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I want to power a led matrix of 256 leds and my controller on the road. I calculated an approximation of the required current for the leds at 5.1A and the controller at 0.1A making 5.2A @5v together, though I think it will be lower depending on the animations.

I happen to have a 13600 mAh powerbank from Xiaomi lying around which supports quick charge through 2 micro usb outputs. 2.4A @ 5v.

I was thinking if I could combine these in parallel to increase current that would make 4.8A. Now that is slightly less but I could just dim the leds a little bit to make up for that last little bit.

Do you think that would be possible? I came up with the following circuit but as a starting embedded software engineer my experience is still limited so I might be missing something.

Basically, I just want to put the outputs in parallel and have a diode to protect against current flowing back into an output from another output and use a capacitor for peaks.

sketch

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  • \$\begingroup\$ 5120 mAH is not a current, it is a measure of energy. What is the current required for load and controller? You are mixing battery capacity and current as though they are the same \$\endgroup\$ – Paul S Dec 9 '17 at 13:45
  • \$\begingroup\$ Ah my bad, the numbers were correct but I named it improperly. Required current for leds and controller is 5120mA. I edited the main post. \$\endgroup\$ – Rick vm Dec 9 '17 at 14:03
  • \$\begingroup\$ Overall, your general concept seems plausible, but the loss through the diodes will drop the voltage from 5 to maybe 4 or 4.3 depending on diode selection. This will likely be too low for your needs \$\endgroup\$ – Paul S Dec 9 '17 at 14:42
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You're looking for is an ideal diode or powerpath controller. Essentially a mosfet and control circuit that turns on to let current flow but doesn't have the drawback of the diode voltage drop. Check out the wide variety from linear or others.

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I don't think you need any diodes or else. In most powerbanks two ports are fed from the same rail, and 2.4A limit comes from connector contact carrying limitations. So having them in parallel is just fine.

This "Xiaomi" bank, however, has two Quick Charge ports, so it is likely that each port has independent power controllers. Technically you would need some "summing" circuitry like diodes or ideal diodes. However, chargers are not the standard sources of hard-driven voltage levels, they are designed with soft-cutoff, sort of going into constant-current mode if the capability limit is reached. So they already have some circuitry that would equalize two voltages.

I would try a simple connection first (with monitoring load balance with small shunt resistors 0.1-Ohms or something), and see how the powerbank behaves before spending extra money and time for something that is already there.

Keep in mind that typical micro-USB connector has contact rating of 1.8 A only, so this arrangement will sag a bit, and be warm at full load. Also, micro-USB cables are usually pretty slim, AWG26, so there will be another loss there. You might need to open the powerbank up, and solder your wires directly.

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