The important component in the triode, the difference between NPN and PNP

Many people know PLC, so do you know the difference and application of NPN and PNP? In the field of industrial control, it is generally limited by the choice of foreign PLC types. I chose Japanese PLC and German PLC and chose two different control interfaces. The concepts of these two interfaces are very vague in many cases, and the differences between the two will be elaborated here.

The interface of Japanese PLC is generally NPN type (drain output), that is, the open-collector output mode. Because the Japanese are more cautious and the disclaimer is better, it generally likes to control the ground GND. The power supply is given by you and burned. Things count for you. The interface of German PLC is generally PNP type (source output), that is, the way to control Power. Because Germans prefer to hold the initiative in their own hands, you can only act if I give you Power. It is safer if you don’t give you Power. , How do you want to burn something without Power?

What is the difference between NPN and PNP?

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

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 of B→E (IB) to control the current (IC) of C→E. The E pole has the lowest potential, and normally the C pole has the highest potential during normal amplification, that is, VC> VB> VEPNP is the E→B current ( IB) Control the current (IC) of E→C, the E pole has the highest potential, and usually the C pole has the lowest potential during normal amplification, that is, VC

3. Voltage difference

The NPN base has a very high voltage, and the collector and emitter are short-circuited. Low voltage, open collector and emitter. It also doesn’t work. PNP base is extremely high voltage. If the collector and emitter are open, it does not work. If the base is applied with a low potential, the collector and emitter are short-circuited.

working principle:

There are two types of transistors according to their materials: germanium tubes and silicon tubes. Each of them has two structural forms, NPN and PNP, but the most used are silicon NPN and PNP transistors. Except for the power polarity, the two transistors have the same working principle. Only NPN silicon transistors are introduced below. The principle of current amplification.

For the NPN tube, it is composed of two N-type semiconductors sandwiched between 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 by the collector region and the base region is called For the collector junction, the three leads are called emitter e, base b and collector c respectively. When the potential at point b is higher than the potential at point e by a few volts, the emitter junction is in a forward biased state, and when the potential at point C is a few volts higher than the potential at point b, the collector junction is in a reverse biased state, and the collector power source Ec is higher than the base. Polar power Ebo.

When manufacturing the triode, the majority carrier concentration in the emitter region is deliberately made larger 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, the emitter junction is positively biased. , The majority carriers (electrons) in the emitter region and the majority carriers (holes) in the base region can easily diffuse to 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 a flow of electrons, which is called the emitter current Ie.

Because the base region is very thin, coupled with the reverse bias of the collector junction, most of the electrons injected into the base region cross the collector junction into the collector region to form a collector current Ic, and only a few (1-10%) remain The electrons recombine in the holes in the base area, and the recombined holes in the base area are recharged 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, namely: 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. Because the values ​​of β1 and β are not much different at low frequencies, sometimes for convenience, the two are not strictly distinguished, and the β value 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 kind of current amplifying device, but in actual use, the current amplifying effect of the triode is often used, which is transformed into a voltage amplifying effect through resistance. The above is the difference and application of NPN and PNP, I hope to help you.

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