0V on a bench power supply = common?? - Page 1
Forum section: electronics / beginners

author: jaunty
author_rank: Regular Contributor
timestamp: December 06, 2018, 04:36:58 pm
content: here's a dumb 'beginner' question ... seems there are a lot of weird little things like this that eluded me over the decades.I'm building an amplifier circuit and the test instructions say emphatically to ensure that both this and that terminal have a solid connection to 0v on your power supply ... it's a complementary circuit requiring +/- voltages ... so i assume that would mean a floating 'ground'? someone else mentioned that i have to bridge the two sides of my power supply to get 0V - i think this would be the case for a dual rail supply that DIDN'T have a neg output (?) but my HP 6236B has a -20v output ...sooo ... it's basically a euphemism for 'floating ground' ?signed, slightly confused

author: ogden
author_rank: Super Contributor
timestamp: December 06, 2018, 04:46:10 pm
content: Some supplies have two isolated/floating channels with both, '-' and '+' terminals available for each, so you have to connect '-' of one supply to '+' of another to get bipolar supply or just double the output voltage. Your supply is bipolar supply "out of the box" where this is done already, in "common" terminal which obviously is ground.Quote from: jaunty on December 06, 2018, 04:36:58 pmNo it's not. This ground we are talking about is as non-floating as you can get.

author: rstofer
author_rank: Super Contributor
timestamp: December 07, 2018, 02:42:55 am
content: Think about 2 batteries stacked as they would be in a flashlight. The bottom battery (+) terminal butted against the top battery (-) terminal.Fine, the (+) of the top battery is the PS (+) output, the negative of the bottom battery is the (-) output of the PS and the junction of the two batteries is the 0V or 'common' output of the PS. Let's stay with 0V because a) the instructions say so and b) we have no idea whether that is 'ground'. Or even 'which' type of ground.

author: cdev
author_rank: Super Contributor
timestamp: December 07, 2018, 02:49:56 am
content: Think of it as the "middle" point of the (all voltages are relative to something) voltage range thats supplied.You can connect it to ground if you want to but its not the same thing as ground.You may have another terminal thats ground. (thatsalways connected to thecase)

author: Brumby
author_rank: Unknown
timestamp: December 07, 2018, 03:10:29 am
content: 0V is just a reference point. An ordinary single supply will have one terminal that is usually assigned this reference point - and, by convention, this is usually the "negative" terminal.With split supplies, the usual convention is to label the mid point as 0V.The following diagrams show the exact same circuit. The ONLY difference is where the 0V reference point is chosen.

author: jaunty
author_rank: Regular Contributor
timestamp: December 07, 2018, 05:07:45 pm
content: Quote from: ogden on December 06, 2018, 04:46:10 pmwell 'about as non floating as you can get' to my mind - would be chassis or 'outlet' ground ... but this doesn't seem to be that at all ...

author: ogden
author_rank: Super Contributor
timestamp: December 07, 2018, 05:36:09 pm
content: Quote from: jaunty on December 07, 2018, 05:07:45 pmRight. AFAIK there are many meanings for floating ground term. Few I know are: Mains equipment may have floating ground which means that it's case is not earthed which is earthing fault. Then two interconnected electronic devices may have floating grounds to each other, they may even have proper earthing each in it's own building but their ground potentials may differ, especially when lightning strikes nearby . Then there is improper use of "floating ground" term in devices/circuits when virtual ground term shall be used instead. Virtual ground means that "ground" have little or no current handling capacity, at least compared to specs of the power supply.

author: chris_leyson
author_rank: Super Contributor
timestamp: December 07, 2018, 06:04:54 pm
content: QuoteWell, not really. From the HP6236B manual "The supply's three outputs share a common output terminal, which is isolated from chassis ground so that any one output terminal can be grounded"0V or common is floating and ground means earth in the context of a power supply. Ground is a term that is used quite loosely, if there is an earth connection involved then ground = earth, if there is no earth connection and people use the term ground then they probably mean 0V. From Wikipedia "Ground (electricity), the reference point in an electrical circuit from which voltages are measured". Sometimes you have read between the lines to understand what the writer means when they say ground. I would go with the Wiki definition "a reference point from which voltages are measured". It could be floating or it could be earthed but in the context of a power supply ground would usually mean earth.

author: rstofer
author_rank: Super Contributor
timestamp: December 07, 2018, 07:56:54 pm
content: Brumby did a much nicer job of showing the possible configurations than I did before him.Your situation is the leftmost sketch. 0V is in the middle.I don't want to talk about 'ground' for the various reasons given above. It turns into a huge mess unless you are looking at a specific circuit.I would expect modern multiple output power supplies to have each channel floating and not connected to the others. But even a supply like the Rigol DP832 has the 5V negative terminal connected internally to the output 2 negative terminal. There is no way to remove this connection and this has implications that are discussed in the User Manual. Basically, output 1 will be the -15V supply, output 2 will be the +15V supply and output 3 will be the +5V supply.