Bob,
Some additional thoughts on the same lines ..
You can wrap a few turns of copper wire on top of the transformer that
already exists. (2 or 3 turns, enough to drive the transistor.) The
coupling is not a big issue, but try to make the winding as tight as
possible to get maximum possible coupling. Since there is hardly very
little current drawn, it's not an issue at all. This winding you can
be consider as an auxiliary winding.
If you have a LCR meter you can check and compare the inductance of
the primary to the auxiliary, so that the primary and the auxiliary to
be a 1:1 ratio. It's not absolutely necessary that you need a 1:1
ratio, but you will get a reference for your calculations for the
feedback. The winding you can use as a reference to control the
primary side PWM, to avoid looking for high voltage components.
Cost wise this would be more efficient, as it cost you peanuts, as all
components are low voltage components itself. Also, you might have all
the components around you.The auxiliary winding can drive a small
transistor to control the base drive for the Power Transistor. You
will have some fiddling to do, but would be a very nice mod, maybe you
can probably fit the mod on the same flyswatter board itself. Saves a
lot of work for another PCB too..
Maybe that would be a less than 1 USD Mod! :-)
Cheers,
Manu
On Fri, Nov 16, 2018 at 10:22 AM Manu Abraham <***@gmail.com> wrote:
>
> Hi Bob,
>
> A combination of primary side regulation along with HV regulation
> might work quite well.
>
> I came up on this thread:
> https://rimstar.org/science_electronics_projects/electric_fly_swatter_zapper_racket.htm
>
> If it is possible to increase the output power by changing the
> resistor, decreasing it also would probably be fine.
>
> Saw a discussion on EDN. goo.gl/6iN9wN
> That could fire off some neurons. The BU508A is used in old CRT TV
> set's can go up to about 700V
>
> Cheers,
> Manu
> On Fri, Nov 16, 2018 at 9:43 AM Bob Blick <***@outlook.com> wrote:
> >
> > Suppose I repurpose a handheld electronic flyswatter power supply as a high voltage DC bias supply. These things generate over 600 volts from 3 volts using a circuit very similar to those in disposable camera xenon flashes(uses a transformer with three terminals on the primary, two on the secondary plus one transistor, one diode and a few resistors and capacitors).
> >
> > But I want a lower, regulated output voltage, +-5 percent is fine.
> >
> > How do I do this without drawing a lot of current? Even 1 mA at 500V is going to consume gobs of juice. So no shunt regulators, either.
> >
> > Can I get decent enough regulation by basing it on the flyback voltage in the primary?
> >
> > Any ideas would be welcome.
> >
> > Thanks, Bob
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