Giovanni Gritti

High-power-factor quasi-resonant flyback converters draw sinusoidal input current

This paper presents a novel control methodology that enables high-power-factor quasi-resonant flyback converters with peak current mode control to ideally draw a sinusoidal current from the input source, thus performing like boost converters operated in the same way. It is a well-known fact that the traditional quasi-resonant control methodology, used in a number of control chips commercially available, when applied to high-power-factor flyback converters provides an inherently distorted input current. Although the resulting distortion level is such that compliancy with IEC61000-3-2 regulation on the limits for harmonic current emissions can be easily achieved, recently this inherent distortion is becoming a problem in Solid-state Lighting (SSL), where this topology is extremely popular. In fact with the traditional method it is difficult to meet the Total Harmonic Distortion (THD) target (<; 10% or even lower) that is becoming a market requirement in some geographical areas [1]-[3]. The novel control method aims to overcome this issue.

Novel voltage-mode control for DCM/CCM boundary PFC boost converters achieves high efficiency and low THD

This paper presents a novel control methodology that enables DCM/CCM Boundary PFC Boost converter operating in voltage mode to draw ideally a sinusoidal current from the power line also when techniques that maximize system efficiency especially at medium-light load are implemented (e.g. “valley skipping” operation to limit the converter switching frequency). It is a well-known fact that in these systems the switching frequency is inversely proportional to the load [1]-[2] and that limiting the switching frequency the input current distortion increases [3]. This results in a trade-off between efficiency and total harmonic distortion (THD), especially at medium-light load. The novel control method aims to overcome this issue.

Novel approach to current-mode control in DCM/CCM Boundary Boost PFC

Traditionally, DCM/CCM Boundary Boost PFC Converters with current-mode control require line voltage sensing (via a resistor divider) to define the sinusoidal shape of the reference for the inner current loop and a multiplier to adjust the amplitude of this reference to regulate the output voltage. In contrast, using voltage-mode control neither line voltage sensing nor a multiplier is needed. Lower external part count, lower cost of control and lower power consumption (particularly useful when considering no-load conditions) are the resulting benefits. This paper presents a novel approach to current-mode control that changes this paradigm. With the proposed technique the sinusoidal reference of the inner current loop is synthesized with no sensing of the line voltage and in a way that does not require a multiplier to adjust its amplitude. In this way Power Supply Designers can enjoy both the performance of current-mode control and the savings offered by voltage-mode control.

Primary-controlled constant current LED driver with extremely low THD and optimized phase-cut dimming compatibility

This paper describes a novel control method for high-power-factor quasi-resonant (Hi-PF QR) flyback converters able to meet simultaneously three control objectives: a) performing constant-current control with primary sensing regulation (CC-PSR); b) achieving ideally no harmonic distortion of the ac input current; c) being fully compatible with real-world “phase-cut” wall dimmers. Simulation results and experimental verification data are provided to validate the method, which has been implemented in a control IC targeting solid state lighting applications (LED drivers).