Downey Brand LLP
Short circuit protection
A measured voltage drop across a power-line transistor is used as a sensing element to measure the current and detect an over-current condition for an LED backlight system. An over-current or short condition is detected when the measured voltage drop exceeds a threshold. Accurate detection of the over-current condition is achieved by calibrating the RDS-ON (i.e., internal resistance between drain and source, when transistor is on) of the power-line transistor. In one embodiment, the calibration of RDS-ON is performed by ramping down the threshold from an initial value and using the tripped threshold to determine the actual value for RDS-ON. In another embodiment, the calibration of RDS-ON is performed by using two thresholds, a first threshold to calibrate RDS-ON and a second threshold to detect the over-current condition.
Apple Inc.
H H G Y H H H
H05B H05B G06F Y02B H02M H05B H02M
inventional inventional inventional additional inventional inventional additional
Mohammad J. Jingdong Asif Manisha P.
Navabi-Shirazi Chen Hussain Pandya