# Combining 5V power supplies in parallel to obtain more current

I need to power 20 5V RGB LED strips, each consuming 1A at full white. I'm working with off the shelf 10A supplies, so technically I can power them all by combining two 10A supplies.

I read that by protecting the 5V DC output from each supply with a reverse bias diode, I can connect them on the output side in parallel to achieve 20A. I can calculate the required cable diameters just fine (yes they're big!) so will be feeding power at several points instead of all at one end. But I do need some help figuring out the exact specs of the Schottky diode I should use for this. Can anyone help me calculate this please?

• Not sure you need the diode. I think I would try it without the diode first. I would definitely use a fuse in series with each supply. Maybe a 15A slow blow fuse. Commented Feb 2, 2020 at 5:16
• You also need current balancing resistors in series with each output since no two supplies are perfectly matched and the stronger supply will supply all the load current. Commented Feb 2, 2020 at 5:19
• Why not just power half of the strips from one power supply and the other half from the other power supply? Seems less complicated to me. But maybe I'm missing something.
– jonk
Commented Feb 2, 2020 at 5:22
• why would you want to combine if in the first place is actually you can connect without it? you said 20 of 5V led strip . just split 10 to each supply. never combine switching supply if doesn't have feature combining each module to be one module. because it will have load difference even voltage difference. if you bought the switching supply with feature combining power port (usually they have another port for sensing voltage, and 2 others for paralleling signal from both side) then you can, if not please don't. Commented Feb 2, 2020 at 5:28
• If the grounds are combined and LEDs are driven by drivers that are related to LEDs on the same supply it should not matter that your Arduino controller derives its supply from one or other 20V power supply. Commented Feb 2, 2020 at 6:04

I need to power 20 5V RGB LED strips, each consuming 1A at full white. I'm working with off the shelf 10A supplies, so technically I can power them all by combining two 10A supplies.

Multiple independent supplies can be used if required, as long as they all share a common ground.

If the grounds are combined and LEDs are driven by drivers that are related to LEDs on the same supply it should not matter that your Arduino controller derives its supply from one or other 20V power supply.

If the LED supply is from V+ via LED to say MOSFET to ground, and Arduino supply is 5V, shares the same ground and drives the FET gate, then the source of the 5V and the source of the 20V is unimportant. The common ground is the essential factor.

Even if the switches (MOSFETS here) are on the "high side" between +20V and LED then as long as the control signal is translated up to the FET gate correctly the source of one or more 20V supplies and of the 5V supply may be independent as long as they share a common ground.

In this diagram, 20V supply A, 20V supply B and 5V supply C may be separate power supplies, with their ground (negative) connections joined.

Circuit A uses a "low side driver" and circuit B uses a "high side driver", both driven from the ground referenced controller on circuit C.

simulate this circuit – Schematic created using CircuitLab

• Thank you for this detailed response! There's a small error that snuck in: Both Arduino and LEDs are 5V, it's 20A, not V, that are required to power the LEDs and the Arduino. I don't suppose that changes anything though? Arduino and first strips can be powered by supply A, and the second bunch of strips from supply B, so long as they share the common ground? Also, the arduino is providing the data signal on one of the digital out lines. Commented Feb 2, 2020 at 21:49
• @Balthasar Agh Whoops! :-). | Yes, no change. Arduino from same supply as some LEDs and not others is equally good as what is shown here. FET M2 could be driven directly by 5V Arduino. FETs need to be fully on at 5V drive. Commented Feb 3, 2020 at 1:11