ON-OFF MOSFET Switch for Induction Heater

Question

The induction heater was tested using a relay as an ON-OFF switch before and worked so i just want to focus on the MOSFET switch part of the schematic.

When i tested the circuit using a MOSFET switch it worked but after a few tests the OFF state just stopped working. After taking a look at the P Channel MOSFET I noticed that it was always ON even with everything turned off. I suppose something must have burned the MOSFET.

And my question is what may have caused this to happen?

What is "Output Control" is in the schematic. Also why are there 2 outputs? You might start by googling "inductive flyback" and reading the articles that come up. Also, similar articles here: https://electronics.stackexchange.com/questions/357392/selecting-flyback-diode-for-inductive-load https://electronics.stackexchange.com/questions/408176/minimum-specs-before-a-flyback-diode-is-needed-for-a-relay https://electronics.stackexchange.com/questions/388111/flyback-diodes-for-inductive-loads-with-long-wire-runs https://electronics.stackexchange.com/questions/303240/use-of-flyback-diodes — scorpdaddy, May 13 '19 at 16:09

DKNguyen · Accepted Answer · 2019-05-13T16:15:21.973

4

You blew your PMOS. Semiconductors usually fail short.

You are cutting it real close with your PMOS's max Vgs (25V max). Any ringing or spike and you blow your PMOS gate. My money is on that.

It's so close that 24V zeners or TVS diodes to clamp the gate voltage would not help. Use a 12V or 15V clamping diode instead.

schematic

^{simulate this circuit – Schematic created using CircuitLab}

edited May 13 '19 at 16:15

answered May 13 '19 at 16:09

DKNguyen

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Thanks for the information! I'll try making that change in the circuit and see if it solves the problem. – TJCRodrigues May 13 '19 at 16:53

score 1 · Answer 2 · answered May 13 '19 at 16:05

It's probably inductive kickback when you switch the PMOS off. Put a diode in there; cathode to PMOS drain, anode to ground (so it's reverse-biased when the PMOS is on). When you turn off the PMOS the two inductors will pull current from ground until they're discharged.

score 0 · Answer 3 · answered May 13 '19 at 16:28

There a re two ways to address your problems:

Put a high power diode across the switched 24V supply
Put a small wattage Zener diode and diode from Drain to ground

You also need to address the V(GS) for the device you used. That alone may be killing your device.

schematic

^{simulate this circuit – Schematic created using CircuitLab}

ON-OFF MOSFET Switch for Induction Heater

3 Answers3