# Snubber turn-off Circuit for Power Mosfet

Discussion in 'The Projects Forum' started by brunounreal, Nov 30, 2011.

1. ### brunounreal Thread Starter New Member

Apr 23, 2010
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0
Hi,
I'm designing a step up for a project and when i was measuring to see how it was working i found a wierd situation. I was having some kind of noise at the mosfet drain. Someone told me that it could be solved ( or at least improved ) using a turn off snubber circuit. Could anyone give me a help with that? I never design one. if anyone knows where i can get usefull information or knows ou do design one please help.
I'm using a Power Mosfet.

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2. ### SgtWookie Expert

Jul 17, 2007
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brunounreal likes this.
3. ### crutschow Expert

Mar 14, 2008
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What is the load on the drain?

4. ### brunounreal Thread Starter New Member

Apr 23, 2010
26
0
its a 300 Ω resistor!
first im testing with with a transformer 230/9V and a load of 300 ohms .
but the ideia is project for a trasnformer of 230/30V , to 52V output with a load oh 40 Ω.

5. ### brunounreal Thread Starter New Member

Apr 23, 2010
26
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This is my circuit

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6. ### ErnieM AAC Fanatic!

Apr 24, 2011
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Something seems odd here. Is that waveform the drain of Q1? Then what you are seeing there is the inductor "running out of current" meaning the current built up during the 10uS Q1 on time is fully discharged into the load during the next 10uS of off time, which implies a larger load then 300 ohms, a different inductor value, or something else.

When Q1 is off, as long as there is current flowing thru L1 then the drain should be a diode drop above the output voltage.

7. ### brunounreal Thread Starter New Member

Apr 23, 2010
26
0
i've aplied a simple RC snubber with R=150Ω and C=1μF(electrolitic) and this was the Drain!
May the problem have something to do with the transformer dont have enough power do feed the load?

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