Hi,
We are adjusting power in lots of heaters on the 240VAC mains by trailing edge "phase cutting".
Total power when on full power is some 3kW.
Would you agree, we really must use back-to-back IGBTs rather than FETs as the phase cutting switch,
since FETs would not be able to switch off when a short circuit occurs (eg a heater goes short circuit).
A FET would die, an IGBT would not.
Better would be a GTO Thyristor, but they have more loss than IGBT.
We do plan to have a short circuit detector, which triggers a comparator and turns off the IGBTs when short circuit occurs...unfortunately the short cct current will rise very quickly and so the IGBTs will have to break a very high current.
MOSFET datasheets do not even have a "maximum breaking current" rating, whereas IGBT datasheets do.....some people mistake the "pulsed current rating" of a MOSFET as the allowable breaking current....but if the MOSFET tried to break such a current, it would explode due to the switching loss.
Eg this SIHG70N60 FET has a "pulsed current " rating of 170 Amps, but it would die if it tried to break that current (switch it off)
We are adjusting power in lots of heaters on the 240VAC mains by trailing edge "phase cutting".
Total power when on full power is some 3kW.
Would you agree, we really must use back-to-back IGBTs rather than FETs as the phase cutting switch,
since FETs would not be able to switch off when a short circuit occurs (eg a heater goes short circuit).
A FET would die, an IGBT would not.
Better would be a GTO Thyristor, but they have more loss than IGBT.
We do plan to have a short circuit detector, which triggers a comparator and turns off the IGBTs when short circuit occurs...unfortunately the short cct current will rise very quickly and so the IGBTs will have to break a very high current.
MOSFET datasheets do not even have a "maximum breaking current" rating, whereas IGBT datasheets do.....some people mistake the "pulsed current rating" of a MOSFET as the allowable breaking current....but if the MOSFET tried to break such a current, it would explode due to the switching loss.
Eg this SIHG70N60 FET has a "pulsed current " rating of 170 Amps, but it would die if it tried to break that current (switch it off)
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