精品文档---下载后可任意编辑第一章 开关电源简介 1.1 开关电源原理分析开关电源是通过脉宽调制或频率调制，控制 MOS 管导通时间，继而控制电感线圈的磁通量，同时又要保证电感线圈不会达到磁饱和状态，从而控制输出电压的高低。同时通过反馈电路保证负载变化和输入电压变化时，输出电压仍能保证在一定范围内的稳定。、开关电源分类DC/DC 变换是将固定的直流电压变换成可变的直流电压，也称为直流斩波。斩波器的工作方式有两种：一是脉宽调制方式 Ts 不变，改变 ton(通用)；二是频率调制方式，ton 不变，改变 Ts(易产生干扰)。其具体的电路由以下几类：(1) Buck 电路——降压斩波器，其输出平均电压 Uo 小于输入电压 Ui，极性相同。(2) Boost 电路——升压斩波器，其输出平均电压 Uo 大于输入电压 Ui，极性相同。(3) Buck-Boost 电路——降压或升压斩波器，其输出平均电压 Uo 大于或小于输入电压 Ui，极性相反，电感传输。(4) Cuk 电路——降压或升压斩波器，其输出平均电压 Uo 大于或小于输入电压 UI,极性相反，电容传输。第二章 3843 设计的 CUK DC-DC 电路、3843 性能介绍The 3842A(AM)/43A(AM)/44A(AM)/45A(AM ) are fixed frequency current mode PWM controller. They are specially designed for OFF− Line and DC to DC converter applications with a minimal external components. Internally implemented circuits include a trimmed oscillator for precise duty cycle control, a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totempole output ideally suited for driving a power MOSFET. Protection circuitry includes built undervoltage lockout and current limiting. The 3842A(AM) and 3844A(AM) have UVLO thresholds of 16 V (on) and 10 V (off). The corresponding thresholds for the 3843A(AM)/45A(AM) are 8.4V (on) and 7.6V (off) . The MIK3842A(AM) and MIK3843A(AM) can operate within 100% duty cycle. The 3844A(AM) and UC3845A(AM) can operate within 50% duty cycle.The 384XA(AM) has Start-Up Current 0.17mA (typ).Features精品文档---下载后可任意编辑...
