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-200 VDC regulator
-200 VDC regulator
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Old 3rd January 2008, 12:18 PM   #1
jogas is offline jogas  Italy
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Default -200 VDC regulator

Hi,

I need to reduce a -270 VDC down to -200 at 20 mA.
Is there any three pin component available?
I only found a VB408 that is a positive regulator

Thanks in advance for your help
Giuseppe
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Old 3rd January 2008, 12:21 PM   #2
Nordic is offline Nordic  South Africa
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a fat 3k5 resistor maybe? 2 - 5W

70/3500 = 0.02A
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Old 3rd January 2008, 12:40 PM   #3
jogas is offline jogas  Italy
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.... I do need a very precise and stable and current independent -200VDC...
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Old 3rd January 2008, 01:12 PM   #4
theAnonymous1 is offline theAnonymous1  United States
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Is it not possible to use two LM137HV? Use one to pre-regulate down to around -235v and the other to drop down to -200v.
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Old 3rd January 2008, 01:39 PM   #5
BWRX is offline BWRX  United States
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Default Re: -200 VDC regulator

Quote:
Originally posted by jogas
I need to reduce a -270 VDC down to -200 at 20 mA.
Is there any three pin component available?
Have you thought about just using a zener (or a string of zeners), resistor(s), and pnp transistor? A 70V drop across a transistor sinking 20mA is only 1.4W. You could also put a resistor in series with the collector to reduce the transistor's dissipation.
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Old 3rd January 2008, 01:58 PM   #6
jan.didden is offline jan.didden  Europe
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Default Re: Re: -200 VDC regulator

Quote:
Originally posted by jogas
Hi,

I need to reduce a -270 VDC down to -200 at 20 mA.
Is there any three pin component available?
I only found a VB408 that is a positive regulator

Thanks in advance for your help
Giuseppe

If your raw supply is floating you can use a pos regulator. Just ground the pos terminal and use the common terminal (which normally would be grounded) as the neg terminal. Works like a charm.

Jan Didden
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Old 3rd January 2008, 01:59 PM   #7
SY is offline SY  United States
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-200 VDC regulator
I'd use a Maida regulator with a 337 and either a HV PNP bipolar or HV p-channel MOSFET. Simple, stable, low output impedance, low noise. And reliable.
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Old 3rd January 2008, 02:06 PM   #8
jogas is offline jogas  Italy
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Thanks for the answers, yes, the easiest way is to use apositive regulator with the output grounde...

SY what is a maida regulator?

Giuseppe
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Old 3rd January 2008, 02:11 PM   #9
SY is offline SY  United States
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-200 VDC regulator
Poke around National Semiconductor's site. There's a nice paper by Michael Maida on using a HV bipolar to limit the voltage across a 317-type regulator. I think the paper is Linear Brief LB-47. This paper only shows positive regulators, but by using PNP (or p-channel FET), a 337, and turning around the diodes, you can make a negative regulator.

Or you could use the positive regulator as published inserted in the ground leg of your raw supply.
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