Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/12425
Title: On the color stability of phosphor-converted white LEDs under DC, PWM, and bilevel drive
Authors: Loo, KH 
Lai, YM 
Tan, SC
Tse, CK 
Issue Date: 2012
Source: IEEE transactions on power electronics, 2012, v. 27, no. 2, 5604702, p. 974-984
Abstract: Most commercial white LEDs are made from nitride-based blue LEDs coated with yttrium aluminium garnet phosphor, which produce spectra that shift in opposite directions under the influences of drive current and junction temperature changes. This property gives rise to different emitted spectra, hence chromaticity properties, when the LED is driven/dimmed by different current waveforms. By using a commercial white LED sample, LUXEON K2, the effects of drive current and junction temperature on the changes of chromaticity coordinates are studied experimentally. The impact of dc, pulse width modulation (PWM), and bilevel current waveform is discussed through a graphical analysis, followed by experimental verification. It is proven that dc offers the best color stability over dimming due to the counteracting influences of drive current and junction temperature variations, whereas an LED constantly suffers from noneliminable chromaticity changes when driven by the PWM. Theoretical explanations are given to justify these cases, and it is found that, for the case of dc drive, an ideal heat sinks thermal resistance can be selected based on a simple equation to minimize the overall chromaticity change over dimming. This paper provides an in-depth discussion on the relations between the chromaticity properties of phosphor-converted (pc) white LEDs and the driving/dimming methods used.
Keywords: Driving method
LED
LED color
phosphor-converted (pc) LED
white LED
Publisher: Institute of Electrical and Electronics Engineers
Journal: IEEE transactions on power electronics 
ISSN: 0885-8993
EISSN: 1941-0107
DOI: 10.1109/TPEL.2010.2086080
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