Peak Detector application in flyback converter

Thread Starter

sunil0790

Joined Feb 11, 2013
12
Hi,

I have attached a typical Input AC DC section of a flyback converter.

In that Peak detector section is being used(D2, C7 and C14), is it necessary to filter the pulsated DC? Since the pulsated DC is again being converted to H.F. AC.Can we avoid that?

If we avoid the same, what are effects of it?

I use PWM converter which has Active PF circuit, I tried testing with out the peak detector, but the PF is same. Does it have any other ill effects? Will it affect the Surge withstanding capability or THD or add more stress on the Semiconductors or Transformers?

Any info would be really helpful.

Thanks in advance.
 

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DickCappels

Joined Aug 21, 2008
5,879
It would be nice to see what that circuit snipett is connected to. My best guess is that the "peak detector" is a snubber circuit to protect the switching transistor from overshoot spikes on the output devices collector or drain when the transistor turns off. If that is the case, then the purpose of the capacitor is to absorb the energy in the spike and then let the energy bleed off through the resistors.

Any chance of seeing more of the circuit?
 

Thread Starter

sunil0790

Joined Feb 11, 2013
12
It would be nice to see what that circuit snipett is connected to. My best guess is that the "peak detector" is a snubber circuit to protect the switching transistor from overshoot spikes on the output devices collector or drain when the transistor turns off. If that is the case, then the purpose of the capacitor is to absorb the energy in the spike and then let the energy bleed off through the resistors.

Any chance of seeing more of the circuit?
Thanks for the reply.

The circuit is purely for Filter purpose, There is a separate Snubber section for Semiconductor device. I have attached the exended snippet.
 

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DickCappels

Joined Aug 21, 2008
5,879
It is still a snubber. The transistor dan only draw energy out of the two 10uf caps through the 1.5 meg resistor -not much energy. This snubber damps the positive peaks of the flyback of L1.
 

Thread Starter

sunil0790

Joined Feb 11, 2013
12
It is still a snubber. The transistor van only draw energy out of the two 10uf caps through the 1.5 meg resistor -not much energy. This snubber damps the positive peaks of the flyback of L1.

Thanks. What are ill effects it might cause by removing that section on a long term basis?
 

DickCappels

Joined Aug 21, 2008
5,879
Thanks. What are ill effects it might cause by removing that section on a long term basis?
Possibly some dead semiconductors. Also the two 33k resistors coming off that line might be some sort of feed-forward signal and if it is then changing the response might lead to instability of the power supply or poor regulation <= that part is speculation.
 
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