Could we connect two 5 Volt enter image description herephone chargers of different ratings in parallel for quick charging with a diode as shown(rectangles being the chargers)

Please excuse me for the drawing I made..

  • \$\begingroup\$ No. Do not parallel supplies, as they are not designed for that, and it can "confuse" their regulation circuitry. \$\endgroup\$ Apr 22, 2014 at 14:46

2 Answers 2


The voltage drop in the diode will make the voltages in the two chargers unequal(as if they already weren't), and one charger will probably carry more current than the other, that one will hit its current limit and might shut down to protect itself. If you leave the diode out of course there might be a short. Paralleling these is generally a bad idea(series on the other hand is a less bad idea with isolated power supplies, but that doesn't help much here)

It might appear to work, but one charger will be pushed to 100% or more, there might be EMI/noise issues, and chargers are too cheap to bother with. And besides, old chargers are great for all kinds of things :)

You might be able to use resistors of just the right size to share current accurately, but why bother?

  • \$\begingroup\$ If we connect another diode to the charger present at left as we connected before...? \$\endgroup\$ Apr 22, 2014 at 8:32
  • \$\begingroup\$ The variations due to inaccuracies in the chargers would probably still be enough to make them not share current evenly. You could maybe use two shottky diodes(they have lower forward voltage than normal diodes) in series with resistors to help balance the current, but you would need to get some 0.25 ohm or so resistors and two shottky diodes, measure everything carefully to be sure the voltages were close enough and the current was even. Or you could use op amps and transistors to balance the current flow, or possibly linear positive tempco thermistors. What are you actually charging? \$\endgroup\$ Apr 22, 2014 at 12:15
  • \$\begingroup\$ I want to charge my smartphone quickly using the chargers I have \$\endgroup\$ Apr 22, 2014 at 13:04
  • \$\begingroup\$ Smartphones handle their own charging internally. On mine, if the charger isn't enough to charge at the maximum speed, it will tell me on the screen when I plug it in. Generally if a charger can provide 1 amp or so, that's about as much as a smartphone can use. Tablets can use 2 amps or so. \$\endgroup\$ Apr 22, 2014 at 13:53

If you had a 5V supply as the power source for a charging circuit, the current drawn would be determined by the circuit being charged. If you connected in parallel two 5V power sources, the current drawn would be exactly the same and therefore no net benefit.

If you put diodes in series with the two supplies you would get maybe 4.5 volts and the charging circuit would not be good at all.

If, however, on the other hand, the power supplies were constant current types then paralleling two supplies could give twice the current BUT, if the constant current power supply is specifically intended for the battery why would you try and charge it at twice the rating? This might damage it.

  • \$\begingroup\$ What's being overlooked here - and clearly a motivation for the question - is that most small power supplies are "constant voltage" only up to some capability limit, at which point they sag or worse. \$\endgroup\$ Apr 22, 2014 at 14:46

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