Connecting multiple bench power supplies - Page 1
Forum section: electronics / beginners

author: advark
author_rank: Contributor
timestamp: September 04, 2018, 02:01:41 am
content: Hi everyone,Most bench power supplies come with 1 to 3 outputs but I need 5 different voltages for testing a circuit (+3.3V, +5V, +12V, and +/-15V). I thought using my DP-832 for my +5V and +/-15V rails and another one (cheaper!) with 2 outputs for the +3.3V and +12V (which I don't own yet, BTW). The goal is to get a ballpark view of the power consumption for my circuit for each power rail in order to design a power supply to go with it.This got a few questions popping in my head:How the heck do I connect the ground(s)? Do I tie both PSU grounds together? I'm pretty sure this is a no go because it would cause a ground loop. Therefore, the "test" circuit would have 2 grounds that sould be isolated from each other because of the ground loop. Am I missing something here?I bit more detail:+3.3V: LCD display power rail (estimation: < 500mA).+5V: Main power rail (MCU, logic, sensors, LEDs, etc) (estimation: 1.5 to 3A, but I can be totally wrong here).+12V: Cooling fans power rail (estimation: ~ 1 to 2A depending on the fan(s)).+/-15V: OpAmp supply rails (estimation: ~100 to 200mA).Thanks for any light you can shed on this shadow.

author: Signal32
author_rank: Frequent Contributor
timestamp: September 04, 2018, 03:31:46 am
content: Yes, you can tie all the PSU grounds together, what do you mean cause a ground loop, they are all independent & isolated. And actually you won't tie all grounds together, you'll tie two grounds together and tie the 3rd PSU + to that shared ground since you need -15v.You can do everything with the DP832 + 2 linear converters:- Get +5V from the 5v Output- Get 3.3v from 5V output + 3.3v regulator.- Get -15v from Output1 - to get -15v tie the + of the Output1 to the shared ground.- Get +15v from the remaining output- Get +12v from the +15v via a 12v regulator.For power estimation you don't even need the +12v since you can just measure how much the fans consume separately.Same for the +3.3v, just apply power to the lcd separately, it shouldn't use significantly more when in use.

author: Brumby
author_rank: Unknown
timestamp: September 04, 2018, 05:54:56 am
content: Let's not get too wound up using the term "ground".First, I would assume all the power supply outputs are floating - if not, then the following could be problematic....Pick a point somewhere - anywhere - that you wan to make as your 0V reference point, then connect each power supply accordingly: If you want +5V, then connect the -ve of a 5V supply to the reference point and use the +ve as the +5V source. If you want -12V then connect the +ve of a 12V supply to the reference point and use the -ve as your -12V source. Continue as necessary for all the supply rails required.Once done, then makeoneconnection between the 0V reference point and a ground connection (you should have several to choose from on the power supplies) - if you want it all ground referenced.

author: KrudyZ
author_rank: Frequent Contributor
timestamp: September 04, 2018, 10:50:41 am
content: You should also make sure of any power sequencing requirements your circuit may have to not inadvertently blow something up.

author: advark
author_rank: Contributor
timestamp: September 04, 2018, 09:08:53 pm
content: Quote from: Signal32 on September 04, 2018, 03:31:46 am