A test circuit for an electronic device including a liquid crystal display (LCD) device. The LCD device includes a pulse width modulator (PWM) to provide voltages to a display panel of the LCD device, a plurality of feedback circuits to output feedback voltages to the PWM, and a power supply to provide an operating voltage for the PWM. When the electronic device is in a test mode, the feedback circuits respectively decrease the feedback voltages, such that the PWM increases the voltages output to the display panel according to the feedback voltages, the increased voltages reach predetermined test voltages and test the electronic device.