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[Electronic Experiment 2] simple electronic doorbell

2022-06-28 23:27:00 【Chenze】

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Catalog

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Electronic production

Introduction of triode

Circuit components

Physical circuit

Simulation diagram

Introduction to circuit principle

Last

Electronic production

Simple electronic doorbell

Introduction of triode

Because the triode is used in this electronic manufacture , So let's introduce the triode .
Semiconductor triode is called triode or transistor for short , Circuit is very commonly used to triode this component . Triode is a great invention ！ The inside of the triode contains two PN junction , There is... On the outside ③ The two pins are ↓
Collector C
The base B
The emitter E
As shown in the figure below

Tips ： The arrow direction is the conduction direction of the emitter , From base to emitter .
The emission region is doped with the most free electrons , That is, the doping solubility is the highest . The high doping solubility in the emission region is to ensure that enough free electrons enter the base region 、 In the collector area .
The doping solubility of the base region is very low , And very thin , Only and micrometers . Here, the base region is made very thin because the electrons in the emission region can easily enter the base region . The low solubility is to form a smaller base current , Only in this way can more free electrons flow to the base point region
A collector is a collection of carriers ( Approximate to none ), But the collector area is very large .
The most obvious function of triode is ： Amplify the current . In a word, why is ： The greater the current flowing through the base , The more free electrons flow through the base region , The corresponding free electrons flow through more collector regions . This is why the triode can control a large current with a small current , This sentence is easy to understand. Read it several times .
All the above can not be separated from the current amplification characteristics of triode , In fact, it means amplifying the signal . However, in the electronic circuit, the function of triode is many, not limited to amplifying the signal , It can also be used as a signal switch , control 、 Processing, etc .
NPN Type tube and PNP The relation of the U-tube is ：Ic = βIb and Ie = Ib+Ic, among β Is the discharge multiple of triode current . From the formula here we can see that , Collector current is base current β times . The current between the three poles ,Ie Maximum 、Ic secondly 、Ib Minimum .Ie and Ic It's all the same , But both are better than the base Ib The current is much higher . The amplification function in the triode is to convert the input current of the base Ib The change law of is transformed into Ic、Ie, therefore , The triode will have the effect of amplifying the current .

Circuit components

name	Number	Parameter evaluation
resistance	R1	10kΩ
Ceramic capacitor	C1	104 = 0.1uf
triode	NPN Q1	9013
triode	PNP Q2	9012
The speaker	BP	8Ω
switch	S1	.
The battery	BT 3V	Two No. 5 batteries
Universal board or hole board	.	.

Physical circuit

Simulation diagram

Introduction to circuit principle

This is a very simple electronic doorbell circuit , When we press the button S1 When , The speaker at this time BP It will emit a loud sound similar to Dudu ~~~~~~~~~~~ The sound of a bell .
When the switch S1 When closed , Current passing Q2 Emitter of → The base →R1→Q1 The base of → The emitter → Negative pole of power supply . In this way Q2 Start to turn on ,Q2 The current output from the collector makes Q1 Rapid saturation conduction . Be careful ： Flow through Q2 The base current is a very small current ,Q2 After conduction , The emitter - The collector current is a slightly larger current , That's what it is. Q1 The key to conduction ！
Q1 After conduction , There is current flowing through the loudspeaker , Make it sound , At the same time capacitance C1 Start charging , The charging current circuit is ：Q2 The emitter → The base →C1→Q1 Collector → The emitter → Negative pole of power supply . because Q1 Saturated conduction , therefore Q1 The collector and emitter are approximately short circuited , capacitance C1 The charging process is very short . At this time, the capacitance C1 The charging voltage is left positive and right negative .
capacitance C1 Left positive and right negative voltage makes Q2 The emission junction is inversely biased ,Q2 Turn off . At this time, the voltage of the power supply is added to the capacitor through the loudspeaker C1 The voltages at both ends are applied together R1 and Q1 The base of , This voltage starts with the supply voltage 2 times , because R1 High resistance , The voltage at both ends of the capacitor decreases continuously due to discharge , send Q1 From initial saturation to amplification , As the voltage of the capacitor decreases , Its base current is also decreasing , Finally make Q1 end .
After capacitor discharge ,C1 The left terminal voltage returns to the initial value . send Q2 It starts to turn on again , It goes to the next process , The circuit works in this way .
The whole oscillation process of the complementary self-excited multivibrator is just like this , The oscillation frequency depends on the resistance R1,C1 The numerical ;R1 And C1 The greater the product of , capacitance C1 The longer the discharge time , The lower the oscillation frequency , On the contrary, the oscillation frequency will become higher .