Research On The Key Techniques Of High Voltage DC-DC Converters And Applications

The key techniques of the high DC-DC converter and LED driver were studied in this thesis for improving the functions and performances, including methodology of modeling and stability analysis, slope compensation, frequency jitter, correlation techniques of precision and low power consumption techniques. Three chips were designed to implement the proposed relevant techniques. The simulation and test results have verified the role of these techniques.Due to the switching mode, the small signal stability analysis of DC-DC converter should be based on modeling. In present work, the system is modeled after the module partitioning, instead of abstract function calculations used in the traditional modeling method. The loop stability was analyzed and compensated after modeling. The time domain response was proposed to verify the system stability, cooperating with frequency domain analysis.Slope compensation is used to solve the harmonic oscillation of current mode controlled DC-DC converter. The principle of the harmonic oscillation was studied. In the design of high voltage DC-DC buck converter with PWM/PSM dual mode control, a novel and simple method of slope compensation was proposed, which can follow the duty cycle and the down slope of the inductor current. The test results show that, the system was stable over the whole working range of input and output voltages.DC-DC converter and its applications have peak energy of EMI in switching frequency, which often exceeds the system EMI limits, but has great margin in other frequency. Frequency jitter can disperse the EMI energy in a small range of the frequency to decrease the EMI peak value and improve the EMI performance. A novel frequency jitter with digital control is proposed. The switching noise was restrained effectively for the novel structure. The simulation and test results were presented to verify the proposed frequency jitter useful to improve the EMI performance.The accuracy and ripple of output voltage is depending on the precision of the DC-DC converter. Based on the analysis of the major factors, which affect the precision, the correlation techniques are studied. A novel current reference circuit was proposed in the subject of high voltage BOOST LED driver with high precision, using a current mirror with cross structure of PMOS cascode, and the upper layer of PMOS were operating in the linear region. Its equivalent resistance adjusts the temperature coefficient together with the resistance of bias. The simulation result of temperature drift was only23.8ppm/℃over the range of-40～120℃.The efficiency is important to DC-DC converter. Based on the analyzing related factors of system efficiency, low power consumption techniques are studied and improved. In the subject of high voltage DC-DC buck converter with PWM/PSM dual mode control, based on the system efficiency analysis and different control modes, automatic switching of dual mode control scheme is proposed to optimize the system efficiency of the whole working range. A module of minimum duty cycle was added into the PWM control loop to realize the PWM/PSM dual mode control. According to the input and output situation, the reasonable switching point can be found automaticly. The control logic was simple, and switched smooth. The module of minimum duty cycle was the key of the dual mode control scheme. The test results show that, the system efficiency under light load was improved obviously due to PSM control, and the system in the whole operating range was high efficiency. For5V output, the highest efficiency was93.5%. In the subject high voltage step-down LED driver with high reliability and high efficiency, the output voltage was design to be7.5V, which can reduce conduction loss of the off-chip switch effectively. Moreover, low quiescent current, low voltage feedback techniques, and techniciques similarly, are adopted. Testing results showed that the highest efficiency was95.3%.Besides, more innovations in circuit were made in this paper. Such as, the soft start circuit is realized with integrated clock, frequency divider and current limiting circuit instead of the peripheral device; the boostup circuit is realized with a logic controlled PMOS instead of the diode to realize; and hiccup protection circuit is designed to realize protection and automatic restoration when the malfunction occurs.