{"id":4724,"date":"2020-10-25T05:18:50","date_gmt":"2020-10-25T03:18:50","guid":{"rendered":"https:\/\/dcaclab.com\/blog\/?p=4724"},"modified":"2020-12-27T15:04:25","modified_gmt":"2020-12-27T13:04:25","slug":"npn-transistor-working-and-application-explained","status":"publish","type":"post","link":"https:\/\/dcaclab.com\/blog\/npn-transistor-working-and-application-explained\/","title":{"rendered":"NPN Transistor Working and Application Explained"},"content":{"rendered":"\r\n

NPN transistor is a three-terminal device having a p-type semiconductor sandwiched between the two n-type semiconductors. It is the most useful of the two bipolar junction devices. The other being the PNP transistor<\/a>. It has various applications and is used mostly for amplification and switching.<\/span><\/p>\r\n\r\n\r\n\r\n

Well, before moving into the concept of NPN transistors, let us have a little knowledge about the basics of transistors.\u00a0<\/span><\/p>\r\n\r\n\r\n\r\n

Transistors<\/span><\/h2>\r\n\r\n\r\n\r\n

Basically, a transistor is an electronic device helpful in amplification and electronic switching. It is a three-terminal device. When we apply a current or voltage at one pair of the terminals, the other terminal pair current controls it.\u00a0<\/span><\/p>\r\n\r\n\r\n\r\n

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Transistors<\/p><\/div>\r\n\r\n\r\n\r\n

As we are saying that it works as an amplifier, so I hope you can predict if the value at output would be higher or lower than the input.\u00a0<\/span><\/p>\r\n\r\n\r\n\r\n

So, what\u2019s the answer??<\/span><\/p>\r\n\r\n\r\n\r\n

Yes, it would be higher.<\/span><\/p>\r\n\r\n\r\n\r\n

The different types of transistors are classified based on structure, electrical polarity, maximum power rating, etc. Depending on the structure, it could be MOSFET, BJT, JFET, IGBT<\/a>, and others.<\/span><\/p>\r\n\r\n\r\n\r\n

But in this particular article, our focus is the bipolar junction transistor, i.e., BJT.\u00a0<\/span><\/p>\r\n\r\n\r\n\r\n

Bipolar Junction Transistor<\/span><\/h3>\r\n\r\n\r\n\r\n

BJT is a semiconductor device having three terminals namely, emitter, base, and collector. It is again divided into two parts, NPN and the PNP transistors. Both transistors have a sandwiched layer of one type between the other on both sides.\u00a0<\/span><\/p>\r\n\r\n\r\n\r\n

In NPN, the current direction is from base to emitter and in PNP it is just the opposite, i.e., from the emitter to the base.<\/span><\/p>\r\n

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Bipolar Junction Transistor<\/p><\/div>\r\n

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Among the two, NPN is the one that is used mostly in the applications. You may ask why?<\/span><\/p>\r\n

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So the answer is because the mobility of electrons is more than that of the holes.<\/span><\/p>\r\n

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NPN Transistor Construction and Symbol<\/span><\/h2>\r\n
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Symbol of NPN<\/p><\/div>\r\n

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Looking at the fig, we can say that an NPN transistor is a combination of two diodes<\/a> connected together back to back. On the basis of the terminal connection, the two diodes are emitter-base and collector-base diodes respectively. Also, the direction of current in the NPN transistor is from the emitter to the base region.\u00a0<\/span><\/p>\r\n

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Construction of NPN transistor<\/p><\/div>\r\n

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The three terminals emitter, base, and collector are all doped differently. The emitter is moderately doped with the least doping in the base region (lightly doped p-semiconductor). The collector region is heavily doped.<\/span><\/p>\r\n

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Here, the base region has the control for ON\/OFF of the transistor based on the input given to it. The emitter region is always connected to the negative supply and the collector with the positive one.<\/span><\/p>\r\n

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Working of NPN Transistor<\/span><\/h2>\r\n

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As shown in the fig, the base-emitter junction is made forward biased with a supply voltage as V<\/span>CC<\/span><\/sub>. Also, the collector-base junction is reverse biased and VEE<\/sub><\/span>\u00a0is the supply for this region.\u00a0<\/span><\/p>\r\n

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Now we must understand here how to make a junction forward or reverse biased?<\/span><\/p>\r\n

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As the n-type of semiconductor comes first when talking about the emitter-base region therefore, the negative of the voltage supply gets connected with it to make it in forward bias. Similarly, for the collector-base region, the positive supply of VCC<\/sub><\/span>\u00a0is connected to the n-type semiconductor and thus made reverse biased.<\/span><\/p>\r\n

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The depletion region of the emitter-base region is smaller as compared to the collector-base region. Please note that the depletion region behaves as the opposition to the flow of current, therefore, the thinner the layer the more the current flow in that region.<\/span><\/p>\r\n

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In an n-type semiconductor the majority charge carriers are the electrons and thus, start moving towards the base junction, thus the name emitter current, <\/span>IE<\/sub>.<\/p>\r\n

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The base region is very lightly doped and is a p-type semiconductor, therefore has a few holes as the charge carriers. The few electrons coming from the emitter get recombined with the holes but maximum electrons cross the base region and enter the collector region.\u00a0<\/span><\/p>\r\n

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The current produced due to the recombination of the electrons and hole is known as the base current, IB<\/sub>.<\/span> This current is quite small. The current flowing in the collector region because of the remaining electrons flow is the collector current, IC<\/sub>.<\/span> It has a higher value than the base current.<\/span><\/p>\r\n

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Basic Formulae of NPN Transistor<\/span><\/h3>\r\n

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