Dual power supply on/off switch for OpAmp - Page 1
Forum section: electronics / beginners

author: rnelsonchem
author_rank: Newbie
timestamp: July 26, 2017, 01:50:27 pm
content: Hello all,I am doing some breadboard testing of a circuit containing a few +/-12 V op amps, and I'm concerned about my current power supply connection procedure.I have two power supplies connected in series to provide the + and - 12 V necessary to power the op amps (and the rest of the circuit); however, in order to power on the device, I've been making the +/-/ground connections in some nonsimultaneous sequence. I am a little worried that this is going to have an adverse effect on my components over time. For example:http://www.analog.com/en/analog-dialogue/articles/improper-power-sequencing-in-op-amps-analyzing-the-risks.htmlI'm trying to think of some solutions, and this is where I could use your advice. Here's my thoughts so far.1. Try to turn on both power supplies at exactly the same time. This is certainly impossible to achieve exactly, so I'm thinking that this might still be a problem over time. I think my supplies are pretty good, but I don't know how quickly they achieve their set point or if there is an initial spike in power.2. Buy some sort of switch. I've found a couple of types of switches that I think should work (below)... But if there was some way I could do this without buying something new, that would be helpful.DIP switch:https://www.digikey.com/product-detail/en/grayhill-inc/78G01T/GH7732-ND/2680805Toggle switch:https://www.digikey.com/product-detail/en/nkk-switches/S31/360-2083-ND/1007140Does anyone have any other suggestions... The easier/cheaper the better, I suppose.Thanks!

author: rstofer
author_rank: Super Contributor
timestamp: July 26, 2017, 02:14:47 pm
content: Either switch will work fine but that dip switch will be easy to use on a breadboard. I kind of like that approach.I don't have any no-dollar solutions.

author: schmitt trigger
author_rank: Super Contributor
timestamp: July 26, 2017, 04:00:05 pm
content: You won't get anything cheaper/simpler than a dual pole switch

author: Kleinstein
author_rank: Super Contributor
timestamp: July 26, 2017, 05:01:48 pm
content: There are cheaper dual pole switched than the on linked.In addition it is a good idea to have 2 diode that prevent GND to go outside the supply range. So something like an 1N4003 from GND to +12 V and -12 V. This alone usually prevents the worst cases.

author: rnelsonchem
author_rank: Newbie
timestamp: July 26, 2017, 08:06:45 pm
content: Thank you all for the comments. I will bite the bullet and pick up those switches. I like the diode suggestion as well, so I'll grab some of those as well.One more question, though. Won't I need a 3 pole switch for my op amp setup? I do agree that dual pole switches are cheaper than the options I linked. However, I was thinking there would need to be a pole for +, -, and ground, which is why I included the links above. If there is a way to do this with a dual pole switch, that seems much better/cheaper.

author: schmitt trigger
author_rank: Super Contributor
timestamp: July 27, 2017, 01:48:45 am
content: Disconnecting the (+) and the (-) is sufficient to un-power the circuit, keep the common connected.

author: Zero999
author_rank: Super Contributor
timestamp: July 27, 2017, 08:36:22 am
content: A circuit needs two wires or more, to form a current path for the circuit.You only need a double pole switch. General convention suggests leaving the 0V connected and disconnecting +V & -V but you could also disconnect 0V & +V or 0V & -V, as long as you disconnect two of the wires, no current will flow through the remaining wire.

author: David Hess
author_rank: Super Contributor
timestamp: July 27, 2017, 09:59:11 am
content: Quote from: Kleinstein on July 26, 2017, 05:01:48 pmDoing this handles most of the worst case scenarios and is often done as a protective measure even when tracking power supplies are used. Actually, my tracking supplies have these diodes built in but they should still be added at the circuit in case a wire breaks.