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'[EE]: High Voltage Controler'
2003\03\03@074127 by Jake Anderson

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howdy ho campers

In simple terms, I have a project that requires controlling many (60-200) output lines at about 40 times a second. The output of each line should be a DC analogue voltage between preferably zero and about 2000 volts (8-12 bits resolution would probbably do me fine). To make life easier the max current is absolute MAX of 5mA and likely allot less (IE <1 mA) and some leakage voltage would probably be ok (provided it was always a constant voltage across all outputs or followed some mathematical function or another). The control side of it would be done with a few PIC's to do the IO and a big computer for processing. I have no experience in dealing with voltages this big (and don't worry with any luck there will be no capacitors of any significant size anywhere on the board). Anyway I was looking for some advice on what circuits are out there or places to start looking for information about this.

thanks guys.

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2003\03\03@080729 by Mike Harrison

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On Mon, 3 Mar 2003 23:41:39 +1100, you wrote:

>howdy ho campers
>
>In simple terms, I have a project that requires controlling many (60-200) output lines at about 40 times a second. The output of each line should be a DC analogue voltage between preferably zero and about 2000 volts (8-12 bits resolution would probbably do me fine). To make life easier the max current is absolute MAX of 5mA and likely allot less (IE <1 mA) and some leakage voltage would probably be ok (provided it was always a constant voltage across all outputs or followed some mathematical function or another).
>The control side of it would be done with a few PIC's to do the IO and a big computer for processing. I have no experience in dealing with voltages this big (and don't worry with any luck there will be no capacitors of any significant size anywhere on the board). Anyway I was looking for some advice on what circuits are out there or places to start looking for information about this.

Optoisolating the drivers would be very advisable for flashover protection. (cheapest way is
probably to use PWM across the opto)  High-voltage transistors or MOSFETs are probably the way to go for the output stages - you might
also be able to use multiple, lower-voltage, more easily obtainable parts in a series arrangement.
This also spreads the power dissipation.  I'd probably go for MOSFETS to simplify the drive. 1KV MOSFETS are readily available. HV
transistors tend to have very low gain.
Assuming you're looking at linear regulation from a common HT supply, Remember that 5mA at 1000V
(half outout voltage - the worst case) is 5 watts of power dissipation. This could be a major issue
as insulating heatsinks to 2KV might be fun. Forced-air cooling may be easier.  
Out of curiosity, What's the application ?

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2003\03\03@084721 by Spehro Pefhany

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At 11:41 PM 3/3/2003 +1100, you wrote:
>howdy ho campers
>
>In simple terms, I have a project that requires controlling many (60-200)
>output lines at about 40 times a second. The output of each line should be
>a DC analogue voltage between preferably zero and about 2000 volts (8-12
>bits resolution would probbably do me fine). To make life easier the max
>current is absolute MAX of 5mA and likely allot less (IE <1 mA) and some
>leakage voltage would probably be ok (provided it was always a constant
>voltage across all outputs or followed some mathematical function or another).
>The control side of it would be done with a few PIC's to do the IO and a
>big computer for processing. I have no experience in dealing with voltages
>this big (and don't worry with any luck there will be no capacitors of any
>significant size anywhere on the board). Anyway I was looking for some
>advice on what circuits are out there or places to start looking for
>information about this.

The 2kV requirement will present interesting design challenges.
Everything else is easy/boring.

You will be near the upper limit of easily available transistors. I suggest
a regulated 2kV supply and use 2kV Vcbo NPN transistors. Do you need
push-pull output or can the load look like a resistor to the 2kV rail?

No PNP/P-channel type devices are commonly available much over about 500V,
so the output topology will be constrained by the requirement to use only
NPN/N-channel type.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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2003\03\03@125934 by Roman Black

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Hi, why try to control the 2000v side??
Since he only needs 40Hz updates, it might be easier
(and more reliable) to generate the HV from a LV
PWM supply via flyback transformers and HV diodes.
HV diodes can be bought quite cheap and you can
get small HV flyback transformers dirt cheap from
many sources, usually sold as "flash or strobe
transformers".

It will probably need a lookup table for the ratio
between input PWM vs output HV, but should be do-able
and maybe even reliable.

So to guess what it is, an EL type monitor???
-Roman



Spehro Pefhany wrote:
{Quote hidden}

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2003\03\03@162029 by Jake Anderson

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its actually an adaptive optics scheme cheap enough and easy enough that it
is actually worth considering for dedicated hobbyists

the load looks like a somewhat leaky capacitor with a moderate amount of
intrinsic resistance

that being the case I would really like to stay away from PWM supplies
because the voltage is directly coupled to the actuation in the optics
system.

i'll look at the MOSFETS and Transisistors thanks (i didnt think they went
that high)
i may be able to drop the voltage requirement if i make the actuator a
little differently, hopefully fit it into one cheap part.

{Original Message removed}

2003\03\03@182702 by Ashley Roll

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Hi Jake,

Do you have a copy of "The Art of Electronics" but Horowitz and Hill?

They have an example in there for exactly this.. Driving Piezo elements for
adaptive optics. It should give you a good idea on how to do it.. Its in the
section on Mosfets, page 169 in my copy (second edition).

Hope that helps ;)

Cheers,
Ash.

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Digital Nemesis Pty Ltd
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Mobile: +61 (0)417 705 718




> {Original Message removed}

2003\03\04@024935 by hael Rigby-Jones

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> -----Original Message-----
> From: Roman Black [SMTP:.....fastvidKILLspamspam@spam@EZY.NET.AU]
> Sent: Monday, March 03, 2003 2:38 PM
> To:   PICLISTspamKILLspamMITVMA.MIT.EDU
> Subject:      Re: [EE]: High Voltage Controler
>
> Hi, why try to control the 2000v side??
> Since he only needs 40Hz updates, it might be easier
> (and more reliable) to generate the HV from a LV
> PWM supply via flyback transformers and HV diodes.
> HV diodes can be bought quite cheap and you can
> get small HV flyback transformers dirt cheap from
> many sources, usually sold as "flash or strobe
> transformers".
>
Because the OP needs 60-200 outputs independantly adjustable, and presumably
just one high voltage supply rather than 60-200 individual supplies.

Regards

Mike




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2003\03\04@101728 by Roman Black

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Michael Rigby-Jones wrote:
>
> > -----Original Message-----
> > From: Roman Black [SMTP:EraseMEfastvidspam_OUTspamTakeThisOuTEZY.NET.AU]
> > Sent: Monday, March 03, 2003 2:38 PM
> > To:   PICLISTspamspam_OUTMITVMA.MIT.EDU
> > Subject:      Re: [EE]: High Voltage Controler
> >
> > Hi, why try to control the 2000v side??
> > Since he only needs 40Hz updates, it might be easier
> > (and more reliable) to generate the HV from a LV
> > PWM supply via flyback transformers and HV diodes.
> > HV diodes can be bought quite cheap and you can
> > get small HV flyback transformers dirt cheap from
> > many sources, usually sold as "flash or strobe
> > transformers".
> >
> Because the OP needs 60-200 outputs independantly adjustable, and presumably
> just one high voltage supply rather than 60-200 individual supplies.


And that's why I suggested it. :o)
I've got plenty of 2.5kV power transistors here,
special purpose rugged units from TV repair stock.
They are NOT cheap and i'll tell you now that 200 of
them linearly controlling a 2kV DC supply is NOT
going to be cheap or even close to reliable.

Considering these transistors cost $4 or more each,
and will still need snubbers, heatsinking etc I think
a cheaper and definitely *more reliable* result will
come from 200x HV diodes and 200x flash transformers
driven by cheap rugged transistors.
-Roman

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2003\03\04@105234 by hael Rigby-Jones

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{Quote hidden}

You don't have to use transistors with that high a voltage rating, it's
entirely possible to use 2 (or more) lower voltage transistors to spread the
voltage drop.

Mike


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2003\03\04@114525 by William Chops Westfield

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>    come from 200x HV diodes and 200x flash transformers
>    driven by cheap rugged transistors.

Ah, Roman and his wonderful parts distributers...  Where exactly did you say
you could get these cheap flash transformers?  I know that for one or two
you can raid your local photo processor for disposed disposable cameras, but
I'd hardly want to unsolder 200+ for a project...  I always assumed that
these were custom-manufactured for the disposable camera industry,
unavailable to mere mortals (but I wouldn't mind having a source, even for
traditional flash-like projects (I really do want a microcontroller
sequenced multi-flash unit...)

BillW

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2003\03\04@115615 by William Chops Westfield

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BTW, I doubt that a "cheap flash transformer" is capable of operating
at 2000V.  I think most generic "wire" is rated for about 600V, and much
above that the insulation is prone to breaking down, causing arcing between
the winding (or between layers of winding.)  I've actually caused this to
happen by abusing some fluorescent CCFL inverters.

(OTOH, cheap fluorescent inverters might be a more appropriate volatge
source, being aimed closer to the desired voltages (cheap flash output
voltage is about 300V) - does anyone happen to know how easy it might be to
modify one of those cheap TDK inverters floating around the surplus market
to provide a regulated and variable output voltage?)

BillW

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2003\03\04@160444 by Roman Black

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Michael Rigby-Jones wrote:

> You don't have to use transistors with that high a voltage rating, it's
> entirely possible to use 2 (or more) lower voltage transistors to spread the
> voltage drop.


Wonderful! So now you need 200 optos to the "high
side" transistors, 400 HV transistors draped across
2kV DC supply and just about *any* bias fault or
glitch is going to fry 2 transistors up big time! :o)

The little transformers are available in 10s quantity
from Altronics (similar to Digikey) for around $1
USD each. I've also seen them (and similar) on
hobby and surplus sites very cheap. Maybe they're
not big enough, I don't know what total power is
required per pole?

Or what about diode/cap ladders (like tripler etc),
these are often used in low-power laser tube supplies
and might be a decent way to drive it with PWM from
(say) 200v supply. And *when* things fry it will be
a cheap cap or diode to be replaced...
-Roman

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2003\03\05@015759 by Roman Black
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Roman Black wrote:

> Wonderful! So now you need 200 optos to the "high
> side" transistors, 400 HV transistors draped across
> 2kV DC supply and just about *any* bias fault or
> glitch is going to fry 2 transistors up big time! :o)


Whoops, sorry Michael, I just re-read that post and it
sounds quite rude and sarcastic and that wasn't my intent.
It was meant to be a "cheeky chuckle" about the joys
of chasing 400 transistors around a 2kV supply, as an
ex-TV guy it seemed amusing when I wrote it. :o}
I apologise, sorry dude!
-Roman

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