I travel a lot for my work as a photographer. For this I'm building a custom full spectrum lamp.

I have no issue running my build with a normal adjustable power supply from my studio.
To be able to adjust the brightness, I build the lamp with a switch to turn on additional led's. Which is why my amp changes from 3,6-4,8A.
Also there is a cooling fan which is meant to be for 5V but it works at 3,5V just fine.

However when traveling I use power banks for everything. So I would have liked to run my lamps off them as well.

Here is where I'm stuck:
I need a rather small and efficient way of transforming 5V into the desired 3.5V (led's work form 3,1 - 3,7V according to the manufacturer).
This has to work with power banks, which usually automatically adjust their output voltage to the device.

Thanks for your time.

  • \$\begingroup\$ What is a power bank? \$\endgroup\$ – MadHatter Jul 5 '19 at 1:34
  • \$\begingroup\$ @MadHatter Common name for a portable rechargeable battery pack with USB ports for charging things with. \$\endgroup\$ – Hearth Jul 5 '19 at 2:16
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    \$\begingroup\$ I've never seen a power bank that adjusts its output voltage to the device, unless you're talking about USB-PD or QC, both of which require the device to do special things to request more than 5V. And both of which are rather rare in power banks, last I checked. Ignore the QC/PD stuff and just treat it as a constant 5V power source, because that's what it is unless you have circuitry specifically designed to ask it for more. \$\endgroup\$ – Hearth Jul 5 '19 at 2:18
  • \$\begingroup\$ That amount of power will be hard to get out of a power bank, if your talking about the typical ones used for phones etc. \$\endgroup\$ – MadHatter Jul 5 '19 at 2:22
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    \$\begingroup\$ @PogchampLetsgodude This is either USB-PD or QC, and is never done without the explicit permission of the device drawing power. If you don't add special circuitry specifically to negotiate the higher voltage, you will get 5V out. If you get any voltage other than 5V without specifically negotiating it, the power bank is broken and should be replaced. \$\endgroup\$ – Hearth Jul 5 '19 at 13:02

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