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.