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**Electronic circuits / What happens when L and C are not matched?**

« **on:**May 08, 2019, 04:42:35 PM »

Mads-

The formula for resonant frequency is: "Freq. = 1/(2pi X sqrt(L X C)).

This formula would imply, to me, anyway that ANY values of L and C will produce some resonant frequency.

But, I can find many references that say:

"Resonance occurs when capacitive and inductive reactances are equal to each other."

Well, that's fine, but we know that circuits DO oscillate when L and C are NOT equal.

Is this just a "play on words"? The resonant frequency formula that I quote above doesn't seem to deal with that issue at all.

I studied resonant circuits back in the early 1950's. I vaguely remember that there is some negative "cost" to having L and C too far away from eachother, but I don't know why.

In my hobbyist work with the small ZVS induction heaters, I see that I can at least double capacitance or double inductance and still get the thing to oscillate.

My question:

So what is the "cost" of "unbalanced" L and C in an oscillating circuit?

In my experiments so far, the main problem I see is reducing L and/or C so far that the oscillation frequency is so high that the Mosfet gates can't turn on fast enough. (This, of course, leads to overheating and failure.)

But that still does not address that issue of "unbalanced" L and C.

The formula for resonant frequency is: "Freq. = 1/(2pi X sqrt(L X C)).

This formula would imply, to me, anyway that ANY values of L and C will produce some resonant frequency.

But, I can find many references that say:

"Resonance occurs when capacitive and inductive reactances are equal to each other."

Well, that's fine, but we know that circuits DO oscillate when L and C are NOT equal.

Is this just a "play on words"? The resonant frequency formula that I quote above doesn't seem to deal with that issue at all.

I studied resonant circuits back in the early 1950's. I vaguely remember that there is some negative "cost" to having L and C too far away from eachother, but I don't know why.

In my hobbyist work with the small ZVS induction heaters, I see that I can at least double capacitance or double inductance and still get the thing to oscillate.

My question:

So what is the "cost" of "unbalanced" L and C in an oscillating circuit?

In my experiments so far, the main problem I see is reducing L and/or C so far that the oscillation frequency is so high that the Mosfet gates can't turn on fast enough. (This, of course, leads to overheating and failure.)

But that still does not address that issue of "unbalanced" L and C.