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Snubber/Clamp for Center Tapped Secondary.

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cyaniccypher

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Hello.

We have a full bridge power supply. And the secondary side of the transformer rings pretty heavily with low load and no load conditions. What is a good snubber/clamp design that can be used here that does not dissipate large amounts of power. (see attached image).

Here are some of the specs:
Switching frequency: 150kHz
Output Voltage: +-125V
Output Current: 0.25A (60W power).

Thanks for the help.

Transformer.JPG
 

Snubber/clamp design depends on the specific transformer used and its parameters (such as leakage inductance). So, not much can be said by just looking at a schematic.

You should experiment with different values of R and C. Start with a set of values such as 1k and 1n. Then, decrease and increase the values of R and C until you get the desired output.

Hope this helps.
Tahmid.
 

Sounds like you may be observing ringing due to operation in DCM at lightly loads (assuming it's a PWM full bridge, not phase shifted). If so, that's completely normal and not cause for alarm. Hard to tell without seeing a more complete schematic, or actual waveforms.

edit: actually I see no inductor in your schematic, so it doesn't seem to be a full bridge converter at all. You need to post a full schematic.
 

mtwieg said:
Sounds like you may be observing ringing due to operation in DCM at lightly loads (assuming it's a PWM full bridge, not phase shifted). If so, that's completely normal and not cause for alarm. Hard to tell without seeing a more complete schematic, or actual waveforms.

edit: actually I see no inductor in your schematic, so it doesn't seem to be a full bridge converter at all. You need to post a full schematic.
Click to expand...


It is unregulated just has 50% duty cycle all the time. The input voltage is always 15V and the transfomer is is 1 to 16 so we always should get 250V total on the output or + and - 125. And we do when the thing is loaded. The problem is only at light loads as you say. But how do we stop the light load ringing?
 

Light load ringing is normal. Which frequency is the ringing you are talking about? It may be some LC ringing between transformer and filter capacitors.
While the ringing can be attenuated using RC snubber, the design can also be modified to reduce this behavior: I would recommend placing an inductor instead of capacitors after the diode bridge... Instead of BRIDGE-C-L-C-L-C use BRIDGE-L-C-L-C.
 

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