Snubber circuit is too hot

If your P6KE200 is reading about 60 to 70 C is not consider too hot in a power supply circuit. If you feel it is very hot, may be you are not correctly measuring the device temperature. So if the real temperature is 70 C, there is no problem. If the device is really hot, you must get a much higher reading.

Using a Thermal Imager I detect 100ºC in the region of Snubber circuit. I supose that temperature is too high, isn't? What can I do to reduce it? Redesign the Transformer? Change the snubber topology?

Antonio:

Could you Please post your schematic, transformer design (including a diagram of the construction), PCB layout, your supply specifications (VIN range, Output power,…) and if possible, measure the transformer primary inductance and leakage inductance. If you do not have a inductance meter you can take a look to http://www.powerint.com/en/design-support/appstv to estimate how to measure your transformer primary inductance and leakage inductance.

After I see your documents we can decide what the best way to reduce the temperature of your snubber.

I am sending the schemactic and the transformer design. The primary inductance is about 1mH. The Voltage input range is from 90VAC...265VAC. If you need more information please let me know.

Thanks,

Antonio.

The worst case for the TVS (Transient Voltage Suppressor) is at low line (90VAC), full Load and maximum operation temperature. I would say 100C is on the border line if you are measuring at worst conditions.

The simplest thing I would do to remove heat form the TVS is to increase C30 to 2.2 - 4.7 nF and to reduce R1 to about 80 K. Also you may increase R2 to about 100 ohms but you need to make sure VD( DRAIN voltage) never exceeds 670 volts. You can measure VD at start up with maximum Vin and maximum load. These changes will make your TVs to run cooler. Let me know if this works for you. Otherwise you will need to make some changes to the transformer to reduce your leakage inductance or to reduce IP (primary peak current). Thank you. PI-Worf

my friend, it should be easily possible for you to dissipate almost nothing in your snubber......you should use a resistor in series with the p6ke tvs.

...it means your drain voltage go higher....and you must of course make sure not too high......
powerint.com have app note on RCDZ snubber for you.

of course , greater experts than me will comment on your design in respect of leakage inductance.....because the outer windings on your trafo will have terrible large leakage terms.........and i suspect that this is what yuo are suffering from............because multi-output designs are assocaiated with large leakage, and hence you dissipate much in your snubber........