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What's the 'ground' terminal for on all these DC power supplies?

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Sorry if this is a dopey question. On all these Atten/GW Instek/Wun Hung Lo bench power supplies (typically 0V-30V, 0A-3A~5A) that I'm looking at, there's a positive and negative terminal, and ground. What's ground connected to?

Ages ago I built a simple 317/337 +/-20V power supply (hasn't everyone?) which has a 'real' ground - you can clip a scope earth connection to it, power a sine wave generator with it and see a waveform symmetrical around 0V. I haven't seen anything to suggest that these DC bench power supplies can be used like that - that if the supply is set to 30V then the negative terminal is at -15V relative to ground. Maybe it ain't so?  Maybe it's too obvious to need stating? - but equally there are supplies out there that *don't* have a ground terminal. What are they doing differently?

Help relieve my ignorance!


It's connected to the ground pin in the mains plug. The power supply is floating, so if you want a grounded supply, you connect either the positive or the negative output terminal to this terminal, depending on whether you want the voltage to be positive and negative relative to ground. This is much more flexible than a power supply with a 'real ground', since you can freely put floating supplies in parallel/series. If you need +/- 15 V, you can take two 15 V supplies, connect the positive terminal from supply 1 to the negative terminal of supply 2, and to ground.

I usually tie at least one of the supply rails to ground if I don't have any other ground connections. This prevents the rails from floating to undesirable potentials when accidentally connected to some other voltage source (eg. mains). I only disconnect (one of) the connection(s) to ground when putting multiple supplies in series or when ground loops may be an issue.

Uncle Vernon:

--- Quote ---What's the 'ground' terminal for on all these DC power supplies?
--- End quote ---
It's for connecting stuff to ground.


--- Quote from: alm ---{Helpful stuff}

--- End quote ---

Thanks; that explains it perfectly.

--- Quote from: Uncle Vernon ---It's for connecting stuff to ground.

--- End quote ---
08:25:41 > 08:20:51
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Uncle Vernon:

--- Quote from: icon on April 01, 2012, 10:45:22 pm ---Sadly, you lose the Internet race. But thanks for playing along.
--- End quote ---
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