what is the filter used in DC-DC flyback converter input ?

Thread Starter

Younes Thabet

Joined Jan 9, 2019
95
Hello,

I was looking into using something similar to what is used in this reference design by TI. But I didn't understand the input side of this circuit, especially the purpose of the input series resistors and capacitors C1, C2, and C3.

ques.png

Can someone please explain the input side of this circuit and the function of each block?

Thank you.
 

ericgibbs

Joined Jan 29, 2010
16,748
hi YT,
That series line of CapsC1,2,3 is so that low Voltage caps can be used across a 1000v line, the resistors are voltage balancing resistors for the caps.
E
BTW: I guess you know that most common resistors are rated at a maximum of 150Vdc or 250Vdc, so that is the reason for the use of multiple series resistors.
 
Last edited:

Thread Starter

Younes Thabet

Joined Jan 9, 2019
95
hi YT,
That series line of CapsC1,2,3 is so that low Voltage caps can be used across a 1000v line, the resistors are voltage balancing resistors for the caps.
E
BTW: I guess you know that most common resistors are rated at a maximum of 150Vdc or 250Vdc, so that is the reason for the use of multiple series resistors.
Thanks, Eric.
So instead of putting a +1000V cap they decided to put 3x 400V caps to gain some space !! got it!
diodes D1-D2 and D7-D9 are used as voltage suppressors, right!?
I guess D4-D5 and C6, R14 are used as snubber .. Could you tell me what's the function of Q1 and the surrounding components !!

I very much appreciate your help
 

Ian0

Joined Aug 7, 2020
6,662
That’s a very unusual flyback converter as it is designed for 1kV input. A standard mains-input flyback converter would not be anywhere near that complicated.
 

Thread Starter

Younes Thabet

Joined Jan 9, 2019
95
That’s a very unusual flyback converter as it is designed for 1kV input. A standard mains-input flyback converter would not be anywhere near that complicated.
Yeah, I am kinda used to 85-265VAC input SMPS flybacks but this one I had some trouble understanding specially the input block ..
 
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