Patent ID: 8093863
Filing Date: 2012-01-10
Classification: H01M,H02J,Y02E

Abstract:
1. In a battery pack having a controller providing pulse width modulation (PWM) control of a field effect transistor (FET) in the pack to control current to a motor of a power tool, the FET having a duty cycle and a fixed switching period for each on and off state in the duty cycle, a circuit for performing current limit processing in the pack, comprising: a comparator, which is fed a reference voltage level from the controller representative of a current limit for the pack at a negative input thereof, a current sensor for measuring, with the FET on, instantaneous current flowing through the FET during each given switching period and sending a shunt voltage representative of the measured instantaneous current to a positive input of the comparator, wherein, if the shunt voltage equals or exceeds the reference voltage level in the given switching period, the comparator generates an output signal to the controller to turn off the FET for the remainder of the switching period.