A Driving White Led High Efficiency Boost Dc-dc Converter Control Circuit In The Circuit

Electronic products need high performance's power supply circuits. At the present time, various high efficiency portable electrical devices such as cell phones are being miniaturized. The more functions there are, the more power losses they disspate. Thus they require the battery power supply system's size smaller, weight lighter and efficiency higher. To meet these requirements, high efficiency DC-DC switching mode power supply is adopted. There exists a big gap between China's techniques and overseas'. China's DC-DC power supply market is mainly taken up by foreign brands. Consequently, the research about control circuits in DC-DC power supply for driving white LEDs has important significance.Aimed at the single-chip switching mode power supply circuits, which presently have wide applications in portable devices, control circuits applied in a high efficiency boost DC-DC converter for driving white LEDs have been designed in this thesis. The circuit utilizes 1MHz current-mode Pulse Width Modulation (PWM) control to allow small input and output capacitors and a small inductor, while reducing the circuit's volume and minimizing the input supply ripple to 15mV. It comes to a pulse skipping mode in a low load condition to decrease power loss and increase the operation efficency. It drives up to six white LEDs in series with a constant current to provide display backlighting for two (main and sub-) displays in cell phones and other hand-held devices with the input voltage ranging from 2.6V to 5.5V, and the maximum output current is 22mA. With LEDs series connected, accurate current regulation for uniform illumination can be obtained. The circuit includes a 30V, low RDSON N-channel MOSFET switch for high efficiency up to 84% and maximum battery life. Flexible dimming control utilizes either an analog control signal or direct digital PWM control without external RC filtering. This also increases dimming accuracy at low brightness levels. The circuit has integrated undervoltage protection, overvoltage protection as well as soft-start technology. Compounded with several simple external components, the circuit can construct a white LED driver.The author firstly introduces the developments and investigation significations...