Battery charger circuit

G

Thread Starter

GSO

Hello!

I'm working on a project that includes an rtc,mcu and a display on a ~20mmx20mm pcb. I was thinking about not using a backup battery for my rtc (because the pcb is small) and came up with a circuit like this:
https://postimg.org/image/4byja31yp/
The main concept is that when usb (micro-usb) 5V is NOT connected the P type mosfet is open and the battery feeds into the regulator of 2.5V and powers all the components.
When the usb 5V IS connected the P type mosfet is closed and the battery gets charged, but at the same time my electronics get powered of of 5V microusb.

My question is:
1) Is this a good solution, is there a better solution that will not hurt the bank?
2)Will my electronics, mainly the RTC reset while the P type mosfet switches it's condition?

Also another idea I had is not connecting the 5V directly on the electronics. I was thinking about connecting the battery and the 5V to the regulator that goes to the electronics, so I don't have voltage up's and down's. I would connect the 5V to the + terminal of the regulator and the mosfet would stay the same.

Also I didn't pay attention and I drew a transistor, it should be a mosfet (dmp1045u).

Thank you for the upcoming replies!
 
First question to ask is what is the voltage range allowable for your "digital" devices.
For your circuit to work it should be something like 2.25-5.25V ,is that so?

Second question is ,Do you need the entire "digital " circuit working when the USB isn't connected or just keep the RTC running?

For your question:
Yes the RTC may "reset" when switching if the voltage it gets drops below it's minimum VCC.That can happen in an implementation (yours is only a concept yet).

"Steering" voltage supplies can also be done with diodes.
 
For your circuit to work it should be something like 2.25-5.25V ,is that so?
2.25-5.25V I believe is correct, yes.

Second question is ,Do you need the entire "digital " circuit working when the USB isn't connected or just keep the RTC running?
Just the RTC.
 
Top