DUAL_MODE_BATTERY_LIFE_EXTENDER

Published:2009/7/14 1:42:00 Author:May | From:SeekIC

Most voltage regulators stop functioning when the differential voltage between the input and output is reduced below a certain level. At this level, the regulator's output voltage begins to drop at an accelerated rate, resulting in a much lower voltage's being available to the circuit. To prevent this from happening, the battery voltage is monitored and a low-battery warning signal is issued, indicating the approaching end of battery life. In the circuit presented here, the voltage regulator is bypassed when a low battery level is detected-the battery is connected directly to the circuit. At high battery voltage levels, the output voltage is regulated by the linear regulator, and the low-battery indicator (LBI) comparator output is off. Also, the LB0 pin is pulled to Vbatt (input), keeping the power MOSFET off. As the input voltage drops and approaches the regulator's dropout voltage, the base current to the regulator's pass transistor reaches its maximum, turning it on very hard. Lowering the input voltage any further will result in art increase in the pass transistor's saturation voltage and a reduction in the regulator's output voltage. The input level detector's crossover voltage should be set to Vout + Vsat of the pass transistor. When the input voltage falls below the crossover point, the comparator output is turned on. This pulls the gate voltage to ground, which turns on the power MOSFET. From this point, the voltage available to the circuit is the battery voltage minus the voltage across the power FET, which is insignificant.



Reprinted Url Of This Article:
http://www.seekic.com/circuit_diagram/Basic_Circuit/DUAL_MODE_BATTERY_LIFE_EXTENDER.html

Print this Page | Comments | Reading(3)