Electrical – MOSFET driver circuit configuration for half bridge MOSFETs for power amplifier


I am making a class D audio amplifier and I am using a MOSFET driver to control two MOSFETs in a half bridge configuration as shown in the circuit below

Driver side

When I connected the circuit without the MOSFET half-bridge, I grounded Vs and I got a neat output according to my needs 15 V peak at HO & LO, The problems started when I connected the MOSFETs, The HO & LO terminals started sending out the same signal but with a max voltage of 3 V or probably less, then the circuit drew around 1 AMP from my voltage source and burned the MOSFET driver chip, I knew for sure that it was burned because the resistance between the VDD terminal and the COM terminal was 26 Ohms instead of the high resistance a new chip had. An engineer in my uni suggested that the problem might be caused because I was providing the 15 volts to the MOSFETs from the same node that supplies the same voltage 15 V to my entire circuit, although my circuit was drawing only 40 milliamps from the power supply before connecting the MOSFETs.

I would like to note that the chip is FAN7390. I have fried two so far. I would guess that the common power supply might be the problem?, or it might be that the switching frequency of 125kHz the problem? The Hin and Lin signals are PWM signals with 15 V peak.

Best Answer

Several things wrong with that design!

  • Where is the decoupling? That 15V line needs a whole pile of cap on it....
  • C4???! 22uF for a boost cap, just insane, get rid of it, the 220n should be fine on its own.
  • R13/14 1k, try more like 100k.
  • Those mosfets, 140nC maximum gate charge?! Yea they are very, very butch fets, but you really want something much smaller and with a very much lower Qg.
  • Layout? It really, really matters.
  • Not the cause of the blowup, but R11/12 seem very high in value, especially given the Qg of those mosfets.