Common-Collector Configuration of a Transistor

Summary

The 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).