Design And Research Of Dual-loop Controlled Constant Current Driver Of White Light LED

LED gradually replaces the traditional lighting equipment and becomes a new generation of lighting sources with its advantages of low power consumption and high brightness.Portable electronic devices are widely used as a backlight for LCD screens.LED driver chip is a key part of the lighting system,so the LED driver chip research has an important value.In this paper,combined with today's LED driver for high precision,anti-electromagnetic interference needs,a dual loop control mode anti-EMI constant current driver chip is designed,which can be used as the screen backlight driver of chip mobile phones and other portable electronic devices.In this paper,according to the above application needs,the peak current mode DC-DC switching power supply drive program is chose.As a backlight application,in order to make the brightness of the LED constant,constant current of multiple LED in series is used to drive.The development of lighting equipment is introduced in this paper firstly,and summarizes the development of the driver chip for the backlight driver application.The working principles of the three converters are introduced,and the work of the boost converter is analyzed in different working modes and different system control modes of the work process.Secondly,aiming at the peak current mode control loop adopted in this paper,considering the effect of slope compensation,the AC small signal is modeled accurately,the transfer function of the loop is calculated,and the loop stability simulation is completed by MATLAB.In order to achieve the goal of high precision of LED output current,the factors that affect the current accuracy in the system is analyzed in this paper,and the bandgap reference circuit with high power supply voltage suppression ratio and the high precision inductor current detection circuit is designed based on the analysis result.Because of the scheme of switching power supply chip in this paper,this paper uses frequency jitter technology to complete the design of anti-EMI circuit.It is designed with a fixed frequency as the center frequency;the method of changing the oscillation frequency of the oscillator reduces the electromagnetic interference.The main components of the system are analyzed and designed,including: oscillator module,inductor current sampling module,bandgap reference module,leading edge blanking circuit and so on.At the same time over-voltage,over-temperature and other protection circuits are integrated in the chip to improve the stability of the circuit.Finally,the chip circuit is based on CSMC 0.25?m 5V/40 V BCD process,the Cadence spectre platform is used to simulate every circuit of the chip,and the whole loop is simulated and optimized.The simulation results show that the design of the anti-electromagnetic interference double-loop control of high-precision chip indicators have reached the design goals.The input voltage range of the circuit is 2.7V~5V,the output voltage can maximum reach to 37 V,10 white LEDs can be drive by the chip,the output current reaches 20.2m A.For the calculation of current accuracy,by measuring the current and the average current error in different number of load LEDs,the accuracy of chip eventually achieves ±1.1%.FFT waveform simulation of the chip displays frequency jitter technology can effectively spread the fundamental energy to the adjacent frequency,thus can reduce the chip circuit electromagnetic interference.Finally,the layout of the chip is designed and draw,which area is 1310.1?m×940.1?m.