A high efficiency voltage regulator for generating a regulated output voltage from an AC power source is disclosed. It includes a switch coupled to a voltage source from the AC power source to provide a supply voltage. An input detection circuit is coupled to the voltage source to turn off the switch when the voltage level of the voltage source is higher than a threshold voltage. An output detection circuit is connected to the supply voltage to turn off the switch once the voltage level of the supply voltage is higher than an output-over-voltage threshold. The switch can only be turned on when the voltage level of the voltage source is lower than the threshold voltage and the voltage level of the supply voltage is lower than a hysteresis threshold.