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Old 23rd May 2003, 07:36 PM   #1
cm961 is offline cm961  Canada
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Default How to split a single supply

Hi,

I've got this 0-30V 0-2A supply that I would like to use to test my power amplifier channels because it has current sensing/limiting.

I know theres a way with a few resistors and an op amp that you can split a supply creating a 'virtual ground'. Is there a similar technique which I can use but that would allow for the higher currents? Or would 15-0-15 not be enough to test an amplifier (for basic functionality) anyways?

Pete
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Old 23rd May 2003, 09:14 PM   #2
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a simple full bridge rectifier would yeild you +/- 22 vdc properly filtered which would be fine for low powered amplifiers


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Old 23rd May 2003, 09:17 PM   #3
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I think he was talking about using a DC supply, not a transformer. I don't know of any good way. Sorry I can't help!
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Old 23rd May 2003, 09:23 PM   #4
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oooohhhh ....then I would tap into before its rectified...LOL
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Old 23rd May 2003, 09:30 PM   #5
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Default Re: How to split a single supply

Quote:
Originally posted by cm961
Hi,
I've got this 0-30V 0-2A supply that I would like to use to test my power amplifier channels because it has current sensing/limiting.
Pete
Had the same problem long ago.
If you can afford it, buy a second one. Very flexible, you'll have 60V or 30-0-30 and anything in between it if required, also practical when two different voltages are necessary...

/Hugo - lives with 2 supplies for years now, they never fight.
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Old 23rd May 2003, 09:41 PM   #6
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If you don't need to supply real power into a load, i.e. if you only want to test if it doesen't blow upon power up and if the output voltage looks normal on a scope, then you could use a reasonably sized voltage divider made out of two resistors and two capacitors.
If you want to really load it you might capacitively couple the load to the plus or minus rail.
If these suggestions work at all and if yes, how well, depends mainly on the amplifier under test (one key parameter is bias current).

Regards

Charles
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Old 23rd May 2003, 09:55 PM   #7
cm961 is offline cm961  Canada
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Sweet, thanks for the info guys. I'll see if I can score another one, or else I'll try the divider thing.

Can I use high power op-amps (like lm3785) to buffer the divider?

Pete
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Old 23rd May 2003, 10:18 PM   #8
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Quote:
Originally posted by cm961
Sweet, thanks for the info guys. I'll see if I can score another one, or else I'll try the divider thing.

Can I use high power op-amps (like lm3785) to buffer the divider?

Pete
Well, if you are testing the amplifier and you have the LM3875 in the loop you have to consider its bandwidth etc.
I used a split supply with a floating ground where an LM317/LM337 are used as regulators with pass transistors. It is important, however, that you provide a load AFTER the filter caps attached to a common ground -- a few ma is all you ned, you also need a few ma on the output for the regulators to work correctly.

You will occasionally see dual output Lambda linear supplies on the web.
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Old 24th September 2004, 11:01 PM   #9
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Default I have two 16v DC - how do I get +-15?

I got two 16V 3.3A and want to get + 15 (or 16) anf - 15...
But is it possible to just plug them in, connect the + to the - and use this point as 0 ???

Mankeponken
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Old 26th September 2004, 04:22 AM   #10
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http://tangentsoft.net/elec/vgrounds.html
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