cupoftea
Advanced Member level 6
Hi,
Customer has sent us a Voltage mode , isolated Pushpull SMPS, 24vin, 24vout and 200W, (np/ns = 5:9) each stage 75kHz.
The Pri FETs are IRF540, but there is no primary snubber whatsoever.
So far they only sent us the schem, they say its been working for years, but want us to have a look
after they changed the transformer to a different vendor.
The primary leakage spike must be getting quenched by the FET avalanching, as there is no snubber. Also, the FETs look like they will be slow switched,
so maybe they are burning up the leakage spike in the linear region operation of the switching FETs aswell.
Is this a bona-fide technique?...ie, relying on the avalanche of the primary FETs to handle the leakage spike?
How long might the FETs last on full power like that?
Of course, the customer may be hardly ever using it on on any significant load, but we don't know that, its not
our power supply.
Customer has sent us a Voltage mode , isolated Pushpull SMPS, 24vin, 24vout and 200W, (np/ns = 5:9) each stage 75kHz.
The Pri FETs are IRF540, but there is no primary snubber whatsoever.
So far they only sent us the schem, they say its been working for years, but want us to have a look
after they changed the transformer to a different vendor.
The primary leakage spike must be getting quenched by the FET avalanching, as there is no snubber. Also, the FETs look like they will be slow switched,
so maybe they are burning up the leakage spike in the linear region operation of the switching FETs aswell.
Is this a bona-fide technique?...ie, relying on the avalanche of the primary FETs to handle the leakage spike?
How long might the FETs last on full power like that?
Of course, the customer may be hardly ever using it on on any significant load, but we don't know that, its not
our power supply.
