There is a provided a dual mode clock generator that is applicable to a direct current-direct current converter of a power supply. The dual mode clock generator includes a frequency controller for controlling generation of charge and discharge; a current source unit for generating a charge, and generating a charge; a capacitor for charging a voltage according to the charge current generated by the current source unit; an oscillation controller for controlling switch-on or switch-off to charge and discharge the capacitor; a switch for controlling the charging and discharging of the capacitor through the ON or OFF control of the oscillation controller; and a current sink unit for generating a discharge current according to the second current in the first operation mode and generating a discharge current according to the third current and the fourth current in the second operation mode.