piclist 2002\09\23\101028a >
Thread: 2-tran SMPS 5v reg now 90% efficicient!
www.piclist.com/techref/index.htm?key=tran+smps+reg+efficicient
picon face BY : Morgan Olsson email (remove spam text)



Roman Black wrote:
>The main inductor has THOUSANDS of turns,

NOPE... i measured now, a cheap tiny 470uH inductor, Farnell artno 432-120.
Feeding it 10V p-p 300kHz (used high freq because i wanted to eliminate any Rloss errors) And on one turn it give me 100mV p-p.

This make a turn ratio of 1:10, so for a converter from 12V, ten turn will give 1.2 V which i think is more than enough.  Five turn might suffice.

And this was without taking off the original shrink tubing.  Removing it will probably make slightly better magnetic coupling, plus it is easier to make the wire stick around with the other wire on the ferrite bobbin.

>I take your point of using feedback to Q2 base with
etc..

L1b will make use of C1 as "tank".  Using the amplitude L1b delivers to vary C1 voltage by the same amplitude.  But.. oops, clumsy me... current design will pump peak currents through Q2 base... remedy is to add a series base resistor... or series emitter resistor..... maybe put series emitter resistor on Q2, and replace Rc with wire?  Note resistors must be low enough ohm to make Q2 fully turn on/off, but not too low as that will make excessive peak base current.

good luck experimenting

/Morgan

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