Snubber circuits get hot

Posted by: juinbeh on 06/30/2010

Hi,

I'm working on a 190W 22V power supply using the TOP261YN for universal input.
By using the snubber circuit as attached in the diagram, R=8k2, C=10nF, D=MUR460 & TVS of 200V, after 5 minutes of running at full load, the resistor goes up to 120 deg C and the TVS was around 100 deg C.

What can I do to reduce these temperature.

Thanks!

Comments

There are two areas to look at:

Keeping leakage inductance low -- it looks like you have a split primary which is essential at this power level. You may also need foil winding type output. A longer core will also improve coupling and lower leakage inductance.

Lowering switch peak currents -- using a larger core will allow you to operate more heavily in the continuous mode by designing higher primary inductance without increasing turns.

Thanks for the reply, Surak.

The transformer is already of foil output winding type.
I would look at using either a longer core to improve coupling or larger core to lower the switch peak currents.
Do you have any handy links for transformer core sizes?

Thanks.

Remove C4 and R2

Your power level is very high. So the primary peak current is going to be very high. Your snubber is too small to handle the power dissipated at the snubber.
Change R2 to about 80K, Also increase the rated power of your TVZ or instead of having a single 200V TVS place two 100V in series.

Hi PI-Worf,

I have tried R2 of 68k and using two 120V TVS in series.
the temperature measured was TVS of 135degC after 1min of running at full load.
The resistor was about 80 degC and capacitor was 40degC.

What else can I do to reduce the heat?

Thanks.