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Inverter Mosfets - Burning Hot

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Sarac

New Member
Hi,

I have build a Square Wave Oscilator, amplified the IC's( 555 ) output with two Transistor ( NPN and PNP ) then fed the amplified output to
two Mosfet gates ( IRFZ44 ) via 1K resistor and drived 1kw transformer for obtaining 220 AC volts from 24 DC Volts.

i have obtained 220 AC volts but with following problems

1- The Mosfet drived by NPN transistor gets too Hot and burns after a minute whilst the other is cool and work as it is desired
i have read Drain - Source current as 0.5A ( with no load ) and 1.5 A
( with 75 Wats load ) and also read 53.5 Volts At both Mosfet
My Question is, why Mosfet burning under this low Power since IRFZ 44 should stand upto 50A. And why the other is not burning. it also works under same voltage and amperage.
will there be something wrong with Gate current of the mosfet.
i haven't measured anything for the gate.

2- Although the entire circuits supply 220 volts for a short time ( till the mosfet smoke up ) it generates 220 volts at high frequencies.
i guess something over 200 HZ. what should be done for 50 HZ 220 Volts.
but it generates only 170 volts at 50 HZ.

Anybody has any suggestion Please. :?:

thnx
 

mechie

New Member
Inverters

Is the 555 running a 50% duty cycle?
I assume you have a centre-tapped primary (low voltage side) on the transformer with one MOSFET pushing each half-winding. Your use of a PNP and a NPN transistor confuses me; I would have expected two identical driver stages.

There is no 'dwell' time between one half-phase and the other so the transformer is attempting to produce big harmonics to infinity, will this not absorb power for no good reason?
If the MOSFETs are running "push-push" into a centre-tapped transformer are both switching for the same time?

Regardless of circuitry are you certain they turn fully on and off?, could one be kept partially conducting and so heating that way?
 
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