Electronic – MOSFET overheating in pwm control


I'm using a MOSFET to switch a 24V, 15A load, with the gate input being a 500Hz PWM signal. However, this is causing the MOSFET to overheat and blow. Any suggestions would be appreciated.

R1 = 100 Ohm

R2 = 1000 Ohm

Q1 = IRL3103PbF (Vdss = 30V, Id = 64A)

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Best Answer

Just for conduction losses, the power dissipation in the MOSFET could typically be \$I^2 \cdot R_{ds(on)}\$ or about 5.4W at Tj = 120°C, assuming 4.5V drive, which your 5V micro should be providing. At only 500Hz the switching losses should not be too bad even with a 100R gate resistor, but they can still add.

You need a fairly large heat sink or a fan to dissipate this amount of heat. Without a heat sink it will quickly overheat and destroy itself.

Edit: As Will Dean pointed out in a comment below, you can tell you've got a problem by looking at the thermal resistance junction-to-ambient (that's with no heat sink) from the datasheet.

enter image description here

The temperature rise above ambient would be 5.4W times 62 or 334°C, so in excess of 350°C with a 25°C ambient. That's way above the absolute maximum junction temperature rating, and the part will fail at some before it gets there.

If you already have a large heat sink, I would suspect that D1 is not doing its job. You do not give the part number, but it will have to dissipate quite a bit of power as well, so a Schottky diode is desirable.