A Study Of High Precision Dimmable LED Lighting Driver Chip Design

It was considered that the LED device would have broad application prospects since its naissance. In the background of the cost reduction of LED devices brought by the integrated circuit manufacture process improvement and the growing public awareness of energy crisis and environmental protection, LED lighting has been widely applied and is expected to replace incandescent lamps and fluorescent lights in large application range. However, specific driving chips are needed with LED lighting devices to maintain the normal operation of LED lighting systems. The LED constant current driver can ensure the current through the LED to be constant and internal various protection circuits can make the lighting system deal with a variety of unusual emergencies at the same time. It is concluded that the LED driving chip is the heart of the LED lighting system. It’s a critical link for wide application of LED lighting to develop high precision LED lighting drivers.The high precision dimmable LED lighting driving chip designed in this thesis is a constant current driver which maintains the average current through LEDs constant. By employing a 2? off-chip current sensing resistor, internal 400 m V voltage reference will make the inductor peak current up to 200 m A and this leads to a 100 m A average constant current through LEDs. The effect of line voltage fluctuation on inductor peak current will be mitigated by application of line voltage compensation circuit. It improves the precision of control to inductor peak current. Meanwhile the chip is compatible with several dimming methods such as analog dimming, triac dimming and PWM dimming. Minimum off-time will be automatically adjusted by the minimum demagnetization control circuit to meet demand of the dimming function.The chip is simulated, taped out and tested on EPISIL 0.5μm 5V/40 V Backend 2P2 M process and its size is 1.17×0.84mm2. Test results indicate that the power supply voltage is clamped on 12.5V. It just takes 302 ms to totally startup which meets the latest 500 ms fast startup demand and this shows the advantage of source driving technology. The full range of the AC input voltage and 12-600 V DC input voltage are suitable for this LED driver. 3% LED constant current accuracy and maximum conversion efficiency as much as 95% are achieved in the chip. In the dimming function test, that the inductor peak current appears to change obviously when the dimming angle increases to 35°and the inductor current enters into the discontinuous mode at 105°dimming angle realizes it a 7%-100% dimming range chip. Without an auxiliary winding to supply power, it simplifies the chip design and reduces the system cost. Multiple protection function including LED short-circuit protection and over-temperature protection can meet the application requirement of 700 m A maximum output current.