Patent ID: 7893679

Claim:
A pulse width modulation (PWM) controller, comprising: a voltage transformation module configured to transform an input voltage into an output voltage; a voltage-sensing module coupled to the voltage transformation module and configured to detect a voltage of a first terminal, wherein the voltage of the first terminal is proportional to the output voltage; a timer configured to measure the time duration for which the voltage of the first terminal is lower than a reference voltage, wherein the timer initiates a short circuit signal when the time duration is greater than a predetermined value; wherein the voltage-sensing module compares a divided voltage of the first terminal to a threshold voltage, and the timer measures the time duration for which the divided voltage is lower than the threshold voltage; and wherein the timer includes a resistor-capacitor circuit and a latch; when the divided voltage is lower than the threshold voltage, the latch is activated and a capacitor in the resistor-capacitor circuit is charged, and when the charge of the capacitor exceeds a threshold, the latch initiates the short circuit signal.