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Voltage Regulation From High Voltage

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Turkey9

Tue Mar 30 2010, 09:03PM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

I need a regulated voltage of 12v. It doesn't have to be that well regulated, but the input supply will swing from 250v to 1000v. I need to have the 12v at all input voltages in between the said 250 and 1000v. I've tried a simple zener regulator but to get it to regulate at 250v, the current would kill the diode at 1000v. I have 1 watt diodes that I would really like to use.

mikeselectricstuff

Tue Mar 30 2010, 10:17PM

Registered Member #311 Joined: Sun Mar 12 2006, 08:28PM
Location:
Posts: 253

without specifying the output current range you need, that's an un-answerable question...

Mattski

Tue Mar 30 2010, 10:22PM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

What amount of current do you need (edit: mike beat me

)? One simple answer is to use a bigger zener. Or you can get a high voltage low current IGBT to act as a pass transistor for your zener regulator, that way you can design the zener to pass less current.

Maybe you could put some lower voltage zeners in series to lower the individual power dissipation.

Turkey9

Tue Mar 30 2010, 10:48PM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

oh sorry! this should make it easier... I just need enough current to run a 555 timer. This is for a simple voltage controlled oscillator that I'm using to monitor the charge voltage. It all has to be isolated so I'm reading the frequency by a PIC that is isolated by a couple small capacitors.

Mattski

Wed Mar 31 2010, 12:30AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

They actually make isolation amplifiers for this purpose which might be easier for you, like

. They basically do what you're doing, modulate and transmit optically, through capacitor, or isolation transformer. Check the voltage ratings carefully though, a cheap one like the one I linked to might not be good enough, but there are plenty of expensive ones which I'm sure will work :)

HV Enthusiast

Wed Mar 31 2010, 12:43AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

Just use a 9V battery.
Any type of linear regulator will just dissipate tons of power.

Turkey9

Wed Mar 31 2010, 12:47AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

Man, I should have done more research... Oh well that part is already built and tested. That chip still needs a pretty low supply voltage so either way I would need this regulator!

If this proves to be too much, I can just build a quick isolated power supply for the VCO.

Wolfram

Wed Mar 31 2010, 07:14AM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Isolated DC/DC converters are commonly available and quite cheap. Here's one I found via a quick digikey search that I think might fit the bill:

A.M.

Dr. Slack

Wed Mar 31 2010, 10:07AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

If you just want to monitor the charge voltage, then how about sidestepping the need for a low voltage entirely?

A neon-lamp relaxation oscillator flashes at a rate proportional to the input current, which will be proportional to your input voltage through a large resistor. Job done, it even has an optical output for isolation, and you can read it by eye as a bonus - ideal for debugging, and safety.

You might not be able to guarrantee the same accuracy from a lamp oscillator as from the other ways of doing it. How about throw one together ans see how it performs?

Steve Conner

Wed Mar 31 2010, 01:30PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Oh... That's one of the better ideas I've seen on here recently.

You can also sense DC voltage using, oddly enough, a small transformer. The basic idea is to try to backfeed the DC bus through the transformer and a rectifier, and measure the peak value of the voltage reflected back to the input side, which will of course be the DC bus voltage times the turns ratio.

This is not my idea, it was used in industry since goodness knows when, and there's a DC current transformer that works on a similar principle. Both are related to the fluxgate magnetometer, and all three of these devices were made obsolete by Hall effect sensors.

If you use one of the CMOS versions of the 555 (TLC555, etc) then you can run it with an extremely low current, which might help you.

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