Transistor As an Amplifier | Analog and Digital Electronics - Electrical Engineering (EE) PDF Download

TRANSISTOR AS AN AMPLIFIER

Transistor As an Amplifier | Analog and Digital Electronics - Electrical Engineering (EE)

Common-Emitter Configuration

It is called common-emitter configuration since : emitter is common or reference to both input and output terminals. Emitter is usually the terminal closest to or at ground potential.

 Amplifier design is using connection of CE due to the high gain for current and voltage.

Two set of characteristics are necessary to describe the behavior for CE i.e. input (base terminal) and output (collector terminal) parameters.

Proper Biasing of common-emitter configuration in active region.

 

Transistor As an Amplifier | Analog and Digital Electronics - Electrical Engineering (EE)

 

IB is in microamperes compared to milliamperes of IC.

 IB will flow when VBE > 0.7V for silicon and 0.3V for germanium.

Before this value, IB is very small.

 Base-emitter junction is forward bias. Increasing VCE will reduce IB for different values.

Transistor As an Amplifier | Analog and Digital Electronics - Electrical Engineering (EE)

 

Transistor As an Amplifier | Analog and Digital Electronics - Electrical Engineering (EE)

Output characteristics for common-emitter npn transistor.

For small value of VCE (VCE < VCESAT, IC increases linearly with increasing value of VCE 

and if  VCE > VCESAT, IC does not totally depend on VCE → constant IC

 IB(µA) is very small compared to IC (mA). Small increase in IB causes big increase in IC

 IB=0A → ICEO occurs.

Noticing the value when IC= 0A. There is still some value of current flowing.

Transistor As an Amplifier | Analog and Digital Electronics - Electrical Engineering (EE)

 Beta (β) or amplification factor

The ratio of dc collector current (IC) to the dc base current (IB) is dc beta (βdc ) which is dc current gain where IC and IB are determined at a particular operating point, Q-point (quiescent point).  It is defined by the following equation:

30 < βdc < 300 → 2N3904   (IC no.)

On data sheet, βdc=hfe where h is derived from ac hybrid equivalent circuit. FE are derived from forward-current amplification and common-emitter configuration respectively.

                                  Transistor As an Amplifier | Analog and Digital Electronics - Electrical Engineering (EE)

For ac conditions, an ac beta has been defined as the changes of collector current (IC) compared to the changes of base current (IB) where IC and IB are determined at the operating point. On data sheet, βac=hfe  It can defined by the following equation:

                                       Transistor As an Amplifier | Analog and Digital Electronics - Electrical Engineering (EE)

 

From output characteristics of common emitter configuration, find βac and βdc with an

Operating point at IB=25 mA and VCE =7.5V

                        Transistor As an Amplifier | Analog and Digital Electronics - Electrical Engineering (EE)Transistor As an Amplifier | Analog and Digital Electronics - Electrical Engineering (EE)

Transistor As an Amplifier | Analog and Digital Electronics - Electrical Engineering (EE)

Relationship analysis between α and β

 

Transistor As an Amplifier | Analog and Digital Electronics - Electrical Engineering (EE) 

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FAQs on Transistor As an Amplifier - Analog and Digital Electronics - Electrical Engineering (EE)

1. What is a transistor amplifier?
Ans. A transistor amplifier is a device that uses a transistor to increase the strength or amplitude of an electrical signal. It takes a weak input signal and produces a larger output signal, effectively amplifying the original signal.
2. How does a transistor amplifier work?
Ans. A transistor amplifier works by using a small input current or voltage to control a larger current flowing through the transistor. The input signal is applied to the base of the transistor, which controls the flow of current between the collector and emitter terminals. By varying the input signal, the transistor amplifies the signal at the output.
3. What are the advantages of using a transistor amplifier?
Ans. There are several advantages of using a transistor amplifier. Firstly, transistors are small in size and consume less power compared to other amplifying devices. They also have a longer lifespan and are more reliable. Transistor amplifiers can amplify a wide range of frequencies and are compatible with various types of input signals.
4. Are there different types of transistor amplifiers?
Ans. Yes, there are different types of transistor amplifiers. The most common types include common emitter, common base, and common collector amplifiers. Each type has its own characteristics and is suitable for specific applications. For example, the common emitter amplifier offers high voltage gain, while the common base amplifier provides high current gain.
5. Can a transistor amplifier be used for audio applications?
Ans. Yes, transistor amplifiers are commonly used in audio applications. They can amplify audio signals from devices such as microphones, musical instruments, and audio players. By connecting a transistor amplifier to a speaker or a set of headphones, the amplified audio signal can be heard at a higher volume and with improved clarity.
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