# Can Circuit Boards Be Connected In Series and/or Parallel?

#### martinsbm

Joined Feb 7, 2017
6
Working on a project to take 2 - 5V power sources, and step up / boost from 5V@2A x 2 to 18V@1A x 1.

Have 3 booster boards capable of 18V@350mA each. Bench tested.

Can the output pads of PCBs, in this case booster boards, be connected in parallel (like batteries) to supply the needed 1A?

New to electronics, appreciate your patience. Learning...

#### AlbertHall

Joined Jun 4, 2014
12,026
The booster outputs can probably be connected in parallel without much problem.
You will also need to parallel the two 5V sources as well which, again, will probably be OK.
Please note the 'probably' in both those sentences. I am sure there are plenty which won't mind but also some which will mind and possibly some where such connection will release the magic smoke.

#### martinsbm

Joined Feb 7, 2017
6
Thank you for the reply, AlbertHall. The boards were so cheap, I'm tempted to try it. Since there is a pot to set the output voltage, I was thinking I could scope and tune/match the outputs. But, would they stay as who knows how good the regulation is. Thinking there could be feedback issues, and was considering a diode (e.g. rectifier) in each -minus output path might be helpful. Contemplating...

#### ErnieM

Joined Apr 24, 2011
8,296
Problem. If you put two supplies in parallel the one that has a slightly higher output voltage will try to supply all the current until it falls back in current limit.

#### AlbertHall

Joined Jun 4, 2014
12,026
Problem. If you put two supplies in parallel the one that has a slightly higher output voltage will try to supply all the current until it falls back in current limit.
Yes but, providing the output voltages are not significantly different and the current limit is not of the foldback kind, then all will be well.

#### ErnieM

Joined Apr 24, 2011
8,296
Actually fold back is the preferred type when doing this. If the current limit is a shutdown type then first one then the other supply will shut down when more current than one can supply both will turn off.

Making one supply always run full flat out is not a great way to share current between two supplies. It is a long term reliability issue. I may do such for a one off job for myself where I accept the issue, but I would never do such for any production item.