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What is the role of emitter resistance in the transistor amplifying circuit
- a)To prevent thermal runaway
- b)To prevent increase in gain
- c)To lower the output impedance
- d)To increase gain
Correct answer is option 'A'. Can you explain this answer?
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What is the role of emitter resistance in the transistor amplifying ci...
Early effect is the increase in the collector current without increase in input due to heating of semiconductor material which in turn reduce the resistance thus increases current. The emitter resistor decreases effective input voltage decrease when collector current increases and thus it reduces collector current itself.
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What is the role of emitter resistance in the transistor amplifying ci...
Role of Emitter Resistance in Transistor Amplifying Circuit
The emitter resistance plays a crucial role in transistor amplifying circuits. It serves multiple purposes, but the primary function is to prevent thermal runaway in the transistor. Let's discuss the role of the emitter resistance in detail:
1. Preventing thermal runaway:
Thermal runaway is a phenomenon where the temperature of the transistor increases uncontrollably due to positive feedback within the circuit. This can lead to the destruction of the transistor. The emitter resistor, also known as the emitter degeneration resistor, helps prevent thermal runaway by stabilizing the operating point of the transistor.
When a transistor is biased for amplification, a small change in base current can cause a significant change in collector current. This change in collector current can result in an increase in the junction temperature of the transistor. The emitter resistor acts as a negative feedback element by converting the change in collector current into a voltage drop across itself. This voltage drop reduces the base current, thereby stabilizing the collector current and preventing thermal runaway.
2. Reducing the gain:
While the primary role of the emitter resistor is to prevent thermal runaway, it also has an impact on the gain of the transistor amplifying circuit. The emitter resistor reduces the overall gain of the circuit. This reduction in gain is intentional and desirable in many cases.
By adding an emitter resistor, the transistor operates in the voltage-divider biasing configuration. This configuration helps in achieving better stability and linearity, especially in applications such as audio amplifiers. The emitter resistor reduces the gain by introducing negative feedback, which improves the linearity of the amplifier and reduces distortion.
3. Lowering the output impedance:
The emitter resistor also plays a role in lowering the output impedance of the transistor amplifier. The output impedance determines how much the output voltage changes with a change in the load impedance. By adding an emitter resistor, the output impedance of the amplifier decreases, resulting in better matching with the load impedance and increased power transfer efficiency.
4. Increasing thermal stability:
Apart from preventing thermal runaway, the emitter resistor also improves the thermal stability of the transistor. It reduces the temperature sensitivity of the transistor by providing a voltage drop that is proportional to the collector current. This voltage drop compensates for the temperature-induced variations in the transistor's characteristics, ensuring stable and reliable operation.
In conclusion, the emitter resistance in the transistor amplifying circuit primarily prevents thermal runaway by stabilizing the operating point of the transistor. Additionally, it reduces the gain, lowers the output impedance, and improves the thermal stability of the circuit. These characteristics make the emitter resistor an essential component in transistor amplifier designs.
The emitter resistance plays a crucial role in transistor amplifying circuits. It serves multiple purposes, but the primary function is to prevent thermal runaway in the transistor. Let's discuss the role of the emitter resistance in detail:
1. Preventing thermal runaway:
Thermal runaway is a phenomenon where the temperature of the transistor increases uncontrollably due to positive feedback within the circuit. This can lead to the destruction of the transistor. The emitter resistor, also known as the emitter degeneration resistor, helps prevent thermal runaway by stabilizing the operating point of the transistor.
When a transistor is biased for amplification, a small change in base current can cause a significant change in collector current. This change in collector current can result in an increase in the junction temperature of the transistor. The emitter resistor acts as a negative feedback element by converting the change in collector current into a voltage drop across itself. This voltage drop reduces the base current, thereby stabilizing the collector current and preventing thermal runaway.
2. Reducing the gain:
While the primary role of the emitter resistor is to prevent thermal runaway, it also has an impact on the gain of the transistor amplifying circuit. The emitter resistor reduces the overall gain of the circuit. This reduction in gain is intentional and desirable in many cases.
By adding an emitter resistor, the transistor operates in the voltage-divider biasing configuration. This configuration helps in achieving better stability and linearity, especially in applications such as audio amplifiers. The emitter resistor reduces the gain by introducing negative feedback, which improves the linearity of the amplifier and reduces distortion.
3. Lowering the output impedance:
The emitter resistor also plays a role in lowering the output impedance of the transistor amplifier. The output impedance determines how much the output voltage changes with a change in the load impedance. By adding an emitter resistor, the output impedance of the amplifier decreases, resulting in better matching with the load impedance and increased power transfer efficiency.
4. Increasing thermal stability:
Apart from preventing thermal runaway, the emitter resistor also improves the thermal stability of the transistor. It reduces the temperature sensitivity of the transistor by providing a voltage drop that is proportional to the collector current. This voltage drop compensates for the temperature-induced variations in the transistor's characteristics, ensuring stable and reliable operation.
In conclusion, the emitter resistance in the transistor amplifying circuit primarily prevents thermal runaway by stabilizing the operating point of the transistor. Additionally, it reduces the gain, lowers the output impedance, and improves the thermal stability of the circuit. These characteristics make the emitter resistor an essential component in transistor amplifier designs.
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What is the role of emitter resistance in the transistor amplifying circuita)To prevent thermal runawayb)To prevent increase in gainc)To lower the output impedanced)To increase gainCorrect answer is option 'A'. Can you explain this answer?
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