Using a dual power supply for op-amps - Page 1
Forum section: electronics / projects

author: gfmoore
author_rank: Newbie
timestamp: September 03, 2025, 08:26:01 am
content: Hi all,I have recently purchased a dual power supply (Farnell XA35-2T )I know I can connect a positive to a negative for a ground point. However, this device also has a centre earth point. Should I connect this to the ground point too.I think I should so that my oscilloscope earth point is properly grounded.btw if anyone has the manual pdf for this power supply I'd be grateful. I've got photos but they aren't very good.I can't find it anywhere, not even on the Farnell website.Gordon

author: jwet
author_rank: Frequent Contributor
timestamp: September 04, 2025, 02:35:16 am
content: "Laboratory" power supplies are fully floating. They look to the world like batteries. They can be stacked on other supplies, driven with signals, etc and will act like a theoretical voltage source. General purpose AC operated Oscilloscopes are generally earth grounded so one way or another you're going to have your signal referenced to earth. If you let your power supply float and connect your scope to the common output of your supply, it will be pulled to the ground of your scope. If you ground the common at your power supply and connect your scope, there is a possibility to create a "ground loop"- if your scope ground and your power supply ground aren't equal. In any case, you will have currents flowing in grounds, which is not optimal.Connect your power supply with +- and common to your circuit. Tie your scope ground connection to the common connection of your circuit under test. This will establish "ground" and there should be no extraneous ground currents.Dave has some good videos about the finer points to using a standard earth grounded oscilloscope in various situations, the title is some like how not to blow up your scope- its good watching.Good luck.

author: TimFox
author_rank: Super Contributor
timestamp: September 04, 2025, 02:49:00 am
content: Notice that the two internal power supplies have "output" and "sense" pairs of binding posts.Normally, you connect the sense BP to the corresponding output BP, either directly at the panel or remotely at the load (to remove the effect of voltage drop in the current-carrying wires).Usually, there is an internal diode at those locations to keep the power supply from running away with no sense connection, but the output will not be accurate.

author: jwet
author_rank: Frequent Contributor
timestamp: September 04, 2025, 03:15:56 am
content: Good addition- I didn't notice the 4 terminal connection.

author: gfmoore
author_rank: Newbie
timestamp: September 04, 2025, 08:01:52 am
content: Great info and explanations. Very grateful, thanks

author: Terry Bites
author_rank: Super Contributor
timestamp: September 06, 2025, 03:17:53 pm
content: Not floating enough for some purposes. CM currents get though the transfomer and that can make your voltnuts ache.

author: jwet
author_rank: Frequent Contributor
timestamp: September 06, 2025, 07:34:36 pm
content: Quote-Not floating enough for some purposes. CM currents get though the transfomer and that can make your voltnuts ache.True enough, there is also capacitance associated with them but first order, its something that people should know and what seperates a real lab supply from most home brew stuff in general.

author: Smokey
author_rank: Super Contributor
timestamp: September 06, 2025, 09:02:11 pm
content: Quote from: Terry Bites on September 06, 2025, 03:17:53 pmIf you are working on something where that matters you are probably not asking general questions about power supplies on EEVBlog