Research And Design Of Relaxation Oscillator For Switching Converter

Switching converter is widely used in electronics, communications, instrumentation, marine, medical equipment, aviation and other fields with the advantage of small size, high efficiency. Besides, oscillator generating clock signal is the key circuit of switching converter. With the development of semiconductor technology, integrated circuits tend to high performance, multi-function, small package, low consumption and shorter design cycles. In this article oscillator circuit structure and extension function are studied in order to improve frequency stability and expand oscillator circuit function. The contents and innovative achievements are described as follows:(1)Based on the theoretical analysis, oscillator applications in switching converter are summarized. Besides, relaxation oscillator structure is introduced. Relaxation oscillator structure is designed by comparing commonly oscillator used in switching power, combined with the oscillator stability requirements. In order to insure the stability of oscillator frequency, the core oscillator circuit is proposed, as well as tolerance analysis of the pivotal circuit is made. High-speed comparator circuit is designed after analyzing the factors of transmission delay in comparator. In addition, reference circuit is added to respectively compensate temperature changes of charging and discharging current as well comparator threshold. In this way, oscillation frequency with high stability realized over a wide temperature and voltage range.(2) Relaxation oscillator extension circuits are proposed in this thesis. For the problem of sub-harmonic oscillation in current mode, the adaptive slope compensation circuit is established, which based on theoretical analysis of slope compensation. For the purpose of eliminate difference frequency noises which approach the system of switch main’s parallel connection and series connection, simple interface module is proposed to shape external synchronization signal, achieving the external synchronization function. The frequency jitter principle is adopted to control the electromagnetic interference(EMI) effectively, so frequency jitter performance is realized by spreading spectrum.(3) This article based on OKI 0.5um BCD process, made simulation and tolerance analysis of the basic oscillator circuit and extension circuits through HSPICE simulation tools. Simulation results show that frequency is relatively constant over external condition, which meet the requirement of the design.