I am tring for the following


There would be a Li Ion battery that powers the load and while adaptor is plugged in, the power to the load from the battery should be disconnected and the load should get the power via adaptor and at the same time the Li Ion Battery should also be charged.

When adaptor is removed, the battery should again supply the power to the load

There are two diodes used to drop the voltage to 7.5V (approximately)

Attached Ref schematic (Rough Details)

TESTED SECTIONS

a. LI ION CHARGING
b. SINGLE SWITCH POWER ON/OFF CONTROL (ON/OFF Delay needs to be tested)


MY QUESTIONS


1. When switching from Battery to Adapter power (to the load), there would be a effect of internal diode of MOSFET Q1 and it would also supply the power via battery. How can I resolve this. Is the circuit that I am trying to use is even correct way to do it.


2. When the voltage of the battery drops below certain voltage, I prefer to have a protection to cutt off the battery supply to the load. How can I achieve this.

3. What over voltage protection is best suited (Point 5)

 

If you flip the Mosfet so that D and S are exchanged, the body diode will not supply any more.
Just wondering: If the battery and the load are all close to the 9V-level, will the Mosfet still switch on? Is there enough voltage Vgs? Will the Mosfet still work efficiently as a switch?