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Nov30-07, 04:50 PM
berkeman's Avatar
P: 41,104
For a general lab power supply, or a packaged OEM power supply, you will generally want to give the end user the most flexibility, so you will float the outputs from Earth ground, and provide a banana jack or spade lug or whatever to make it easy to strap V- (or V+) to Earth ground.

For circuitry in situations where significant Earth ground currents can flow (like on electric-powered Subway trains in New York), you will want to isolate all logic grounds from Earth/chassis grounds, and maybe only connect the two occasionally in the devices with a charge bleeder resistor like 1Meg in parallel with a small high-frequency cap like 1000pF.

For devices that don't fit the above, you will generally get the best EMI performance and ESD immunity if you hard tie Logic ground and Earth/chassis ground with a low-inductance connection (like a short metal standoff between a PCB plated-through hole and the metal chassis).

Situations vary, though, so you need to look at the noise environment and end use of the product, in order to determine the best overall grounding scheme.