[Prev][Next][Index][Thread]

Re: Oscillator circuit for solid-state TC



Greetings all

Harri wrote:

>Yes if 1/2 of the length of the wire is used. However, when going to
>high powers remember to keep the flux down. I use about 30-100mT as a
>guidline for 250kHz (or upper) operation. Core losses are limited
>that way. However, winding losses are increased. It is always a kind
>of compromize before optinum is found.

Yes I've come down to about 100mT. I got some indication of
core loss v winding loss by dismalting the transformer after
a run and comparing the heat in the cores as against the wndings.
Definately more loss in the windings.

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.
Spreadsheets are great for playing around with different values.

>If you drive it from the bridge it *is* actually ac. It just lookes
>like pulsating dc on a paper. However, it can be shown a 50/50 square
>wave sentered about zero is actually (according to fourier transform)
>sin wt + 1/3 sin 3wt + 1/5 sin 5wt+... ie. a sine wave with lots of
>decaying odd harmonics. In bridge circuits it is really centered about
>zero because of series capasitor of power supply split capasitors which
>isolate any dc-component.

I remember fourier transform - don't know if I could revive the grey cells
that used to understand it! But its not a bridge - 2 // primary windings
energised alternately. (Another reason for needing a big transformer :(.

So at Rsense the square wave is n_n_n_n_ rather than n-u-n-u-

----- FET ---- Ov
0
0
0
0
---- Rsense--- +140v
0
0
0
0
----- FET ----- 0v

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.

have fun

Alan Sharp