A voltage regulation module coupled to a power conversion module to form a closed loop. The power conversion module includes a PWM circuit and a conversion circuit. The conversion circuit includes serially coupled first and second power switches. The PWM circuit outputs a drive signal to control the first and second power switches to cause the conversion circuit to generate an output current. The voltage regulation module includes subtraction and regulation circuits. The subtraction circuit obtains a voltage related to the output current, and performs a subtraction operation on this voltage and a reference voltage to generate a second regulation voltage. The regulation circuit generates a level voltage, which is directly proportional to the output current, according to the second regulation voltage. The PWM circuit adjusts a voltage level of the drive signal according to the level voltage so that this voltage level follows the output current.