An electronic device includes an impedance detection circuit and a processor. The impedance detection circuit is configured for receiving a test signal, processing the test signal and detecting an impedance of a headphone speaker load by using the test signal to generate a detection result. The processor is coupled to the impedance detection circuit and configured for providing the test signal to the impedance detection circuit, receiving the detection result from the impedance detection circuit, and adjusting a voltage of an audio signal to be provided to the headphone speaker load according to the detection result.