Peak detection methods, apparatus, and circuits

A method of controlling a power factor correction circuit, the method comprising:

• tracking a first peak of a waveform during a first cycle portion of the waveform;
• tracking a second peak of the waveform during a second cycle portion of the waveform;
• and
• tracking a greater of the first peak and the second peak during the second cycle portion of the waveform;
• selectively charging a power factor correction circuit based on the greater of the first peak and the second peak;
• and
• when the waveform satisfies a threshold, setting a first output of a first peak-hold circuit tracking the greater of the first peak and the second peak to a second output of a second peak-hold circuit tracking the second peak.

A peak detector, comprising:

• a first peak-hold circuit having a first input terminal and a second input terminal;
• a second peak-hold circuit having a third input terminal coupled to the first input terminal, and a fourth output terminal, the second peak-hold circuit including:
• a first operational amplifier having a fifth terminal, a sixth terminal and a seventh terminal, the fifth terminal coupled to the third input terminal;
• a first diode having an eighth terminal and a ninth terminal, the eighth terminal coupled to the seventh terminal, and the ninth terminal coupled to the fourth output terminal;
• a first switch having a tenth terminal, an eleventh terminal and a twelfth terminal, the tenth terminal coupled to the seventh terminal and the eighth terminal, the eleventh terminal coupled to the ninth terminal and the fourth output terminal, and the twelfth terminal coupled to a first reset signal;
• and
• a first capacitor having a thirteenth terminal and a fourteenth terminal, the thirteenth terminal coupled to the fourth output terminal, the sixth terminal, the ninth terminal and the eleventh terminal, and the fourteenth terminal coupled to ground.