# Help in understanding this circuit

Discussion in 'General Electronics Discussion' started by arisu1love, Nov 13, 2010.

1. ### arisu1love

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Oct 26, 2010

Could anyone kindly explain to me how to obtain the values of the CLC pi filter on the left of the circuit (C7, C9 and L1)? I would really like to know how to obtain the value of the filter components...say there is a change in mains voltage value or change in frequency....

Last edited by a moderator: Nov 13, 2010
2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
There would be very little change in component values with change in mains voltage or frequency as the frequencies this is trying to attenuate are significantly higher than the mains frequency.

The voltage rating on the capacitors could be lowered if you were redesigning for 110V though.

3. ### arisu1love

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Oct 26, 2010
Hmm....I would guess that the voltage rating for the capacitors to be higher than 240V if I am designing for 240V, is that right?

What I understand is, the varistor is for reducing transient voltage, and the CLC filter is to attenuate unwanted frequencies (sadly I do not understand which frequency is that, is it harmonics of the mains?)

But, the 5A rating of the inductor corresponds to what? Is it the maximum current which is supplied?

4. ### Resqueline

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Jul 31, 2009
The capacitors are to be X-rated, literally, or rather X2. That means they are designed specifically to deal with a hard long life of being wired directly across the mains.
An ordinary capacitor may fail after some time even if rated for two or three times the mains voltage. There's also a difference between the DC & AC ratings of capacitors.
The varistor absorbs transients coming from the mains, & thereby protects the triac.
The filter prevents the harmonics generated by the triac switching getting out on the mains.
Those frequencies will typically be in the vicinity around the MW-band
The 5A rating corresponds with the maximum load current.

5. ### arisu1love

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Oct 26, 2010
Thank you for the new information, I googled X2 capacitors and it did really give me a lot of information which I never knew...quite helpful in understanding I must say

If the frequencies are in the MW band the frequency would be quite high...care to explain why is that so?

Thank you for your reply, I really appreciate all the help I can get...

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Jul 31, 2009