Method for controlling output power of a pick-up head using automatic power control loop

A method for automatically controlling output power of a pick-up head of an optical drive with an automatic power control loop (APC Loop), the automatic power control loop comprising:

• a sensor for detecting the output power of the pick-up head and for generating a corresponding detecting signal;
• a comparator circuit comprising a first input port, a second input port, and an output port, wherein the output port is for outputting a comparative signal;
• a first switch for selecting either an output signal of a power supply or the detecting signal of the sensor, and for transmitting the selected signal to the first input port of the comparator circuit;
• a first signal source for providing a first signal;
• a drive circuit electrically connected to the pick-up head for driving the pick-up head;
• and
• a second switch for selecting either the first signal or the comparative signal, and for transmitting the selected signal to the drive circuit;
• the method comprising:
• utilizing the first switch to connect the first input port of the comparator circuit to the power supply when the output power of the pick-up head is to be changed, and utilizing the second switch to connect the first signal source to the drive circuit so that the drive circuit controls the output power of the pick-up head according to the first signal;
• and
• utilizing the first switch to connect the first input port of the comparator circuit to the sensor while the voltage difference between the first input port and the output port of the comparator circuit stabilizes, and utilizing the second switch to connect the output port of the comparator circuit to the drive circuit so that the drive circuit controls the output power of the pick-up head according to the comparative signal.