need help with power mosfet

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affi

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i am making a power mosfet chopper circuit and i am having some problem. i am using pwm to control it.
i have control speed of a 1.1 kwatt motor with it. The circuit works fine when i apply 5 volts an the control signal but as soon as i apply pwm the mosfet gets burns. I am apply a pwm of 4 kHz. it has to chop voltage from 320 vots dc to 130 volts dc.
plz see the attachments
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Dear affi
Hi
What do you mean by 5 volts , exactly ? is your mean that your GS voltage is 5 volts ???!!! if yes , why not ? my mean is why not your mosfet be burned ?! it is usual ! you should drive your mosfet with 15 volts , not 5 volts ! at the voltages below 12 or 15 volts , your mosfet will be at linear region and it means dissipative region , try to increase your command signal up to 15 volts .
Best Wishes
Goldsmith
 

the N-channel MOSFET is driven by 12V derived from U1 which looks fine.....please provide a discharge path during turned off condition for the Cgs of the MOSFET by providing a Pull down resistor or any active control which might help.......
 

Easiest way would be use IR2121 mosfet driver. so you wont need much of mathematics for choosing components.
 

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