Bipolar Junction Transistor

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We already know  that the diodes which are simple diodes are made up from two pieces of semiconductor material to form a simple pn-junction here, and we will also learn about their characteristics and properties.

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Joining the individuals together which are of two signal diodes back-to-back. This will result in providing us with two PN-junctions which are connected in series that are shared with a common N and P terminal. The diodes which are two in number fusion produce a three layer of the two junction and a three-terminal device which forms the basis of a Bipolar Junction Transistor or we can say BJT for short.

The ability or we can say that the capacity  of the transistor’s to change between these two states that are n and p enables it to have two basic functions: that is  “switching” to digital electronics or the “amplification” that is analogue in electronics. 

There are two types of basics of bipolar transistor construction. The one is  PNP and the other one is the NPN, which describes basically the physical arrangement of the P-type as well as the N-type semiconductor materials from which they are made.

The transistor which is said as the Bipolar Transistor is the basic construction which consists of two PN-junctions which produce three terminals which are connecting and that are each terminal being given a name to identify it from the others. These three terminals are known and labelled as the Emitter that is denoted by letter E , the Base which denoted by letter B and the Collector denoted by letter C respectively.

Bipolar Transistor Construction

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The circuit of the symbols for both the NPN and the PNP bipolar transistor are given above in the diagram with the arrow which is in the circuit symbol. It is always showing the direction of “conventional current flow” that is between the emitter terminal and the base terminal. 

Bipolar Transistor Configurations

As a transistor which is the Bipolar Transistor is a three terminal device. There are three types of ways which are possible to connect it within a circuit. Which when is an electronic circuit with one terminal being common to both the output and input. The very Common Base Configuration   –   which has gain of Voltage but no Current Gain.

The Common configuration of Emitter   –   which has both voltage and Current Voltage Gain.

The Commons Configuration  Collector  –   has the gain of Current But no Voltage Gain.

The Common Base (CB) Configuration

As the  name itself suggests, in the very base of Common or we can call grounded which is base configuration. The base connection is very common to both the output signals and input signal. The signal which is input signal is applied between the transistors base and the emitter terminals. While on the other hand corresponding output signal is taken from between the base and the collector terminals. 

The current of the collector output is less than the emitter current input which is resulting in a current gain for this type of circuit of “1”  that is said as unity or less on the other hand words and the common base configuration that  “attenuates” the input signal.

The Common Base Transistor Circuit

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As the above figure is shown this type of amplifier configuration is a non-inverting voltage amplifier circuit. In that the voltage which is signal voltages that is Vin and Vout are “in-phase”. These types of transistors have an arrangement which is not very common due to its unusually high voltage and the characteristics gain. The input of the whole thing or characteristics represent that of a base which is forward biased diode while the output characteristics represent that of an illuminated diode of photo.


These are the regions which are respectively of p-type and n-type and p type transistor  in a PNP transistor and a n type as well as p type and n type in an NPN transistor. Each region of the semiconductor is connected to a terminal which is appropriately labeled as emitter which is denoted by E, base denoted by B and collector denoted by C.

The base is located physically between the collector and the emitter. And is made from lightly doped which is material of high-resistivity. Resulting in making the resulting value of α which is very close to unity. And it is also giving the transistor a large β. The junction which is bipolar junction transistor is unlike other transistors and is usually not a device which is symmetrical.

FAQ (Frequently Asked Questions)

Q1. Explain how a Bipolar Junction Transistor works?

Ans: The transistors of Bipolar are current devices which are regulating devices which  control the amount of flowing current through them from the Emitter terminal to the Collector terminals in switches proportion.

Q2. Explain what is a Bipolar Junction Transistor used for?

Ans: A bipolar junction transistor bipolar transistor or also we call it the BJT is a type of transistor that uses both holes and electrons as charge carriers. A junction which is bipolar junction transistor also called bipolar transistors, is a device which has three-terminal that can function as electronic switches or signal amplifiers as well.

Q3. Explain the three terminals of a Bipolar Transistor?

Ans: The bipolar transistor is a basic construction which consists of two junctions which is PN that has three connecting terminals with each terminal which is being given a . These three terminals are labelled and called as the Emitter denoted as letter E. The Base is denoted by letter B  and the Collector is denoted by letter C.

Q4. Explain  the two types of BJT Transistor?

Ans: A transistor which is bipolar bipolar junction transistor: denoted by  BJT consists of refin of three semiconductors which are  forming two junctions. There are two types of structure namely the pnp and the  npn. The product with the npn junction is up to 800 denoted by V and pnp up to -600 V. In addition there are also bias resistors which are built-in Transistors  denoted as BRTs.