Hybrid series-parallel PWM dimming technique for integrated-converter-based HPF LED drivers

Two main LED dimming techniques can be found in the literature: (i) analogue dimming, and (ii) PWM dimming, which is known by its three main schemes; the enable dimming, series dimming, and parallel dimming [1]. This paper will present a brief introduction to the known techniques; then a new technique will be proposed, which is a hybrid solution between series and parallel PWM dimming techniques. The converter used for the demonstration is the Integrated-Buck-Flyback-Converter (IBFC) developed in a previous work and proved to be a High-Power-Factor (HPF) LED driver [2]. The analysis of the converter is made through an average model implementation, and then a design for the full converter is presented including the control loops, and a flexible design for the main converter able to work with different techniques. A laboratory test prototype is presented in order to demonstrate the main advantages of the hybrid-series-parallel (HSP) technique compared to other dimming techniques. The proposed technique insures a constant current operation in the LED, a better control scheme owing to the fact that the operation in the new technique will be continuous, as well as offering all the advantages of the PWM dimming over the analogue dimming.