A voltage regulator is disclosed. The voltage regulator includes an output unit for converting an input voltage provided by a power source into a predetermined voltage, and for outputting the converted voltage, a monitoring unit for determining whether the input voltage provided by the power source is greater than a reference voltage, and a step-up unit for stepping up the input voltage provided by the power source if the monitoring unit determines that the input voltage is less than the reference voltage. The output unit includes a converting unit for converting the stepped-up voltage into the predetermined voltage.