PWM photo-power control for light-emitting diode lighting system without photo-diode detection

The drawback in using the light emitting diode as a light source is that its light output power is highly temperature dependent. This paper puts forth the novel idea of neglecting the photo diode as a luminance sensor and taking advantage of pulse-width modulation at the same time. A light emitting diode power controller based on automatic power control technology is introduced. The controller can reduce the power dependence of the electrical component on temperature and regulate light emitting diode brightness according to the pulse-width modulation. In this way, the current flowing through the electrical component can be switched off to reduce the power consumption and to prevent electrical component over heating. Finally, the comparisons between voltage source with ballast resistor, automatic current control and proposed photo-power control are discussed in this paper. All these three compensated mechanisms are without photodiode. The experimental results show the proposed method is effective in providing constant luminous intensity.