An undervoltage protection circuit and an overvoltage protection circuit include a first comparator and a second comparator. The first comparator has a first input terminal, a second input terminal, and a first output terminal. The second comparator has a third input terminal, a fourth input terminal, and a second output terminal. The third input terminal receives a reference voltage and the fourth input terminal receives a first feedback voltage. The first and the second output terminals are coupled with a logic device. The first feedback voltage is converted to a second feedback voltage by the delay circuit and the voltage level shifter. The first comparator outputs a detection enabling voltage for undervoltage/overvoltage detection when the first feedback voltage crosses the second feedback voltage. The logic device outputs a protection voltage level undervoltage/overvoltage protection when the first feedback voltage crosses the reference voltage.