Re: phase locked loop SSTC

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Jan,

At 06:22 PM 1/2/2002 +0200, you wrote:
>
>I never understood this impedance matching business in conjunction with 
>SSTCs - I mean, driving at 50% duty always (i.e. NO current limiting via
>PWM) and always in-tune guarantees no power is reflected, so impedances
>are always matched. 
>Of course if you were to restrict the primary side impedance by current
>limiting then there is the risk that impedances aren't matched and primary
>side heating losses go up. And ok, mosfets can't handle infinitely high
>currents either and can blow up and generate a "mismatch".
>
>Or am I missing something here?
>
>cheers,
> - Jan
>

Impedance matching and reflected power may not affect your circuit much.
The generator I am using has voltage and current limits that are optimized
for a 50 ohm load so I have to try and match 50 ohms to eneable it to
deliver full power.

There is often a concern with say driving a capacitor.  The voltage and
current to the capacitor are both high but there is no power dissipated.
However, the transmitter is driving full power and heating up it's
transistors just the same.  In high power equipment this is a real concern.
 This is the basis for impedance matching and forward/reflected power.  It
gets far far more messy but newer low source impedance devices are now
making it far less of a concern.  In your case, you probably have such a
low source impedance that you don't need to worry much with it.

Cheers,

	Terry