The Design Of LED Drive Circuit With Self-Adaptive Adjustable Current To Temperature

As a new generation of green light, LED attracts so much attention with the advantage of high efficiency, low energy, no pollution and long life etc that becomes a focus many countries studies of. And its related technology and industry also get rapid development in recent years. Nowadays, LED is widely used in backlight display, signal indicator and kinds of illumination applications. Especially the white LED is gradually replacing traditional light sources to be the main lighting source.However, these advantages of LED have to be secured by driver circuits, because its practical application properties are affected by the instability of voltage and current as well as temperature.For high power LED lighting, the temperature is the important factor of affecting its performance. The allowed maximum current of LED needs to decrease as the temperature increase. Otherwise, the high temperature would lead to serious attenuation for LED’s luminescent property and service life. So the practical LED must be compensated through the driver according to the temperature. Furthermore, the suddenly extinguishment of light which would cause mutation of the visual lighting is usually required to avoid in illumination application. Nevertheless, the schemes of traditional thermal shutoff obviously cannot meet this requirement. At the same time considering the linear correlation of LED’s electro-optic characteristics, the driver that driving current is self-adaptive adjustable with temperature is superior in illumination fields.In this thesis, the research and design of a LED driver which driving current is self-adaptive adjustable with temperature is demonstrated. The linear current regulator with proportional sampling structure, which possesses briefness, low noise and EMI, fast transient response, high precision of constant current and inexpensive, is used by the design. The driver can be work in three different stages, which include normal constant-current output, self-adaptive control output and overheat shutoff protection. In addition, the driver support 3 digital 8 bands-dimming, PWM-dimming and several protect function.The structure and functional block diagram of the driver chip is given, and combining it, the implement principal of current self-adaptive adjusting with temperature is analyzed in paper. Then, according to the indicator of performance determined, the detail schematic design and simulation of some sub-circuit were completed through the circuit design software of Cadence, using the “Bottom-to-up” methodology. Finally, the whole chip simulation and verification were conducted to examine the matching between the design and the requirements of specification.Simulation results show that the chip can be able to work well in the wide input voltage range from 6.5V to 30 V and achieve ±1.8% constant current accuracy in the safe temperature range of 0~80℃. From 80℃ to 110℃, the maximum adjustable amplitude of driving current is 160 mA, which would be able to make the thermal power has up to a 71% reduction, but the visual lighting of human change less than 5%. If there was a serious situation, the driver circuit output would be shutoff while the temperature exceeded 110℃. Meanwhile, the dimming and protection circuits can realize excellent function. The final results of simulation meet the established requirement.