The Study And Design Of A High-Voltage LED AC Driving Chip Based On BCD Process

With the increasing requirement in the LED market and the improvements of divergentadvanced technologies, LED lighting systems, which are considered as the4th generationlighting products, have been widely used. Correspondingly, driving circuits for the lightingLED are attracting more researching contribution. DC drive circuits, the preliminary designsfor the LED lighting systems, have been developed maturely. However, the DC drive circuits,with the innate characteristics of circuits, cannot acquire energy directly from the mains(220V,50Hz). Therefore, an extra device with voltage transformer or switched-mode powersupply to rectify current and buck voltage should be added in the lighting equipment so thatthe development of the DC drive circuits are significantly limited, for both the size of circuitand the energy loss in AC-DC transforming. Hence，the high-voltage AC LED driver is fastdeveloped and attracts great attention for the market.Characteristics of current used in LED lighting systems and their drive chips areanalyzed in this thesis. A new design of high-voltage AC LED driving chip is proposed. Thechip proposed in this thesis, which is applied to drive high-voltage and low-current LEDstring, can be connected to the mains directly. The amounts of the lighted LED are mutativein different phrases of one cycle which is regulated by a control module sampling from thewaves of input voltages and load currents. In this design, the chip can work within the voltagerange of the mains with normal fluctuations (20%), the load current of the LEDs would bebelow20mA or40mA, the threshold which is detected and adjusted by off-chip sensingresistor. The chip could operate properly under105C.It would be suspended when thetemperature is excessive and revive to normal operation state when the temperature dropsback to85Cor less.The efficiency of LEDs could be improved to achieve the expectation of normalillumination by utilizing a high efficiency LED load circuit with high utilization rate of lamps.The chip is inherently based on voltage memory and segme nted current-limiting for samplingdetection which improves the accuracy and efficiency. This design uses1um SPDM5V40V700V monolithic integrated bipolar transistors,high-voltage process (BCD process) CMOS and DMOS devices. Chips of the AC LEDsystem have been designed and simulated in a EDA tool Cadence. After the final layout,simulation results show that the chip could achieve the intended function and meet therequirements of chip design. The designed chip has been sent out to tapeout for verificationcurrently.