The Realization Of A LED Driver Circuit With Current-Regulated, Step-Up DC/DC Converter

With the development of portable electronic product, telecommunication, and computer application, Power Management Chip (PMC) updates and upgrades at all times. Many universities, scientific research centers and semiconductor companies are all taking part in developing PMC.Presently, most of PMC are based on PWM control mode. While a few based on PFM for light load, and PFM/PWM for entire load.In recently years, Companies such as Power Integrations, Analog Integrations, ON Semiconductor release PMC based on PSM (Pulse skipping modulation), which simple designed, low power consumed, low EMI.Subsequently, the topology of the circuit of PSM control mode was upgraded in Power Integration's product. Until now, this control mode is still being improved on. So it makes sense to developing the PMC based on this.In this dissertation, a LED driver circuit based on PSM modulation with step-up dc/dc converter is presented. A piecewise PSM modulation mode based on load status is introduced. With the modulation of output voltage and load current combined, the driver IC implement stability. The driver circuit operates at the frequency500kHz , with 2.7V-5.5V input voltage range, 20V maximum output voltage, 20mA maximum output current. It drives load LED in series. It can control LED brightness with digital mode to implement 5mA,10mA,20mA , three levels, and with analog mode to implement 0~20mA , so it can be used in many conditions. By using the piecewise PSM modulation mode based on load status, it improves the peak current of inductor and the wave of output voltage, and keeps away from audio noise range. It can work in the temperature range ?4 0 C~85 C ; It can be shutdown to save energy, has inherent soft start and LED short protection.The driver circuit's power switcher and control circuit are designed in integrated circuit, which makes the component needed minimum. The IC part is design by using Hynix 0.6um 5V/25V CMOS Process. The guideline of driver circuit is met when simulated by HSPICE. It exhibits well efficiency, with the maximum82.5%, and shutdown current much smaller than 1uA.The dissertation focuses on the analysis of piecewise PSM modulation mode based on load status and analog sub block circuit mainly.Based on the analysis and simulation of typical PSM modulation mode in boost in chapter two, it can be said that power switcher will go into audio noise range in light load condition, and that the peak current of the inductor and the wave of output voltage is big in heavy load. In chapter three, a simpler PSM modulation mode in boost is introduced, which can improve the wave of output voltage. By choosing the inductor at the full load, making the duty factor changeable and pro-rata with load energy, then the piecewise PSM modulation mode based on load status is formed.The dissertation mainly expatiates on current source, band gap reference, voltage to current converter, and voltage comparator. In current source, a current fed back by current source biases the amplifier, which makes the circuit simple. The folded cascoded amplifier is used in band gap reference to get more gain. A compensation method is introduced to make the loop stable with high PSRR in voltage to current converter. The critical guideline of the circuit above is simulated and analyzed.