单片机50瓦/ 8欧姆功率放大器
艾略特-特别是杖(从设计的课堂笔记,国家半导体)。
电路的描述,
有很多情况下,当一个简单而可靠的功率放大器是必要的——后和中心为复合信道扬声器,强化了PC喇叭,等等。
该项目(不像大多数人)几乎直接对“典型”电路应用国家半导体技术。原来,典型的应用电路并不坏,我会说高保真的?刚好也许,以警告。它具有良好的隔音、扭曲人物,是非常简单的建立,如果你有印刷电路板。
2000年9月26日
从测试的原型板,我有点更关键的一切。声音质量优良的!只要保护电路是绝对不允许的操作,表现为模范。
最新版本的ESP P19板(Rev-B)已删除的SIM(音障碍监测。我非常喜欢这个主意,没有别的似乎很感兴趣,所以少量的PCB房地产从而解放了将提供空间布局和输入(权力)连接器。
图一显示了原有的示意图显示该项目最初出版。这几乎是相同的应用注(这个)、聚酯旁路电容已经被加入到游戏,哑巴电路已被冻结(这个函数将更广泛地应用于连在前置放大器,并不是特别有用,反正清规戒律)。
图1 - LM3876T功率放大器电路框图(原版本)。
电压增益27dB如图所示,但这是可以改变的用不同的价值的反馈电阻器,目前22k路径(沪之间,以及3针。电感由10的0.4mm包铜线、伤身体周围的10欧姆电阻。绝缘材料必须被完全从每端和电线被焊接到两端的电阻。
10欧姆欧姆的电阻和2.7必须1瓦特的类型,和所有其他人应该1%的金属薄膜(如我总是推荐)。所有的铝电解电容器应价50V如果可能的话,100nF(0.1uF)碳排放控制标准供应应该尽可能的IC防止振荡。
在电源电压应该在+ / - 35伏在满载,这将让这个小家伙提供了最大的美国瓦茨(额定输出在25℃最少。使最大的力量,这是很重要的,最低的案例来排出的热阻。这将是通过安装任何绝缘云母垫圈,但被警告,排出将在负电源电压和将被隔绝于其上。为更多的信息,减少热阻读这篇文章的设计heatsinks -这个原则同样可以应用到芯片——甚至在平行运行。我从来没有试过这个单位,但它是可能的,用一个低电阻串联在输出负载平衡。
图2 - Revision-B功率放大器电路原理图
图示为Revision-B板上面所示。这几乎是相同的,除了SIM连接已经删除和一些组件指派被挪动。像原来的,有优秀的车载脱钩,使用220uF电解和100nF片式陶瓷电容器聚酯或者在每个轨道。虽然我已经证明双极电3.3uF C1作为,你可以用聚酯帽,如果你的愿望。如果放大器是用于中型或高音单元在biamped或triamped系统,可以减少碳的价值在72Hz 100nF(-3dB)。对于一般的使用,你可以用一个1uF聚酯,给-3dB 7.2Hz频率,但是低音延期将更好地与一个更高的价值,如图所示。
新的PCB允许你操作安培为双单色-印刷电路板的轨迹可分裂,每个安培是动力从它自己的供应。虽然国际海事组织没有太多,这也使得PCB被切成两半,每一半都有它自己的供应连接器。输出连接可使线路板别针,或者你可以使用印刷电路板上的铲”(aka quick-connect提着-理事会规定。
全部工程的细节都可当你购买了多氯联苯,所有的选择。
正如你所看到的,有规定使用LM3886一样。该电路,几乎是相同的,但是有较高的规格。有一些连结PCB上连销1 ~ 5(这些不应该被连接的LM3876)。使用LM3886,董事会可在大桥桥荷载线下或取得绑成8欧姆120W周围。我建议P87B被用来提供异相信号需要手术。线下虽然这是常见的运行一个放大器反向,这是作为一个非常低阻抗的前置音箱,可能会导致不可接受的加载和可能扭曲。这个P87B将推动各放大器分开,并为更好的方式来驱动放大器。
同时并行操作经常推荐,我绝对不推荐你运行这个放大器在平行。有很严格的要求,得到宽容并网运行——通常是放大器应当配合在0.1%或更好的音频带宽和超越。因为很低输出阻抗电路、甚至是不匹配的100mV的瞬间,在(电压和频率)将会引起大的环流电流通过集成电路。虽然0.1Ω电阻通常建议,100mV电压匹配(0.15%在峰值电压的60V)将会引起循环电流的0.5A。这导致过热而触发的忿怒的保护电路。
图2 - IC梢出
图二显示梢出的LM3876,值得注意的是,这种装置上的别针预留足够的大小电路板摇摇晃晃的运行轨道电路。这个3886已(几乎)相同,且能适应梢出相反如果一点力量是必需的。唯一的区别是,针梢出5必须连接到+ ' ve供应LM3886。对于这一环节上提供的印刷电路板。
对于这个放大器的PCB板是立体声扩大,是单站,并提供引线定位于印刷电路板。整个音响板包括四个融合是什么(如很小的x 40毫米)。这个Revision-B板是一模一样的大小,并使用相同的间距,让retro-fitting电路,如果必要的话。
照片放大(与电源完成)。
我重申了这个地方,从来没有一个电源放大器操作,即使测试(这一点也同样适用于几乎所有的放大器)。这将导致非常迅速,虽然内部的保护将会关闭安培下保护它从伤害,这不是你想要测试是没有理由的。
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它听起来如何?
健全的质量非常好——当我开始说的,我就叫它刚好高保真-与变量。提供安培是绝对不允许去接近保护范围这听起来很好。这是rub——因为这是综合过载保护装置(我向来不喜欢在任何形式)这个放大器提供更多文物,它要求比一个“正常”的片段放大器。35V推荐的供应和名义±8欧姆负载时,你将需要一个良好的散热槽,以确保设备温度保持低于70°C。这通常会确保保护电路,不要操作,即使安培夹在流动。4欧姆负载,我建议的电源电压降低限额±30V。
保护电路称为穗™由国家——这代表了自我峰瞬时温度(度),将保护放大器从差不多什么都能做。虽然在理论上,这是一件好事,它不是很好的时候保护电路操作,因此保证安培的仅是用于应用在剪裁永远不会发生的事情,或者是比较轻易装载。
这听起来像一个很高的目标,但对于后置扬声器系统,或在一个围绕放一些严重到那些400W PMPO热键PC喇叭(5W有效值放大器-我不是开玩笑),它是一颗钻石。
它也能作为一个中型和/或在一个tri-amped高音放大器系统——有很多的可能性,所以我要让你想出更多。
Single Chip 50 Watt / 8 Ohm Power Amplifier
Rod Elliott - ESP (From Design Notes from National Semiconductor)
Circuit Description
There are many instances where a simple and reliable power amplifier is needed - rear and centre channel speakers for surround-sound, beefing up the PC speakers, etc.
This project (unlike most of the others) is based almost directly on the "typical application" circuit in the National Semiconductor specification sheet. As it turns out, the typical application circuit is not bad - would I go so far as to say hi-fi in the audiophile sense? Perhaps - with caveats. It has good noise and distortion figures, and is remarkably simple to build if you have the PCB.
26 Sept 2000
From testing the prototype boards, I was a little more critical of everything. The sound quality is excellent! As long as the protection circuitry is never allowed to operate, the performance is exemplary in all respects.
The latest version of the ESP P19 board (Rev-B) has deleted the connections for a SIM (Sound Impairment Monitor). Much as I like the idea, no-one else seemed to be interested, so the small amount of PCB real estate thus liberated was used to refine the layout and provide space for input (and power) connectors.
Figure 1 shows the original schematic as shown when this project was originally published. It is almost the same as in the application note (redrawn), polyester bypass capacitors have been added, and the mute circuit has been disabled (this function would more commonly be applied in the preamp, and is not particularly useful anyway IMHO).
Figure 1 - LM3876T Power Amplifier Circuit Diagram (Original Version)
Voltage gain is 27dB as shown, but this can be changed by using a different value resistor for the feedback path (R3, currently 22k, between pins 3 and 9). The inductor consists of 10 turns of 0.4mm enamelled copper wire, wound around the body of the 10 Ohm resistor. The insulation must be scraped off each end and the wire is soldered to the ends of the resistor.
The 10 Ohm and 2.7 Ohm resistors must be 1 Watt types, and all others should be 1% metal film (as I always recommend). All electrolytic capacitors should be rated at 50V if at all possible, and the 100nF (0.1uF) caps for the supplies should be as close as possible to the IC to prevent oscillation.
The supply voltage should be about +/- 35 Volts at full load, which will let this little guy provide a maximum of 56 Watts (rated minimum output at 25 degrees C). To enable maximum power, it is important to get the lowest possible case to heatsink thermal resistance. This will be achieved by mounting with no insulating mica washer, but be warned that the heatsink will be at the -ve supply voltage and will have to be insulated from the chassis. For more info on reducing thermal resistance, read the article on the design of heatsinks - the same principles can be applied to ICs - even running in parallel. I haven't tried it with this unit, but it is possible by using a low resistance in series with the outputs to balance the load.
Figure 2 - Revision-B Power Amplifier Circuit Diagram
The schematic for Revision-B boards is shown above. It is almost identical, except the SIM connections have been deleted and a few component designations have been moved around. Like the original, there is excellent on-board decoupling, using a 220uF electrolytic and a 100nF polyester or monolithic ceramic capacitor on each rail. While I have shown C1 as a 3.3uF bipolar electro, you can use a polyester cap if you desire. If the amp is to be used for midrange or tweeter in a biamped or triamped system, C1 may be reduced in value to 100nF (-3dB at 72Hz). For general use, you can use a 1uF polyester, giving a -3dB frequency of 7.2Hz, however bass extension will be better with a higher value as shown.
The new PCB allows you to operate the amp as dual mono - the PCB track can be split, and each amp is powered from its own supply. While IMO there isn't much point, this also allows the PCB to be cut in half, and each half has its own supply connector. Output connection can be made to PCB pins, or you can use a PCB mount 'spade' (aka quick-connect) lug - the board has provision for this.
Full construction details are available when you purchase the PCBs, and all options are explained in detail.
As you can see, there is provision to use the LM3886 as well. This IC is almost identical, but has a higher specification. There are links on the PCB to connect pins 1 and 5 (these should not be connected for the LM3876). Using the LM3886, the board can be operated in bridge (BTL or bridge tied load) to obtain around 120W into 8 ohms. I suggest that the P87B be used to provide the out-of-phase signals needed for BTL operation. While it is common to run one amp as inverting, this presents a very low impedance to the preamp, and may cause unacceptable loading and possibly distortion. The P87B will drive each amplifier separately, and is the better way to drive the amplifiers.
While parallel operation is often recommended, I absolutely do not recommend that you run the amps in parallel. There are very strict requirements for gain tolerance for parallel operation - typically the amplifiers should be matched to within 0.1% or better over the entire audio bandwidth and beyond. Because of the very low output impedance of the ICs, even a mismatch of 100mV (instantaneous, at any voltage or frequency) will cause large circulating currents through the ICs. While 0.1Ω resistors are usually suggested, a 100mV voltage mismatch (0.15% at a peak voltage of 60V) will cause a circulating current of 0.5A. This causes overheating and will invoke the wrath of the protection circuits.
Figure 2 - IC Pinouts
Figure 2 shows the pinouts for the LM3876, and it should be noted that the pins on this device are staggered to allow adequate sized PCB tracks to be run to the IC pins. The 3886 has (almost) identical pinouts, and can be used instead if a little more power is required. The only difference in pinouts is that pin 5 must be connected to the +ve supply for the LM3886. Provision for this link is on the PCB.
The PCB for this amp is for a stereo amplifier, is single sided, and supply fuses are located on the PCB. The entire stereo board including four fuses is 115mm x 40mm (i.e. really small). The Revision-B board is exactly the same size, and uses the same spacing between ICs to allow retro-fitting if necessary.
Photo of Completed Amplifier (With Heatsink)
To reiterate a point I have made elsewhere, never operate this amp without a heatsink - even for testing (this applies to nearly all amplifiers). It will overheat very quickly, and although the internal protection will shut the amp down to protect it from damage, this is not something you want to test for no good reason.
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How Does It Sound?
The sound quality is very good - as I said at the beginning, I would call it audiophile hi-fi - with caveats. Provided the amp is never allowed to go anywhere near the protection limits it sounds very good indeed. This is the rub - because of the comprehensive overload protection (which I have never liked in any form) this amp provides more and nastier artefacts as it clips than a "normal" amplifier. With the recommended ±35V supplies and a nominal 8 ohm load, you will need a good heatsink to ensure that device temperature is kept below 70°C. This will usually ensure that the protection circuits don't operate even if the amp clips on transients. For 4 ohm loads, I suggest that the supply voltage be reduced to a maximum of about ±30V.
The protection circuitry is called SPiKe™ by National - this stands for Self Peak instantaneous Temperature (°Ke) (sic) and will protect the amp from almost anything. Although in theory this is a good thing, it's not so good when the protection circuits operate, so make absolutely sure that the amp is only used in applications where clipping will never occur, or is relatively lightly loaded.
This might sound like a tall order, but for rear speakers in a surround system, or to put some serious grunt into those 400W PMPO PC speakers (with the 5W RMS amplifiers - I'm not kidding), this amp is a gem.
It could also be used as a midrange and/or tweeter amp in a tri-amped system - there are a lot of possibilities, so I will leave it to you to come up with more.
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