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Reflected Power




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From:  Scott Stephens [SMTP:stephens-at-enteract-dot-com]
Sent:  Thursday, January 29, 1998 11:56 AM
To:  Tesla List
Subject:  Re: Reflected Power

At 11:54 PM 1/27/98 -0600, you wrote:

>> >I'm in the process of rewinding the secondary of the output
>> >transformer of my flyback converter. In an attempt to match the
>> >impedence of the Tesla coil I'm adding more turns. Are there any ham
>> >radio operators on the list that knows what reflected power looks
>> like
>> >on a O,scope? I've been seeing a strange waveform on the scope and I
>> 
>> Unfortunately there is no visual difference in reflected and real
>> power.

and

>  Another question I would like to ask is when you increase the turns
>ratio to increase voltage will this cause a coresponding increase in
>current draw? My reasoning says it should but I would like to get some
>feedback from someone with experiance.

Yes, it will cause an increase in current.

I've been troubled by the same problem lately. If I make my primary
resonant, and try to operate at near maximum voltage, and don't dissipate
all my power in my load, VSWR (the reflected wave) will add and destroy my
transistors.

But I have no load until a spark occurs. And after a spark, I have to charge
up my coil again, resulting in a heavy load. So the requirement is realy for
a variable primary.

Solutions:

Directional coupler and pulse-width/rate modulation. The directional coupler
can redirect the reflected power into a dummy load. Otherwise my
snubber/transorbs will die. The modulation can prevent overload of the
transistors.