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Help in understanding this circuit

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

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  1. arisu1love

    arisu1love

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    Oct 26, 2010
    [​IMG]

    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*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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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

    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

    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

    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... :)
     
  6. Resqueline

    Resqueline

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    Jul 31, 2009
    Glad to help bring about understanding in the world! ;)
    If the mains voltage is at it's peak when the triac triggers then the voltage across the triac drops to 1V within microseconds.
    At the same time the voltage across the load increases from zero to full mains peak voltage within the same short time.
    Even if this all happens only 100 or 120 times/second the rise/fall time represents the same risetime that you would find in a MW transmitter sinewave output.
    If the mains is very close to its zero crossing when trigging occurs then the effect is much less severe. Zero-cross switching can actually do w/o any filters.
     
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