IRFz44N gate shorting to drain

1

Hi

I am using IRFz44N where gate is driven by BC547 with 33K resistor connected with its collector and power supply of 12VDC. the load is connected in between positive of same 12VDC and drain of mosfet. Source is connected to GND. gate is controlled by PWM of 1KHz max. This configuration works well for sometimes, somedays and sometimes a months too, but after sometimes, the Drain and Source get short circuit, why? Can you suggest something to protect drain and source to get short circuited.

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Hi Siddiq.
The only ting that comes to mind is if the load had any inductance at all. You would then treat this load the same as a motor by inserting a diode across it.
This diode has to be a fast schottky and connect across the load with the cathode to positive supplying the anode to negative or Mosfet Drain
A suitable diode would be MBR20100CT. This might seem a bit of an over kill but this device is commonly used in motor drive applications and is proven to work well. It has in fact 2 diodes (clearly marked on the package) in the one pack so just connect the 2 in parallel which is the normal thing to do for this application.
Cheers Bob.
Add on: The other thing I noticed is you are using 33kΩ series gate resistor. As the gate capacitance is 1470pF this will slow down the switching time with possible overheating the Mosfet and subsequent failure.
You could reduce this to 3k3Ω or even as low as 1k.

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