How does sound amplify weak sounds

How does sound amplify weak sound ？1947 In, three American scientists invented such a device , When we put a tiny current into it , It can output a signal hundreds of times larger than the original signal , Do you know what this device is ？ It is the transistor that changes the world , These three scientists also obtained 1956 Nobel lecture in .

Look at all the electronic circuits , From the simplest amplifier to the complex CPU, But it contains the most basic device, the transistor , Transistor is a general term for semiconductor devices , It includes a diode 、 triode 、 FET, thyristor, etc , Why are these devices matched by crystals ？

Because either diode or triode is made of monocrystalline silicon or monocrystalline germanium semiconductor materials , Next, let's explain what a triode is , And its working principle and application , The triode we are talking about now is basically a semiconductor triode , It is called semiconductor triode , Because in 1906 year , Lideforrester has invented the first triode , It is a vacuum triode .

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The defect of this triode is its large size 、 High power consumption , It's also calorific , The world's first general-purpose computer eniac The vacuum triode is used , Its size is amazing , Covering an area of about 170 Square meters , The power consumption is as high as 150 kW , And now the semiconductor technology , Tens of billions of transistors can be integrated in one nail space , And the power consumption can be neglected compared with the vacuum tube .

Only those who have experienced the vacuum tube era will truly marvel at the greatness of semiconductors , Let's introduce the triode , The triode has roughly these three packaging forms , It is called a triode , Because the triode has three poles , They are the bases 、 Collector 、 The emitter , How to understand these three levels ？

Take a look at this picture ,B It can be regarded as a valve controlling the flow of water ,C The first stage is the water tank , It is also the entrance of water source ,E The first stage is the water outlet , When the valve is closed , The water in the tank is difficult to leak , When we start turning the valve , The flow of water slowly increases , This is the function of the three pins of the triode , Now let's talk about how the triode amplifies the current .

Before the explanation , We need to know the following parameters ,Ib To flow through B Level current ,IC Flow through C Level current ,IE To stay E Polar current , among IE be equal to IB and IC The sum of ,VBe yes BE Voltage between poles ,VCB yes CB Voltage between poles ,VCE yes CE The voltage between , Next, let's have a basic understanding of the triode around the three states .

When vbb When the voltage is zero , The triode is off , At this time, the valve is closed , Even if there is water in the tank, it will not flow down , This is the cut-off state , Then saturation , Let's first look at a function image , It expresses VCE and IC The relationship between , then B Pole up connection 5V,C Cascade connection 0V, At this time, the valve is opened , But there is no water in the tank , At this time, the triode is in a saturated state .

keep Vbb unchanged , We slowly increase VCc The voltage of , It's like there's water in the tank , Start to flow down , here VCe and IC With VCc To increase by , stay VCe Less than 0.7 Before v , That is to say VB Greater than VC Before the point of potential , The triodes are saturated , in the meantime IC Changed a lot ,VCe Almost unchanged , Stay in 0.7 Within volts .

If we continue to increase VCc, here VC The potential will be greater than VB The triode enters the amplified state , The graph of the function looks like this , During this period, the triode is in the amplification state , in the meantime VCe Change intensifies , and IC Pretty much the same , here IC It's about Ib100 To 200 times , This is the amplification characteristic of triode , If VCc Too much , The triode will break down instantly , Cause permanent damage .

As for how much voltage the triode can withstand ？ You can go to its data book , This is a 2N3904 The data book for , The first item is Vce The maximum withstand voltage is 40 v , And the maximum current it can pass through is 200 Ma , More than the value on this list , The triode may be completely damaged , One of the most annoying points is that the saturation amplification state is used for what occasions ？

Let's start with saturation , If you want to control the rotation of this fan , We hope that the triode is a switch ,12 V voltage should be clamped on the fan as much as possible , The voltage drop of the triode should be as small as possible , At this time, the saturated state of the triode is very suitable for this scenario , Because in a saturated state , its VcE A very small , Only a few tenths of a volt , It's like the switch is closed .

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When the triode is in the cut-off state , It's like the switch is off , The triode switch is used to cut off the saturation state , Working in the amplification state is to maximize the amplification of the triode IB Electric current , The saturation state is far less than the magnification of the amplification state .

What is the magnification factor ？ You also need to consult the data manual , In the enlarged state , Even if the supply voltage changes , Output IC And almost unchanged , A typical application is audio amplification , You can amplify the weak small signal of the earphone , To drive the speaker to make sound .

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