A power conversion apparatus includes a rectifier to rectify a voltage of an input alternating current (AC) power source and a voltage drop device to output a dropped voltage using the voltage from the rectifier, and the voltage drop device includes a transformer and a communication voltage output device provided at a secondary side of the transformer to output a first direct current (DC) voltage for operation of a communication device. The communication voltage output device includes a first resistor provided at the secondary side of the transformer to reduce an output change rate of the first DC voltage and first and second zener diodes connected between the first resistor and ground to limit an upper limit of the first DC voltage. Accordingly, it is possible to stably supply a voltage to a communication unit while reducing standby power.