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I'm a bit of a noob, I have a battery charger circuit connected to a step up converter to get 5V (see 1st image below). The 5V feeds a circuit that draws between 50mA (standby) to 500mA (on). The battery is an EEMB LP-603449.

The problem is the charger never stops charging the battery (the LED1 never lights while the LED2 is constantly on when connected to power), I figure because there is a constant current draw from the battery (is this true?) Can I fix this issue by putting a diode between the power supply of the charger (VIN) and the input of the step-up converter and another diode between the battery charger output and the step up converter (see 2nd image below)? If so what should be the parameters of the diodes? Is there a diode you can recommend for this purpose? Thanks in advance for your help.

[Edit:] I found this page, solution number 2 seems to be what I'm looking for.

[Edit 2:] I found this page, seems they are doing exactly what I'm looking for using a Schottky diode and a MOSFET. When the charge LED is on the battery is cut off from the load and the load is powered through the diode from the power source.

Battery Charger Like this: Battery Charger with diodes

Hamid
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What you’ve shown will draw power from either the charger or the battery, whichever has the higher voltage. It won’t charge the battery though, is that your intention? You’ve tagged LiPo but haven’t specified it explicitly. It’s important not to charge LiPos beyond about 4.3V, although I see that the TP4056 takes care of this. Perhaps more important than it to make sure the battery doesn’t discharge below about 3.0V. Some cells have this protection built in, otherwise battery management (BMS) chips and modules are available.

In summary, there should be no problem leaving the charger attached all the time, it will power your circuit and keep the battery charged to maximum.

Frog
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  • Thanks for your answer, the battery is an EEMB LP-603449 and the description says "Battery Protection Circuit (BPC) included" and further down lists "over-discharge protection" as a feature. I assume this will protect against discharging to lower than 3.0V? (and perhaps the FS312F is redundant and I can just leave it out) You mention "It won't charge the batter though", do you mean the top version or the bottom version with the diodes added? Could you briefly explain why? Thanks again for your help! – Hamid Mar 19 '23 at 12:58
  • Over-discharge protection means that the cell will self-protect against excessive discharge, so there’s nothing to worry about there. In your second drawing, D1 will prevent current from flowing into the cell (I.e. charging it). The first drawing, where the circuit runs from the battery and the charger keeps it topped up, is likely what you need. – Frog Mar 19 '23 at 18:45
  • Yea I put D1 there exactly for that purpose, I don't want any current going to the battery except from the TP4056, which has a constant current envelope for charging properly (in the above configuration it starts at 750mA and goes down as the battery is charged) – Hamid Mar 19 '23 at 19:30