Research And Design Of Triac Dimming Circuit To LED Drive Chip Based On Current Sampling

Under the background of global energy crisis becoming increasingly prominent, the light-emitting diode light has become one of the most promising lighting method, for its absolute advantages, like energy efficient, environmental protection, and so on. The widespread use of LED has also promoted its driver’s research and development. How to improve driving safety and driving performance is the focus of current research in this field. Dimming technology can not only improve out visual effects, but also improve the quality of our daily life, at the same time, it can save energy for further and prolong the life of the LED. The fluorescent lamp and the incandescent lamp using TRIAC dimming accounted for the majority in the current market, so designing a LED driver that can also using TRIAC dimming will save costs and dominate the market quickly.Based on TRIAC dimming, this paper presents a LED driver chip with constant current output. The chip has a high power factor, enabling precise control of TRIAC dimmer for output current. The entire feedback loop is realized by digital circuits, thus reduced the errors due to process variation. Using the advanced current sampling technology, it realized the monitoring for input line voltage, and at the same time it reduced the number of the chip pin, saving space and cost. Based on innovation technology for the measurement of cutaway phase angle, we have designed a clock tunable frequency oscillator circuit, which frequency can change as the same as the input voltage’s frequency, and their frequency meet a quantitative relationship, thus got flicker-free constant-current output. Ingenious design of the on-time extension circuit, has increased the accuracy of zero-crossing detection, in which the zero-crossing comparator with low-power design reduced chip power consumption. The chip has a widely using range, it can work properly when the AC input voltage RMS ranges from 85 V to 265 V, the frequency varies from 47 Hz to 63 Hz.This paper analyzed the core modules of the chip, including the current-sampling circuit, the zero-crossing detection and over-current detection circuit, on-time extension circuit and the cutaway phase angle measurement, and also simulated the whole chip. Finally, based on TSMC 0.5 μm BCD technology, using Hspice and under the temperature 25℃, we got the simulation results. It shows that this LED driver with TRIAC dimming, based on the current sampling technology and constant current output, can meet the requirements very well. The LED loads won’t flick when the AC input voltage changes.