LM3886音响电路图
[lm386功放电路图]lm386制作的随身听、小功放电路
![[lm386功放电路图]lm386制作的随身听、小功放电路](https://img.taocdn.com/s3/m/71b47f25366baf1ffc4ffe4733687e21af45ffc7.png)
[lm386功放电路图]lm386制作的随身听、小功放电路扩音机的实验可以作为随身听、微弱信号放大器，当你在家自制一扩音机，把随身听中美妙的音乐通过扩音机放出，不再用耳机，你不觉很有成就感吗？扩音机的基本原理是利用功放集成电路LM386进行控制，其电路原理图如图1所示。
lm386的功放电路电路原理LM386由于它的应用广泛，有万能功放电路之称。
它的工作电压范围宽，最小为4V，最大为15V。
静态功耗为4mA，最大增益为46dB,即200倍。
LM386的封装形式如图2所示，它有2个输入端：同相输入端3脚和反相输入端2脚，输入信号可从任意端输入，将另1个输入端接地。
增益控制端为1、8脚，调整RP2可调整增益高低。
5脚为功放输出端，R与C4组成高频衰减电路以提高音质。
7脚接C3，避免增益过高时产生自激。
6脚接电源正极，4脚接地。
LM（)386引脚图LM386实物图篇二 : LM386应用电路实例_LM386简单功放电路图之前写了简单的延时电路_RC电阻电容延时电路，很多朋友很表示很有用，这次写点别的。
LM386这主要是个音频放大芯片，说白了就是放大声音的。
具体的引脚介绍可以看器件手册，毕竟这个是最权威的，查询器件手册的网址是datasheet5，百度一搜就是。
芯片分为几个系列，有M系列，有N系列：LM386N-1，LM386M-1，LM386美眉-1，供电电压6V，负载8欧姆，最大功率0.325W；LM386N-3，电压9V，负载8欧姆，最大功率0.7W；LM386N-4，电压16V，负载32欧姆，最大功率1W。
敲这些型号很累，我就不写了，具体参数看文档。
这个电路是用到光话机上面的，本来只用耳麦就好了，但是老板一定要加外放。
于是就想到了386.看了下器件手册，挺简单的1个芯片，照着图接就行了，根本没啥难度。
但是，我用的声音信号是从MIC里过来的，然后板子上供电电压稳定的只有5V，所以单功放声音不给力，我用了双功放的电路。
LM3886
LM3886Overture ™Audio Power Amplifier SeriesHigh-Performance68W Audio Power Amplifier w/MuteGeneral DescriptionThe LM3886is a high-performance audio power amplifier capable of delivering 68W of continuous average power to a 4Ωload and 38W into 8Ωwith 0.1%(THD +N)from 20Hz–20kHz.The performance of the LM3886,utilizing its Self Peak In-stantaneous Temperature (˚Ke)(SPiKe ™)Protection Cir-cuitry,puts it in a class above discrete and hybrid amplifiers by providing an inherently,dynamically protected Safe Oper-ating Area (SOA).SPiKe Protection means that these parts are completely safeguarded at the output against overvolt-age,undervoltage,overloads,including shorts to the sup-plies,thermal runaway,and instantaneous temperature peaks.The LM3886maintains an excellent Signal-to-Noise Ratio of greater than 92dB with a typical low noise floor of 2.0µV.It exhibits extremely low (THD +N)values of 0.03%at the rated output into the rated load over the audio spectrum,and provides excellent linearity with an IMD (SMPTE)typical rat-ing of 0.004%.Featuresn 68W cont.avg.output power into 4Ωat V CC =±28Vn 38W cont.avg.output power into 8Ωat V CC =±28V n 50W cont.avg.output power into 8Ωat V CC =±35V n 135W instantaneous peak output power capability n Signal-to-Noise Ratio ≥92dB n An input mute functionnOutput protection from a short to ground or to the supplies via internal current limiting circuitryn Output over-voltage protection against transients from inductive loadsn Supply under-voltage protection,not allowing internal biasing to occur when |V EE |+|V CC |≤12V,thus eliminating turn-on and turn-off transients n 11-lead TO-220package Applicationsn Component stereo n Compact stereon Self-powered speakers n Surround-sound amplifiers nHigh-end stereo TVsTypical ApplicationOverture ™and SPiKe ™Protection are trademarks of National Semiconductor Corporation.DS011833-1*Optional components dependent upon specific design requirements.Refer to the External Components Description section for a component functional description.FIGURE 1.Typical Audio Amplifier Application CircuitMay 1999LM3886Overture Audio Power Amplifier Series High-Performance 68W Audio Power Amplifier w/Mute©1999National Semiconductor Corporation Connection DiagramPlastic Package(Note12)DS011833-2 Note1:Preliminary:call you local National Sales Rep.or distributor for availabilityTop ViewOrder Number LM3886Tor LM3886TFSee NS Package Number TA11B forStaggered Lead Non-IsolatedPackage or TF11B(Note1)forStaggered Lead Isolated Package 2Absolute Maximum Ratings(Notes6,5)If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.Supply Voltage|V+|+|V−|(No Signal)94V Supply Voltage|V+|+|V−|(Input Signal)84V Common Mode Input Voltage(V+or V−)and|V+|+|V−|≤80V Differential Input Voltage(Note16)60V Output Current Internally Limited Power Dissipation(Note7)125W ESD Susceptibility(Note8)3000V Junction Temperature(Note9)150˚C Soldering InformationT Package(10seconds)260˚C Storage Temperature−40˚C to+150˚C Thermal ResistanceθJC1˚C/W θJA43˚C/W Operating Ratings(Notes5,6)Temperature RangeT MIN≤T A≤T MAX−20˚C≤T A≤+85˚C Supply Voltage|V+|+|V−|20V to84VElectrical Characteristics(Notes5,6)The following specifications apply for V+=+28V,V−=−28V,I MUTE=−0.5mA with R L=4Ωunless otherwise specified.Limits apply for T A=25˚C.Symbol Parameter ConditionsLM3886Units(Limits) Typical(Note10)Limit(Note11)|V+|+|V−|Power Supply Voltage(Note14)V pin7−V−≥9V182084V(min)V(max)A M Mute Attenuation Pin8Open or at0V,Mute:OnCurrent out of Pin8>0.5mA,Mute:Off11580dB(min)P O (Note4)Output Power(Continuous Average)THD+N=0.1%(max)f=1kHz;f=20kHz|V+|=|V−|=28V,R L=4Ω|V+|=|V−|=28V,R L=8Ω|V+|=|V−|=35V,R L=8Ω6838506030W(min)W(min)WPeak P O Instantaneous Peak Output Power135W THD+N Total Harmonic Distortion Plus Noise60W,R L=4Ω,30W,R L=8Ω,20Hz≤f≤20kHz A V=26dB 0.030.03%%SR (Note4)Slew Rate(Note13)V IN=2.0Vp-p,t RISE=2ns198V/µs(min)I+(Note4)Total Quiescent Power SupplyCurrent V CM=0V,V o=0V,I o=0A5085mA(max)V OS (Note3)Input Offset Voltage V CM=0V,I o=0mA110mV(max)I B Input Bias Current V CM=0V,I o=0mA0.21µA(max) I OS Input Offset Current V CM=0V,I o=0mA0.010.2µA(max) I o Output Current Limit|V+|=|V−|=20V,t ON=10ms,V O=0V11.57A(min)V od (Note3)Output Dropout Voltage(Note15)|V+–V O|,V+=28V,I o=+100mA|V O–V−|,V−=−28V,I o=−100mA1.62.52.03.0V(max)V(max)PSRR (Note3)Power Supply Rejection Ratio V+=40V to20V,V−=−40V,V CM=0V,I o=0mAV+=40V,V−=−40V to−20V,V CM=0V,I o=0mA1201058585dB(min)dB(min)CMRR (Note3)Common Mode Rejection Ratio V+=60V to20V,V−=−20V to−60V,V CM=20V to−20V,I o=0mA11085dB(min)A VOL (Note3)Open Loop Voltage Gain|V+|=|V−|=28V,R L=2kΩ,∆V O=40V11590dB(min)GBWP Gain-Bandwidth Product|V+|=|V−|=30Vf O=100kHz,V IN=50mVrms 82MHz(min)3Electrical Characteristics(Notes5,6)(Continued)The following specifications apply for V+=+28V,V−=−28V,I MUTE=−0.5mA with R L=4Ωunless otherwise specified.Limits apply for T A=25˚C.Symbol Parameter ConditionsLM3886Units(Limits) Typical(Note10)Limit(Note11)e IN (Note4)Input Noise IHF—A Weighting FilterR IN=600Ω(Input Referred)2.010µV(max)SNR Signal-to-Noise Ratio P O=1W,A-Weighted,Measured at1kHz,R S=25Ω92.5dBP O=60W,A-Weighted,Measured at1kHz,R S=25Ω110dBIMD Intermodulation Distortion Test60Hz,7kHz,4:1(SMPTE)60Hz,7kHz,1:1(SMPTE)0.0040.009%Note2:Operation is guaranteed up to84V,however,distortion may be introduced from SPIKe Protection Circuitry if proper thermal considerations are not taken into account.Refer to the Thermal Considerations section for more information.(See SPIKe Protection Response)Note3:DC Electrical Test;refer to Test Circuit#1.Note4:AC Electrical Test;refer to Test Circuit#2.Note5:All voltages are measured with respect to the GND pin(pin7),unless otherwise specified.Note6:Absolute Maximum Ratings indicate limits beyond which damage to the device may occur.Operating Ratings indicate conditions for which the device is functional,but do not guarantee specific performance limits.Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits.This assumes that the device is within the Operating Ratings.Specifications are not guaranteed for parameters where no limit is given,however,the typical value is a good indication of device performance.Note7:For operating at case temperatures above25˚C,the device must be derated based on a150˚C maximum junction temperature and a thermal resistance of θJC=1.0˚C/W(junction to case).Refer to the Thermal Resistance figure in the Application Information section under Thermal Considerations.Note8:Human body model,100pF discharged through a1.5kΩresistor.Note9:The operating junction temperature maximum is150˚C,however,the instantaneous Safe Operating Area temperature is250˚C.Note10:Typicals are measured at25˚C and represent the parametric norm.Note11:Limits are guaranteed to National’s AOQL(Average Outgoing Quality Level).Note12:The LM3886T package TA11B is a non-isolated package,setting the tab of the device and the heat sink at V−potential when the LM3886is directly mounted to the heat sink using only thermal compound.If a mica washer is used in addition to thermal compound,θCS(case to sink)is increased,but the heat sink will be isolated from V−.Note13:The feedback compensation network limits the bandwidth of the closed-loop response and so the slew rate will be reduced due to the high frequency roll-off.Without feedback compensation,the slew rate is typically larger.Note14:V−must have at least−9V at its pin with reference to ground in order for the under-voltage protection circuitry to be disabled.Note15:The output dropout voltage is the supply voltage minus the clipping voltage.Refer to the Clipping Voltage vs Supply Voltage graph in the Typical Perfor-mance Characteristics section.Note16:The Differential Input Voltage Absolute Maximum Rating is based on supply voltages of V+=+40V and V−=−40V.Test Circuit#1(DC Electrical Test Circuit)DS011833-34Test Circuit#2(AC Electrical Test Circuit)DS011833-4Single Supply Application CircuitDS011833-5*Optional components dependent upon specific design requirements.Refer to the ExternalComponents Description section for a component functional description.FIGURE2.Typical Single Supply Audio Amplifier Application Circuit5Equivalent Schematic(excluding active protection circuitry)6External Components Description(Figure1and Figure2)Components Functional Description1.R IN Acts as a volume control by setting the voltage level allowed to the amplifier’s input terminals.2.R A Provides DC voltage biasing for the single supply operation and bias current for the positive input terminal.3.C A Provides bias filtering.4.C Provides AC coupling at the input and output of the amplifier for single supply operation.5.R B Prevents currents from entering the amplifier’s non-inverting input which may be passed through to the loadupon power-down of the system due to the low input impedance of the circuitry when the under-voltagecircuitry is off.This phenomenon occurs when the supply voltages are below1.5V.6.C C(Note17)Reduces the gain(bandwidth of the amplifier)at high frequencies to avoid quasi-saturation oscillations of the output transistor.The capacitor also suppresses external electromagnetic switching noise created from fluorescent lamps.7.Ri Inverting input resistance to provide AC Gain in conjunction with R f1.8.Ci(Note17)Feedback capacitor.Ensures unity gain at DC.Also a low frequency pole(highpass roll-off)at: f c=1/(2πRi Ci)9.R f1Feedback resistance to provide AC Gain in conjunction with Ri.10.R f2(Note17)At higher frequencies feedback resistance works with C f to provide lower AC Gain in conjunction with R f1 and Ri.A high frequency pole(lowpass roll-off)exists at:f c=[R f1R f2(s+1/R f2C f)]/[(R f1+R f2)(s+1/C f(R f1+R f2))]11.C f(Note17)Compensation capacitor that works with R f1and R f2to reduce the AC Gain at higher frequencies.12.R M Mute resistance set up to allow0.5mA to be drawn from pin8to turn the muting function off.→RMis calculated using:R M≤(|V EE|−2.6V)/I8where I8≥0.5mA.Refer to the Mute Attenuation vs.Mute Current curves in the Typical Performance Characteristics section.13.C M Mute capacitance set up to create a large time constant for turn-on and turn-off muting.14.R SN(Note17)Works with C SN to stabilize the output stage by creating a pole that eliminates high frequency oscillations.15.C SN(Note17)Works with R SN to stabilize the output stage by creating a pole that eliminates high frequency oscillations.f c=1/(2πR SN C SN)16.L(Note17)Provides high impedance at high frequencies so that R may decouple a highly capacitive load and reduce the Q of the series resonant circuit due to capacitive load.Also provides a low impedance at low frequencies to short out R and pass audio signals to the load.17.R(Note17)18.C S Provides power supply filtering and bypassing.19.S1Mute switch that mutes the music going into the amplifier when opened.Note17:Optional components dependent upon specific design requirements.Refer to the Application Information section for more information.OPTIONAL EXTERNAL COMPONENT INTERACTIONAlthough the optional external components have specific desired functions that are designed to reduce the bandwidth and elimi-nate unwanted high frequency oscillations they may cause certain undesirable effects when they interact.Interaction may occurfor components whose reactances are in close proximity to one another.One example would be the coupling capacitor,C C,andthe compensation capacitor,C f.These two components act as low impedances to certain frequencies which will couple signals from the input to the output.Please take careful note of basic amplifier component functionality when designing in these compo-nents.The optional external components shown in Figure2and described above are applicable in both single and split voltage supply configurations.7Typical Performance CharacteristicsSafeAreaDS011833-18SPiKeProtection ResponseDS011833-19Supply Current vs Supply VoltageDS011833-20Pulse Thermal Resistance DS011833-21Pulse Thermal ResistanceDS011833-65Supply Current vs Output VoltageDS011833-22Pulse Power Limit DS011833-23Pulse Power LimitDS011833-24Supply Current vs Case TemperatureDS011833-25 8Typical Performance Characteristics(Continued)Input Bias Current vs Case TemperatureDS011833-26Clipping Voltage vs Supply VoltageDS011833-27Clipping Voltage vs Supply VoltageDS011833-28THD +N vs Frequency DS011833-29THD +N vs Frequency DS011833-30THD +N vs FrequencyDS011833-31THD +N vs Output Power DS011833-32THD +N vs Output Power DS011833-33THD +N vs Output PowerDS011833-34THD +N vs Output Power DS011833-35THD +N vs Output Power DS011833-36THD +N vs Output PowerDS011833-379Typical Performance Characteristics(Continued)THD +N vs Output PowerDS011833-38THD +N vs Output PowerDS011833-39THD +N vs Output PowerDS011833-40THD +N Distribution DS011833-41THD +N Distribution DS011833-42THD +N DistributionDS011833-43THD +N Distribution DS011833-44THD +N DistributionDS011833-45Output Power vs Load ResistanceDS011833-46 10Typical Performance Characteristics(Continued)Max Heatsink Thermal Resistance(˚C/W)at the Specified Ambient Temperature(˚C)Maximum Power Dissipation vs Supply VoltageDS011833-9 Note:The maximum heat sink thermal resistance values,øSA,in the table above were calculated using aøCS=0.2˚C/W due to thermal compound.Power Dissipationvs Output PowerDS011833-47Power Dissipationvs Output PowerDS011833-48Output Powervs Supply VoltageDS011833-49IMD60Hz,4:1DS011833-50IMD60Hz,7kHz,4:1DS011833-51IMD60Hz,7kHz,4:1DS011833-52 11Typical Performance Characteristics(Continued)Application InformationGENERAL FEATURESMute Function:The muting function of the LM3886allows the user to mute the music going into the amplifier by draw-ing less than 0.5mA out of pin 8of the device.This is accom-plished as shown in the Typical Application Circuit where the resistor R M is chosen with reference to your negative supply voltage and is used in conjuction with a switch.The switch (when opened)cuts off the current flow from pin 8to V −,thus placing the LM3886into mute mode.Refer to the Mute At-tenuation vs Mute Current curves in the Typical Perfor-mance Characteristics section for values of attenuation per current out of pin 8.The resistance R M is calculated by the following equation:R M (|V EE |−2.6V)/I8where I8≥0.5mA.Under-Voltage Protection:Upon system power-up the under-voltage protection circuitry allows the power supplies and their corresponding caps to come up close to their full values before turning on the LM3886such that no DC output spikes occur.Upon turn-off,the output of the LM3886is brought to ground before the power supplies such that no transients occur at power-down.IMD 60Hz,1:1DS011833-53IMD 60Hz,7kHz 1:1DS011833-54IMD 60Hz,7kHz,1:1DS011833-55Mute Attenuation vs Mute CurrentDS011833-56Mute Attenuation vs Mute CurrentDS011833-57Large Signal ResponseDS011833-58Power Supply Rejection RatioDS011833-59Common-Mode Rejection RatioDS011833-60Open LoopFrequency ResponseDS011833-6112Application Information(Continued)Over-Voltage Protection:The LM3886contains overvolt-age protection circuitry that limits the output current to ap-proximately 11Apeak while also providing voltage clamping,though not through internal clamping diodes.The clamping effect is quite the same,however,the output transistors are designed to work alternately by sinking large current spikes.SPiKe Protection:The LM3886is protected from instanta-neous peak-temperature stressing by the power transistor array.The Safe Operating Area graph in the Typical Perfor-mance Characteristics section shows the area of device operation where the SPiKe Protection Circuitry is not en-abled.The waveform to the right of the SOA graph exempli-fies how the dynamic protection will cause waveform distor-tion when enabled.Thermal Protection:The LM3886has a sophisticated ther-mal protection scheme to prevent long-term thermal stress to the device.When the temperature on the die reaches 165˚C,the LM3886shuts down.It starts operating again when the die temperature drops to about 155˚C,but if the temperature again begins to rise,shutdown will occur again at 165˚C.Therefore the device is allowed to heat up to a relatively high temperature if the fault condition is temporary,but a sustained fault will cause the device to cycle in a Schmitt Trigger fashion between the thermal shutdown tem-perature limits of 165˚C and 155˚C.This greatly reduces the stress imposed on the IC by thermal cycling,which in turn improves its reliability under sustained fault conditions.Since the die temperature is directly dependent upon the heat sink,the heat sink should be chosen as discussed in the Thermal Considerations section,such that thermal shutdown will not be reached during normal ing the best heat sink possible within the cost and space con-straints of the system will improve the long-term reliability of any power semiconductor device.THERMAL CONSIDERATIONSHeat SinkingThe choice of a heat sink for a high-power audio amplifier is made entirely to keep the die temperature at a level such that the thermal protection circuitry does not operate under normal circumstances.The heat sink should be chosen to dissipate the maximum IC power for a given supply voltage and rated load.With high-power pulses of longer duration than 100ms,the case temperature will heat up drastically without the use of a heat sink.Therefore the case temperature,as measured at the center of the package bottom,is entirely dependent on heat sink design and the mounting of the IC to the heat sink.For the design of a heat sink for your audio amplifier applica-tion refer to the Determining The Correct Heat Sink sec-tion.Since a semiconductor manufacturer has no control over which heat sink is used in a particular amplifier design,we can only inform the system designer of the parameters and the method needed in the determination of a heat sink.With this in mind,the system designer must choose his supply voltages,a rated load,a desired output power level,and know the ambient temperature surrounding the device.These parameters are in addition to knowing the maximum junction temperature and the thermal resistance of the IC,both of which are provided by National Semiconductor.As a benefit to the system designer we have provided Maxi-mum Power Dissipation vs Supply Voltages curves for vari-ous loads in the Typical Performance Characteristics sec-tion,giving an accurate figure for the maximum thermal resistance required for a particular amplifier design.This data was based on θJC =1˚C/W and θCS =0.2˚C/W.We also provide a section regarding heat sink determination for any audio amplifier design where θCS may be a different value.It should be noted that the idea behind dissipating the maxi-mum power within the IC is to provide the device with a low resistance to convection heat transfer such as a heat sink.Therefore,it is necessary for the system designer to be con-servative in his heat sink calculations.As a rule,the lower the thermal resistance of the heat sink the higher the amount of power that may be dissipated.This is of course guided by the cost and size requirements of the system.Convection cooling heat sinks are available commercially,and their manufacturers should be consulted for ratings.Proper mounting of the IC is required to minimize the thermal drop between the package and the heat sink.The heat sink must also have enough metal under the package to conduct heat from the center of the package bottom to the fins with-out excessive temperature drop.A thermal grease such as Wakefield type 120or Thermalloy Thermacote should be used when mounting the package to the heat sink.Without this compound,thermal resistance will be no better than 0.5˚C/W,and probably much worse.With the compound,thermal resistance will be 0.2˚C/W or less,assuming under 0.005inch combined flatness runout for the package and heat sink.Proper torquing of the mounting bolts is important and can be determined from heat sink manufacturer’s specification sheets.Should it be necessary to isolate V −from the heat sink,an in-sulating washer is required.Hard washers like beryluum ox-ide,anodized aluminum and mica require the use of thermal compound on both faces.Two-mil mica washers are most common,giving about 0.4˚C/W interface resistance with the compound.Silicone-rubber washers are also available.A 0.5˚C/W ther-mal resistance is claimed without thermal compound.Expe-rience has shown that these rubber washers deteriorate and must be replaced should the IC be dismounted.Determining Maximum Power DissipationPower dissipation within the integrated circuit package is a very important parameter requiring a thorough understand-ing if optimum power output is to be obtained.An incorrect maximum power dissipation (P D )calculation may result in in-adequate heat sinking,causing thermal shutdown circuitry to operate and limit the output power.The following equations can be used to acccurately calculate the maximum and average integrated circuit power dissipa-tion for your amplifier design,given the supply voltage,rated load,and output power.These equations can be directly ap-plied to the Power Dissipation vs Output Power curves in the Typical Performance Characteristics section.Equation (1)exemplifies the maximum power dissipation of the IC and Equations (2),(3)exemplify the average IC power dissipation expressed in different forms.P DMAX =V CC 2/2π2R L (1)where V CC is the total supply voltageP DAVE =(V Opk /R L )[V CC /π−V Opk /2](2)where V CC is the total supply voltage and V Opk =V CC /π13Application Information(Continued)P DAVE=V CC V Opk/πR L−V Opk2/2R L(3)where V CC is the total supply voltage.Determining the Correct Heat SinkOnce the maximum IC power dissipation is known for agiven supply voltage,rated load,and the desired rated out-put power the maximum thermal resistance(in˚C/W)of aheat sink can be calculated.This calculation is made usingEquation(4)and is based on the fact that thermal heat flowparameters are analogous to electrical current flow proper-ties.It is also known that typically the thermal resistance,θJC(junction to case),of the LM3886is1˚C/W and that usingThermalloy Thermacote thermal compound provides a ther-mal resistance,θCS(case to heat sink),of about0.2˚C/W asexplained in the Heat Sinking section.Referring to the figure below,it is seen that the thermal resis-tance from the die(junction)to the outside air(ambient)is acombination of three thermal resistances,two of which areknown,θJC andθCS.Since convection heat flow(power dis-sipation)is analogous to current flow,thermal resistance isanalogous to electrical resistance,and temperature dropsare analogous to voltage drops,the power dissipation out ofthe LM3886is equal to the following:P DMAX=(T Jmax−T Amb)/θJAwhereθJA=θJC+θCS+θSABut since we know P DMAX,θJC,andθSC for the applicationand we are looking forθSA,we have the following:θSA=[(T Jmax−T Amb)−P DMAX(θJC+θCS)]/P DMAX(4)Again it must be noted that the value ofθSA is dependentupon the system designer’s amplifier application and its cor-responding parameters as described previously.If the ambi-ent temperature that the audio amplifier is to be working un-der is higher than the normal25˚C,then the thermalresistance for the heat sink,given all other things are equal,will need to be smaller.Equations(1),(4)are the only equations needed in the de-termination of the maximum heat sink thermal resistance.This is of course given that the system designer knows therequired supply voltages to drive his rated load at a particularpower output level and the parameters provided by the semi-conductor manufacturer.These parameters are the junctionto case thermal resistance,θJC,T Jmax=150˚C,and the rec-ommended Thermalloy Thermacote thermal compound re-sistance,θCS.SIGNAL-TO-NOISE RATIOIn the measurement of the signal-to-noise ratio,misinterpre-tations of the numbers actually measured are common.Oneamplifier may sound much quieter than another,but due toimproper testing techniques,they appear equal in measure-ments.This is often the case when comparing integrated cir-cuit designs to discrete amplifier designs.Discrete transistoramps often“run out of gain”at high frequencies and there-fore have small bandwidths to noise as indicated below.Integrated circuits have additional open loop gain allowingadditional feedback loop gain in order to lower harmonic dis-tortion and improve frequency response.It is this additionalbandwidth that can lead to erroneous signal-to-noise mea-surements if not considered during the measurement pro-cess.In the typical example above,the difference in band-width appears small on a log scale but the factor of10inbandwidth,(200kHz to2MHz)can result in a10dB theoreti-cal difference in the signal-to-noise ratio(white noise is pro-portional to the square root of the bandwidth in a system).In comparing audio amplifiers it is necessary to measure themagnitude of noise in the audible bandwidth by using a“weighting”filter(Note18).A“weighting”filter alters the fre-quency response in order to compensate for the average hu-man ear’s sensitivity to the frequency spectra.The weightingfilters at the same time provide the bandwidth limiting as dis-cussed in the previous paragraph.Note18:CCIR/ARM:A Practical Noise Measurement Method;by RayDolby,David Robinson and Kenneth Gundry,AES Preprint No.1353(F-3).In addition to noise filtering,differing meter types give differ-ent noise readings.Meter responses include:1.RMS reading,2.average responding,3.peak reading,and4.quasi peak reading.Although theoretical noise analysis is derived using trueRMS based calculations,most actual measurements aretaken with ARM(Average Responding Meter)test equip-ment.Typical signal-to-noise figures are listed for an A-weighted fil-ter which is commonly used in the measurement of noise.The shape of all weighting filters is similar,with the peak ofthe curve usually occurring in the3kHz–7kHz region asshown below.DS011833-12DS011833-13DS011833-1414Application Information(Continued)SUPPLY BYPASSINGThe LM3886has excellent power supply rejection and does not require a regulated supply.However,to eliminate pos-sible oscillations all op amps and power op amps should have their supply leads bypassed with low-inductance ca-pacitors having short leads and located close to the package terminals.Inadequate power supply bypassing will manifest itself by a low frequency oscillation known as “motorboating”or by high frequency instabilities.These instabilities can be eliminated through multiple bypassing utilizing a large tanta-lum or electrolytic capacitor (10µF or larger)which is used to absorb low frequency variations and a small ceramic capaci-tor (0.1µF)to prevent any high frequency feedback through the power supply lines.If adequate bypassing is not provided the current in the sup-ply leads which is a rectified component of the load current may be fed back into internal circuitry.This signal causes low distortion at high frequencies requiring that the supplies be bypassed at the package terminals with an electrolytic ca-pacitor of 470µF or more.LEAD INDUCTANCEPower op amps are sensitive to inductance in the output lead,particularly with heavy capacitive loading.Feedback to the input should be taken directly from the output terminal,minimizing common inductance with the load.Lead inductance can also cause voltage surges on the sup-plies.With long leads to the power supply,energy is stored in the lead inductance when the output is shorted.This energy can be dumped back into the supply bypass capacitors when the short is removed.The magnitude of this transient is re-duced by increasing the size of the bypass capacitor near the IC.With at least a 20µF local bypass,these voltage surges are important only if the lead length exceeds a couple feet (>1µH lead inductance).Twisting together the supply and ground leads minimizes the effect.LAYOUT,GROUND LOOPS AND STABILITYThe LM3886is designed to be stable when operated at a closed-loop gain of 10or greater,but as with any other high-current amplifier,the LM3886can be made to oscillate under certain conditions.These usually involve printed cir-cuit board layout or output/input coupling.When designing a layout,it is important to return the load ground,the output compensation ground,and the low level (feedback and input)grounds to the circuit board common ground point through separate paths.Otherwise,large cur-rents flowing along a ground conductor will generate volt-ages on the conductor which can effectively act as signals at the input,resulting in high frequency oscillation or excessive distortion.It is advisable to keep the output compensation components and the 0.1µF supply decoupling capacitors as close as possible to the LM3886to reduce the effects of PCB trace resistance and inductance.For the same reason,the ground return paths should be as short as possible.In general,with fast,high-current circuitry,all sorts of prob-lems can arise from improper grounding which again can be avoided by returning all grounds separately to a common point.Without isolating the ground signals and returning the grounds to a common point,ground loops may occur.“Ground Loop”is the term used to describe situations occur-ring in ground systems where a difference in potential exists between two ground points.Ideally a ground is a ground,butunfortunately,in order for this to be true,ground conductors with zero resistance are necessary.Since real world ground leads possess finite resistance,currents running through them will cause finite voltage drops to exist.If two ground re-turn lines tie into the same path at different points there will be a voltage drop between them.The first figure below shows a common ground example where the positive input ground and the load ground are returned to the supply ground point via the same wire.The addition of the finite wire resistance,R 2,results in a voltage difference between the two points as shown below.The load current I L will be much larger than input bias current I I ,thus V 1will follow the output voltage directly,i.e.in phase.Therefore the voltage appearing at the non-inverting input is effectively positive feedback and the circuit may oscillate.If there were only one device to worry about then the values of R 1and R 2would probably be small enough to be ignored;however,several devices normally comprise a total system.Any ground return of a separate device,whose output is in phase,can feedback in a similar manner and cause instabili-ties.Out of phase ground loops also are troublesome,caus-ing unexpected gain and phase errors.The solution to most ground loop problems is to always use a single-point ground system,although this is sometimes im-practical.The third figure below is an example of a single-point ground system.The single-point ground concept should be applied rigor-ously to all components and all circuits when possible.Viola-tions of single-point grounding are most common among printed circuit board designs,since the circuit is surrounded by large ground areas which invite the temptation to run a device to the closest ground spot.As a final rule,make all ground returns low resistance and low inductance by using large wire and wide traces.Occasionally,current in the output leads (which function as antennas)can be coupled through the air to the amplifier in-put,resulting in high-frequency oscillation.This normally happens when the source impedance is high or the input leads are long.The problem can be eliminated by placing aDS011833-1515。
3-11 LM386音频放大电路[共8页]
![3-11 LM386音频放大电路[共8页]](https://img.taocdn.com/s3/m/2a55680576a20029bc642dae.png)
- 135第三章巧制作134按照这张图纸在面包板上制作，接通电源。
我们对着话筒拍手，“啪”，LED 亮了。
再拍一次，LED 熄灭。
这样就达到了基本的效果。
接下来是调试接收声音的频率。
声音有高频、中频、低频，虽然我们用的话筒是全指向性全频的，但在电路中也会因为电容值的不同而倾向于某一段频率。
话筒偏压的电路中使用的是0.1μF 电容，这款电容的容值小、充放电的速度快，对高频声音有很好的通过率。
也就是说，使用0.1μF 电容可接收中、高频声音。
改用0.01μF 电容则只会接收高频的声音。
反之，用2.2μF 或4.7μF 则会更多的通过低频声音信号。
如此一来，靠更换电容值便能达到调整接收声音频率的效果。
如果你想用喊话开关灯，就用2.2μF 或4.7μF 电容。
想击掌开关灯，就用0.1μF 电容吧。
若是想用吹哨开关灯，那就用0.01μF 的最棒了。
声音频率越高受到的干扰声音就越少，明白了这些道理，再去调试电路就有了理论依据。
具体的制作过程和拓展的电路设计我就不多讲了，大家有兴趣自己拓展一下吧，相信大家一定能用之前学过的知识举一反三，发现创新可能，那将是你学有所成最好的证明。
3-11 LM386音频放大电路之前的内容介绍过三极管放大电路，三极管放大虽然是放大电路的基础，但实际上很少单独使用。
因为电路设计不断复杂化、集成化，采用多管放大的集成电路芯片在性能和功能上都优于独立的三极管。
所以在明白三极管放大原理之后，应该学习一下常用的放大芯片作为补充，在今后的电路设计与制作中用最适合的芯片达到最佳性能。
本节介绍一款非常有名的音频功率放大芯片LM386，你可以用它制作助听器、小音箱等有趣又实用的音频放大装置。
LM386的引脚少、外围元件少、电路简单，是电子爱好者入门放大器芯片的首选芯片。
【认识LM386】LM386是美国国家半导体公司生产的音频功率放大器芯片，2011年该公司被德州仪器公司（TI）收购，所以现在由德州仪器公司生产。
lm3886 4766 1876开关机静音电路
LM3886和LM4766的内部静音电路相同，静噪脚须加负电压绝对值大于2.5V（比-2.5V更负）,每路静音端输出电流大于0.5mA才能静噪。
而LM1876静噪脚电压至少大于＋2.5V才能静噪。
第一张图电路简单只能实现开机喇叭防冲击，关机无效。
第二张是LM3886和LM4766的喇叭开、关机防冲击电路，第三张图是LM1876喇叭开、关机防冲击电路。
图中变压器副端指变压器副级两个AC端子任意一个（中心抽头除外）。
< 1 >< 2 >< 3 >我是楼主很久没来了，一楼图没标清楚这里说明一下：图中变压器副端是指副级的两个AC端子任意一端（中心抽头除外）。
简述一下原理，先看下面A,B、C三张IC内部图的静音部分电路，LM4766和LM3886静音电路一样而LM1876不同，但共同点是只要三张图中三极管T3截止就可以实现静音。
要实现开关机防冲击对LM4766（LM3886)来说只要在开关机时让T1截止使得T3截止就实现静音，正常时两管导通。
对LM1876来说要实现开关机防冲击必须让T1导通使得T2、T3就截止实现静音，正常时T1截止T2、T3导通，放大电路正常工作了。
自己分析一楼电路原理就清楚了。
A图（LM4766):B图（LM3886)：C图(LM1876):由于LM4766(LM3886)的静音控制端接内部的三极管发射极，所以需要较大的电流（每声道大于0.5mA)才能保证后一级T3可靠导通，而且电流方向是从IC内部流出。
而LM1876静音控制端是接内部三极管基极，所以控制电流可以小很多，方向为静音控制端往IC内部流入。
至于控制端电压加多大看IC内部输入端的两个二极管加上三极管共3个PN结至少得绝对值2V以上，可靠运行得绝对值2.5V以上才可以。
制作简单的LM386吉他音箱放大器
制作简单的LM386吉他音箱放大器展开全文尊敬的读者您好，上期发表了果冻罐吉他放大器的制作，这期公布从电路原理图到原型板的电路制作。
步骤1：零件清单1个9V碱性电池1条9v电池卡扣连接器1个带nc（并联）开关的单声道1/4英寸插孔1个立体声1/4英寸插孔1个LM386放大器。
任何版本都可以，我喜欢LM386N-41个66mm聚酯薄膜锥形扬声器1个红色LED电阻：1470欧姆1 1K欧姆1 10欧姆电容器：1100nF1 47nF2220uF洞洞板烙铁和焊锡步骤2：洞洞板这种洞洞板是为集成电路制作的，方便引线和焊接。
零件都含在没有铜箔的一面。
最好是先规划一下，免得走线混乱引起错误。
步骤3：将原理图转换为原型板因此，一旦您设计好电路并制作了原理图，就可以开始研究原型板的布局了。
您将铅笔拿到纸上，然后开始在protoboard插图上布置组件。
这需要一些技巧。
需要一些时间。
这将花费大量的纸张。
在上方，您可以看到原理图和原型板上的成品轮廓。
计划原型板上的组件位置时，我会分阶段进行计划。
我将从芯片的放置开始。
我从左到右工作，所以我将布局如下：输入---- IC芯片----输出该电路的输入非常简单，因此芯片将放置在原型板的左侧。
这为输出组件留出了空间。
下一步是布置电路的所有电源。
下一步是布置输入和输出组件。
下一步是添加增益组件和LED电源指示灯下一步是添加外围组件，例如输入和输出插孔。
每个阶段都建立在最后一个阶段。
从最简单到更复杂。
分阶段进行构建可以使您在进行过程中进行测试和故障排除，以便在出现错误的情况下更早发现并可以将其与构建中的先前阶段隔离开来。
将原理图转换为原型板图之后，就该构建真正的电路了。
我将原型板图分解成几张纸，每张纸都包含一个阶段或构建的一部分。
因此，我可以打印出构建的每个部分，并在进行过程中检查放置在真实原型板上的组件，以确保没有遗漏任何东西。
这对于复杂的构建尤其重要。
对于此特定电路，我们将分4部分进行构建。
LM3886高保真大功率音频IC
LM386音频功率放大器 音频功率放大器 概述(Description): 概述 LM386是美国国家半导体公司生产的音频功率放大器,主 是美国国家半导体公司生产的音频功率放大器, 是美国国家半导体公司生产的音频功率放大器 要应用于低电压消费类产品.为使外围元件最少, 要应用于低电压消费类产品.为使外围元件最少,电压增 益内置为20.但在1脚和 脚之间增加一只外接电阻和电容, 脚和8脚之间增加一只外接电阻和电容 益内置为 .但在 脚和 脚之间增加一只外接电阻和电容, 便可将电压增益调为任意值,直至200.输入端以地位参考, 便可将电压增益调为任意值,直至 .输入端以地位参考, 同时输出端被自动偏置到电源电压的一半, 同时输出端被自动偏置到电源电压的一半,在6V电源电压 电源电压 它的静态功耗仅为24mW,使得 使得LM386特别适用于电池 下,它的静态功耗仅为 使得 特别适用于电池 供电的场合. 供电的场合. LM386的封装形式有塑封 引线双列直插式和贴片式. 的封装形式有塑封8引线双列直插式和贴片式 的封装形式有塑封 引线双列直插式和贴片式. 特性(Features): 特性 * 静态功耗低,约为 静态功耗低,约为4mA,可用于电池供电. 可用于电池供电. 可用于电池供电 * 工作电压范围宽,4-12V or 5-18V. 工作电压范围宽, . * 外围元件少. 外围元件少. * 电压增益可调,20-200. 电压增益可调, . * 低失真度. 低失真度.
LM3886高保真大功率音频 高保真大功率音频IC 高保真大功率音频 LM3886是美国国家半导体公司新出的一款带过压,过高 是美国国家半导体公司新出的一款带过压, 是美国国家半导体公司新出的一款带过压 温保护的高保真大功率音频IC,其外围电路简单, 温保护的高保真大功率音频 ,其外围电路简单,制作方 其性能如下: 便.其性能如下: VCC=±28V OUTPUT=68W/4 ,38W/8 ± VCC=±35V OUTPUT=50W/8 ± 峰值功率:135W 峰值功率: 峰值功率 信噪比 信噪比≥92db 信噪比 转换率:19V/us 转换率: 转换率 互调失真:0.04% 互调失真: 互调失真 11脚TO-220封装 脚 封装 静音功能 静音功能 SPiKeTM保护功能 保护功能 LM3886有两种型号:LM3886TF和LM3886T,前者 有两种型号: 有两种型号 和 , 散热片绝缘,后者不绝缘. 散热片绝缘,后者路图之增益 应用电路图之增益=20 应用电路图之增益
优秀的功放IC，LM3886基本应用电路图
优秀的功放IC，LM3886基本应用电路图LM3886是单声道、中功率、高性能音频功放IC，是美国国家半导体(NS)公司的“序曲”(OVerture)音频功放系列具有代表性的IC之一。
它采用11脚TO-220封装并具有输入静音功能，适合小型有源音箱、环绕声放大器和高保真立体声电视机等用作功放。
LM3886主要性能简介1、连续平均输出功率：60W／4Ω(Vcc=±28V)30W／8Ω(Vcc=±28V)50W／8Ω(Vcc=±35V)2、瞬时最大输出功率： 150W3、失真度：(THD+噪声)0.03％(20Hz～20kHz)4、噪声电平：2.0μV5、信噪比：＞92dB6、互调失真：(按SMPTE标准)0.004％此IC的最大特点是自身保护功能齐全，无须外接各种保护电路，它内含NS公司研制的SPIKe(自身瞬时温度)保护电路，对输出级晶体管的安全工作区(SOA)进行动态检测与保护，从而全面实现过压、欠压、过载、输出短路(包括短路到地与短路到电源)、热失控和瞬时温度冲击等保护功能。
附图1是3886内部等效电路。
电路工作原理简析R2为LM3886的同相输入端提供偏压；并联在两个输入端的C2是用来减小放大器的高频增益，以免输出管出现振荡，同时抑制输入的电磁干扰噪声；R5、R4、C4组成反馈回路，放大器的低频响应和高频转折频率fH取决于R3、C3；R4、C4、R5和R3决定高频增益和低通转折频率fL(fH、fL的计算公式略)。
C4是补偿元件，它与R4、R5共同起减小高频增益的作用。
R8、R9、C5与开关(图中虚线所示)组成静音控制电路：当开关断开时，LM3886停上输出，即静音起作用；接通开关时静音解除，R8将⑧脚输出电流限制到0.5mA(LM3886的⑧脚电流≥0.5mA)。
C5为静音通、断提供较大的时间常数。
R6、C6的作用为防止放大器产生高频振荡。
L1、R7作用：如果负载呈容性(如扬声器电缆较长)，则放大器在高频下会过载，并使方波响应出现转折，为避免此现象，在输出端串入LR组成的并联电路，此时L呈现较大感抗，10Ω电阻将放大器与容性负载隔离开来并降低L与容性负载所构成回路的Q值；低频下则10Ω电阻被L短路，放大器通过感抗很小的L直接驱动负载。
lm3886功放电路
;文章:行业新闻┆EDA文摘┆电源技术┆无线通信┆测量仪表┆嵌入式类┆电子技术┆制造技术┆半导体┆网络/协议┆展会┆实验┆家电维修下载:EDA教程┆电源技术┆电子书籍┆电子元件┆无线通信┆通信网络┆电路图纸┆嵌入式类┆单片机┆传感/控制┆电子教材┆模拟数字┆.... 音视频类┆消费电子┆机械电子┆行业软件┆C/C++┆FPGA/ASIC┆规则标准┆家电维修┆DSP┆IC资料┆ARM┆软件┆电路图┆电子技术论坛硬件工程师必读功略数字信号处理器(DSP)入门宝典PDF 【资源共享】单片机/ARM/DSP/FPGA/PCB 【经典资料】毕业设计大礼包位置：电子发烧友 > 行业新闻 > 电子技术 > 电路图 > 功率放大器电路图 >lm3886功放电路退出登录用户管理栏目导航Google 提供的广告电阻成型机音频放大器电路图电路原理图汽车电瓶·保护电路图·嵌入式类电子电路图·电源技术电子电路图·无线通信电子电路图·光电隔离电子电路图·光电开关电子电路图·信号处理电子电路图·消费类电子电路图·照明灯电路图·光电报警电子电路图·耳机电路图·电动机控制电路图·功率放大器电路图·汽车电路图·遥控电路图·电工基础电路图·电工仪表电路图·可控硅电路图·彩灯电路图·IC应用电路图·电视机电路图·555集成电路大全·运算放大器电路·电子管功放电路·定时器电路图热门文章·[组图]电子元器件基础知识...·[图文]USB接口定义·[图文]三极管开关电路图·[组图]RS232 RS485接口原理...·[组图][组图]电动车充电器...·[组图]高品质音调电路的制...lm3886功放电路作者：本站来源：本站原创发布时间：2008-5-5 21:55:43lm3886功放电路这款功放的末级电流放大电路未介入环路负反馈，有效地抑制了瞬态互调失真（ＴＩＭＤ）、界面互调失真（ＩＩＭＤ）和相位互调失真（ＰＩＭＤ）等，改善了高音域的层次感，减小了“音染”。
LM386功放电路图
LM386组成的助听器电路图助听器主要是由微型拾音器(话筒)、放大器和耳机三部分组成的微小型扩音机。
尽管助听器的电路结构与一般扩音机在形式上较为相似，但二者的要求有差异。
扩音机是按正常人的听力范围及音域设计的，而助听器则根据耳聋患者的失音特征和程度来设计的。
一般助听器对频率响应、谐波失真、噪音等要求虽然没有扩音机那么高，放大器级数也少于扩音机，不过对有关的性能指针均有一定的要求，通常助听器的传声增益要在15～55dB左右，频响在100～600Hz，失真度小于10%～15%。
显然采用LM386集成块是可以满足的。
LM386高频响应可达300kHz，电源电压范围为1～6V时，其静态电源为4mA，适用于电池供电。
图101-1图101-2图101-1为LM386组成的助听器电路。
图中LM386被连接成正相放大器电路。
1、8 脚接有10μF电容，故电路增益被提至最大。
这样做的原因在于LM386的增益不太大，用于助听器时余量并不足，尤其当话筒灵敏度较差时比较明显，调低增益常常不能满足要求。
话筒信号通过RP1和C1耦合至脚，经LM386放大后从5脚输出，再推动耳机发声，RP1用于音量调节，S1为频响选择开关。
当S1置于1、2、3位时，对应的电路频响分别是3000、4500和6000Hz左右，该频响选择电路实际上是一电容衰减电路。
设置它的目的是压缩电路的频响，减弱和消除耳聋者不需的音频成分和噪音，以提高清晰度和减轻耳朵的疲劳感。
C1为输出耦合电容，C4为电源去耦电容。
R1是驻极体话筒BP内场效应管的负载。
助听器的印制电路板如图101-2所示。
元器件焊装完检查无误后，接通电源就能使助听器正常工作。
不过在使用前测一下电路的静态电流是否为1mA左右(DC＝4.5V时为3.5mA左右)。
若电流太大，通常是C4或印制板漏电而引起，也可能是LM386质量欠佳，应查明原因修复好。
印制板装完后，将它放入小塑料盒中固定，电源用5～8号小电池或大的钮扣型电池。
用LM3886制作了一款功放电路
用ＬＭ３８８６制作了一款功放电路，在用学校ＤＶＤ机试听时，总感到声音效果不如人意，响度也达不到标称功率效果。
虽经多次调整电路参数（包括提升了电源电压），但收效甚微。
后来看到有关刊物介绍ＬＭ３８８６放大倍数偏小，需要有足够幅度的激励信号，才能收到较好的效果。
为此，笔者选用“运放之星”ＮＥ５５３２制作了一款前置放大电路加在功放输入端，再次试听，音效、响度明显得到了改善。
现将制作的前放电路介绍如下：图１为前放电路的直流伺服电源电路，给前放电路提供稳定的±１２Ｖ电源。
稳压电路采用三端集成稳压块，并且使用一片ＮＥ５５３２构成伺服电路，实现对输出电压的实时跟踪与调整。
图２为前置放大电路，电路采用了“运放之星”ＮＥ５５３２构成同相比例运算放大电路，其放大倍数为５倍左右（主要由Ｒ９、Ｒ７、Ｒ１０、Ｒ８决定），Ｃ１５、Ｃ１６在电路中具有提升高音频信号的作用。
Ｊ１接环变的双１２Ｖ输出端，Ｊ２为信号输入端，Ｊ３为信号输出端（接功放输入端）。
图３为印刷电路板图，图４为元件布置图。
具体安装时，可将此电路板安装在功放箱中靠近背面的附近。
通孔，并经过Ｊ２（双信号插座）接音源。
本电路也适用于其他音源幅值较小的组合系统作为功放的前置放户外演出和歌舞厅所使用的专业音响，多数为进口设备，应该说可靠性较高。
主要问题是操作者专业素质不齐，真正配备合格调音师的单位很少。
本文针对中、小型歌舞厅音响设备操作要点进行解说，可做为制订操作规程的参考。
另外，在中小型歌舞厅由于话筒声反馈造成的自激啸叫现象，是常见的令使用者头疼的问题，因为经常出现啸叫会令宾客扫兴，音响效果无从谈起，严重者会造成设备损坏。
所以，自激啸叫现象是歌舞厅音响使用中的一个重要问题，下面分别叙述。
一、音响设备开、关机顺序应按由前到后顺序开机，即由音源设备(CD机、LD机、DVD机、录音机、录像机)、音频处理设备(压限器、激励器、效果器、分频器、均衡器等)到音频功率放大器到电视机、投影机、监视器。
lm3886 4766 1876开关机静音电路
LM3886和LM4766的内部静音电路相同，静噪脚须加负电压绝对值大于2.5V（比-2.5V更负）,每路静音端输出电流大于0.5mA才能静噪。
而LM1876静噪脚电压至少大于＋2.5V才能静噪。
第一张图电路简单只能实现开机喇叭防冲击，关机无效。
第二张是LM3886和LM4766的喇叭开、关机防冲击电路，第三张图是LM1876喇叭开、关机防冲击电路。
图中变压器副端指变压器副级两个AC端子任意一个（中心抽头除外）。
< 1 >< 2 >< 3 >我是楼主很久没来了，一楼图没标清楚这里说明一下：图中变压器副端是指副级的两个AC端子任意一端（中心抽头除外）。
简述一下原理，先看下面A,B、C三张IC内部图的静音部分电路，LM4766和LM3886静音电路一样而LM1876不同，但共同点是只要三张图中三极管T3截止就可以实现静音。
要实现开关机防冲击对LM4766（LM3886)来说只要在开关机时让T1截止使得T3截止就实现静音，正常时两管导通。
对LM1876来说要实现开关机防冲击必须让T1导通使得T2、T3就截止实现静音，正常时T1截止T2、T3导通，放大电路正常工作了。
自己分析一楼电路原理就清楚了。
A图（LM4766):B图（LM3886)：C图(LM1876):由于LM4766(LM3886)的静音控制端接内部的三极管发射极，所以需要较大的电流（每声道大于0.5mA)才能保证后一级T3可靠导通，而且电流方向是从IC内部流出。
而LM1876静音控制端是接内部三极管基极，所以控制电流可以小很多，方向为静音控制端往IC内部流入。
至于控制端电压加多大看IC内部输入端的两个二极管加上三极管共3个PN结至少得绝对值2V以上，可靠运行得绝对值2.5V以上才可以。
LM3886TF制作的纯直流电流负反馈功放电路
LM3886TF制作的纯直流电流负反馈功放电路LM3886TF制作的纯直流电流负反馈功放电路LM3886TF是美国NS公司推出的新型的大功率音频放大集成电路，其后面的TF为全绝缘封装，和LM1875T相比，它的功率较大，在额定工作电压下最大可达68Ｗ的连续不失真平均功率，同样具有比较完善的过压过流过热保护功能，最可贵的是它具有自动抗开关机时的电流冲击的功能，使扬声器能够安全的工作。
LM3886优异的性能，使得它在近几年音响制作中广泛的应用，许多成品功放机中就有直接的应用它担任后级功放或者用它作为重低音放大电路。
采用了美国NS 公司（国家半导体公司）推出的新型高保真音响功放集成电路LM3886TF作功率放大，用运放NE5532或AD827作前置线性放大和音调放大。
其特点有：输出功率大（连续输出功率68W）、失真度小（总失真加噪声<003％）、保护功能（包括过压保护、过热保护、电流限制、温度限制、开关电源时的扬声器冲击保护、静噪功能）齐全，外围元件少，制作调试容易，工作稳定可靠。
由于用它制作功率放大电路具有简易，适用的特点，特别适合于烧友以及电子爱好者的制作。
LM3886TF的电气参数如下：LM3886在VCC=VEE=28V、4欧负载时能达到68W的连续平均功率，在VCC=VEE=35V，8欧负载时能达到50W的平均功率。
具有较宽的电源电压范围VCC+VEE为20V-94V；总谐波失真+噪声：60W 20Hz<f<20kHz AV=26dB 时的值为0.03%转换速率(SLEW RATE):VIN=2.0VP-P、tRISE=2ns 时的值为19V/us总静态电流：50mA输入偏流： 0.2uA增益带宽乘积: 8 MHZ在谈及功放的放音品质时，元器件的选取，电路的设计很重要，但是还有一个很重要的，就是电路板的设计，PCB布线不合理，再好的电路和最发烧级的元件也无济无事，对音响爱好者来说，交流噪声和声道的串音都是不能接受的，在设计本站的第一款出台的LM3886功放前，笔者曾参考研究过一些国内外的音响功放电路板，最简单的资料来源一些著名的半导体生产厂商的推荐应用电路的PCB图，力求达到将功放板的音量开到最大，将耳朵贴近音箱，没有交流哼声的效果，并且将声道间的串挠减到最小。
用LM3886制作了一款功放电路
用ＬＭ３８８６制作了一款功放电路，在用学校ＤＶＤ机试听时，总感到声音效果不如人意，响度也达不到标称功率效果。
虽经多次调整电路参数（包括提升了电源电压），但收效甚微。
后来看到有关刊物介绍ＬＭ３８８６放大倍数偏小，需要有足够幅度的激励信号，才能收到较好的效果。
为此，笔者选用“运放之星”ＮＥ５５３２制作了一款前置放大电路加在功放输入端，再次试听，音效、响度明显得到了改善。
现将制作的前放电路介绍如下：图１为前放电路的直流伺服电源电路，给前放电路提供稳定的±１２Ｖ电源。
稳压电路采用三端集成稳压块，并且使用一片ＮＥ５５３２构成伺服电路，实现对输出电压的实时跟踪与调整。
图２为前置放大电路，电路采用了“运放之星”ＮＥ５５３２构成同相比例运算放大电路，其放大倍数为５倍左右（主要由Ｒ９、Ｒ７、Ｒ１０、Ｒ８决定），Ｃ１５、Ｃ１６在电路中具有提升高音频信号的作用。
Ｊ１接环变的双１２Ｖ输出端，Ｊ２为信号输入端，Ｊ３为信号输出端（接功放输入端）。
图３为印刷电路板图，图４为元件布置图。
具体安装时，可将此电路板安装在功放箱中靠近背面的附近。
通孔，并经过Ｊ２（双信号插座）接音源。
本电路也适用于其他音源幅值较小的组合系统作为功放的前置放户外演出和歌舞厅所使用的专业音响，多数为进口设备，应该说可靠性较高。
主要问题是操作者专业素质不齐，真正配备合格调音师的单位很少。
本文针对中、小型歌舞厅音响设备操作要点进行解说，可做为制订操作规程的参考。
另外，在中小型歌舞厅由于话筒声反馈造成的自激啸叫现象，是常见的令使用者头疼的问题，因为经常出现啸叫会令宾客扫兴，音响效果无从谈起，严重者会造成设备损坏。
所以，自激啸叫现象是歌舞厅音响使用中的一个重要问题，下面分别叙述。
一、音响设备开、关机顺序应按由前到后顺序开机，即由音源设备(CD机、LD机、DVD机、录音机、录像机)、音频处理设备(压限器、激励器、效果器、分频器、均衡器等)到音频功率放大器到电视机、投影机、监视器。