【作者】 段立业；

【导师】 曾云；

【作者基本信息】 湖南大学 ， 微电子学与固体电子学， 2009， 硕士

【摘要】 高效率智能化的绿色电源是任何一个优良的有源电子系统所应具备的。集成了多模式控制和监视保护功能的脉宽调制(PWM)集成电路芯片,是当今开关电源系统的核心部分,优良的PWM控制集成电路芯片可以大大减小了当今开关电源的体积并提高效率和可靠性。本文设计了一款多模式高效率高可靠性低干扰的绿色开关电源控制芯片。准谐振(QR)与脉频调制(PFM)联合的工作模式为在非常宽的输出功率范围内实现高转换效率提供了可能。可控脉冲触发(Burst)的待机模式保证在待机情况下功耗小于300mW。准谐振工作模式在提高转换效率的同时减小了电磁干扰。为了实现可靠的准谐振工作模式,设计准确的波谷检测电路是十分关键的,因为只有在功率管漏极的电压极低值开启功率开关管(MOSFET)才可以将开启损耗降到最小。在开关电源启动时,负载端的储能电容两端电压为零,相当于一个非常大的负载,可能引起错误的过载过流保护动作。在芯片启动时将过载过流保护屏蔽一段时间可以解决此问题,但是这样做不仅降低了芯片的可靠性,还可能使输入端产生“浪涌电流”造成输入电压波形塌陷使供电质量变差,还带来电磁干扰(EMI)等诸多问题。本文在控制器中设计了一个软启动电路,使开关电源能够在开启的一段时间内逐步提高占空比来给负载电容充电,当负载电容电压达到输出额定电压后,软启动结束并自动切换到正常工作模式。为了提高芯片的稳定性和可靠性,本文还设计了完善的各保护电路,包括过载保护、过压保护、欠压锁定、过流保护、过温保护等,目的是让芯片在任何可预见的恶劣情况下都能使保护电源系统和芯片本身,使之成为一款真正的绿色智能芯片。针对准谐振电流模式开关电源在一定程度上牺牲了电流模式中的电压前馈特性。本文详细分析了问题产生的原因,研究了解决的方法,设计了线电压前馈补偿模块。仿真结果的对比表明,在同一电源系统中,采用加入电压补偿模块的芯片可将原系统0.5%的输入电压调整率降至0.17%以内。电压前馈特性的改善不仅可以提高电源输出的质量,还可以减小滤波电容的大小节约电源成本,而且小的滤波电容对只有无源功率因数矫正(PPFC)的小容量电源提高功率因数也有一定的意义。更多还原

【Abstract】 Efficient green mode power supplies are indispensable parts in active electronic systems. Integrated circuit with multi-mode control and protect functions is the kernel of the power supply system. Advanced PWM control integrated circuits can obviously reduce the size of today’s power supplies and improve their efficiency and reliability.In this paper, we designed a highly efficient low-interference green mode switching power supply controller. Multi-mode operation which include Quasi- Resonant, PFM and Burst mode make it possible to achieve high conversion efficiency in a wide range of load. Burst mode ensures that power consumption in standby time is less than 0.3 watt. Quasi-resonant mode can improve the conversion efficiency and reduce the electromagnetic interference at the same time.In order to achieve reliable quasi-resonant operation, the design of an accurate valley detection circuit is very critical, Because opening the power MOSFET at time when the MOSFET drain voltage is lowest can minimize opening lose.In switching power supply was activated, the voltage between the two ends of the capacitor in load side is zero, which is equivalent to a very heavy load, may result in false overload or over-current protection. To resolve this problem we can shield the protection for a short time after the system starts, but that not only reduces the reliability of the chip, but also causes "inrush current" at input side, which debase the quality of power line, meanwhile it causes electromagnetic interference (EMI) and many other issues. So we designed a soft-start circuit to charge the load capacitor step by step after the system starts. The soft start process is over when the load capacitor voltage reaches the rated output voltage and the system automatically switches to normal mode.In addition, in order to enhance the stability and reliability of the chip, we designed advanced protection circuits, including overload protection, over-voltage protection, under-voltage lockout, over-current protection, over-temperature protection and so on, They can protect the power supply system and the chip itself in all foreseeable severe environments.To resolve the problem that voltage feed-forward characteristics are sacrificed to some extent in current mode quasi-resonant converters. The cause of the problem is analyzed and a solution is proposed in this paper. A voltage feed-forward compensation module was designed. With this module in chip, the voltage regulation can be reduced to 0.17% from 0.5% in the same power supply system. The improvement of voltage feedforward can not only improve the quality of power output, but also reduce the size of filter capacitors to save manufacturing costs. In small-capacity power supply with only passive power factor correction (PPFC) circuit, a small filter capacitor can also help the system improve power factor.更多还原