Camera White Led Drive Circuit Design

Having the characteristic of small size, high luminous efficiency, low cost, low-power consumption and long life-span, white LED becomes a new generation illuminant. It has substituted some traditional light, such as camera flash and LCD backlight. More and more new applications indicated that the white LED has a vast marketplace. Because of its separate optics and easily influenced by temperature, the white LED therefore needs to be driven by a special designed power source management circuit.In this thesis, A new white LED driver circuit aiming at the the application of camera flash was designed. The circuit have four operation modes: movie, strobe, precharge and shutdown, it can drive up to five series connected white LED, and the LED current can be set by user easily.After the analysis of common white LED drivers, we made reasonable chose to the circuit structure. The inductor Boost topology structure, the current control mode and the PSM(Pulse Skipping Modulation)mode are used in the whole chip design. The inductor Boost structure can drive the series connected LED with single lithium battery; the current control mode has better anti-jamming and load current adjusting characteristic compared with the voltage control mode; the PSM mode can solve the disadvantages of lower efficiency in PWM and complicated circuit realization in PFM, and has the characteristice of high operating frequency, fast response speed, strong anti-jamming ability and little EMI which is generated by inductor.Moreover,the sub-circuits such as the bandgap reference, the oscillator, the comparator, the modes selecting circuit, the boost convert control circuit and the current regulator are also analysed and designed. The bandgap reference uses the exponential curvature compensation as the nonlinear compensation and has the better temperature characteristic and high PSRR(Power Supply Rejection Ratio); the oscillator uses the structure of the charge current source is always on but the discharge current source is switched on and off, it can reduce the influence of switch delay to oscillator precision; the comparator uses the rotary structure and has better anti-jamming performance. And some of them can be used in many other applications as common modules.Finally, the whole circuit was simulated with the Hspice simulation software. The...