Re: 3W Emergency Light

Chun,

you may be able to use a comparator powered by the battery such as the ADCMP350

http://www.analog.com/en/special-linear-functions/comparators/adcmp350/products/product.html

you need to rectify the AC with a diode and capacitor and compare that voltage against the internal reference of the ADCMP350.

The open drain can be used to drive a FET to turn on the LED.

A second comparator can be used to enable/disable the charger. In this case a window comparator like the ADCMP670 or a dual comparator with programmable hysteresis like the ADCMP343 may be useful

http://www.analog.com/en/special-linear-functions/comparators/adcmp670/products/product.html

http://www.analog.com/en/special-linear-functions/comparators/adcmp343/products/product.html

We do not have high voltage battary chargers.

Good luck with your project.

LucaV