The main working mode of a DC conversion circuit is pulse width modulation (PWM). The basic principle is to convert DC power into square waves (pulse waves) through switching tubes, and to change the voltage by adjusting the duty cycle of the square waves (the ratio of pulse width to pulse period).
[pdf] This report presents the design and implementation of a bidirectional four-switch synchronous buck-boost DC-DC converter for standalone solar battery charging applications. The converter enables efficient bidirectional power flow between a photovoltaic (PV) source and a 12 V lead-acid battery.
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