Research And Design Of Constant Current Driving Chip For LED Without VCC Capacitor

In recent years,with the rapid development of lighting industry,light emitting diode(LED)is gradually becoming the mainstream by replacing incandescent lamp and fluorescent lamp because of its advantages of green,energy saving and flexible structure design.As an important part of LED lighting,power supply with constant current driving is often the bottleneck to restrict the performance and life of lamps.At the same time,smaller size,lower cost,simpler peripheral circuit and higher stability are required for driving power supply.Here,the core is the driving chip.According to the current development of LED driving power supply and the requirements of the market,this thesis designs a constant current driving chip without VCC(Voltage Current Condenser)capacitor,in which JFET self-power supply is integrated and buck topology is used.Considering the multi-layer ceramic capacitors or electrolytic capacitors chosen by VCC capacitor,the service life is easy to be affected.While capacitance-free scheme can not only reduce peripheral and processing costs,but also improve the reliability of power supply.The chip adopts Silan 0.8μm 500V BCD technology with integrated 500V high-voltage power MOSFET,which reduces the volume of power supply and the cost at the same time.Based on process,the designed chip with built-in high-voltage power supply circuit can eliminate starting resistance and auxiliary winding,and realize rapid start-up of the system.The chip uses a comparator to detect the peak current of the inductance,and the response time of the system is short.In order to ensure that the inductance current works in the critical mode,the gate zero-crossing detection method is adopted.The detection method can save peripheral devices and reduce system cost.The working frequency of the chip is 300 KHz,which effectively reduces the volume of inductance.Therefore,the EE type plug-in inductance could be replaced with the patch inductance such as CD75 or CD77.Power supply realizes full chip production In order to ensure the high frequency characteristics,the decreasing frequency scheme is adopted to reduce the output current when the temperature is too high.The chip realizes design,simulation,taped-out and test,and compares with the mainstream chips in the market.The test results show that the chip designed in this thesis meets the design requirements.The chip is suitable for the integrated lamps less than 25W.