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Hello I was wondering if there is a solution for a power supply to accept a range of 3.7 V to 5 V and output a constant 5 V. Im trying to get a low powered circuit to be able to be powered from either 3.7 V lithium batteries or 5 V battery charger. will something like the modules based on the MT3608 do the trick?

Will something like MT3608 be able to provide 5 V when the input is also 5 V from a wall charger?

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    \$\begingroup\$ Check the webbench of TI \$\endgroup\$
    – Huisman
    Commented Mar 1, 2020 at 22:38
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    \$\begingroup\$ Something like this might. These are "buck-boost" converters and the device mentioned works over quite an input range and provides a fixed 5 V output, regardless. It's for automotive and it appears you cannot get a datasheet without an NDA. (Which means "unobtainium" stuff.) But at least it gets the idea across of what to look for. \$\endgroup\$
    – jonk
    Commented Mar 1, 2020 at 22:41

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No, it will not work if you connect the 5V charger to it. The module in your post is a boost converter, which means the input voltage has to be lower than the output voltage.

If you connect the lithium battery to it fully charged (4.2V) you can use the module, since 4.2V is less than 5V.

You don't mention if you want your system to be automated or illustrate how you are connecting the lithium-ion battery and the 5V charger to the load. You could implement a manual toggle switch to switch between the lithium and boost converter to the 5V charger.

I would also recommend you use something like this: https://www.diyelectronics.co.za/store/solar-management-modules/2160-solar-power-manager-5v.html

It accepts your 5V charger through a micro-USB connector that charges your lithium battery and also outputs a regulated 5V DC supply. In addition, this solar management module also acts as an uninterruptable power supply (UPS). When the 5V charger is disconnected the battery automatically kicks in to still supply your load with a continuous 5V regulated supply. Please note refer to the documents provided in the URL above on how to connect the peripherals to the solar module.

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    \$\begingroup\$ When the input voltage of a boost converter is higher than the desired output voltage, this IC will turn off the switching mosfet: the output will just follow the input through the inductor. The inductor, however, may not like that. \$\endgroup\$
    – Huisman
    Commented Mar 1, 2020 at 22:47
  • \$\begingroup\$ put a diode in series wioth the 5V input, that should loose enough voltage to keep the boost converter happy. \$\endgroup\$
    – Jasen Слава Україні
    Commented Mar 2, 2020 at 5:35
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Will something like MT3608 be able to provide 5v when the input is also 5v from a wall charger?

Unfortunately the MT3608 doesn't do a very good job when the input voltage gets close to the output voltage.

I tested one set to produce 5 V, with a 10 Ω load (~0.5 A current draw). Below 4.85 V in it produced a nice stable 5 V out. From 4.85 V to 5 V the output had ~0.4 V pk-pk sine wave ripple at ~20 kHz. At 5.4 V the ripple was about the same, but the DC output voltage was 5.08 V. At 5.46 V in it stopped oscillating and the output was a clean 5.05 V.

If you don't mind a bit of ripple and reduced regulation with the 5 V supply then it could be OK.

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You can add a diode (for example SS34) like this guy https://www.youtube.com/watch?v=i3gMSRJkoWA to drop 0.6 voltage that will help you with usb input

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