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Re: Oscillator circuit for solid-state TC



On Wed, 16 Oct 1996, Tesla List wrote:
> I also worked out that most of the heat loss is in the primary,
> rather than the secondary, Power loss will be current _squared_
> times the resistance. the secondary may be longer n times the
> number of turns but the current is only 1/n. You also have to figure
> that the average diameter of the secondary windings is greater.

I had just the opposite. I wound a primary with lots of 0.25mm diam
wires twisted. Secundary was on top of it. Secundary did have
therefore longer average turn lenght as you suggest. Secundary
was wound from 0.315mm diam wire which I had lying a round. Secundary did
heat up signifficantly at 1kW+ power level. Nasty. I managed just to
fit around 140 turns maxinum secundary on the core.. :( No room for
bigger wire..

However, do read some transformer books. Minimize leakage inductance
by interleaving primary and secundary. Minimize secundary capasitanse.
If you do not take those precautions they may lead into lots of trouble.
They did for me with traditional pwm-drives. With high turns ratio
you may have secundary capasitance refled to primary side at tens
of nanofarads easily!

> Spreadsheets are great for playing around with different values.

Indeed! 

> The next design project will be a full bridge - advantages - efficency,
> 375v working and single primary transformers. Disadvantage was
> that I previously didn't know how to design it.

Good you do now. It definately has lots of advantages. Push pull were
certainly great if 800V/10A fets at the speed of IRF740 were available
at irf740 price. However, as they are not one will definately want
to go for topologies minimizing the voltage stress. 
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