Cool. :o) Which transformer type did you use?
Was it an off the shelf one??

Your power dropping off is likely because you
used a slow diode. Like a 1N4004 or something?
You need a high speed diode, but a 1N914 or
1N4148 (cheap glass signal diode) will work fine.
You will get more power at 1000Hz to, as well as
higher frequencies.

Also, for one more transistor you can lose the
555 timer! Just 2 transistors and the transformer
and with the output zener you get a 5v regulated
output, that is totally isolated and also will
be current limited to an extent. :o)
-Roman


Richards, Justin P wrote:
>
> Roman your suggestions hit the nail on the head.
>
> Iin 30ma, Iout 10ma(all I need), Vin 15, Vout 12v across 1000 ohm  at about
> 1000hz. Interesting to see as freq increased past this point Iin increases
> rapidily and Iout drops off.
>
> Could not use a 5.1 zener as nearest hobby shop 600kms away. I used any old
> diode for IN4148 and assume you were just giving an example (or is it
> critical).
>
> Thanks
>
> Yes it should be an easy one. :o)
> 20mA is not much, you can just slap a 5.1v zener
> on the output cap. This gives a convenient max (and
> ALWAYS constant) current so you can just tune the
> circuit frequency to the max efficiency to supply
> your fixed current into a fixed 5v load voltage.
>
> You can use a cheap 1:1 transformer from any
> hobby shop, these are tiny (thumbnail size)
> and my cataloge shows one at:
>
> 3kohm:3kohm 16mm 16mm 15mm 450mW 220ohm Rdc
> May be too high resistance, but it has plenty
> of power capacity in that sized package at
> 450mW. You only need about 150mW maybe? I think
> it would work.
>
> You can use a IN4148 for the output rectifier
> diode, set the transformer up as flyback with
> the rect diode, you may need to reverse the
> tranformer output leads to get it in flyback
> mode. Then stick a pot on your 555 timer and
> crank up the speed until you get the required
> 5.1v on the zener diode at 25mA or so, using an
> ammeter on the input and output. Since Vin and
> Vout shoult be constant you can just measure
> Iin and Iout and turn the pot until it's at
> its most efficient.
>
> I think your idea is pretty clever as a cheap
> way to get isolated 9v from 12v. It will probably
> run quite efficiently at a few kHz.
> -Roman
>
> --
> http://www.piclist.com#nomail Going offline? Don't AutoReply us!
> email listserv@mitvma.mit.edu with SET PICList DIGEST in the body
>
> --
> http://www.piclist.com hint: To leave the PICList
> mailto:piclist-unsubscribe-request@mitvma.mit.edu

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads