Over voltage protection control method and circuit for four-switch buck-boost converter

An apparatus, comprising:

• a) a buck-boost converter comprising a first switch coupled to an input terminal and an inductor, a second switch coupled to ground and a common node of said first switch and said inductor, a third switch coupled to ground and a common node of a fourth switch and said inductor, wherein said fourth switch is coupled to an output terminal of said buck-boost converter;
• b) an over voltage detection circuit comprising a comparator configured to receive a voltage feedback signal indicative of an output voltage of said buck-boost converter at a first input terminal, and an over voltage threshold signal at a second input terminal, and to generate an over voltage signal;
• c) a first control circuit configured to generate a first PWM control signal according to an operation mode of said buck-boost converter;
• d) a first logic circuit configured to receive said first PWM control signal and said over voltage signal from said comparator, and to control said first and second switches;
• e) a second control circuit configured to generate a second PWM control signal according to said operation mode of said buck-boost converter;
• and
• f) a second logic circuit configured to receive said second PWM control signal and said over voltage signal from said comparator, and to control said third and fourth switches, wherein said second and third switches are controlled to be on, and said first and fourth switches are controlled to be off, when said voltage feedback signal is greater than said over voltage threshold signal.