I am designing a circuit for charging Lipo battery with control and using the same circuit for switching to Lipo battery supply when there is no power source. I am using the following circuit:
(You can also see the simulation at http://tinyurl.com/htwynv2)
Control Input is from micro-controller (3.3V or GND). 4.18V Power Supply is used which is converted from 12V using SMPS.
3.3V/GND Control Input is given to transistor (NPN) for turning charging ON/OFF.
When Power Source is available,
- At 3.3V control input, the transistor is ON and voltage at point P is low, so PMOS is ON and battery is On charging.
- At 0V (GND) control input, the transistor is OFF and voltage at point P is 4.18V (High) and PMOS is OFF and battery is isolated.
When Power Source is not available,
- Due to the intrinsic diode of PMOS (which is in the forward direction from drain to source), Battery voltage will be reflected to the power source and current will flow through this diode.
4.18V supply is used for driving GSM module, which operated between 3.4V to 4.4V and while posting to server, the module takes 2A burst current (~1ms).
I have some basic doubts:
- Is this circuit is suitable for switching to Lipo battery supply?
- Is working of this circuit is same as I described above?
- When there is no power source, circuit switches to battery supply with a drop of around 0.4V between drain and source of the PMOS. Can I reduce it by using any other PMOS?
- When power is from the battery, then GSM module is facing power reset while posting to the server. I believe this is because of surge current of 2A. Maybe due to the current limitation of a diode or anything else? Should I switch to other PMOS with the low dropout of diode?
Also, it will be great if you people can suggest any better circuit for this purpose.