7.4V Li Ion Battery Charger and Power Management

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)

Before one can choose any design, one must design the specifications;

Min-typ-max where appropriate or important for;

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Vin from Adapter: 9V to 9.5V
Charging Current Used: 500mA
Vout Needed: 7.4V (Li-Ion Battery output that goes to the load)

I have finalised on major parts involved. The issue that I need to solve would probably take a few passive components and a MOSFET (Especially power management)

Hi,

Q1 body diode will be condictive only when drain voltage is smaller than source voltage.
So if wall adapter output is 9V then there will be no current flow.

Klaus

You need to study the spec's of a lithium rechargeable battery:
1) A 2-cells battery is not 7.4V. Instead it averages 7.4V because it is 6.4V when it is almost dead and should have its load disconnected, and it is 8.4V when it is fully charged.
2) When its charging voltage reaches 8.4V it is not yet fully charged (it is about 70%) until its charging current drops to a low amount. Therefore its charging current must be monitored.
3) Its charging current must be limited to its rated charging current.

I am using BQ2057 and it does all the process of CV, CC... and indicates when fully charged..

I am more concerned about power management (between battery and adaptor and vice versa to the load) by use of MOSFET

You are using a very nice charger IC.

Anyone who can help me with the MOSFET switching between battery and DC from Adapter