[Elecraft] OT: Dual Range Bench Supply Use

Wed Mar 24 15:24:01 2004

Bill:
You've pretty much guessed it, but here's the deal...
You have a supply with both rails floating.  
Lab supplies are designed to be above ground to give you some options with
respect to the way they are used.  Sometimes you want a totally floating
supply, so nothing is grounded.  
Ordinarily, you would run the minus terminal to ground, regardless of which
psotion the rangew switch is in, and route the plus to your device. In a ham
shack, that should be the best procedure, since the neg will find it's way
to ground somewhere, and a floating supply might be more prone to RFI. 
If you had a device that required a positive ground, you would do the
opposite;  ground the + , and run the - to the device.  
Often in a lab environment, you're dealing with circuits that require both
polarities with respect to ground, like +15V and -15V for example. Assuming
that ground is the reference, you would use two identical power supplies;
one with the Pos to ground, one the neg to ground, and the grounds wired
together.  On occasion, you have to float the whole thing, and wire the two
supplies in series, with the center as your neutral reference.
Hope that makes sense !
73, George - K1GXT 

-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of Bill Acito W1PA
Sent: Wednesday, March 24, 2004 2:42 PM
To: [email protected]
Subject: [Elecraft] OT: Dual Range Bench Supply Use

I picked up a used HP variable bench supply 
(6204B DC, 0-40V at 0.3A, 0-20V at 0.6A) 
for QRP supply and test (no docs).

Question for any bench techs out there....

There is a switch on the front for the two ranges, and 
the supply has three output plugs: +, - and GND

Is it correct that I should use the + and - for 40v, and
the + and GND (w/ the GND shorted to -) for 20V, or the same
+ and -?

When is GND used? For, say, Op-amps that have + and - 
supplies relative to GND?

Bill W1PA
(embarrassed that he does not know this off the top of his head)

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