Don't know if this helps, but I made a high voltage supply with a 555,
power NPN, and small transformer. Since it just had to charge and hold
(for a Xenon flash circuit), the voltage feedback was just a 120V
zener to the enable input of the 555.
It was wired to generate a voltage negative with respect to ground. It
reaches Zener breakdown, it pulls the Enable input of the 555 low and
stops oscillation.
I did sort of a delayed hysteresis. The zener had a resistor in series
with it to limit current, and there was a capacitor from the 555
Enable input to ground. The delay created by that series resistor and
the capacitor meant it kept charging for a fraction of a second after
reaching zener breakdown.
It's very important to note that there were two diodes on the Enable
input wired to limit voltage there so it was always between ground and
V+, within a diode drop.
All designed to be extremely low current, it rarely had to turn on
again to top off the High Voltage capacitor when not being "fired".
This was for a Sci Fi prop blaster. I just left it on all weekend at
conventions.
It could be isolated by using an optoisolator.
You could wind your own transformer. I have always found Amidon's info
to be very helpful.
Alien Steve
--- In Electronics_101@..., "Curtis Sakima" <csakima@m...>
wrote:
Been casually following this thread and .....
Curious how the 555 goes to the "NPN and PNP transistor". I'm
guessing
you have it hooked up as a complementary/symmetry (like the output of a
audio amp)??
Second, what do you mean by, "I just have to feed the trans. out-put
back to
the bases to make it automatic-- inversely that is"?? Feeding back
to the
bases would imply that you're making a transistor-astable-oscillator.
<Thinking>But why would you need to have the tranny's oscillate ....
when
it's the 555 that does the "oscillating"?? Aren't the trannys just for
power out's??
Curtis
Dazzle Mom this coming Mother's Day season with flowers!
----- Original Message -----
From: genteelu4ia <vortex_9x@h...>
To: <Electronics_101@...>
Sent: Sunday, April 25, 2004 1:24 PM
Subject: [Electronics_101] Re: Help! 555 inverter
Thanks for your prompt reply, Stefan;
Your right I suppose actually I only need a 30v potential and I
already have what I need. Actually the out-put of the 555 goes to
the base of two transistors one PNP and the other NPN which in turn
control the input to the transformer. Right now (on the breadboard)
there is a pot. that controls both in-put and out-put of the
transformer I just have to feed the trans. out-put back to the bases
to make it automatic-- inversely that is. Probably get some kind of
hysterisis going and the thing will blow-up in my face.<grin> Next
is the holding circuit. I did find a Hammond audio transformer with
1 to 3 ratio but they want $75.00 for it (WOW) and I'm looking for
something much cheaper.
Thanks again, U4ia
Steven AE7HD