# Voltage switch problem, most optimum solution ?

Discussion in 'Hobby Electronics' started by Mike, Mar 24, 2006.

1. ### MikeGuest

Hi chaps,

240v ac with a 'or' from two sources, turned out ok...

Here's a different problem I've been toying around with
and I dont like the feel of what I've done so far, so looking
to do a little brainstorming, here it is...

Have a single source of power that goes from 9v steady DC to 500v pulsed
(not AC), in that in the first few seconds its a fairly steady 9v +20%,
then starts pulsing at 500v with a duty cycle of 5% but returns to
30v for 20% of the time and 12v for the remaining 75% of the period.
Period is approx 30ms overall but can reduce to 10ms, complication is
the 500v pulse is same period, so the duty cycle for that relatively
goes up as overal period goes down.

With this single source of power I need to draw off about 0.5W and
drive a 'module' at 9 to 11v with some cmos logic along with a few
leds etc.

My problemo is keep the cost down <guh>, no relays unfortunately but
drive this module without having it blow up or be unreliable
because its only power source line goes from 9v steady to
500v pulsed.

The circuit I have so far is a high voltage transistor configured
as a constant current drive into a resistor and 12v zener to spread
the dissipation and filter with a 100uF electro 25VW.
This seems to be ok but uses a few components and there isnt much
gain at the low volts of the constant current source to charge up
the electro quickly enough before the 500v pulses start coming...

So I'm opening this to the public forum to see if any lateral ideas
come up <shrug> cause I have exhausted mine (so far, afaik)

--
Regards
Mike
* GMC/VL Commodore, Calais VL Turbo FuseRail that wont warp or melt !
* Twin Tyres to suit most sedans, trikes and motorcycle sidecars
http://niche.iinet.net.au

2. ### MikeGuest

Interesting, I didnt know that, do they have a small relay to make
it cheap, cause any semi to handle that isnt reliable if its cheap,
unless its low down on the failure/repair curve etc...
Now thats a good idea, the last thing I thought of using there was an
inductor but it does make a lot of sense. The 500v pulse is only for roughly
10 microseconds so that makes it a pretty viable idea, thanks
The last one is providing some visual aid to the hearing impaired where
a single row of switches runs an outside light and a couple of fans, they
dont hear the fans and they can't always notice the outside light, having
an inside flashing led on the switch cluster derived from an 'OR' was ideal
as a reminder that something on the cluster was left on...

This one is for a vehicle ignition system, be able to supply some power
to some logic but make it plug compatible so installer doesnt have to run
an extra cable for 12v power, get it via the coil return etc
The 500v pulse is back emf from the coil, so I would guess fairly low
in that the primary impedance is low, I dont want to snub the pulse
if at all possible as it would then reduce the striking voltage to
overcome the spark gap on the sec. The LC seems pretty much the perfect
solution, the output of the LC would be seriously damped when the pulse
arrives as the rise time is fairly short on the 500v pulse and yet have
low impedance to get enough power inbetween pulses, prob wouldnt need an
SMPS as a resistor, clamping zener and cap would be plenty for the amount
of power I would like to supply which is only about 50 or so mA.

Hey CHris, you didnt go to WAIT in WA some many moons ago did you ?

--
Regards
Mike
* GMC/VL Commodore, Calais VL Turbo FuseRail that wont warp or melt !
* Twin Tyres to suit most sedans, trikes and motorcycle sidecars
http://niche.iinet.net.au

3. ### MikeGuest

Yeah me too, fascinating, have speculated how to do that, can run a cmos
pwm timer off a few microamps, then just need a hivolt mosfet as regulator,
but heck it would have a really wide range pwm, pfm or ppm drive...
Prob not that much an issue re saturation, afterall the 500v is fairly short
and even if the core does saturate there will be a series resistor, just need
to go through a few iterations. ie Some of the current not snubbed by the
coil will be handled by a series resistor and some dumped into a zener, the
trick will be to get the tree balanced in terms of dissipation whilst allowing
enough current when the pulses arent present, will get to this during week,
should be an interesting exercise
I was going to use an MJE13007 as series current regulator, but the LC
instead of those active devices would be heaps more reliable and more
interesting, thanks
no problem, he had identical name and was heavily into electronics, was
a member of Salvation army and knew an old friend Phil - be about 25years
--
Regards
Mike
* GMC/VL Commodore, Calais VL Turbo FuseRail that wont warp or melt !
* High grade milspec ignition driver electronics now in development
* Twin Tyres to suit most sedans, trikes and motorcycle sidecars
http://niche.iinet.net.au

4. ### Simone MerrettGuest

1. Are you sure the 500V is a low-impedance source? - EG Put 50 Ohm across
it, and see if it stays at 500V (or smoke for R <1W Diss.)

2. My first thought was a > 50V zener, or other similar fast switch turning
OFF a series switch to a regulator.
There are lots of alternatives.. like having the ">50V ? Detector"