Improvement of constant-on-time control for transition mode PFC Boost pre-regulators

This paper presents an innovative improvement of the Constant On-Time (COT) control of DCM/CCM Boundary PFC Boost converter, to improve the total harmonic distortion (THD) of the input current at medium/light load. It is a wellknown fact that using a conventional COT control [1], the THD is increased with respect to a peak current-mode control due to the parasitic elements (e.g. C
OSS
power switch capacitance) that causes a negative offset in the inductor current shape [2], [3]-[4]. The Enhanced COT control (ECOT) introduced in [5] improves the THD, extending the power switch on-time T
ON
to compensate for the negative contribution. As a drawback, this control algorithm produces a minimum level of manageable output power, P
OUT_MIN
[6]. If the P
OUT_MIN
is higher than the power required by the load, the converter to keep the output voltage regulation stops the operation for some time (aka burst-mode [7]), significantly increasing the THD. The proposed improvement of the existing ECOT control method aims to overcome this issue.