Adaptive On-time Control Circuit for Buck Converters

The conventional fixed-frequency pulse width modulated control scheme for power converters is commonly used with current-mode control circuit instead of voltage-mode control circuit. However, adaptive on-time control circuits can achieve a faster transient response than the pulse width modulated control scheme because the former uses a comparator to control the on-time generator without an error amplifier. Thus, adaptive on-time control circuits do not exhibit system loop delay from the error amplifier. However, adaptive on-time control circuits do not meet the requirements of output equipment or devices to achieve a faster transient response. This chapter shows that adaptive on-time control circuits with a quick dynamic response can achieve a faster transient response than those without a quick dynamic response for buck converters. Implementing a quick dynamic response with constant frequency on-time control circuit for buck converter is showed in this chapter. The concept uses the quick dynamic response to filter Vout at the load transient to change the on-time width dynamically, preventing Vout from dropping markedly. Finally, 12 V input voltage, 3.3 V output voltage, and 60 W output power with a quick dynamic response are implemented to achieve afast load transient response for the integrated circuit of the proposed constant frequency constant on-time control circuit for buck converter. Experimental and SIMPLIS simulation results are compared to verify the viability and superiority of the proposed approach