The device principle of operation and the difference N-P-N and P-N-P transistors

There are two basic types of transistors: bipolar and field. Bipolar transistors, in turn, are divided into the type with a P-N-P and N-P-N junction. In this article I will tell you about the structure of bipolar transistors, and we'll talk about the principle of operation and what their main difference. So there you go.

A little history

According to the official history records the date 16.12.1947 year can be considered the official birthday of one of the main elements of all modern electronics. It was presented to the public on this day, the first transistor, which was assembled by three scientists, namely: D. Bardeen, W. Shockley and W. Brattain.

The emergence of a bipolar transistor is allowed to abandon the use of vacuum tubes. All modern electronics would be impossible without this product. That's such an important discovery was made in the mid-20th century. Now, from the history of our move to a bipolar transistor.

How does the bipolar transistor

Thus, the bipolar transistor can be schematically represented as follows:

Look closely at the picture, you do not it remind you of anything? Yes, you are right, if you look closely and mentally divide the N zone - transition, then we have two interconnected diodes (remember this moment, in the future we'll need).

To determine a conductivity before contact diode, it is enough to read the direction of P-N junction. The illustration above we conductivity type P-N-P. This means that we face a transistor forward conduction (since it is assumed that the current flows from plus to minus).

But in the transistor N-P-N type conductivity reciprocal

Have you noticed that in both embodiments, there are three conclusions entitled:

Emitter (source generator), Base (base) and collector (collector, storage).

Schematic symbols transistors

From all the above written, you probably already knew that there are transistors, negative and positive sequence, which means that the schemes such elements should have differences. Let's look at them.

Thus, the designation of the transistor forward conduction on the schemes will be the following:

But the reverse conduction transistor has designated as follows:

In the old Soviet manuals transistors are marked with the letter "T", and now the designation was changed to "VT".

As a scheme to determine N-P-Nor P-N-P transistor before you

In fact determined by the type of bipolar transistor circuit is quite simple, just remember the following rule:

As it is known in the N - semiconductor, a large quantity of free electrons, and a P-type semiconductor is located a "hole" - positively charged particles. A generally accepted theory of current flows from the "plus" to "negative".

If you look at the chart, you will see that the emitter is shown with an arrow that is directed either to the base or from it. So if the transistor N-P-N type, i.e. formed of P- base semiconductor, the current flows from the base (arrow emitter-base). If the base is made of N - semiconductor, the current (arrow) flows into the base.

How does the P-N-P transistor

With the designation and the device like everything is clear, and here is how it works, let's understand:

Let us imagine a bipolar transistor as a water pipe valve with a spring mechanism.

As seen from the figure from top to smooth the flow of water through the tube prevents the valve spring mechanism, if we put a little effort (open valve compressing the spring), the water freely It will flow through the tube. If we let go of the spring, it will straighten and return the latch into place, thereby blocking the pipe and the water flow is stopped.

Now imagine that this pipe - a transistor P-N-P type, so its findings can be summarized as follows:

It turns out that the current flows from the emitter to the collector (recall that the direction of current flow coincides with the direction of the arrow on the emitter) to do so that the current out of the base, or to put it simple: apply for minus the base.

Let's visually check the operation of the transistor. For this we take KT814B and collect a simple circuit with two power supplies.

In order to properly connect the transistor need to know what conclusion is the emitter, base and collector. To do this, we find technical documentation and determine:

A light bulb, I'll use the most ordinary car, designed for 12 volts. The assembled circuit will look like this:

So, to expose our scheme to work on the power supply of 12 volts №2. And on the first power supply start very smoothly (from scratch) to raise the voltage exactly to the moment until our lamp lights.

Scheme earned at a voltage of 0.66 volts at the first source.

That is, there was the "discovery" of the transistor and through the emitter-collector circuit began to pass current.

In other words, the voltage, which opened our transistor - it is nothing but a voltage drop across the P-N the base-emitter voltage, which is precisely located within the range of 0.5 to 0.7 V for silicon transistors.

And how are things with transistors, which use N-P-N junction.

The operating principle of N-P-N transistor

If you look closely at the technical documentation to the transistor KT814B, you can find a record that complementary to the transistor pair is KT815B, and it differs only in that it uses N-P-N transition.

And the wiring diagram looks like this:

Look carefully at this circuit and switching circuit KT814B, you do not notice anything? That's right, the only difference between the two transistors lies in the fact that the transistor with P-N-P transfer called "minus" (since the base is applied the negative potential), but the transistor N-P-N opened "Plus".

conclusion

In this we are introduced to the material of the BJT, their construction and principle of operation, and so they are indicated in the diagrams. If the article is to provide you with interesting and useful, you will appreciate it Like. Thank you for your attention!