Every year more and more electronic devices appear, and they often break. A lot of money is spent on repairs, sometimes reaching up to 50 percent of the cost of the device. And what is annoying, some of these breakdowns could be eliminated by yourself, with the initial knowledge of how the transistor works. Why he? It is the transistors that most often fail.
Content
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Types of transistor
- Bipolar
- Field
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Operating principle
- Field work
- How bipolar works
- Precautionary measures
Types of transistor
To more easily understand the operation of a transistor, you need to have an idea of it. It is a semiconductor, which indicates its ability to conduct current in one direction and not in the other. Various manufacturing methods are used to achieve these characteristics. All these devices by their nature of work are divided into two groups:
- bipolar
- polar
Although both of them belong to the same class - transistors, the processes occurring in them are very different.
Bipolar
The movement of electrons in a closed circuit is called an electric current. Roughly speaking, the more electrons, the greater the current. If an atom donates electrons, it becomes positively charged and, conversely, attracting excess electrons, it becomes negatively charged.
When impurities are added to silicon and germanium, they become a necessary material from which bipolar transistors are made.
Bipolar electronic devices are called, consisting of two, having different charges of the layers. Moreover, the two outermost ones have the same charge. The layer that has a positive charge is called "p" and the negative one is called "n". In this regard, the following types are distinguished:
- p-n-p
- n-p-n
The boundary between these layers is called a transition.. The inner area, separated by two transitions, is called the base. The two outer regions are called the emitter and the collector. The single crystal is made in such a way that one outer region transfers energy carriers to the base and is called an emitter. Another outer area picks up these media and is called a collector.
In the electrical diagram, a bipolar transistor is indicated in the form of a circle, inside which a dash is drawn, and three straight lines fit to it. One fits at a 90 degree angle and marks the base, the other two are tilted. The one with an arrow indicates the emitter, the other - the collector. The device itself usually has three leads corresponding to these areas.
Field
Another type is called field or unipolar. Unlike a bipolar pn junction, it works differently. Its single crystal has a homogeneous composition. The channel through which energy carriers move can be hole or electronic. In the hole carrier are positively charged stationary ions, in the electron carrier - negatively charged. These channels are also designated by the letters "p" and "n" respectively.
Around and almost along the entire length of this channel, ions of opposite polarity are injected, implanted. This area is called the gate, and it is it that regulates the conductance of the channel. The edge of the channel through which charged particles enter the crystal is called the source, and through which they leave, the drain.
To improve the electrical characteristics, a dielectric was added between the metal channel and the gate. If we classify transistors by structure, then two families can be distinguished:
- МДП (these include MOS - metal-oxide-conductor)
- JGBT
МДП stands for metal-dielectric-conductor. It's outfield. The new JGBT transistor combines the advantages of a bipolar, but has an insulated gate.
Operating principle
One of the complex radioelements is a transistor. The principle of its operation is as follows:
- adjustment
- gain
- generation
Bipolar ones are more powerful and can operate at higher frequencies. However, if you need a wide range of amplification, then you cannot do without a field one.
Field work
Let's take a look at how a transistor works. It is difficult for novice radio amateurs to make sense of all these transitions. To show the principle of operation of a transistor in simple terms, let's pay attention to the following example.
A valve-type water tap is capable of very smoothly changing the water pressure. This is achieved by gradually changing the orifice. The operation of a field-effect transistor is based on the same principle.
The shutter surrounds the passageway. When a blocking voltage is applied to it, the electric field, as it were, squeezes the passage, thereby reducing the flow of charged particles. As well as when closing the valve, it is necessary to apply a small force, and the power of the shutter, in comparison with the main channel, is very small. The similarity is also in the fact that with small changes in the gate voltage, the cross-section of the passage also changes insignificantly.
How bipolar works
The operation of a bipolar device is somewhat different from that of a field. First of all, the method of controlling the movement of charged particles differs. In the field, an electric field is used, in a bipolar one, the current between the base and the emitter.
Depending on the type of device, the emitter arrow on the diagram will either be directed to the base, then it is p-n-p type, or from the base, then it is n-p-n. When a voltage of the same name is connected to these terminals (“p” is connected to “+”, and “n” is connected to “-”), a current arises in the emitter-base circuit. More charge carriers appear in the base, and the more charge carriers there are, the greater the current in this circuit.
Reverse voltage is applied to the collector, i.e. “-” is connected to “p”, and “+” is connected to “n”. Since a potential difference arises between the emitter and the collector, a current appears between these terminals. It will be the more, the more charge carriers there are in the base.
When a power supply of the opposite sign is connected to the emitter and base, the current stops, the transistor turns off. What will help you better understand the operation of the transistor? It is important for dummies to understand one truth. If the emitter-base junction is open (direct voltage is applied), then the device itself is open, otherwise it is closed.
Precautionary measures
Field effect transistors are very sensitive to overvoltage. When working with them, it is necessary to prevent the possibility of hitting them with static voltage. This can be achieved by wearing a grounded wrist strap. When selecting an analog, it is important to take into account not only the operating voltage, but also the permissible current. And if the device operates in frequency mode, then its frequency.
