PHOTOVOLTAIC_ISOLATOR_WITH_FAST_RESET

Published:2009/7/16 23:05:00 Author:Jessie | From:SeekIC

Photovoltaic isolators (PVIs) provide an isolated gate drive for MOSFETs and IGBTs. At turn-off, however, they don't pull the gate down to drain the gate charge. Using a programmable junction transistor (PUT) provides a very fast gate pull-down, pulling as much as 5 A to discharge the gate in less than 0.2 s. The PUT is a four-layer structure, much like a silicon-controlled rectifier, but with a much more sensitive anode gate. In this application, the PUT gate is driven by the PVI to a voltage equal to or greater than that of the anode that holds the PUT in the blocking state so that no current flows through the anode-cathode channel. When the PVI is turned off , the PUT gate voltage drops below the anode voltage, triggering the PUT and causing the anode-cathode channel to conduct. Conduction continues until the MOSFET gate voltage drops to about 0.5 V, at which time the PUT stops con-ducting and recovers for another cycle.



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