Author Topic: Connecting multiple bench power supplies  (Read 2218 times)

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Offline advarkTopic starter

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Connecting multiple bench power supplies
« on: September 04, 2018, 02:01:41 am »
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.
 

Offline Signal32

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Re: Connecting multiple bench power supplies
« Reply #1 on: September 04, 2018, 03:31:46 am »
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.
 

Offline Brumby

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Re: Connecting multiple bench power supplies
« Reply #2 on: September 04, 2018, 05:54:56 am »
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 make one connection 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.
 

Offline KrudyZ

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Re: Connecting multiple bench power supplies
« Reply #3 on: September 04, 2018, 10:50:41 am »
You should also make sure of any power sequencing requirements your circuit may have to not inadvertently blow something up.
 

Offline advarkTopic starter

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Re: Connecting multiple bench power supplies
« Reply #4 on: September 04, 2018, 09:08:53 pm »
Yes, you can tie all the PSU grounds together, what do you mean cause a ground loop, they are all independent & isolated.
Quote

LOL! So true! I guess I was over-thinking the problem... :palm:

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.

I thought of it but I don't have the specs for the fans (those were salvage from an old computer. All I know is they are 12V). Plus having them all independent would make it easier to play with voltage/current limitation and see how the protection circuirty will react for each rail.

Thank you all for your wisdom  ;)
 


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