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Old 28th May 2012, 02:56 PM   #1
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Default snubber designing for full bridge power supply

Hi, I want to design snubber for full bridge power supply. I don,t know what to do!!!! what snubber is suitable? and how it will be connect to mosfet? whai is it's calculation?plz help me with this.
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Old 28th May 2012, 03:27 PM   #2
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Hi boy. Normally, snubbers can´t be calculated., they are only aproximations.. I read some literature at the respect, and in conclusion, the trouble is easily solved empirically in the circuit.

The best way is the following: with the circuit working in normal conditions, measure the frequency of the ringing to be eliminated. So, try small capacitors in parallel to the primary of the transformer to tune to 1/2 such frequency, or any other frequency of your interest. Then, start to add small resistor in series with the capacitor, and go increasing its value to damp completely the ringing. Be careful with high voltages in the circuits and the power of the resistor, which obviously must be non inductive.

If you want, you can distribute the cap and the r in two MOSFET´s, or in the 4 ones.

Good luck.
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Old 28th May 2012, 10:37 PM   #3
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Jim Hagerman at Hagerman Technology has an old paper:

"Calculating Optimum Snubbers"

http://www.hagtech.com/pdf/snubber.pdf
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Old 4th June 2012, 11:55 AM   #4
Fanuc is offline Fanuc  United Kingdom
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Default Snubbers

Thanks for the link to that article SpeedSkater.

It appears to me now that it's the RLC resonant tank circuit that is the problem (ie. using soft recovery or shottky diodes is mostly irrelevant and ineffective.)

Toriodals are wideband also. Huge reservior capacitor's do not help.

It's hard to get the data on transfromers unfortunately, but the author's suggested methods to measure transformer inductance and interwinding capacitance do not seem that difficult.

At least we do not need the impedance network part!!

Regards

Kevin
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