Negative Supply - Page 1
Forum section: electronics / beginners

author: lugaw
author_rank: Regular Contributor
timestamp: May 23, 2023, 03:45:56 pm
content: I have an oscillator that uses -12V as power.I tried to power it by using a DC power supply by connecting the Positive side to the GND (as I understand it) of the Oscillator and the COM pole of the power supply to the -12V of the oscillator and it didn't work and it was shorting out.Since my power supply have a COM, Negative, Positive outputs I connected the COM to the GND of the Oscillator and the Negative of the power supply to the -12V of the oscillator and it is working.I want to understand why it didn't work by just reversing the polarity of the supplied voltage.

author: BeBuLamar
author_rank: Super Contributor
timestamp: May 23, 2023, 04:01:13 pm
content: I think because the COM and the Negative of the power supply are connected together. Try using only the Negative and Positive. Don't connect the COM.

author: IanB
author_rank: Super Contributor
timestamp: May 23, 2023, 04:04:10 pm
content: I think you have not provided enough information. If you ONLY connected two wires from the power supply to the oscillator it would have worked in both cases, and nothing could short out because there are not enough connections to create a short circuit.However, if you have other connections and other items being powered, perhaps with some common ground somewhere, then it would matter how you arrange the connections.

author: IanB
author_rank: Super Contributor
timestamp: May 23, 2023, 04:04:57 pm
content: Quote from: BeBuLamar on May 23, 2023, 04:01:13 pmNo, this is nonsense! How could COM and negative be connected?

author: lugaw
author_rank: Regular Contributor
timestamp: May 23, 2023, 04:19:52 pm
content: Quote from: IanB on May 23, 2023, 04:04:10 pmThat was also my thought too, that it would work by just swapping them to have negative power. There are no other circuits involve, because I was too lazy to swap the wires to the negative port of the PSU. It was using the max 1amp I set on the power supply and the oscillator was not oscillating. Thinking I would break my oscillator I stopped and used the negative leads and it just works.I will try it again and set a low current.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 23, 2023, 04:41:27 pm
content: You have to know your power supply.You can only swap such connections if the power supply itself is completely floating.It looks like a quite old but nice power supply.It also states it has 3 voltage outputs, but it only has two voltage control knobs. I assume the left button is for the black and red banana outputs and is adjustable between 0 to 6V.The other is labeled Plus and Minus 0 to 18V, and it would be logical if the green "COMmon" would be the in the center of those symmetrical outputs.If it does not work this way, then start with searching for and reading the manual. My next guess for troubleshooting is that this power supply may be partially broken. It looks like it's about 50 year old so it may need some maintenance.

author: IanB
author_rank: Super Contributor
timestamp: May 23, 2023, 05:02:05 pm
content: Yes. Looking at the picture of the power supply, it would appear that the two terminals on the left are (−) and (+) for the single output supply, then mains ground is in the middle (green), then the three terminals on the right are (−) (COM) (+) for the dual output supply.

author: lugaw
author_rank: Regular Contributor
timestamp: May 23, 2023, 05:08:27 pm
content: Quote from: Doctorandus_P on May 23, 2023, 04:41:27 pmThe power supply is fine and works perfectly, it's a triple output power supply 0-6v (the control on left) +-18v that can be set by selecting the white button and set the voltage.I was able to make it work now (using COM +port reversed or COM -port connected to the oscillator).I don't know what happened with the oscillator. I recently acquired it and it was the first time I powered it on. I didn't see any big capacitor inside that could make power supply to limit it to 1amp. Maybe the diode protection on the oscillator outside the case was broken then suddenly works? Right now the oscillator is consuming 0.13amp and oscillating. Thanks for all the answers.