Specially Designed Driver Circuits to Stabilize LED Light Output Without a Photodetector

This study proposes a novel light-emitting diode (LED) driver circuit that stabilizes the lighting output without a photodiode. The LED driver circuit is composed of a self-alignment circuit to compensate for the photo-power deviation and a feedback control system instead of a conventional photodetector to maintain the electrical power of the LED. The LED characteristics, based on electrical and optical measurements that varied with temperature, were built to be a lookup reference of the generated LED photopower, which serves as a compensator. A commercial full color LED system, which comprises red, green, and blue (RGB) LED chips, was implemented according to the novel concept. The impact of a conventional current regulator, a proposed electrical-power stabilization circuit, and a self-aligned photo-power stabilization circuit was studied graphically, followed by experimental verification. The maximal and minimal rate of change of the radiant flux Φ driven by the proposed LED drivers are 3.467% in a red LED, and 2.848% in green LED, respectively, over the ambient temperature range of 0.5-85 °C. The experimental results verified the implementation of a lighting power stabilization control system without the use of a photodiode for RGB LEDs.