amount; and a controller connected to control said first isolation switch and said second isolation switch, said controller connected to receive said first output from said first power supply monitoring circuit and, if said first power supply output voltage deviates from said first pre-selected voltage level by said first pre-selected amount, turn said first isolation switch to an OFF mode to prevent current from flowing therethrough and turn said second isolation switch to an ON mode to allow current to flow therethrough from said second power supply; a first reverse current monitoring circuit which detects reverse current flowing through said first isolation switch and generates a reverse current indicator if reverse current is detected; wherein if said reverse current is detected flowing through said first isolation switch, said first reverse current monitoring circuit turns said first isolation switch to said OFF mode and turns said second isolation switch to an ON mode; and wherein said first reverse current monitoring circuit comprises: a first differential amplifier operatively connected between a first input and a first output of said first isolation switch to generate a first differential amplifier output representative of a voltage drop between said first input and said first output; and a first voltage comparator operatively connected to receive said first differential amplifier output and a pre-selected voltage reference to generate a first voltage comparator output indicative of whether reverse current is flowing through said first isolation switch.