I am designing a PCB where there is a load with peak power of 15 Watts to be powered from a user selectable voltage source.

There are a 35V and a 24V sources and it should be only one of the voltage sources to be active.

The user should be able to chose this, so I decided to go with some jumpers (2 in parallel to increase current capability). Now the problem is, if user leaves all jumpers in, the voltage sources will push against each other and for sure something will go KA-BOOM!

I can only think of adding two diodes per each source, in case user puts the wrong jumpers in.

The problem is, I do not know what rating these diodes should have. Should the diode have power dissipation rating same as the load? what characteristics the diodes should have for this scenario? e.g. should it be fast like schotkey or just a rectifier diode or zener will do?

I think 1N4007 is not the correct choice as datasheet says 1A load is the max. My load can draw up to 5A but usually sits around 2A.

Here is my draft schematic: enter image description here

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    \$\begingroup\$ Have you considered a double-throw (two position) switch, rather than jumpers? \$\endgroup\$ Commented Sep 8, 2018 at 23:12
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    \$\begingroup\$ 5A at 24V is almost 100W and 15Wpk seems wrong maybe you meant 150W Pk or 6Apk in which case 10A diodes are cheap. \$\endgroup\$ Commented Sep 8, 2018 at 23:13
  • \$\begingroup\$ @PeterBennett Yes but that costs way higher than the jumper...so I want to stick with jumpers. Thanks for pointing it out anyway! \$\endgroup\$
    – DEKKER
    Commented Sep 8, 2018 at 23:13
  • \$\begingroup\$ They can be cheap Silicon diodes since the V difference is so high \$\endgroup\$ Commented Sep 8, 2018 at 23:15
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    \$\begingroup\$ Dual Schottky CC 10A $0.66 (1) digikey.com/product-detail/en/diodes-incorporated/… \$\endgroup\$ Commented Sep 8, 2018 at 23:21

1 Answer 1


The rated masimum forward current of the diodes should be higher than the maximum current to your load. The maximum reverse voltage of the diodes should be greater than 35V.

If your load can draw up to 5A then it must have a power consumption of at least 120W, or you have misled us somehow.


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