Common-Collector Configuration of a Transistor

Neso Academy

10 Jun 201605:44

Summary

TLDRThe video script discusses the common collector configuration of a transistor, where the collector is common to both the input and output sides. It explains the current relationships, including the base current (Ib) as the control current, and the collector current (Ic) as the main current. The script also covers the graphical representation of the output characteristics, showing the relationship between output current (Ic), emitter current (Ie), and output voltage (V) for different base current levels. It emphasizes the importance of the current amplification factor, denoted by gamma (γ), and how it relates to the change in emitter current to the change in base current. The summary also touches on the practical application of common emitter transistors and their output characteristics, concluding with an exploration of the relationship between alpha (α), beta (β), and gamma (γ) in the context of transistor operation.

Takeaways

📌 The last type of transistor configuration discussed is the common collector configuration, also known as the emitter follower.
🔌 In common collector configuration, the collector is common to both the input and output sides, with the emitter as the current source and the collector as the current sink.
📈 The base current (Ib) is the control current, and the collector current (Ic) is the output current, which is also the current that flows through the load.
🔗 The relationship between the output current (Ic) and the output voltage (Vc) is graphically represented, showing how they vary with different input current (Ib) values.
🔄 The current gain (α) is the ratio of the collector current to the base current, and it typically ranges from 0.95 to 0.98, which is near unity.
🔄 The collector current (Ic) is approximately equal to the base current (Ib) multiplied by α, indicating that the output characteristic of a common emitter transistor is similar to that of a common collector transistor.
📊 The graphical relationship between the emitter current and the voltage for various levels of base current is discussed, which is crucial for understanding the transistor's behavior.
🔢 The current amplification factor, denoted by γ, is the ratio of the change in emitter current to the change in base current, and it is equal to α times Ib.
🔄 The input current (Ib) is equal to the base current plus the collector current, and the collector current (Ic) is equal to α times Ib.
🔧 The output characteristic of a common emitter transistor is simplified to Ic = Ib + Ic, which helps in understanding the relationship between input and output currents.
🔍 The next lecture will delve into the relationship between α, β, and γ, providing further insights into the operation and characteristics of transistors.

Q & A

What is the common collector configuration in a transistor?
-In a common collector configuration, the collector is common to both the input and the output sides of the transistor circuit.
What are the current components in a common collector configuration?
-The current components in a common collector configuration are the base current (I_B), the emitter current (I_E), and the collector current (I_C).
Why is an NPN transistor used in active mode in this configuration?
-An NPN transistor is used in active mode because the emitter-base junction is forward biased and the collector-base junction is reverse biased, allowing proper amplification.
What is the graphical relation plotted for the output characteristics of a common collector configuration?
-The graphical relation plotted for the output characteristics is between the emitter current (I_E) and the output voltage (V_CE) for different values of input current (I_B).
How is the emitter current (I_E) related to the collector current (I_C) and the base current (I_B)?
-The emitter current (I_E) is equal to the sum of the collector current (I_C) and the base current (I_B), represented as I_E = I_C + I_B.
What is the approximate value of the current gain alpha (α) in a common collector configuration?
-The current gain alpha (α) is approximately between 0.95 to 0.98, which is nearly equal to 1.
How does the collector current (I_C) compare to the emitter current (I_E) in practical purposes?
-For all practical purposes, the collector current (I_C) is nearly equal to the emitter current (I_E) in a common collector configuration.
What is the current amplification factor in a common collector transistor and how is it denoted?
-The current amplification factor in a common collector transistor is denoted by gamma (γ) and it is the ratio of the change in emitter current to the change in base current.
How can the emitter current (I_E) be expressed in terms of alpha (α) and the base current (I_B)?
-The emitter current (I_E) can be expressed as I_E = (1 / (1 - α)) * I_B, where (1 / (1 - α)) is the current amplification factor gamma (γ).
What will be discussed in the next lecture as per the transcript?
-The next lecture will cover the comparison between the current gain parameters alpha (α), beta (β), and gamma (γ).

Outlines

00:00

🔍 Understanding Common Emitter Transistor Configuration

This paragraph discusses the common emitter configuration of a transistor, where the collector is common to both the input and output sides. It explains the current relationships, with the base current (Ib) being the control current and the collector current (Ic) being the main current. The paragraph also covers the graphical representation of the output characteristics, plotting the output current (Ic) against the output voltage (Vce) for different base currents (Ib). It emphasizes the importance of the current gain (β), which is near to 1, indicating the relationship between the collector current and the base current.

05:01

📈 Current Amplification Factor in Common Emitter Configuration

The second paragraph delves into the current amplification factor, denoted by gamma (γ), in the common emitter configuration of a transistor. It explains that gamma is the ratio of the change in emitter current to the change in base current and is equivalent to the current gain (β) times the base current plus the emitter current. The paragraph simplifies the understanding of the output current by expressing it as a function of the input current, highlighting the relationship between the collector current and the input current. It also sets the stage for the next lecture, which will explore the relationship between alpha (α), beta (β), and gamma (γ).

Mindmap

Keywords

💡Transistor

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is a key component in modern electronics. In the video's context, the script discusses the configuration and characteristics of transistors, particularly focusing on common collector configuration where the collector is common to both the input and output sides.

💡Common Collector Configuration

This refers to a specific type of transistor configuration where the collector terminal is shared between the input and output. The script mentions this configuration as a way to illustrate the basic operation and current relationships within a transistor circuit, emphasizing its role in the amplification process.

💡Emitter Current (I_B)

Emitter current is the total current that flows into the emitter terminal of a transistor. It is a fundamental concept in the script, which discusses how this current is the base for understanding the transistor's behavior, with the script stating 'I_B is the base' and further explaining its relationship with other currents within the transistor.

💡Collector Current (I_C)

Collector current is the current that flows out of the collector terminal of a transistor. The script explains that it is closely related to the emitter current and is an important parameter for characterizing the transistor's performance, using the symbol 'I_C' to represent it.

💡Base Current (I_B)

Base current is the current that flows into the base terminal of a transistor. The script mentions it in the context of the relationship between the emitter current and the base current, indicating that the base current is a controlling factor for the emitter current, as suggested by the phrase 'I_B is the base'.

💡Alpha (α)

Alpha, represented by the symbol 'α', is the ratio of the collector current to the emitter current in a transistor. The script discusses its significance in determining the current gain of the transistor, mentioning that it ranges from 0.95 to 0.98, which is near to 1, indicating high efficiency in current transfer.

💡Output Characteristics

Output characteristics refer to the graphical representation of the relationship between the output current (I_C) and the output voltage (V_CE) for different values of input current (I_B). The script describes plotting these characteristics to understand the behavior of the transistor in different operating conditions.

💡Current Amplification Factor (Beta, β)

Beta, denoted by 'β', is the ratio of the change in collector current to the change in base current. The script refers to it as a measure of how much the transistor amplifies the input current, with 'β' being equivalent to the change in emitter current to the change in base current.

💡Graphical Relation

The script mentions the graphical relation between the emitter current and voltage, and between the collector current and base current. These graphical relations are essential for visualizing and analyzing the transistor's behavior in response to varying input conditions.

💡Common Emitter Configuration

Common emitter configuration is a type of transistor configuration where the emitter is common to both the input and output. The script implies that the output characteristics of common emitter and common collector configurations are similar, indicating the importance of understanding the common emitter configuration for practical purposes.

💡Input Characteristics

Input characteristics describe the relationship between the base current and the emitter current. The script suggests that understanding these characteristics is crucial for analyzing the transistor's operation, especially in the context of the base current's role in controlling the emitter current.

Highlights

The last type of transistor configuration is the common collector configuration.

In this configuration, the collector is common to both the input and output sides.

The base current (iB) is the input current, and the emitter current (iE) is the output current.

We are using an NPN transistor in active mode where the emitter-base junction is forward biased and the collector-base junction is reverse biased.

The common collector configuration can be represented using the symbol of a transistor.

In the common collector configuration, the output voltage Vout is equal to Vc - Ve.

The graphical relation between the emitter current (iE) and the output voltage (Vc) is plotted for different values of the base current (iB).

The collector current (iC) is nearly equal to the emitter current (iE) since alpha is close to 1.

The output characteristic of a common emitter transistor is similar to the output characteristic of a common collector transistor.

The current amplification factor in a common collector transistor is denoted by gamma (γ).

Gamma is the ratio of the change in emitter current to the change in base current.

The emitter current (iE) is equal to the collector current (iC) plus the base current (iB).

The equation for the collector current is iC = alpha * iE + iB.

By substituting the value of the collector current, the emitter current can be simplified as a function of the base current.

The next lecture will cover the relationship between alpha, beta, and gamma.