problem face Humming and Clamping Diode issue

Hi Ketan,
Did you have your transformer varnished? It could help reduce the audible noise. Also, can you send us Vds (Voltage at Drain to Source) during 80V-90V with 3A to 5A current? I would like to check if the circuit in is audible noise range.
Regarding primary snubber diode,it's VBR is only 200V (nominal based on datasheet). It would be better to use higher rating like 1000V. You may check the actual voltage reading across the snubber diode to assess the optimized diode rating that you should use.
Regards,
Jedidiah

Hi Jedidiah,

Transformer is varnished. Voltage of the drain to source pin is as follows.
At 3A load
Input voltage 80VAC = 338V
85VAC = 350V
90VAC = 360V
At 4A load
Input voltage 80VAC = 342V
85VAC = 352V
90VAC = 364V
At 5A load
input voltage 80VAC = 376V
85VAC = 374V
90VAC = 370V

Here i also attached schematic of power supply in which u can see Primary snubber diode VR1 (P6KE200A) from that u will get idea which diode i am talking about.

Thanks and Regards,
Ketan

Hi Ketan,
Can you also get the temperature reading on P6KE200A? If the snubber circuit is too heavy, there will be very high power dissipitation on it.
Regards,
Jedidiah

Hi Jedidiah,

We don't have any temperature reading meter.but we observe diode's temperature is goes very high because diode's soldering point is melt during testing.

Regards,
ketan

Hi Ketan,
Try to increase the value of R3 and R2 to near 400k value each. This would lessen the power dissipation on the snubber circuit and observed if the diode will still get damaged.
Regards,
Jedidiah

Hi Jedidiah
It's not working. Diode is still damage.

Regards,
ketan

Hi Ketan,
Can you send some waveforms across Drain to Source Pins? Also, measure for the waveforms across the zener diode.
Regards,
Jedidiah