High-Efficient Hybrid Buck Converter With Switch-on-Demand Modulation and Switch Size Control for Wide-Load Low-Ripple Applications

Considering the tradeoff between efficiency and output ripple over a wide load range, a monolithic dc–dc buck converter with switch-on-demand modulation (SODM) and switch size control (SSC) is presented in this paper. SODM achieves a hybrid mode of pulse skip and pulse width modulation (PWM) without mode detection circuit. The converter's on time is adaptively adjusted with the load demand, achieving low output voltage ripple. Detecting the output of the error amplifier by a comparator, the SSC circuit can select appropriate switch size according to load current for reducing switching loss in a light load. The threshold level of the comparator varies with respect to the amount of slope compensation, which maintains a substantially constant switch size changing point. Experimental results show that the fabricated converter with the proposed scheme achieves high efficiency from 83% to 96% over a wide load range from 10 mA to 5 A. The switch size is 1/4 of the maximum value when load current is below 1 A with 0.5-A hysteresis. Also, the measured maximum output ripple is less than 10 mV.