Dead-time detector includes an N-type power switch and a resistor. The N-type power switch includes a first end coupled to the output end of the output-stage circuit for receiving an output voltage, a second end for outputting a dead-time detecting signal, and a control end for receiving a gate-controlling voltage. The resistor is coupled between the second end of the N-type power switch and a voltage source providing a high voltage for keeping the voltage of the dead-time detecting signal when the N-type power switch does not output the dead-time detecting signal representing “ON”. When the output voltage is so lower than the gate-controlling voltage that the N-type power switch is turned on, the N-type power switch outputs the dead-time detecting signal representing “ON”. When the dead-time detecting signal represents “ON”, the output-stage circuit leaves the dead-time state.