Check out the infamous Sam's circuits at http://www.repairfaq.org.  I've
seen just such a circuit to produce a 300V supply from a penlight cell.

However it does use a hand-wound transformer to give you this.

While on this topic, I'm looking for a 6000 VAC supply that I can vary
from HZ to KHZ.  It can run of 120VAC.

Yet another PIC project...

Craig

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Donald L Burdette
> Sent: January 19, 2000 2:23 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [OT] 300V Switcher
>
>
> I'm trying to figure out how to build a 300VDC power supply that will be
> powered from a battery, nominally 3V, 6V, or 9V (customer wishes to have
> one board that can be stuffed for 3 different versions).
>
> I only need about 3-5 mA at 300V, and I wouldn't have much of a problem
> with this except for one thing - the board with components needs to fit
> in an area 1.1" (28mm)  wide and 0.2" (5mm) high!  He's being generous
> and allowing me to make it several inches long.
>
> This design isn't too bad until you run the numbers and realize that the
> duty cycle on a standard boost circuit would be 97-99%, and most
> controllers won't go higher than 85-90%.  If I try to use a flyback
> transformer, the inductance of the secondary has to be 7-10 mH, which is
> quite high.
>
> I've thought about trying to see how laptop display backlight conrtollers
> work, but I don't know where to look.
>
> Anyone got any ideas?
>
> BTW, this is not completely OT since the micro on this board is a 16F873.
>
> Thanks.
>
> Don
>