Bipolar Junction Transistors and operation .pptx

A transistor is a type of semiconductor device that can be used to conduct and insulate electric current or voltage. A transistor basically acts as a switch and an amplifier.

1. Bipolar Junction Transistors (BJT) Neeta Ukirade( Gatkal ) Pratibha College of Commerce and Computer Studies

2. CONTENTS INTRODUCTION TO BJT TYPES OF BIPOLAR JUNCTION TRANSISTOR BIPOLAR JUNCTION TRANSISTOR STRUCTURE BIPOLAR JUNCTION TRANSISTOR OPERATION BIPOLAR JUNCTION TRANSISTOR CONFIGURATIONS Common Emitter Configuration input and output characteristics

3. INTRODUCTION What is a transistor? A transistor is a type of  semiconductor  device that can be used to conduct and insulate electric current or voltage . A transistor basically acts as a switch and an amplifier . Parts of a Transistor A typical transistor is composed of three layers of semiconductor materials or, more specifically, terminals which help to make a connection to an external circuit and carry the current . There are three terminals for a transistor. They are listed below: Base: This is used to activate the transistor. Collector: It is the positive lead of the transistor. Emitter: It is the negative lead of the transistor.

4. Types of transistor

5. Bipolar Junction Transistor (BJT) A Bipolar junction transistor, shortly termed as  BJT  is called so as it has two PN junctions for its function.  The three terminals of BJT are the base, emitter and collector. A very small current flowing between the base and emitter can control a larger flow of current between the collector and emitter terminal . The concept of BJT refers to a three-terminal semiconductor device consisting of two p-n-junctions that are formed by sandwiching either p-type or n-type semiconductors between two p-type semiconductors. Transistors can be used to transfer input signals through the circuits having lower to higher resistance.

6. Types of BJTs PNP Bipolar Junction Transistor NPN Bipolar Junction Transistor

7. BIPOLAR JUNCTION TRANSISTOR OPERATION BJT operates in three regions : a) Active region b) Saturation region c) Cut-off region Active region:  The transistor is on in this region. When the collector-base junction is reverse-biased while the emitter-base junction is in forward-bias, then BJT works in the active area. As a result, BJT is used as an amplifier. The collector current is proportional to and controlled by the base current and relatively insensitive to VCE. In this region the transistor can be an amplifier . Saturation region:  The saturation region arises when the collector-base junctions and the emitter-base junction are both forward-biased. The transistor is on. The collector current varies very little with a change in the base current in the saturation region . Cut-off region:  Because the emitter and collector junctions are both in the reversed bias, so the BJT is off in this condition and vary small amount of current flows from  collector to the emitter. There is no current between emitter and the collector.

8. Operation of NPN Transistor With the forward-biased emitter-base junction and reverse-biased collector-base junction, it can be seen that the forward bias causes the flow of electrons from the n-type emitter into the p-type base . This constitutes the emitter current (). As these electrons flow through the p-type base, they tend to combine with the holes . Since the base is lightly doped and very thin, hence, only a small number electrons (less than 5%) combine with the holes to constitute the base current (). The remaining (more than 95%) electrons cross over the base region and reach to the collector region to constitute the collector current ().

9. BIPOLAR JUNCTION TRANSISTOR CONFIGURATIONS There are basically three possible ways to connect BJT in an electric circuit are : Common Collector Configuration Common Base Configuration Common Emitter Configuration. Common Base Configuration The base of transistor is grounded in common base characteristics , with the emitter acting as the input and the collector as the output . The emitter-base junction is  biased forward, whereas the junction between the collector and the base is reverse biased.  Low voltage gain but high current gain is offered by the CB arrangement . Current Amplification factor ( α)

10. Common Collector Configuration The configuration in which the collector is common between emitter and base is known as CC configuration. In CC configuration, the input circuit is connected between emitter and base and the output is taken from the collector and emitter. The collector is common to both the input and output circuit and hence the name common collector connection or common collector configuration . Current Amplifier Factor (Y) Relation Between Υ and α

11. Common Emitter Configuration The configuration in which the emitter is connected between the collector and base is known as a common emitter configuration. The input circuit is connected between emitter and base, and the output circuit is taken from the collector and emitter. Thus , the emitter is common to both the input and the output circuit, and hence the name is the common emitter configuration .   Current Amplification Factor (β) The relation between Β and α can be derived as

12. Common Emitter Configuration input and output characteristics

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