[AMPS] Choke input PS question

[Peter Chadwick]

Randall said:

>Resonant-choke filter?  I'm not 100% sure I understand
>what you mean.... but I'm guessing that you're meaning
>resonance with respect to the ripple?? 


As I said in my previous, you don't actually resonate the choke.

A parallel tuned circuit looks  like a pure resistance at resonance. That's
using the definition of resonance that applied voltage and curent are in phase:
the approximation used at RF that XL = XC won't do here, because you can't
neglect the choke resistance. As you go higher in frequency from resonance, the
inductive reacatance increase and the capacitive reactance decreases, so
capacity wins and the circuit looks capacitive. Below resonance, the effect is
the other way round. A long way below resonance, the choke has it nominal
inductance; as resonance is neared coming from LF, the choke starts looking
bigger and bigger. This means that amount of physical there choke inductance
needed to achieve critical inductance is less. Critical inductance is that
required such that the current flow in the choke is constant over the cycle.

So a 'tuned' choke for a 50Hz system with a full wave bridge (100Hz ripple)
would be less use than teats on a bull in a 60Hz system......so the system isn't
a good choice if you can't be fairly certain of supply frequency stability. If
you get the choke resonant, you can get enormous voltages built up by the
resonance, with all sorts of problems.

Hope this helps.

73

Peter G3RZP

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