MOSFET buring out while switching

[venkates2218]

Refer to the circuit, please.
This is the circuit that controls an industrial horn.
When the horn is turned on, it can draw up to 7A of current.
The issue is that sometimes the MOSFET fails.
All of the buzzers we use have the same specs.
Help resolving the problem.

 

[crutschow]

That circuit makes no sense.
There is no MOSFET and the TRIAC in the DC circuit can never be turned off unless power is removed.

 

[betwixt]

I fully agree with Crutschow's comments.
I suppose if it really is a triac (an SCR would be more appropriate) and it really does run on DC, it is possible the horn is a type that draws intermittent current through magnetically operated but spring returned contacts. That might be enough to turn the device off but some kind of snubber would definitely be needed. I suspect the schematic or description is wrong though.

Brian.

 

[BigBoss]

There isn't MOSFET here, OK.
If L1=3.3 H, this inductor will accumulate so high energy during turning off period and this HV might destroy the TRIAC.
Is it an typo error ??

 

[dick_freebird]

If the horn is electromechanical with a coil and interrupting
switch, that's going to constantly generate flyback voltage
excursions across the coil. Many old buzzers were that way.

Think of them as relays with the NC contact controlling coil
power. Set that up and you'll hear the relay arm buzz.

Maybe if you cut power by this alleged MOSFET at just the
wrong time, its now-open-circuit drain might leave the coil
flyback energy noplace nice to go, and punch out the FET
gate (D-G breakdown).

Or maybe repetitive avalanching is not something the FET
is built for (avalanche rated is a special feature).

 

[D.A.(Tony)Stewart]

In spite of errors in question, flyback energy must be absorbed in a lossy component that must dissipate energy when switched off. If measurements are accurate I estimate 25W across coil such as a lamp of same voltage.