Important components in transistors, the difference between NPN and PNP

Many people know about PLC, but do you know the difference and application of NPN and PNP? In the field of industrial control, the choice of foreign PLC types is generally limited. Japanese PLC and German PLC are chosen with two different control interfaces. For The concepts of these two interfaces are often vague. Here we will elaborate on the differences between the two.

The interface of Japanese PLC is generally NPN type (sink output), that is, open collector output mode. Since the Japanese are more cautious and have better disclaimers, they generally like to control the ground GND. The power supply is provided by you, and it is burned. The stuff is yours. The interface of German PLC is generally PNP type (source output), that is, the power control mode. Since Germans prefer to have the initiative in their own hands, you can only act after I give you power. It is safer not to give you power. , if you want to burn something, how can you burn it without power?

What are the differences between NPN and PNP?

1. NPN and PNP are mainly different in current direction and voltage sign.

NPN: It is composed of two N-type semiconductors and one P-type semiconductor.

PNP: It is composed of two P-type semiconductors and one N-type semiconductor.

2. Current direction

NPN uses the current (IB) of B→E to control the current (IC) of C→E. The E electrode has the lowest potential, and usually the C electrode has the highest potential during normal amplification, that is, VC > VB > VEPNP uses the current of E→B ( IB) controls the current (IC) of E→C. The E electrode has the highest potential, and the C electrode usually has the lowest potential during normal amplification, that is, VC < VB < VE.

3. Voltage difference

The NPN base has high voltage, and the collector and emitter are short-circuited. Low voltage, open collector and emitter. Also not working. PNP base is high voltage. If the collector and emitter are open circuit, it will not work either. If the base is applied to a low potential, the collector and emitter are short-circuited.

working principle:

There are two types of transistors based on materials: germanium tubes and silicon tubes. Each type has two structural forms: NPN and PNP, but the most commonly used are silicon NPN and PNP transistors. Except for the different power polarity, their working principles are the same. Only NPN silicon transistors are introduced below. The principle of current amplification.

For an NPN tube, it is composed of two N-type semiconductors sandwiching a P-type semiconductor. The PN junction formed between the emitter region and the base region is called the emitter junction, and the PN junction formed between the collector region and the base region is called It is the collector junction, and the three leads are called emitter e, base b and collector c. When the potential of point b is a few tenths of a volt higher than the potential of point e, the emitter junction is in a forward biased state. When the potential of point C is a few volts higher than the potential of point b, the collector junction is in a reverse biased state, and the collector power supply Ec is higher than the base voltage. Extreme Power Ebo.

When manufacturing a transistor, we consciously make the majority carrier concentration in the emitter region greater than that in the base region. At the same time, the base region is made very thin, and the impurity content must be strictly controlled. In this way, once the power is turned on, due to the forward bias of the emitter junction , the majority carriers (electrons) in the emitter region and the majority carriers (holes) in the base region easily diffuse toward each other across the emitter junction.

However, because the concentration base of the former is greater than that of the latter, the current passing through the emitter junction is basically an electron flow. This electron flow is called the emitter current Ie.

Since the base region is very thin and the collector junction is reverse biased, most of the electrons injected into the base region cross the collector junction and enter the collector region to form the collector current Ic, leaving only a small amount (1-10%). The electrons recombine in the holes in the base area, and the recombinated holes in the base area are resupplied by the base power supply Eb, thus forming the base current Ibo. According to the principle of current continuity: Ie=Ib+Ic

This means that by adding a small Ib to the base, a larger Ic can be obtained on the collector. This is the so-called current amplification effect. Ic and Ib maintain a certain proportional relationship, that is: β1=Ic/Ib

In the formula: β1--called the DC amplification factor,

The ratio of the change in collector current △Ic to the change in base current △Ib is: β= △Ic/△Ib

In the formula, β is called the AC current amplification factor. Since the values ​​of β1 and β are not much different at low frequencies, sometimes for the sake of convenience, strict distinction between the two is not made. The value of β is about tens to more than one hundred.

In the same way, PNP transistors mainly form hole currents, and the other principles are basically similar. The triode is a current amplification device, but in actual use, the current amplification effect of the triode is often used, and converted into voltage amplification through a resistor. The above is the difference and application of NPN and PNP. I hope it can help you.