Voltage switch problem, most optimum solution ?

[Mike]

Hi chaps,

I made a previous post about driving a flashing led from
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

 

[Chris Jones]

Mike wrote:

Hi chaps,

I made a previous post about driving a flashing led from
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)



What do they do inside Braun shavers? My old one can take anything from

12VDC to 240VAC through the same plug which is a pretty wide range.

How well can you rely on the duty cycle of the 500V being small? If you
knew very surely that it would be a small duty cycle then you could try
putting a L-C filter at the input of your circuit with a high value
inductor. If you follow that with a switched-mode converter then the whole
circuit could be quite efficient. Might not be cheap though.

Just out of interest, where do you come up with such weird requirements?
Some background info would help e.g. supply impedance etc.

Chris

 

[Mike]

In article <12291tgac538p96@corp.supernews.com>, lugnut808@nospam.yahoo.com says...

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...
No there is nothing mechanical in there except the shaving part. It charges
a single NiMH cell, but the SMPS can also just about run the motor by
itself when the battery is flat. I was impressed by the voltage range.

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...

The thing I worry about is that you will need a high value of inductance
combined with the ability to pass a reasonable amount of current without
saturating the core, and also fairly low capacitance would help, I suspect,
since otherwise it will affect the ignition pulses. If you could get the
current consumption of your load down then that would make everything a lot
easier. I would consider using the primary of a small mains transformer as
an inductor, but the current would probably saturate it.

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

There might be an alternative solution with a high voltage MOSFET or TV line
output transistor somehow, but if it were me, I would be trying very hard
to run an extra wire to the normal battery voltage.

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

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

No never been to WA. Different Chris I suppose.

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
ago now <sigh>

Chris

--
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

 

[Simone Merrett]

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"
additionally loading the 500V spike to ground, through, EG a low value
resistor or a 100uF capacitor, (that includes a parallel resistor).
This is essentially an active, non-linear filter to attempt prenveting
spike reaching low-voltage part of supply.

3. As previously suggested, a passive L-C at front would do at lot of good
to start with.

Dave Merrett

"Mike" <erazmus@iinet.net.au> wrote in message
news:44239101$0$4656$5a62ac22@per-qv1-newsreader-01.iinet.net.au...

Hi chaps,

I made a previous post about driving a flashing led from
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