Dual-mode Inverting Buck-boost Converter using Set-time Variable PWM Method

This paper proposes a dual-mode inverting buck-boost DC-DC converter using a set-time variable PWM (SPWM) method. To obtain high efficiency in all load ranges, this dual-mode converter operates in the PWM mode under heavy load, and in the SPWM method under light load in which the switching frequency of the set-time is modulated in proportion to the load current in the PWM mode. In this PWM-SPWM dual mode, it is possible to realize a small circuit by adding only the additional circuit using a voltage-controlled oscillator which varies the switching frequency under light load, based on the PWM mode. Also, the converter can vary output voltage by changing its reference voltages and has variable maximum and minimum switching frequencies for a number of applications. The converter was fabricated with 0.35 mu m standard CMOS process technology and occupies an area of 0.93 mm X 0.90 mm. The experimental results show that when the input voltage range is 2.9 V- similar to 4.2 V, the circuit produces an output voltage range of -1.0 V similar to -0.7 V with a ripple voltage of 3 mV and has a power efficiency of 68% similar to 82.1% for a load current of 5 mA similar to 250 mA.