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Old 28th May 2005, 11:07 AM   #1
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Default -50V negative supply

Hi all,
I want to use Gary Pimm's CCS serf bias on the cathode of a long tailed pair and I need a negative supply that can provide something between -40V and -50V. Ripple is not a problem, I just need something quite stable. The long tailed pair is polarized with 4mA. The reference chain absorb only 0.35mA. Maybe a simple zener shunt regulator can works good but, if there is on the market something similar to Lm337 that can support -50V on its output, maybe a three pin regulator could be a better idea. Have you an advice?

Mark
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Old 28th May 2005, 11:11 AM   #2
EC8010 is offline EC8010  United Kingdom
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337 can support -50V on its output. The device's voltage rating is the input/output differential, not an absolute voltage.
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Old 28th May 2005, 11:22 AM   #3
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Mhmm...ok thankyou. I'll look at the datasheet, design a simple regulator and I'll post it here. Just to be sure that I'm not making another mistake

Mark
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Old 28th May 2005, 01:12 PM   #4
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like EC8010 says, use a zener on the adjustment pin to lift it from groundpotential.. there are several schematics on the web, good luck!
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Old 28th May 2005, 02:03 PM   #5
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Quote:
Originally posted by Mr. Triatic
like EC8010 says, use a zener on the adjustment pin to lift it from groundpotential.. there are several schematics on the web, good luck!
What EC8010 means is that the voltage rating of the device is what it sees between the "input" and "output" pins. The device doesn't know if it is providing 50V or 500V. In fact, devices such as this can be used to regulate HT for valve amps (albeit with supporting circuitry).

The zener would be superfluous.
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Old 28th May 2005, 03:09 PM   #6
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Here I am...thankyou for the replies.
Please look at the schematic. What do you think of it?

Mark
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Old 28th May 2005, 05:42 PM   #7
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Looks good to me. You might want to choose quieter diodes than 1N4004, and you'll want to check that the ripple on your reservoir doesn't cause the regulator to drop out at the chosen current. You may need to heatsink the 337.
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Old 28th May 2005, 06:22 PM   #8
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Thankyou EC8010

What kind of diodes should I use? MUR120 (200V/1A 50ns) maybe? I think that I will use the chassis as an heatsink (with mica insulator).

Regarding the ripple...maybe I could use a simple crc filter. Something like 330uF/500Ohm/330uF. The voltage in front of the LM would be 64V and the ripple shouldn't be a problem, I think.

I'll try to check this issue...

Mark
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Old 29th May 2005, 10:50 AM   #9
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I expect MUR120 will do fine if they're soft recovery (don't have a data sheet to hand). I can't imagine they need to be on a heatsink - you're not passing much current! Try using Q = CV = It for calculating the ripple on the back of an envelope, or PSUD if you like graphical answers and like to play.
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Old 30th May 2005, 11:14 AM   #10
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Thankyou ec8010.
For the crc idea I've used PSU Designer II. The ripple is not a problem. Mur120 are very fast and soft recovery indeed
I'll try to build the circuit and evaluate if it works properly.

If the load is higher ( same tension but more current) the lm337 would be happier, right?
So, if I'd try a different tube in the driver stage (as 6h30 or 5687 instead e88cc), I could use the same circuit, maybe only with an adjustment of the R in the C-R-C filter. Do you agree?

Mark
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