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MOSFET emergency

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Karkas

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Hello, I had a problem today with three MOSFETs 2SK1212. I have a chopper and everything is working perfectly, my triggering circuit with the optocoupler, the trhee phase diode bridge with the filters, but when I connect the transistor it starts up closed, I mean i don't have a DC controller because the switch is not working. I had a problem with the first one and it was that when I connected the Vgs control signal it went to zero, I realizaed that the transistor was damaged with the static charge, then I tried with a new one and the control signal kept "intact" that was when I connected it to the chopper and powered it but it started up closed, I tried and tried and finally changed it for a new one and it did the same, they walways start up closed, and I never conected it to the Vgs control signal.

That doesn't make any sense to me, I think they came damaged, if you have a different explanation for this a would really appreciate it, actually I would appreaciate any help. I made all the tests withouth any load, in the simulation I used a 100 Ω Load to test the current.
 

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Add a resistor from gate to source (say 10K) to make sure the FET is off with no input.
 
I found out what was happening, if I run tests without any load the 311V will appear in the output completely. I put the load and it worked perfectly.

Problem solved.
 
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