Dimming of High-Brightness LEDs by Means of Luminous Flux Thermal Estimation

• Published in: IEEE transactions on power electronics 2009-04, Vol.24 (4), p.1107-1114
• Main Authors: Garcia, J., Dalla-Costa, M.A., Cardesin, J., Alonso, J.M., Rico-Secades, M.
• Format: Article
• Language: English
• Subjects: Applied sciences; Circuit properties; Digital circuits; Digital control; Dimming; Driver circuits; Drivers; Electric currents; Electric, optical and optoelectronic circuits; Electrical engineering. Electrical power engineering; Electrical machines; Electronic circuits; Electronic equipment testing; Electronic lighting; Electronics; Emittance; Estimators; Exact sciences and technology; Flux; high-brightness LEDs; Light; light dimming; Light emitting diodes; Lighting control; Optoelectronic devices; PN junction devices; Prototypes; Pulse duration modulation; Pulse width modulation; Regulation and control; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Space vector pulse width modulation; Strategy; Temperature control; Temperature sensors; Testing. Reliability. Quality control
• ISSN: 0885-8993; 1941-0107
• DOI: 10.1109/TPEL.2008.2011989

Usually, pulsewidth modulation (PWM) operation is selected as the best dimming strategy to drive high-brightness LEDs. Nevertheless, to obtain an enhanced full linear dimming control of the device, the luminous flux should be measured. This paper proposes a control method based on an estimator of the luminous flux emitted by the LED. Based on the characterization of the LEDs, this estimator is defined. The estimator provides the flux value from only two temperature values (the case temperature and the ambient temperature). Once the estimator is validated, the electronic driver to supply the LEDs, as well as the digital control scheme, are presented. Such a control scheme is suitable for both AM and PWM dimming strategies. A prototype of the electronic driver has been built and tested, and experimental measurements of AM and PWM dimming are presented. It can be concluded that with the proposed estimator, the flux emitted by the LEDs can be accurately estimated. Thus, the output light control of the LEDs can be accomplished by sensing temperature rather than luminous flux. The final output characteristic of the system shows linearity between the output flux and the reference value, with AM as well as with PWM dimming of the LEDs.