Bipolar junction transistor - Wikipedia

 

practical applications of bipolar junction transistor

Bipolar Junction Transistors Working Principle and Applications. BJT was invented in by William Shockley, Brattain, and John Bardeen which has remolded not only the world of electronics but also in our day to day life. The Bipolar junction transistors uses both charge carriers that . Mar 16,  · Application of bipolar junction transistor (BJT) are given below, The bipolar junction transistor (BJT) is used in logic circuits. The BJT is used as an oscillator. It is used as an amplifier. It is used as a multivibrator. For wave shaping, it is used in clipping circuits. Used as a detector or demodulator. It is also used as a modulator. A bipolar junction transistor is a three terminal semiconductor device consisting of two p-n junctions which is able to amplify or magnify a signal. It is a current controlled device. The three terminals of the BJT are the base, the collector and the emitter.


Applications of Bipolar Junction Transistor or BJT | History of BJT | Electrical4U


A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. Or A transistor is a device that regulates current or voltage flow and acts as a switch or gate for electronic signals. Transistors consist of three layers of a semiconductor material, each capable of carrying a current.

In this section, you will see practical applications of bipolar junction transistor semi-conductive materials are used to form a BJT, practical applications of bipolar junction transistor, and you will learn the standard BJT symbols.

Physical representations of the two types of BJT are shown in above Fig. A wire lead connects to practical applications of bipolar junction transistor of the three regions,are shown, practical applications of bipolar junction transistor. These leads are labeled E,B and C for emitter,base and collector,respectively. The base region is lightly doped and very thin compared to the heavily doped emitter and the moderately doped collector region. The reason for this is discussed in the next section.

Notice that the both cases the base-emitter BE junction is forward-biased and the base collector BC junction is reverse-biased. The base has a low density of holes, which are the majority carriers,as represented by the white circles. A small percentage of the total number of free electrons injected into the base region recombine with the holes and move as valence electrons through the base practical applications of bipolar junction transistor and into the emitter region as hole current,indicated by the red arrows.

When the electrons that have recombined with holes as valence electrons leave the crystalline structure of the base,they become free electrons in the metallic base lead and produce the external base current. Most of the free electrons that have entered the base do not recombine with holes because the base is very thin. A s the free electrons move toward the reverse-biased BC junction,they are swept across into the collector region by the attraction of the positive collector supply voltage.

The free electrons move through the collector region, into the external circuit,and then return into the emitter region along with the base current,as indicated. Watch also how transistor work? Notice that the arrow on the emitter inside the transistor symbols points in the direction of conventional current.

These diagrams show that the emitter current I E is the sum of the collector current I C and the base current I Bexpressed as follow:.

The capital-letter subscripts indicate dc values. Finally, maximum ratings of a BJT are discussed. Although in this chapter we are using separate battery symbols to re[present the bias voltages, in practice the voltages are often derived from a single de power supply. All you practical applications of bipolar junction transistor to know now is that:.

The alpha is a less-used parameter than beta in transistor circuits. The input circuit is a forward-biased diode through which there is base current. Recall that independent current source symbols have a circular shape. Consider the basic transistor bias circuit configuration. The transistor de currents and three de voltages can be identified. When the base-emitter junction is forward-biased,it is like a forward-biased diode and has a nominal forward voltage drop of.

Keep in mind that the characteristic of the base-emitter junction is the same as a normal diode curve like the one in the above Figure. For this condition, both the base-emitter junction and the base-collector junction are forward-biased because the base is at approximately 0.

When both junctions are forward-biased the transistor is in the saturation region of its operation. Saturation is the state of a BJT in which the collector current has reached a maximum and is independent of the base current. This i indicated by the portion of the characteristic curve between points A and B.

This is shown by the portion of the characteristic curve between point B and C. A transistor should never be operated in this breakdown region. With the base lead open, resulting in a base current of zero. In cutoff, neither the base-emitter nor the base-collector junctions are forward-biased. The subscript CEO represents collector- to-emitter with the base open. Cutoff and saturation can be illustrated in relation to the collector characteristic curves by the use of a load line.

A de load line drawn on a family of curves connecting the cutoff point and the saturation point. A BJT, like any other electronic device,has limitations on its operation. Typically, maximum ratings are given for collector-to-base voltage, collector-to-emitter voltage,emitter-to-base voltage, collector current,and power dissipation. In this text, italic capital letters are used for both dc and ac currents I and voltages V.

This rule applies to rms, average, peak, and peak-to-peak ac values, practical applications of bipolar junction transistor. DC quantities always carry an uppercase roman nonitalic subscript.

AC and all time-varying quantities always carry a lowercase italic subscript. For example,I b practical applications of bipolar junction transistor, I cand I practical applications of bipolar junction transistor are the ac transistor currents. V beV cband V ce are the ac voltages from one transistor terminal to another. The rule is different for internal transistor resistances. The forward-biased base-emitter junction presents a very low resistance to the ac signal.

The ac base voltage is:. The ac collector voltage, V cequals the ac voltage drop across R C. In the previous section, you saw how a BJT can be used as a linear amplifier. When The square wave is at 0 V, the transistor is in cutoff; and since there is no collector current,the LED does not emit light.

In a Photo-transistor the base current is produced when light strikes the photosensitive semiconductor base region. Except for the way base current is generated, the phototransistor behaves as a conventional BJT. In many cases,there is no electrical connection to the base. The relationship between the collector current and the light-generated base current in a phototransistor is:.

The schematic symbol and some typical photo-transistors are shown practical applications of bipolar junction transistor above Fig. Since the actual photo-generation of base current occurs in the collector-base region,the larger the physical area of this region,the more base current is generated. Thus,a typical photo-transistor is designed to offer a large area to the incident light, as the simplified structure diagram in above Figure:. A phototransistor can be either a two-lead or a three-lead device.

In the three-lead configuration,the base lead is brought out so that the device can be used as a conventional BJT with or without the additional light-sensitivity feature. In the two-lead configuration, the base is not electrically available, and the device can be used only with light as the input. In many applications, the phototransistor is used in the two-lead version.

Phototransistors are used in a variety of applications. An optocouplers use an LED optically coupled to a photodiode or a phototransistor in a single package. Examples of typical packages are shown Figure:. The CTR is an indication of how efficiently a signal is coupled from input to output and id expressed as the ratio of a change in the LED current to the corresponding change in the photodiode or phototransistor current.

It is usually expressed as a percentage. A key parameter in optocouplers is the CTR current transfer ratio. Certain types of packages contain multiple transistors. Pin configurations may vary. Several faults can occur in a simple transistor bias circuit. Several faults that can occur in the circuit and the accompanying symptoms. Symptoms are shown in terms of measured voltages that are incorrect. Examples of faults and symptoms in the basic transistor bias circuit, practical applications of bipolar junction transistor.

A transistor viewed as two diodes:. An open diode is the most common type of failure. Typical DMM test of a properly functioning npn transistor. Leads are reversed for a pnp transistor.

If the transistor is working properly, you will typically get an OL indication. The process just described is repeated for the base-collector junction. For a pnp transistor, the polarity of the meter leads are reversed for each test. Testing a defective npn transistor, practical applications of bipolar junction transistor. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment.

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BJT | Bipolar Junction Transistor ? Working Principal & Applications ()

 

practical applications of bipolar junction transistor

 

Bipolar Junction Transistors Working Principle and Applications. BJT was invented in by William Shockley, Brattain, and John Bardeen which has remolded not only the world of electronics but also in our day to day life. The Bipolar junction transistors uses both charge carriers that . There are various application of bipolar junction transistor. These days electronics cannot be imagined without transistor because basic building block of IC (analog or digital, microcontroller or microprocessor) is transistor. Here are some basic application listed below. Transistor can be used as switch (Some example are given below). A bipolar junction transistor is a three terminal semiconductor device consisting of two p-n junctions which is able to amplify or magnify a signal. It is a current controlled device. The three terminals of the BJT are the base, the collector and the emitter.