A method, applied in a driving circuit comprising a bidirectional circuit coupled between a voltage source and a load, comprising: receiving a feedback signal from the load and an input signal; generating a plurality of pulse width modulation, abbreviated to PWM, signals (SU, SD) according to the input signal and the feedback signal; driving the load by the bidirectional circuit according to the plurality of PWM signals (SU, SD), such that the input signal and the feedback signal are substantially proportional to each other, wherein the input signal is a time varying signal; wherein the step of generating a PWM signal among the plurality of PWM signals according to the input signal and the feedback signal comprises: determining a difference (DLT act = IN^ - FB*) according to the input signal and the feedback signal; characterised in that the step of generating the PWM signal according to the input signal and the feedback signal further comprises: determining a step-size number (NSTP) according to the difference (DLT act); obtaining a first address according to the input signal or obtaining a second address according to the step-size number (NSTP); fetching an entry from a look-up table according to the first address or according to the first address and the second address, wherein the look-up table is stored in a memory; and generating the PWM signal with a pulse width, wherein the pulse width is determined according to the entry; wherein the bidirectional circuit drives the load to have a voltage change within a switching cycle, and the voltage change is proportional to the step-size number (NSTP); wherein the entry represents a pulse width control code corresponding to the pulse width for generating the voltage change. receiving a feedback signal from the load and an input signal; generating a plurality of pulse width modulation, abbreviated to PWM, signals (SU, SD) according to the input signal and the feedback signal; driving the load by the bidirectional circuit according to the plurality of PWM signals (SU, SD), such that the input signal and the feedback signal are substantially proportional to each other, wherein the input signal is a time varying signal; wherein the step of generating a PWM signal among the plurality of PWM signals according to the input signal and the feedback signal comprises: determining a difference (DLT act = IN^ - FB*) according to the input signal and the feedback signal; characterised in that the step of generating the PWM signal according to the input signal and the feedback signal further comprises: determining a step-size number (NSTP) according to the difference (DLT act); obtaining a first address according to the input signal or obtaining a second address according to the step-size number (NSTP); fetching an entry from a look-up table according to the first address or according to the first address and the second address, wherein the look-up table is stored in a memory; and generating the PWM signal with a pulse width, wherein the pulse width is determined according to the entry; wherein the bidirectional circuit drives the load to have a voltage change within a switching cycle, and the voltage change is proportional to the step-size number (NSTP); wherein the entry represents a pulse width control code corresponding to the pulse width for generating the voltage change. determining a step-size number (NSTP) according to the difference (DLT act); obtaining a first address according to the input signal or obtaining a second address according to the step-size number (NSTP); fetching an entry from a look-up table according to the first address or according to the first address and the second address, wherein the look-up table is stored in a memory; and generating the PWM signal with a pulse width, wherein the pulse width is determined according to the entry; wherein the bidirectional circuit drives the load to have a voltage change within a switching cycle, and the voltage change is proportional to the step-size number (NSTP); wherein the entry represents a pulse width control code corresponding to the pulse width for generating the voltage change.