I'm trying to design a circuit that gets a power supply cable of 12V as input (that was connected directly to a Motherboard), and from this power supply I want to to add a branching for 3 connectors that should be connected to wires that pass ~2A and supply a power voltage to an extension that is intended to pass USB2 data. (not important for the question).

I built the following circuit as a solution, and I was wondering if this circuit makes sense in terms of power.

enter image description here

before adding my circuit (the part inside the red rectangle), VCC and GND were the supply voltage for a motherboard that consumes 60 [Watts], and the original wires passed 12[v] and 5[A].

after adding my circuit, I want to make connectors pass ~2A. (this is the limitation for the wires that should be connected there), and also to make the traces on my circuit wide enough to be able to pass ~10A for the motherboard eventually (as opposed to 5A that it used to get before).

according to my analysis, if I want to deliver 10 Amps to the motherboard, it means I need 16 amps to be at the input in order to satisfy KCL all the way until I reach the output, and that doesn't make sense to me since the power at the input would be 192 [watts].

I might not have understood my mission right for 100%, and I'm going to have a follow-up questions to my supervisor in order to have better understanding of the specifications, but before that I wanted to understand if my first intuition is right and see if I have some missing elements that should be considered. I would be glad to get some clearance about the right process that should be taken to achieve these specifications.

  • \$\begingroup\$ The ratings of each branch may exceed the max supply current or power rating with the assumption that all are not used at the same time. The same is true for a 8 Port USB Hub limited at 2.5A/port = 96W but may be supplied with 85W as not all mobiles may be in CC mode at the same time. But the bigger Q? Is why 12V \$\endgroup\$ Nov 15, 2020 at 17:53
  • \$\begingroup\$ You ought to choose conductors handle more than you intend to use and choose a supply that meets your needs. Your question assumes the USB2 5V port draws the same current from 12V which is a poor assumption. The wiser choice is do NOT use a Linear regulator for 5V from 12V \$\endgroup\$ Nov 15, 2020 at 18:09
  • \$\begingroup\$ Thanks. what about adding capacitors at the input and output which can be used as small batteries instead of a voltage spike? do you suggest? in case the answer is yes, how do you choose the capacitor values? \$\endgroup\$
    – Xhero39
    Nov 16, 2020 at 13:46
  • \$\begingroup\$ Voltage spikes generally occur due to LdI/dt so the actual load , damping factor depends on the total impedance over f to snub and damp the current with the right impedance. A battery has several T=RC equiv circuits and a motor has an L/R=T cut when released with a BEMF voltage vs RPM or current if shorted due to DCR, so without details no suggestion is optimal \$\endgroup\$ Nov 16, 2020 at 18:16

1 Answer 1


The following would be required:

  1. A 12 V power supply, capable of delivering 16A minimum.

  2. The two PCB main traces, sized for 16A minimum.

  3. The six PCB sub traces, sized for 2A minimum.

  4. All main cables sized for 16A minimum.

  5. All sub cables sized for 2 A minimum.

  • \$\begingroup\$ thanks, what about the transition from original wires (outside the red box) and the wires inside? how does a wire that used to pass 5A will behave while connected to a wire that should pass 16A, the same current must go in both of them. can you clarify this point? \$\endgroup\$
    – Xhero39
    Nov 16, 2020 at 7:08
  • \$\begingroup\$ Sorry, I missed that point. I have amended my answer. \$\endgroup\$
    – vu2nan
    Nov 16, 2020 at 7:19

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