Let's say the output of the adapter is 7.45VDC, and the voltage of the battery is less than 4.2V. When charging, the voltage at the input of the voltage regulator is more than 3.25V, so the output can turn the transistor on and turn the LED on. When the battery is fully charged, the voltage at the input of the voltage regulator is reduced due to the voltage drop of the battery. Then the LED will be turned off if the input voltage is less than 1.25V. Right?
But the battery is still being charged right? Then it will still be overcharged if the supply is regulated. Or I'm wrong??
Thanks