Transition mode power factor correction device with built-in automatic total harmonic distortion reduction feature

A controller used in a transition mode power factor correction device and suitable for achieving an automatic THD optimization, which comprises:

• a THD Reducer for setting an appropriate offset voltage to force the valley of a scale-down rectified sinusoidal line voltage close to a reference value through a feedback control;
• an Error Amplifier for generating an output voltage error signal corresponding to a deviation between a scale-down Output Voltage and a predetermined reference voltage;
• a Multiplier for combining the scale-down rectified sinusoidal line voltage with the output voltage error signal to generate a sinusoidal reference signal;
• a Comparator for generating a logic signal for setting a Power Switch on period by comparing a received current sense signal with the sinusoidal reference signal;
• a Zero Crossing Detector for generating an edge logic signal to turn on the Power Switch;
• a RS Flip-Flop Register and a Gate Driver combined to create a required analog waveform pattern for driving the Power Switch and thereby approximating the shape of the current running through to the sinusoidal waveform of the rectified sinusoidal line voltage and in the meantime to keep the valley of the scale-down rectified sinusoidal line voltage close to a reference value.

A THD Reducer for setting an appropriate offset voltage to force the valley of a scale-down rectified sinusoidal line voltage close to a reference value through a feedback control;

• wherein, said THD reducer comprise:
• two comparators, an Up-down Counter and a Digital to Analog Converter, wherein;
• the first Comparator is used to extract a rectified AC line frequency to produce a clock signal for the Up-down Counter;
• the second Comparator is used to detect the zero crossing of the scale-down rectified sinusoidal line voltage relative to the reference value,
• the Up-down Counter is used to record a number of difference between non-zero crossing and zero crossing events with running time elapse;
• the DAC is used to convert the numerical digital value from the Up-down counter to an analog DC voltage.