摘要 |
<p>FET protection circuit (10; 100) senses the temperature of a FET (11) and, via a control circuit (24), increases FET conduction in response to sensed FET temperature exceeding a high temperature threshold (160<o>C) close to the maximum rated junction temperature (175<o>C) of the FET. This allows the FET to survive excessive drain-to-source voltages which occur during load dump conditions even when load dump is sensed by a zener diode (26) which initially turns on the FET. During load dump after a zener diode (26) turns on the FET, in response to sensing excessive FET temperature the FET is turned on harder so as to reduce the drain-to-source voltage (VDS) and minimize power dissipation during load dump thereby protecting the FET. Normal overcurrent and maximum temperature turn off circuitry (44, 33, 60-63) is effectively overridden by high temperature threshold turn-on circuitry (50). Preferably, a majority of the control circuit (24) is provided on an integrated circuit, but an external resistor (31) allows effective adjustment of two temperature thresholds (150<o>C, 160<o>C) above which control signals provided to the FET will be modified. <IMAGE></p> |