Basic question:

Lets say i have two power sources, one supplying 1V and 100mA, the other supplying 2V and 200mA

What would be the difference if i connected them in series or in parallel?

As far as i know, connecting them in series would add up the voltage to 3V, but what about the current? And if in parallel, the current would add up to 300mA, but what about the voltage?

But im totally not sure, thats why i came here to ask

  • 2
    \$\begingroup\$ SAFETY NOTE: Only connect power supplies in series if you are absolutely certain the negative terminals of the supplies are not tied to a common ground! In other words, the supplies are fully isolated. \$\endgroup\$
    – Dan Laks
    Mar 30, 2016 at 2:45

2 Answers 2


If you connected the 1V @ 100mA power supply in SERIES with the 2V @ 200mA power supply, you would have a total of 3 volts. However the current is limited by the power supply with the least capacity, so you could expect only 100mA.

OTOH, connecting two power supplies of DIFFERENT voltages in parallel is an extremely bad idea. The two power supplies will fight with each other and may actually kill each other. NEVER RECOMMENDED.

Even connecting two power supplies of the SAME voltage together is not typically recommended because here in the Real World, they are never EXACTLY the same voltage. Ways around this include using diodes to isolate the power supplies from each other. Or using low-value resistors to provide a "buffer" between each supply and the load.


In series, you would have 3 volts at 100 mA - the supply with the lowest rated current will limit the usable current you can draw from the combined supply.

In parallel, you have a problem - the 2 volt supply will try to pull the 1 volt supply's output up to 2 volts. If the 1 volt supply is capable of sinking current, it will try to pull the 2 volt supply down to 1 volt, and a large current will flow between the supplies - the resulting voltage and available current will depend on the nature of the two supplies.


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