Hi, I am building a project where I'd require a backup power when the primary supply fails. The project is basically a ESP8266 circuit (interfacing a GPS module and an RF Card Reader module). This will be just a prototype and I don't want to create a PCB right away. For this I was using readily available modules to connect them with jumper wires and check the system live. Here I could not find an affordable Battery Charger and Power Path Controller module. There are lots of lithium charger modules available, but none of them has got a power path switcher in-built. Can anyone please refer me to a ready made module please?
You have a functional problem "switch to backup-Power"
You are hooked on "it must be a power-path-switcher"
If you post a "classical" schematic of your circuit from where do you supply with "main-power" and from where do you supply with "backup-power" I guess you will get more answers.
Most ESP8266 have a diode onboard that protects the USB-port against backward-voltage from Vin-pin.
best regards Stefan
Hi Stephen, Thanks for the response. The main supply will be from a 5V DC supply, and the secondary (backup) power will be a lithium battery. I'll be using a boost converter to get 5V (while running from the lithium battery). So my 5V DC supply will feed the load and charge the battery as well (simultaneously), when the 5V DC supply fails, I want the battery to feed the load. I was looking at battery charger module like TP4056, but it does not have a built in power path management. So I'll have to use a MOSFET based circuit to manage the power path (similar to one discussed here TP4056:Disconnect load while charging and avoid battery discharge below 3v). Basically the MOSFET disconnects the load from battery when the battery is charging or external power is available and connects the battery to the load when the external source goes off. But as I said, I don't want to build a PCB, unless there is any module available with Charger and Power Path Management integrated.
I'm aware of one module, but only one, that includes the power path function. Search Ebay or Aliexpress for an MCP73871 module. I actually have one somewhere, but have never used it. The module comes with a giant 4700uF elctrolytic capacitor, and it doesn't have a USB port. And I think I concluded that it was set up for a maximum 500uA charging current. So it's far from an ideal solution.
I'd suggest you consider just adding the power path circuit between the TP4056 charger module and the boost converter. It's only three parts - the mosfet, a schottky diode and a resistor:
Or, there's a module called the 18650 Battery Shield V3 that contains the charger, the boost converter and the battery holder, which can be modified to add the power path (aka load sharing) circuit:
https://www.youtube.com/watch?v=T70mBHeIOZA
Edit: I want to look at the possibility of modifying the TP4056 charger module - the one with battery protection built in - to add the power path function. The BAT+ and OUT+ terminals are actually shorted together, but if you cut that trace, and reverse the functions of those two terminals, then I think you can add in the power path parts without an additional circuit board - except a little adapter board for mounting the SOT-23 mosfet package. I may give that a try when I get some time.
Thanks @ShermanP , Yes, I believe that I need to do a small 3 component PCB to modify the TP4056 charger. BTW, the youtube video is super cool. He explained it so well. Thank you again.
He is me. 
Thanks, and you're welcome.
Instead of a separate board for the three parts, you can modify the typical TP4056 module to add the three parts if it's the one that has protection built in. On the module, the OUT+ and B+ holes are shorted together, but if you cut that trace, then the load sharing parts can be added. You will still need the little adapter board for mounting the SOT-23 package mosfet. Or perhaps you have a mosfet in a TO-220 package. The last one of those that worked well for this was the NDP6020P, which has been discontinued.
Hi @ShermanP That makes absolutely sense. I'll get that mosfet and modify the board to test it really quick.. Thank you for all the valuable suggestions and links and schematics..
Well good luck finding a mosfet these days.
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