《低频功率放大器》PPT课件.ppt

6.1 基本放大电路 6.2 共发极放大电路的结构、特点、用途。 6.3 共集电极放大(射极输出器)电路 的结构、特点、用 途。 6.4 差分放大电路。 6.5 互补对称功率放大电路。 第六项 低频功率放大 LOGO 1.理解这两种最基本放大电路的结构、特点。 2.了解差分的工作原理及作用。 3.了解互补对称功率放大工作原理及性能特点。 本项基本要求 LOGO 6.1基本放大电路 放大的基本概念 放大是将微弱变化信号放大成较大的信号 实质是通过输入微小的信号能量去控制晶 体三极电流的作用。 即通过放大电路将直流能量转换成交流电 能量输出。 放大电路的基要： 1.要有 足够大的放大倍数(电流、电压、功率)。 2.要求放大信号波形实真尽量小。 3.要求工作稳定。 基本放大电电路类类型 v1、共发射极放大电路 v 电路组成如图6-1（a）所示 v2、共集电极放大电路 v 电路组成如图6-1（b）所示 v3、共基极放大电路 v 电路组成如图6-1（c）所示 v v（a）共发射极放大电路 （b）共集电极放大电路 （c）共基极放大电路 v图6-1基本放大电路类型 6.2 共发极放大电路的结构、特点、用途。 v一、基本共发射极放大电路 v 1、电路组成: v （1）三极管T; v （2）电源VCC：为JC提供反偏电压 ，一般几 几十伏; v （3）集电极电阻Rc：将IC的变化转换为 Vo的变化，一般几K几十 K。 VCE=VCC-ICRc ， Rc与 VCC 同属集电极回路。 （4）VBB：为发 射结提供正偏。 （5）Rb：一般为几十K几千K，Rb VBB同属基极回路 （6）Cb1，Cb2：耦合电容或隔直电容，其作用是通交流隔直流。 （7）Vi：输入信号 （8）Vo：输出信号 （9）公共地或共同端，电路中每一点的电位实际 上都是该点与公 共端之间的电位差。图中各电压 的极性是参考极性。 2.静态工作点 如图6-2所示 ui=0时，电路的IB、IC、UBE、UCE值静态工作点 记作：IBQ、ICQ、UBEQ、UCEQ 其中：UBEQ= 0.60.8V 硅管 0.10.3V 锗管 IBQ=VBB-UBEQ/Rb ICQ=IB UCEQ=VCC-ICCRC ICQ UCEQ IBQ VCC Rb VBB c b e RC UB E 图6-2所示静态工作点示意图 (IBQ,UBEQ) 和( ICQ,UCEQ )分别对应于输入输出特性曲线上 的一个点称为静态工作点。如图6-3所示 iB uBE IBQ UBEQ Q iC uCE ICQ UCEQ Q 图6-3 静态工作点 3. 设置静态工作点的必要性 既然放大的对对象是动态动态 信号，为为什么在输输入信号为为零时时 要求晶体管有合适的直流电电流和电压电压 ？ （1）交直流并存：uBE=UBEQ+ui，iB=IBQ+ib （2）设置合适Q点，交流驮载到直流上，保证ui在整个 周期内，T 工作在放大状态，uo不失真。 静态时输入短路UBEQ=0、IBQ=0，输出电压必然失真！ 图6-4静态工作点示意图 第二章 基本放大电路 iB uBE Q iC uCE ib t ib t ic t ui t uce t 4.基本共射放大电路的工作原理(放大过程) uCE怎么变化 、相位如何 ui uBE iB iC uCE 当|uCE|ui| 放大 2.2 基本共射放大电路 当输入缓慢变 化信号时： 第二章 基本放大电路 动态信号驮载 在静态之上 输出和输入反相 ！ 只有设置合适静Q点，使交流驮载在直流 之上，保证在信号的整个周期内晶体管始 终工作在放大区，uO波形才能不失真！ 波形分析 2.2 基本共射放大电路 第二章 基本放大电路 阻容耦合放大电路 各点波形和静态工作点 Rb +VCC Rc C1 C2 ui t iB t iC t uC t uo t ui iC uC uo iB IBQ=(VCC-UBEQ)/Rb ICQ=IBQ UCEQ=VCC-ICQRc 第二章 基本放大电路 讨论: 用PNP型管组成一个共射放大电路 4.5.1 共集电极放大电路 2.静态分析 1.共集电极电路结构如图示 该电路也称为射极输出器 由 得 直流通路 6.3共集电极放大电路 小信号等效电路 2.动态分析 电压增益 输出回路： 输入回路： 电压增益： 其中 一般，则电压增益接近于1， 电压跟随器 即。 3、在共集电电极电电路特点 在共集电极电路中，输入信号是由三极管的基极与集电极两 端输入的,再在交流通路里看，输出信号由三极管的集电极 与发射极两端获得。因为对交流信号而言，（即交流通路里 ）集电极是共同接地端，所以称为共集电极电路。 共集电极电路具有以下特性： （1）输入信号与输出信号同相； （2）无电压放大作用，电压增益小于1且接近于1，因此共 集电极电路又有“电压跟随器”之称 ； （3）电流增益高，输入回路中的电流iB输出回路中的电 流iE和iC； （4）有功率放大作用； （5）适用于作功率放大和阻抗匹配电路。 6.4共基极放大电电路 元器件 电阻： 容电 二极管 晶体三极管 电位器 元器件 1.电阻 电阻的作用：阻碍电流的流动。在电路中主要是分流分压的作用。 2.电容 电容作用： 1.具有通交隔直。 2.具有充电放电。 3.具有储存能量。 电解电容 普通电容 3. 晶体二极管 发光二极管 普通二极管 晶体二管种类比较多：发光二极管、稳压二极 管、整流二极管、光电二极管、变容二极管等 。 晶体二极的特点：具有单向导电性。 正向电阻小，反向电阻大。 4.晶体三极管 Click to edit title style 2. 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