# Re: SSTC theory

```Original poster: "Antonio Carlos M. de Queiroz" <acmdq-at-uol-dot-com.br>

Tesla list wrote:
>
> Original poster: Marco.Denicolai-at-tellabs-dot-com
>
> Hello Antonio,
>
> I find very interesting this new (at least to me) starting point to
> design a TC. If I get it right, you design a Butterworth bandpass filter
> with given center frequency and end up with a setup where L1*C1=L2*C2.

Yes. That design reduces the network to an ideal transformer.

> But isn't it true that the voltage vs. frequency diagrams is the usual
> one? I mean two peaks, more or less separated depending on the coupling
> coefficient (if I recall)?

Yes, and really, the response has two peaks if the driver impedance is
negligible. The two peaks would reduce to one if the impedance of the
driver were identical to the designed input resistance of the network.
The network can also be designed so there is only one peak when the
output loading is as designed, but it seems that this design is not
so good. See the plots at the end of my page.
http://www.coe.ufrj.br/~acmq/tesla/sstc.html

> I am just wondering, isn't it so that if one wants to drive a
> traditional TC with an SSTC driver (remove the RSG, use an IGBT/FET
> bridge), the correct drive frequency is simply
> f=1/(2*PI)*SQRT(1/(L1*C1)), supposing that L1*C1=L2*C2?

Hummm. Looking better at my equations I see that L1*C1=L2*C2 is
valid for the prototype filter, and that for it the driving
frequency is really as you say. But observe that in the network
with transformer, Lb*Cb = (1-kab^2)*La*Ca = L1*C1.
So, in this network the primary and secondary circuits are -not-
tuned to the same frequency!
The driving frequency is the resonant frequency of the secondary
circuit alone. The primary circuit is tuned to a slightly lower
frequency. Strange, but true.

Antonio Carlos M. de Queiroz

```