Alternatives to snubber circuit for MOSFET RINGING

Thread Starter

annapurna

Joined Feb 11, 2016
19
My mosfet open circuit voltage- 400 volts.
Switching frequency-70000
I am not using Snubber CIRCUIT to eliminate ringing .Are there any other options to eliminate ringing.Now i am using an active clamp circuit(tvs diode between Gate and Drain).I don't want to waste power at snubber circuit.Am i correct with TVS Diode?Please suggest me how to deal with this ringing.
 

kubeek

Joined Sep 20, 2005
5,587
Switching what exactly? Show your whole circuit and you will get reasonable responses.
 

Thread Starter

annapurna

Joined Feb 11, 2016
19
Switching what exactly? Show your whole circuit and you will get reasonable responses.
its a interleaved boost converter with diode bridge at the input to the boost converter
input voltage to the diode bridge=230 volts ac
output voltage=400V
input power=2300W
 

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AlbertHall

Joined Jun 4, 2014
8,186
You do in effect have a snubber circuit with the two diodes feeding the output capacitor.
It is probably not a good idea to have the clamp between drain and gate. If an excessive voltage on the drain reaches the breakdown voltage, the clamp will pass that high voltage back to the gate and risk breaking down the gate insulation. The usual breakdown voltage for MOSFET gate is 20V.
 

kubeek

Joined Sep 20, 2005
5,587
Exactly, why do you have the snubbers connected to the gate at all? That sure does not help them work correctly.
 

Thread Starter

annapurna

Joined Feb 11, 2016
19
You do in effect have a snubber circuit with the two diodes feeding the output capacitor.
It is probably not a good idea to have the clamp between drain and gate. If an excessive voltage on the drain reaches the breakdown voltage, the clamp will pass that high voltage back to the gate and risk breaking down the gate insulation. The usual breakdown voltage for MOSFET gate is 20V.
you are right that it will damage gate insulation but i am providing protection to gate source ( using zener diode having breakdown voltage as 18V). so now will it have problem?
 

AlbertHall

Joined Jun 4, 2014
8,186
you are right that it will damage gate insulation but i am providing protection to gate source ( using zener diode having breakdown voltage as 18V). so now will it have problem?
There is a resistor in series with that zener diode which would limit the protection provided by the zener.
In any case, to protect the MOSFET the clamp should be between drain and source, but as already stated the output diodes limit the maximum drain voltage to the output voltage so the extra clamp is unnecessary.
 

Thread Starter

annapurna

Joined Feb 11, 2016
19
There is a resistor in series with that zener diode which would limit the protection provided by the zener.
In any case, to protect the MOSFET the clamp should be between drain and source, but as already stated the output diodes limit the maximum drain voltage to the output voltage so the extra clamp is unnecessary.
There is a resistor in series with that zener diode which would limit the protection provided by the zener.
In any case, to protect the MOSFET the clamp should be between drain and source, but as already stated the output diodes limit the maximum drain voltage to the output voltage so the extra clamp is unnecessary.
How to select that clamp zener diode between drain and source ? and also please comment on the loss in the capacitor(in the output capacitor).
thankyou.
 

Thread Starter

annapurna

Joined Feb 11, 2016
19
Exactly, why do you have the snubbers connected to the gate at all? That sure does not help them work correctly.
thanks a lot for your idea.we got your point.please tell me how can i protect my MOSFET in case of A BUCK CONVERTER?Again the idea is same that i don't want loss energy in the snubber
 

Thread Starter

annapurna

Joined Feb 11, 2016
19
There is a resistor in series with that zener diode which would limit the protection provided by the zener.
In any case, to protect the MOSFET the clamp should be between drain and source, but as already stated the output diodes limit the maximum drain voltage to the output voltage so the extra clamp is unnecessary.
Got it .
In this case we don't need any protection .................for mosfet
And also please comment on the loss in the capacitor
thanks a lot......
 
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