A dynamic bias current generator includes a detection circuit and at least one current generating circuit. The detection circuit is used for generating a detection signal, and includes: current source coupled to the power supply voltage; a first set of transistors coupled between the current source and the ground voltage; a second set of transistors coupled between the power supply voltage and the ground voltage; a first capacitor coupled to the power supply voltage; and a second capacitor coupled to the ground voltage. The at least one current generating circuit is used for generating dynamic bias current according to the detection signal, and includes multiple transistors and a terminal for outputting voltage signal corresponding the dynamic bias current. The dynamic bias current may be used to increase the reaction speed of the comparator and may be used in a power down detection circuit.