Do-it-yourself diode transistor. Do-it-yourself solar battery from transistors: step-by-step instructions, assembly video. Diffusion and electrolysis

You only need two components to assemble a simple inverter that converts 12V DC to 220V AC.

Absolutely no expensive or scarce items or parts. Everything can be assembled in 5 minutes! You don't even need to solder! Twisted with wire and everything.

What do you need for an inverter?

• Transformer from receiver, tape recorder, center, etc. One winding is network for 220 V, the other for 12 V.
• Relays for 12 V. These are used in many places.
• Wires for connection.

Assembly of the inverter

It all boils down to connecting the relay and transformer as follows. First of all, we put a load on the network winding of the transformer in the form of an LED light bulb - this will be the output of the inverter.
Then we connect the low-voltage winding in parallel with the relay. Now one contact is powered by the battery, and the second is connected to another battery contact, but only through a closed relay contact. Plus or minus doesn't matter.

Everything! Your inverter is ready! Super easy!
We connect it to the battery - we have it as a 12 V source and the 220 V lamp starts to glow. At the same time, you hear the squeak of the relay.

How does this inverter work?

It's very simple: when you turn on the power, all the voltage goes through the closed contacts on the relay. The relay is energized and the contacts open. As a result, the relay is de-energized and it drives the contacts back to closed. As a result, the cycle is repeated. And since a step-up transformer is connected in parallel with the relay, powerful pulses of constant on-off are supplied to it and converted into alternating high-voltage current. The frequency of such a converter ranges from 60-70 Hz.
Of course, such an inverter is not durable - sooner or later the relay will fail, but it's not a pity - it costs a penny or even free, if you take the old one. And the output voltage by the nature of the current and the spread is simply terrible. But this simple converter can help you out in some serious situation.

After we began to study bipolar transistors, a lot of messages about them began to come to personal messages. The most common questions are something like this:

If a transistor consists of two diodes, then why not just use two diodes and make a simple transistor out of them?

Why does electric current flow from the collector to the emitter (or vice versa) if the transistor consists of two diodes that are connected either by cathodes or anodes? After all, current will flow only through a diode connected in the forward direction, after all, it cannot flow through another one, can it?

But the truth is yours ... Everything is logical ... But something seems to me that somewhere there is a catch ;-). And here is where this “highlight” we will consider in this article ...

The structure of the transistor

So, as you all remember from previous articles, any bipolar transistor, let's say, consists of two diodes. For

the equivalent circuit looks like this:

And for NPN transistor

something like that:

And what to be wise? Let's do a simple experiment!

We all have our favorite Soviet transistor KT815B. It is an NPN silicon conductance transistor:

Assembling a simple schematic OE (O general E mitter) to demonstrate some of its properties. I have shown this experience in previous articles. But as they say, repetition is the mother of learning.

To demonstrate the experience, we need a low-power incandescent light bulb and a couple of power supplies. Putting it all together like this:

where are we Bat1- this is a power supply that we turn on between the base and the emitter, and Bat2- the power supply, which we turn on between the collector and the emitter, and in addition, another light bulb clings in series.

It all looks like this:

Since the light bulb normally shines at a voltage of 5 V, I also set 5 V on the Bat 2.

On Bat 1, we gradually increase the voltage ... and at a voltage of 0.6 V

we have a light bulb. Therefore, our transistor "opened"

But since a transistor is made up of diodes, why don't we take two diodes and "make" a transistor out of them? No sooner said than done. We assemble the equivalent circuit of the KT815B transistor from two diodes of the 1N4007 brand.

In the figure below, I have labeled the leads of the diodes as anode and cathode, and have also labeled the leads of the “transistor”.

Putting it all together in the same way:

Since our KT815B transistor was silicon, and the 1N4007 diodes were also silicon, in theory, the diode transistor should open at a voltage of 0.6-0.7 V. Add the voltage to Bat1 to 0.7 V ...

and…

no, the light is not on

If you pay attention to the Bat1 power supply, you can see that the consumption at 0.7 V was already 0.14 A.

Simply put, if we had energized a little more, we would have burned the base-emitter diode, if, of course, we recall the current-voltage characteristic (CVC) of the diode.

But why, what's the matter? Why does the KT815B transistor, which essentially consists of the same silicon diodes, pass an electric current through the collector-emitter, and two diodes soldered also do not work as a transistor? Where is the dog buried?

Do you know how these “diodes” are located in the transistor? If we take into account that the N semiconductor is bread, and the thin layer of ham is the P semiconductor, then in the transistor they are located something like this (we don’t look at the salad):

The point is that the base in the transistor is very thin in width, like this ham, and the collector and emitter are as wide as these halves of bread (I'm exaggerating a little, of course, they are a little smaller), therefore, the transistor behaves like a transistor :-), that is, it opens and passes current through the collector-emitter.

Due to the fact that the base is very thin in width, it means that two P-N junctions are at a very small distance from each other and interaction occurs between them. This interaction is called transistor effect. And what can be the transistor effect between diodes, in which the distance between two P-N junctions is like to the moon?

Alternative energy sources are gaining popularity every year. Constant increases in electricity tariffs contribute to this trend. One of the reasons why people look for non-traditional power sources is the complete lack of connectivity to public networks.

The most popular alternative power sources on the market are. These sources use the effect of generating electric current when exposed to solar energy on semiconductor structures made of pure silicon.

The first solar photoplates were too expensive, their use for generating electricity was not profitable. Technologies for the production of silicon solar cells are constantly being improved and can now be purchased at an affordable price.

Light energy is free, and if mini-silicon power plants are cheap enough, then such alternative power sources will become cost-effective and very widespread.

Suitable materials at hand

Scheme of a solar battery on diodes Many hotheads ask themselves the question: is it possible from improvised materials. Of course you can! Many from the times of the USSR have preserved a large number of old transistors. This is the most suitable material for creating a mini power plant with your own hands.

It is also possible to make a solar cell from silicon diodes. Another material for the manufacture of solar panels is copper foil. When using foil, a photoelectrochemical reaction is used to obtain a potential difference.

Stages of manufacturing a transistor model

Selection of parts

The most suitable for the manufacture of solar cells are powerful silicon transistors with the letter marking KT or P. Inside they have a large semiconductor wafer that can generate an electric current under the influence of sunlight.

Expert advice: choose transistors of the same name, as they have the same technical characteristics and your solar battery will be more stable in operation.

Transistors must be in working order, otherwise they will not be of any use. The photo shows a sample of such a semiconductor device, but you can take a transistor of a different shape, most importantly, it must be silicon.

The next step is the mechanical preparation of your transistors. It is necessary, mechanically, to remove the upper part of the housing. The easiest way to do this operation is with a small hacksaw.

Training

Clamp the transistor in a vise and carefully make a cut along the contour of the case. You see a silicon wafer that will act as a photocell. Transistors have three terminals - base, collector and emitter.

Depending on the structure of the transistor (p-n-p or n-p-n), the polarity of our battery will be determined. For the KT819 transistor, the base will be a plus, the emitter and collector will be a minus.

The greatest potential difference, when light is applied to the plate, is created between the base and the collector. Therefore, in our solar battery we will use the collector junction of the transistor.

Examination

After sawing off the case of transistors, they must be checked for operability. To do this, we need a digital multimeter and a light source.

We connect the base of the transistor to the positive wire of the multimeter, and the collector to the negative one. We turn on the measuring device in the voltage control mode with a range of 1V.

We direct the light source to the silicon wafer and control the voltage level. It should be between 0.3V and 0.7V. In most cases, one transistor creates a potential difference of 0.35V and a current of 0.25 µA.

To recharge a cell phone, we need to create a solar panel of about 1000 transistors, which will produce a current of 200 mA.

Assembly

It is possible to assemble a solar battery from transistors on any flat plate made of a material that does not conduct electricity. It all depends on your imagination.

When transistors are connected in parallel, the current increases, and when connected in series, the source voltage increases.

In addition to transistors, diodes and copper foil, aluminum cans, such as beer cans, can be used to make solar panels, but these will be batteries that heat water, and not generate electricity.

Watch the video in which the specialist explains in detail how to make a solar battery from transistors with your own hands:

We learned how a transistor works, in general terms, we examined manufacturing technologies germanium and silicon transistors and figured out how they are marked.

Today we will conduct several experiments and make sure that the bipolar transistor really consists of two diodes connected back to back, and that the transistor is signal amplifier.

We need a low-power p-n-p germanium transistor from the MP39 - MP42 series, an incandescent lamp rated for a voltage of 2.5 Volts and a 4 - 5 Volt power source. In general, for beginner radio amateurs, I recommend assembling a small adjustable one with which you will power your designs.

1. The transistor consists of two diodes.

To verify this, let's assemble a small circuit: the base of the transistor VT1 connect to the minus of the power source, and the output of the collector with one of the outputs of the incandescent lamp EL... Now, if the second terminal of the lamp is connected to the plus of the power source, the lamp will light up.

The light bulb lit up because we applied to the collector junction of the transistor direct- forward voltage, which opened the collector junction and flowed through it direct current collector Ik... The magnitude of this current depends on the resistance filament lamps and internal resistance power source.

And now let's consider the same circuit, but we will depict the transistor in the form of a semiconductor plate.

Major charge carriers in the base electrons, overcoming the p-n junction, fall into the hole region collector and become irrelevant. Having become minor, the base electrons are absorbed by the majority carriers in the hole region of the collector holes... In the same way, holes from the collector region, falling into the electronic region of the base, become minor and are absorbed by the majority charge carriers in the base. electrons.

The base pin connected to the negative pole of the power supply will to act almost unlimited number electrons, replenishing the decay of electrons from the base region. And the collector contact, connected to the positive pole of the power source through the filament of the lamp, is capable of to accept the same number of electrons, due to which the concentration of holes in the region will be restored bases.

Thus, the conductivity of the p-n junction will become large and the current resistance will be small, which means that the collector current will flow through the collector junction Ik... And what more this current will be brighter the lamp will be on.

The light bulb will also burn if it is included in the emitter junction circuit. The figure below shows exactly this version of the circuit.

And now we will slightly change the circuit and the base of the transistor VT1 connect to plus power source. In this case, the lamp will not burn, since we included the p-n junction of the transistor in reverse direction. And this means that the resistance of the p-n junction has become great and through it flows only a very small reverse current collector Ikbo incapable of incandescent lamp filament EL... In most cases, this current does not exceed a few microamperes.

And in order to finally verify this, we again consider a circuit with a transistor depicted as a semiconductor plate.

Electrons located in the region bases, will move to plus power source, moving away from the p-n junction. holes in the area collector, will also move away from the p-n junction, moving to negative power supply pole. As a result, the boundary of the regions is, as it were, will expand, which results in the formation of a zone depleted of holes and electrons, which will provide great resistance to the current.

But, since in each of the areas of the base and collector there are minor charge carriers, then small exchange electrons and holes between the regions will still occur. Therefore, a current many times smaller than the direct current will flow through the collector junction, and this current will not be enough to light the filament of the lamp.

2. Transistor operation in switching mode.

Let's make another experiment showing one of the transistor operation modes.
Between the collector and emitter of the transistor, we turn on a power source connected in series and the same incandescent lamp. We connect the plus of the power source to the emitter, and the minus through the filament of the lamp to the collector. The lamp does not light. Why?

Everything is very simple: if you apply a supply voltage between the emitter and the collector, then for any polarity one of the transitions will be in the forward direction, and the other in the opposite direction and will interfere with the passage of current. This is not difficult to see if you look at the following figure.

The figure shows that the emitter base-emitter junction is included in direct direction and is open and ready to accept an unlimited number of electrons. The collector base-collector junction, on the contrary, is included in reverse direction and prevents the passage of electrons to the base.

Hence it follows that the majority charge carriers in the emitter region holes, repelled by the plus of the power source, rush to the base region and there they mutually absorb (recombine) with the main charge carriers in the base electrons... At the moment of saturation, when there are no free charge carriers left on either side, their movement will stop, which means that the current stops flowing. Why? Because from the side of the collector there will be no make-up electrons.

It turns out that the main charge carriers in the collector holes attracted by the negative pole of the power source, and some of them are mutually absorbed electrons coming from the minus side of the power supply. And at the moment of saturation, when there is no left on both sides free charge carriers, holes, due to their predominance in the collector region, will block the further passage of electrons to the base.

Thus, a zone depleted of holes and electrons is formed between the collector and the base, which will provide great resistance to the current.

Of course, due to the magnetic field and thermal effects, a meager current will still flow, but the strength of this current is so small that it is not capable of heating the filament of the lamp.

Now add to the diagram wire jumper and we will close the base with the emitter to it. The light bulb included in the collector circuit of the transistor will again not light up. Why?

Because when the base and emitter are closed with a jumper, the collector junction becomes just a diode, to which the opposite voltage. The transistor is in the closed state and only a small reverse collector current flows through it. Ikbo.

And now we will change the circuit a little more and add a resistor Rb resistance 200 - 300 Ohm, and another voltage source GB in the form of a finger battery.
Connect the battery minus through a resistor Rb with a transistor base, and plus batteries with an emitter. The lamp is on.

The lamp lit up because we connected the battery between the base and the emitter, and thereby applied to the emitter junction direct release voltage. The emitter junction opened and went through it straight current, which opened collector junction of the transistor. The transistor opened and along the circuit emitter-base-collector drip collector current Ik, many times greater circuit current emitter base... And thanks to this current, the light bulb lit up.

If we change the polarity of the battery and apply a plus to the base, then the emitter junction will close, and the collector junction will close with it. The reverse collector current will flow through the transistor Ikbo and the lamp will turn off.

Resistor Rb limits the current in the base circuit. If the current is not limited and all 1.5 volts are applied to the base, then too much current will flow through the emitter junction, as a result of which thermal breakdown transition and the transistor will fail. As a rule, for germanium transistors, the trigger voltage is not more than 0,2 volt, and for silicon no more 0,7 volt.

And again we will analyze the same circuit, but we will present the transistor in the form of a semiconductor plate.

When a trigger voltage is applied to the base of the transistor, the emitter transition and free holes from the emitter begin to mutually absorb with electrons bases, creating a small forward base current Ib.

But not all holes introduced from the emitter into the base recombine with its electrons. Typically, the base area is done thin, and in the manufacture of transistors of the p-n-p structure, the concentration of holes in emitter and collector make many times greater than the concentration of electrons in base, therefore, only a small part of the holes is absorbed by the base electrons.

The bulk of the emitter holes passes through the base and falls under the action of a higher negative voltage acting in the collector, and already together with the holes of the collector moves to its negative contact, where it is mutually absorbed by the input electrons by the negative pole of the power source GB.

As a result, the resistance of the collector circuit emitter-base-collector decreases and direct collector current flows in it Ik many times the base current Ib chains emitter base.

How more more holes is introduced from the emitter into the base, the more significant current in the collector circuit. And vice versa than less unlocking voltage on the base, the less current in the collector circuit.

If, at the time of transistor operation, a milliammeter is included in the base and collector circuits, then with the transistor closed, there would be practically no currents in these circuits.

With the transistor open, the base current Ib would be 2-3 mA, and the collector current Ik would be around 60 - 80 mA. All this suggests that the transistor can be current amplifier.

In these experiments, the transistor was in one of two states: open or closed. Switching the transistor from one state to another occurred under the action of the trigger voltage on the base Ub... This type of transistor is called switching mode or key... This mode of operation of the transistor is used in instruments and automation devices.

We will finish this, and in the next part we will analyze the operation of a transistor using the example of a simple audio frequency amplifier assembled on a single transistor.
Good luck!

Literature:

1. Borisov V.G. - Young radio amateur. 1985
2. E. Iceberg - Transistor? .. It's very simple! 1964

The principle of semiconductor control of electric current was known as early as the beginning of the 20th century. Despite the fact that engineers working in the fields of radio electronics knew how the transistor worked, they continued to design devices based on vacuum tubes. The reason for such distrust of semiconductor triodes was the imperfection of the first point transistors. The family of germanium transistors did not differ in the stability of their characteristics and was highly dependent on temperature conditions.

Serious competition for vacuum tubes was made by monolithic silicon transistors only at the end of the 50s. Since that time, the electronic industry began to develop rapidly, and compact semiconductor triodes actively replaced energy-intensive lamps from the circuits of electronic devices. With the advent of integrated circuits, where the number of transistors can reach billions, semiconductor electronics has won a convincing victory in the struggle for miniaturization of devices.

What is a transistor?

In the modern sense, a transistor is called a semiconductor radio element designed to change the parameters of an electric current and control it. A conventional semiconductor triode has three outputs: a base to which control signals are applied, an emitter and a collector. There are also high power composite transistors.

The size scale of semiconductor devices is striking - from a few nanometers (unpackaged elements used in microcircuits) to centimeters in diameter of powerful transistors designed for power plants and industrial equipment. Reverse voltages of industrial triodes can reach up to 1000 V.

Device

Structurally, the triode consists of semiconductor layers enclosed in a housing. Semiconductors are materials based on silicon, germanium, gallium arsenide and other chemical elements. Today, research is being carried out that prepares some types of polymers, and even carbon nanotubes, for the role of semiconductor materials. Apparently in the near future we will learn about the new properties of graphene field-effect transistors.

Previously, semiconductor crystals were located in metal cases in the form of hats with three legs. This design was typical for point transistors.

Today, the designs of most flat, including silicon, semiconductor devices are made on the basis of a single crystal doped in certain parts. They are pressed into plastic, glass-metal or ceramic-metal housings. Some of them have protruding metal plates for heat dissipation, which are mounted on radiators.

The electrodes of modern transistors are arranged in one row. This arrangement of legs is convenient for automatic board assembly. The terminals are not marked on the housings. The type of electrode is determined by reference books or by measurements.

For transistors, semiconductor crystals with different structures are used, such as p-n-p or n-p-n. They differ in the polarity of the voltage on the electrodes.

Schematically, the structure of a transistor can be represented as two semiconductor diodes separated by an additional layer. (See figure 1). It is the presence of this layer that makes it possible to control the conductivity of the semiconductor triode.

Rice. 1. The structure of transistors

Figure 1 schematically shows the structure of bipolar triodes. There is another class of field-effect transistors, which will be discussed below.

Basic principle of operation

At rest, no current flows between the collector and emitter of a bipolar triode. The resistance of the emitter junction, which arises as a result of the interaction of the layers, prevents the electric current. To turn on the transistor, it is required to apply a slight voltage to its base.

Figure 2 shows a diagram explaining how a triode works.

Rice. 2. Working principle

By controlling the base currents, you can turn the device on and off. If an analog signal is applied to the base, it will change the amplitude of the output currents. In this case, the output signal will exactly repeat the oscillation frequency at the base electrode. In other words, there will be an amplification of the electrical signal received at the input.

Thus, semiconductor triodes can operate in the mode of electronic keys or in the mode of amplifying input signals.

The operation of the device in the electronic key mode can be understood from Figure 3.

Rice. 3. Triode in key mode

Designation on the diagrams

Common notation: "VT" or "Q" followed by a positional index. For example, VT 3. In earlier diagrams, obsolete designations can be found: “T”, “PP” or “PT”. The transistor is depicted as symbolic lines indicating the corresponding electrodes, circled or not. The direction of the current in the emitter is indicated by an arrow.

Figure 4 shows a ULF circuit, in which transistors are labeled in a new way, and Figure 5 shows schematic representations of different types of field-effect transistors.

Rice. 4. An example of a ULF circuit on triodes

Types of transistors

According to the principle of operation and structure, semiconductor triodes are distinguished:

• field;
• bipolar;
• combined.

These transistors perform the same functions, but there are differences in the principle of their operation.

Field

This type of triode is also called unipolar, because of the electrical properties - they have a current of only one polarity. According to the structure and type of control, these devices are divided into 3 types:

1. Transistors with a control p-n junction (Fig. 6).
2. With an insulated gate (there are with a built-in or with an induced channel).
3. MDP, with the structure: metal-dielectric-conductor.

A distinctive feature of an insulated gate is the presence of a dielectric between it and the channel.

Parts are very sensitive to static electricity.

Field triode circuits are shown in Figure 5.

Rice. 5. Field-effect transistors
Rice. 6. Photo of a real field triode

Pay attention to the name of the electrodes: drain, source and gate.

FETs consume very little power. They can last over a year on a small battery or accumulator. Therefore, they have found wide application in modern electronic devices such as remote controls, mobile gadgets, etc.

Bipolar

Much has been said about this type of transistor in the subsection “Basic principle of operation”. We only note that the device received the name "Bipolar" because of the ability to pass charges of opposite signs through one channel. Their feature is a low output impedance.

Transistors amplify signals and act as switching devices. A sufficiently powerful load can be included in the collector circuit. Due to the large collector current, the load resistance can be reduced.

We will consider in more detail about the structure and principle of operation below.

Combined

In order to achieve certain electrical parameters from the use of one discrete element, transistor developers invent combined designs. Among them are:

• with resistors embedded and their circuit;
• combinations of two triodes (identical or different structures) in one case;
• lambda diodes - a combination of two field triodes forming a section with negative resistance;
• constructions in which an insulated gate field triode controls a bipolar triode (used to control electric motors).

Combined transistors are, in fact, an elementary microcircuit in one package.

How does a bipolar transistor work? Instructions for dummies

The operation of bipolar transistors is based on the properties of semiconductors and their combinations. To understand the principle of operation of triodes, we will deal with the behavior of semiconductors in electrical circuits.

Semiconductors.

Some crystals, such as silicon, germanium, etc., are dielectrics. But they have one feature - if you add certain impurities, they become conductors with special properties.

Some additives (donors) lead to the appearance of free electrons, while others (acceptors) form “holes”.

If, for example, silicon is doped with phosphorus (donor), then we get a semiconductor with an excess of electrons (n-Si structure). When boron (acceptor) is added, doped silicon will become a hole-conducting semiconductor (p-Si), that is, positively charged ions will predominate in its structure.

Unidirectional conduction.

Let's conduct a thought experiment: let's connect two heterogeneous semiconductors to a power source and bring current to our design. Something unexpected will happen. If you connect the negative wire to an n-type crystal, the circuit will close. However, when we reverse the polarity, there will be no electricity in the circuit. Why is this happening?

As a result of the connection of crystals with different types of conductivity, a region with a p-n junction is formed between them. Part of the electrons (charge carriers) from the n-type crystal will flow into a crystal with hole conductivity and recombine holes in the contact zone.

As a result, uncompensated charges arise: in the n-type region - from negative ions, and in the p-type region from positive ones. The potential difference reaches a value of 0.3 to 0.6 V.

The relationship between voltage and impurity concentration can be expressed by the formula:

φ= V T*ln( N n* Np)/n 2 i , where

V T – thermodynamic stress value, N n and Np – the concentration of electrons and holes, respectively, and n i denotes the intrinsic concentration.

When connecting a plus to a p-conductor, and a minus to an n-type semiconductor, electric charges will overcome the barrier, since their movement will be directed against the electric field inside the p-n junction. In this case, the transition is open. But if the poles are reversed, the transition will be closed. Hence the conclusion: the p-n junction forms one-way conduction. This property is used in the design of diodes.

From diode to transistor.

Let's complicate the experiment. Let's add one more layer between two semiconductors with the same structures. For example, between p-type silicon wafers, we insert a conductive layer (n-Si). It is not difficult to guess what will happen in the contact zones. By analogy with the process described above, regions with p-n junctions are formed that block the movement of electric charges between the emitter and collector, regardless of the polarity of the current.

The most interesting thing happens when we apply a slight voltage to the interlayer (base). In our case, we apply a current with a negative sign. As in the case of a diode, an emitter-base circuit is formed, through which current will flow. At the same time, the layer will begin to be saturated with holes, which will lead to hole conduction between the emitter and collector.

Look at Figure 7. It shows that positive ions have filled the entire space of our conditional design and now nothing interferes with the conduction of current. We have obtained a visual model of a p-n-p bipolar transistor.

Rice. 7. The principle of operation of the triode

When the base is de-energized, the transistor very quickly returns to its original state and the collector junction closes.

The device can also operate in amplifying mode.

The collector current is directly proportional to the base current. : ITo= ß* IB , where ß – current gain, IB – base current.

If you change the value of the control current, then the intensity of the formation of holes on the base will change, which will entail a proportional change in the amplitude of the output voltage, while maintaining the frequency of the signal. This principle is used to amplify signals.

By applying weak pulses to the base, at the output we get the same amplification frequency, but with a much larger amplitude (set by the voltage applied to the collector-emitter circuit).

NPN transistors work in a similar way. Only the polarity of the voltages changes. Devices with an n-p-n structure have direct conduction. P-n-p type transistors have reverse conductivity.

It remains to add that a semiconductor crystal reacts in a similar way to the ultraviolet spectrum of light. By turning the photon flux on and off, or by adjusting its intensity, one can control the operation of the triode or change the resistance of a semiconductor resistor.

Bipolar transistor switching circuits

Circuit engineers use the following connection schemes: with a common base, common emitter electrodes and switching on with a common collector (Fig. 8).

Rice. 8. Wiring diagrams for bipolar transistors

For amplifiers with a common base is typical:

• low input impedance, which does not exceed 100 ohms;
• good temperature properties and frequency characteristics of the triode;
• high allowable voltage;
• requires two different power supplies.

Common emitter circuits have:

• high current and voltage gains;
• low power gain;
• inversion of the output voltage relative to the input.

With this connection, one power supply is sufficient.

The connection scheme according to the "common collector" principle provides:

• high input and low output impedance;
• low voltage gain (< 1).

How does a field effect transistor work? Explanation for dummies

The structure of a field-effect transistor differs from a bipolar one in that the current in it does not cross the p-n junction zones. The charges move along an adjustable area called the gate. Gate bandwidth is regulated by voltage.

The space of the p-n zone decreases or increases under the action of an electric field (see Fig. 9). Accordingly, the number of free charge carriers changes - from complete destruction to ultimate saturation. As a result of such an impact on the gate, the current at the drain electrodes (contacts that output the processed current) is regulated. The incoming current flows through the source contacts.

Figure 9. FET with p-n junction

Field triodes with a built-in and induced channel work on a similar principle. You saw their schemes in Figure 5.

FET switching circuits

In practice, connection schemes are used by analogy with a bipolar triode:

• with a common source - gives a large amplification of current and power;
• common-gate circuits providing low input impedance and low gain (of limited use);
• common-drain circuits that work in the same way as common-emitter circuits.

Figure 10 shows various wiring diagrams.

Rice. 10. Image of field triode connection diagrams

Almost every circuit is capable of operating at very low input voltages.

Video explaining the principle of operation of the transistor in simple terms