The Design And Implementation Of High-efficiency Constant-current White LED Driver Based On The Charge Pump Technology

The white light-emitting diode (LED), as a high-quality backlight source, has been used widely in the portable electronic products. The charge-pump technology has been one of the best choices of the LED driver, due to its advantages of less EMI (Electro-Magnetic Interference), lower cost and less size, especially because of its promising prospects of larger output current, lower output resistance and higher efficiency. In this thesis, a LED driver based on the constant-current charge-pump circuits has been designed and realized. The driver would be applied in the cell phones, the digital cameras, the MP3 players and other portable electronic products.The self-adaptive 1X/1.33X/1.5X/2X modes have been introduced in the driver in order to assure the highest output efficiency in the whole scope of input voltage. The current of each LED can be adjusted independently by its corresponding current regulator so that the current matching and the emission intensity uniformity can be obtained easily. The full scale LED current would be determined by an external resistor, which improves the flexibility of the driver. The LED brightness could be controlled by the digital input signals, which results in the possibility of the continuous adjusting of the LED lightness and enlarges the application of the driver. In addition, the circuits own the functions of soft start and over temperature protection, and so on.In this thesis, the theory about the driver and the circuit diagram are introduced firstly. Then the charge-pump technology and its key parameters are discussed, the 1.33X mode are proposed, and some methods of LED constant current driving and brightness regulating are analyzed. The four sub-blocks, including the bandgap reference circuit, the operational amplifier, the oscillator and the over-temperature protection circuit are designed respectively. The whole chip functions and the key performances are simulated and the results show that the LED driver has achieved the design specification. Finally, we design the layout of the chip and test its performance after tape out of the chip.