Patent ID: 8466669

Claim:
A buck circuit having a fast transient response mechanism comprising: a high side MOS to receive an input voltage; a low side MOS connected between the high side MOS and a ground potential, wherein the high side MOS and the low side MOS are connected at a connection point for generating an output voltage to an external load according to the input voltage; a transient control module comprising: a transient control comparator to compare a first comparison result with at least one transient reference voltage to generate a second comparison result; and a transient control logic connected to a gate of the low side MOS; and an operation control module comprising: an operation comparator for receiving an operation reference voltage and a feedback voltage to generate the first comparison result accordingly, in which the feedback voltage is a divided voltage of the output voltage; a pulse width modulator for receiving an oscillating signal and the first comparison result to generate a control signal; and an operation control logic connected to the gate of the low side MOS through the transient control logic and connected to the gate of the high side MOS; wherein when the external load does not turn from a heavy load state to a light load state, a function of the transient control logic of the transient control module is disabled according to the second comparison result, and the operation control logic controls the operation of the high side MOS and the low side MOS according to the control signal; wherein when the external load turns from the heavy load state to a light load state such that the output voltage raises over a predetermined level, the function of the transient control logic of the transient control module is enabled according to the second comparison result to turn on the low side MOS for discharging to pull down the output voltage.