第1章 绪论1.1 课题背景将输入信号放大并向负载提供足够大功率的放大

第1章 绪论
1.1 课题背景
将输入信号放大并向负载提供足够大功率的放大器叫功率放大器。由于功率放大器运行中的信号幅度（电压、电流）大，其突出的问题是要解决非线性失真和各种瞬态失真。所以，功率放大器的主要任务是在不失真前提下放大信号的功率。一般在电路结构上采用不同形式，来减小信号的失真，提高输出功率，满足人们对音响设备的不同需求。
低频功率放大器是一个技术已经相当成熟的领域，几十年来，人们为之付出了不懈的努力，无论从线路技术还是元器件方面，乃至思想认识上都取得了长足的进步。但目前市场上的功放产品价格偏高。少则几百元、多则几千元的价格还是让工薪阶层难以接受。
1.2 课题的目的及意义
熟悉分立元件的组成及实现的功能。力求设计出一种简单实用、制作成本低廉的低频功率放大器的设计方案，并给出实际测试结果，为音响发烧友提供一种实用方案。功率放大可由分立元件组成，也可由集成电路完成。由分立元件组成的功放，如果电路选择得好，参数恰当，元件性能优越，制作调试得好，则性能要高于较好的集成功放。本次设计功放采用分立元件组成。








第2章 电路设计任务与要求
2.1 设计任务
设计并制作具有小信号放大能力的低频功率放大器。
2.2 电路要求
放大通道在正弦信号输入电压幅度为(5-700)mV，等效负载电阻RL=8Ω下，放大通道应满足：
（1）额定输出功率POR≥10W；
（2）带宽BW≥(50-1000)Hz；
（3）在POR下和BW内的非线性失真系数≤3％；
（4）在POR下的效率≥55％；
（5）在前置放大级输人端交流短路接地时，RL=8Ω上的交流声功率≤10mV；
（6）自行设计并制作满足设计要求的稳压电源。














第3章 单元电路的设计与计算
3.1 系统组成
系统主要由前置放大级、波形变换、数字音量控制电路、功率放大器和稳压电源电路5部分组成。系统框图如图3-1所示。




图3-1 系统硬件框图

其中前置放大级主要完成小信号的电压放大任务；数字音量控制级是对前置放大级的增益进行控制；功率放大级则实现对信号的电压和电流放大任务；直流稳压电源部分则为整个功放电路提供能量。正弦波方波转换电路，因为方波中含有丰富的高次谐波分量，可通过对方波信号的测试来检验功放的转换速率、失真度、效率等指标。
3.2 系统的设计
由于系统要求输出额定功率不小于10W，考虑留出50%的裕量，故设计输出功率应在15W以上。
3.2.1 前置放大级设计
前置放大级主要完成小信号电压放大的任务，其失真度和噪声对系统的影响是优先考虑的指标。考虑到功率要求，初步选定输出功率Po=16W，由


于负载为9Ω（市场上大功率电阻无8Ω标称值），则要求输出正弦波幅值VOM＝（2×Po×R）1／2＝（2×16×9）1／2≈17V。这一幅值同电源电压选择及效率密切相关。由于输入正弦波幅值最小为5mV，故整个放大通道的第一级前置级增益为：AU1 =(R2/R1)=(150kΩ/10kΩ)=15≈24dB。第二级前置级增益为：AU2 =(R5/R4)=(150kΩ/10kΩ)=15≈24dB。
考虑到输入信号的变化范围很大，在两级间串一个电位器来改变整个系统的增益，同时也起到对信号的衰减作用。前置放大采用集成运放LF353，同众多的运放相比，它具有高精度、低噪声、高速、高阻抗、频带宽等优良性能，具体指标参数为：转换速率9V/μs，增益带宽积10MHz，直流增益为105倍，最高工作电压为±22V，这种运放的高速转换性能可大大改善电路的瞬态性能，较宽的带宽能保证信号在低、中、高频段均能不失真地输出，使电路的整体指标大大提高。前置放大电路LF353参数及功能如表3-1如下：


表3-1 集成电路LF353参数


引脚 引脚代码 引脚功能 参数 备注
1
2
3
4
5
6
7
8 AMP OUT1
IN1 －
IN1 +
Vee
IN2 +
IN2 －
AMP OUT2
Vcc 运放输出1
反相位输入1
同相位输入1
电源
同相位输入2
反相位输入2
运放输出2
电源 1.32
0.98
0.98
-5.72
0
0
12.00 1 该集成块为双列直插8脚封装

2 电源4脚－5.75V 8脚为＋12.00V

3 主要用途：低噪声运放器

前置放大电路如图3-2所示。






图3-2 前置放大电路
3.2.2 波形变换电路设计
利用运放的正反馈作用，使转换部分的波形上升沿和下降沿都变得很陡，利用稳压管将电压稳定在6.2V左右，然后利用电阻分压得到要求的正负对称的峰-峰值为200mV的方波信号。运放选用NE5532电路如图3-3所示。

結果 (中文) 2:

The first chapter
1.1 background
amplifies the input signal is provided to load and large enough power amplifier called power amplifier.Because the power amplifier in the operation of the signal amplitude (voltage, current), the outstanding problem is to solve the nonlinear distortion and transient distortion.Therefore, the power amplifier is a major task in the undistorted premise to amplify the signal of the power.General in the circuit structure adopts different forms, to reduce signal distortion, improve the output power, satisfy the people to the different needs of audio equipment.
low-frequency power amplifier is a technology is already quite mature field, for decades,People to pay unremitting efforts, from either the line or components, and ideas have made great progress.But at present the work on the market price.Is little criterion hundreds of yuan, many thousands of yuan price let working-class difficult to accept.
1.2 purpose and significance of
familiar discrete components of the composition and function of.To design a kind of simple and practical, low manufacture cost low frequency power amplifier design, and gives the actual test results, to provide a practical scheme of audio fancier.Power amplifier can be composed of discrete components, but also by the integrated circuit.From the amplifier composed of discrete components, if the circuit is a good choice, the appropriate element parameters, superior performance, making debugging well, the performance is better than the better integrated power amplifier.The design of power amplifier using discrete components.








chapter second circuit design tasks and requirements of design task

2.1 design and production with small signal amplification capabilities of the low frequency power amplifier.
2.2 circuit
amplifying channels in sinusoidal input voltage range (5-700) mV, equivalent load resistor RL=8 Ω, enlarge the channel should meet:
(1) rated output power POR ≥ 10W;
(2) bandwidth BW ≥ (50-1000) Hz;
(3) in POR and BW within the nonlinear distortion coefficient is less than 3%;
(4) under the POR efficiency ≥ 55%;
(5) in the preamplifier stage output terminal of AC short circuit grounding RL=8 Ω, AC acoustic power less than 10mV; and (6) to design and production to meet the design requirements of the regulated power supply.














chapter third unit circuit design and calculation of
3.1 system
system mainly comprises a preamplifier stage, waveform conversion, digital volume control circuit, power amplifier and power supply circuit composed of 5 parts.System block diagram as shown in figure 3-1.






3-1 block diagram of system hardwareThe preamplifier stage mainly small signal voltage amplification task; digital volume control level is the preamplifier stage gain control; power amplifier stage is the realization of the signal voltage and current amplification task; DC power supply part for the entire power amplifier circuit to provide energy.Sine wave square wave conversion circuit, because of the square wave contains abundant harmonic components, through the square wave signal testing amp conversion rate, distortion, efficiency index.Design of
3.2 system
due to system requirements rated power output of no less than 10W, consider the set aside 50% margin, therefore the design output shall be above 15W.
3.2.The 1 preamplifier stage design
preamplifier stage mainly completes the task of small signal voltage amplification, the distortion and noise impact on the system is a priority indicator.Considering the power requirements, the initial selection of the output power of Po=16W, by: to load to 9 Ω (market power resistance no 8 ohm nominal value), requires the output sine wave amplitude (VOM = 2 × Po × R) 1 / 2 = (2 x 16 x 9) 1 / 2 = 17V.The amplitude and power supply voltage selection and efficiency is closely related to.Since the input sine wave amplitude minimum is 5mV, so the whole amplification channel first stage front stage gain is: AU1 = (R2/R1) = (150k Ω /10k Ω) =15 ≈ 24dB.Second stage front stage gain is: AU2 = (R5/R4) = (150k Ω /10k Ω) =15 ≈ 24dB.
considering the variation of the input signal range is very big, in two series between a potentiometer to change the overall system gain, but also plays the role of signal attenuation.Preamplifier using integrated operational amplifier LF353, with numerous operational, it has high accuracy, low noise, high speed, wide frequency band, high impedance and good performance, specific parameters: conversion rate of 9V/ μ s, the gain bandwidth product 10MHz, DC gain of 105 times, the maximum working voltage of ± 22V, the operational amplifier high speed switching performance can be greatly improved the circuit's transient performance,Wide bandwidth to ensure signal in low frequency section, in, can not distortion of output, so that the circuit's overall index is improved greatly.A preamplifier circuit of LF353 parameters and functions such as table 3-1 as follows: 3-1 LF353 parameters: scale integrated circuit pin pin code: pin function parameters of
1
2
3
4
5
6
7
8 AMP OUT1
IN1
Vee
IN2
IN2 remarks
IN1
AMP OUT2
Vcc op amp output 1
reverse phase 1
and phase 1
power input input input 2
reverse phase
in phase with the input amplifier output power 2
2
1.32
0.98
0.98
-5.72
0
0
12.00 1 the integrated block for dual-in-line 8 pin package.2 power supply 4 feet 5.75V 8 feet + 12.00V

3 applications: low noise operational amplifier, a preamplifier circuit as shown in figure 3-2.






3-2 preamplifier circuit
3.2.2 waveform transform circuit design
using op amp positive feedback effect, converting part of the waveform rising and falling edges have become very steep, using zener voltage stability is controlled in 6.2V, and then use the resistor divider are required to call the positive and negative peak - peak is 200mV. Wave signal.Operational amplifier using NE5532 circuit as shown in figure 3-3.