Bench power supply

This could be a naive question but I notice lots of switched mode power supplies come with three terminals:

Does anybody know what the Ground terminal is for? I can think of a few possibilities:

• Gnd connects to mains earth and is made available for safety or to ground static. OR
• Gnd connects to chassis, and either the Plus or Minus terminal can be connected to it. This would allow the PSU to be configured to power 3 different combinations: positive ground equipment, negative ground equipment, or floating ungrounded equipment. OR
• Gnd connects to chassis with positive and negative arranged equally around it. So if the PSU is set to 18V out, -9V would be available on the black terminal and +9V on the Red - both relative to Gnd, a split rail supply.

Dave

On mine the +/- are floating unless one side grounded.  The same is true on most lab linear PSUs as well, desirable feature to avoid ground loops in certain situations.

Edited By John Haine on 27/01/2023 16:04:00

I can confirm what John said.
The "GND" terminal is connected to the chassis AND mains supply protective conductor "Earth". The low voltage DC output is isolated from GND/Earth. The user can connect one or other of the output terminas to GND if they wish. This can help with electrical noise and safety or for compatibility with connected circuits.
The powersupply specification should say how many volts the output can be "floated" above ground without causing damage. A lot of low cost power supplies don't say. The output of these should not be taken much more than the maxium outut voltage above ground.

Some dual supples will have a 0V, positive, negative and GND terminals. For these the output is always symmetrical about 0V and any output terminal can be connected to ground. If the output is set to 12V and negative connected to ground the 0V terminal will be at plus 12V measured to ground and positive will be at plus 24V measured to ground.

Robert G8RPI