good evening everyone I have a problem with a Hertz 15kw amplifier that uses IRFP4242 mosfets! The amplifier had a burnt mosfet so after seeing a possible replacement and after also writing to Infineon I replaced the irfp4242 with the IRFP4868! The amplifier with just one pair of MOSFETs works regularly but when I insert all 5 pairs of output MOSFETs the amplifier doesn't start and I have a very bad square wave on the gates! I changed the gate resistance value and by increasing the value from 22 to 56ohm the amplifier turns on but I still don't have a perfect square wave and the mosfets heat up a bit! Do you have any advice to give me?
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Suspect the somewhat higher gate-source capacitance is overloading the gate driver bootstrap capacitor causing it to droop? - increasing gate resistors helps save the capacitor from drooping too much, but slows the transitions leading to greater switching losses.
They are quite close matches but there 30% more capacitance for the replacements - hence my theory. Given the new ones have lower Rds(on) perhaps only fit 4 pairs, not 5? That would help the driver.
They are quite close matches but there 30% more capacitance for the replacements - hence my theory. Given the new ones have lower Rds(on) perhaps only fit 4 pairs, not 5? That would help the driver.
Hi Mark! in fact I did some tests and up to 3 pairs of mosfets it was not necessary to change the gate resistors and I had an excellent square wave on the gates of the mosfets but as I started to increase the pairs of mosfets the problems started! from the driver board I then noticed that after the gate driver there are 2 buffer transistors which should ensure not to overload the ir2110 but evidently it is not enough for these mosfets