High frequency PWM dimming technique for high power factor converters in LED lighting

This paper deals with the capability of dimming operation added to the Integrated Buck-Flyback Converter (IBFC) topology developed in previous works. Firstly, the three main dimming methods that have been identified by the authors such as enable dimming, shunt dimming and series dimming will be briefly commented. Afterwards, the IBFC topology will be tested performing enable dimming at 100 Hz and 200 Hz. Secondly, besides the main dimming methods, a new proposal is introduced: high frequency series PWM dimming, which overcomes the main issues faced when developing series PWM dimming in constant-current fixed-frequency controlled converters. The dimming control loop of this technique will be presented, as well as the laboratory tests performed, obtaining good results in terms of dimming ratio, harmonic content of the input current and power factor.