MOSFET failure & protection

jalathar · ‎2026-05-27

A P-channel MOSFET is currently used for switching the solenoid.

Case 1:
Is it possible for the MOSFET to fail?

Case 2:
If the MOSFET fails, will it become an open circuit or a short circuit?

Case 3:
If the MOSFET fails in short-circuit condition, how can the circuit be protected

Peter BENSCH · ‎2026-05-29

It is not about components from STMicroelectronics, but to help the TO, here is a suggestion for where could insert the fuse mentioned: between drain/R4 and D2/SL.

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Peter BENSCH · ‎2026-05-27

Welcome @jalathar, to the community!

Your questions are questions about the fundamentals of electrical engineering and sound like exam questions from schools.

Yes, there are several reasons why the MOSFET fails
The impact of the failure can depend on several things: the cause of the failure, the design of the MOSFET, the board layout, etc.
For this specific case, only one fuse is necessary.

Is there a specific reason why you’re asking this in a forum for STMicroelectronics devices?

Regards
/Peter

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jalathar · ‎2026-05-28

In case P Channel MOSFET get fail it become open circuit or short circuit (soruce and Drain)?

Peter BENSCH · ‎2026-05-28

A fixed probability for the two cases cannot be stated without specific data. A short circuit between D-S is usually more likely in the event of overload, while an open-circuit fault is more likely if e.g. connection wires, metallisation or mechanical structures fail. The exact cause depends greatly on what the overload looks like.

In short, there can be no general answer to your question.

Regards
/Peter

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jalathar · ‎2026-05-28

My Use of MOSFET is switch the startrer motor solenoid

If possible shortcircuit occur in source to drain ?

AScha.3 · ‎2026-05-28

Yes.

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jalathar · ‎2026-05-28

How to protect the short circuit

Peter BENSCH · ‎2026-05-28

As I already said: this case can be covered by a fuse, but it must be taken into account that it takes time to react.

A better approach than a p-channel MOSFET is an integrated power switch, which, in addition to a p-channel, also includes the corresponding protection functions. They are also available as high-side drivers for automotive and industrial applications.

Regards
/Peter

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Andrew Neil · ‎2026-05-28

As @Peter BENSCH said, there are products specifically designed for this application - which give you protection, diagnostics, etc.

Google* "Automotive solenoid driver" or similar.

* other internet search engines are available

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.

jalathar · ‎2026-05-28

The ignition line of the vehicle is connected to the transistor base, and the transistor collector drives the MOSFET gate. The MOSFET source is connected to the battery supply, while the drain is connected to the positive terminal of the solenoid.

In case the MOSFET fails short between source and drain, the solenoid remains continuously energized. Kindly suggest suitable protection methods for this condition.