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Which transistor configuration provides the best temperature stability for the collector current?
Common Base
Common Emitter
Common Collector
Fixed Bias
Common Base
The Common Base (CB) configuration provides the best temperature stability for the collector current because it has the lowest stability factor among all transistor configurations. Stability factor S represents the rate of change of collector current with respect to the reverse saturation current ICOтАЛ, and a lower value indicates better immunity to temperature variations.
The Common Base (CB) configuration provides the best temperature stability for the collector current because it has the lowest stability factor among all transistor configurations. Stability factor S represents the rate of change of collector current with respect to the reverse saturation current ICOтАЛ, and a lower value indicates better immunity to temperature variations.
ICтАЛ=╬▒IEтАЛ+ICBOтАЛ тАФ Relation between collector and emitter currents
S=1тИТ╬▒(1+╬▓)1тАЛ тАФ Stability factor formula showing dependence on leakage current
ICтАЛтЙИICBOтАЛ тАФ Relationship in CB mode highlighting the isolation from thermal runaway
In the Common Base configuration, the output collector current is related to the input emitter current by the common-base current gain ╬▒. Since ╬▒ is typically very close to unity (approx. 0.99), the collector current is given by ICтАЛ=╬▒IEтАЛ+ICBOтАЛ. The stability factor S=dICBOтАЛdICтАЛтАЛ is approximately 1 for the CB configuration, which is the theoretical minimum, ensuring minimal dependence on leakage current fluctuations.
Common Base configuration has a stability factor SтЙИ1.
Common Emitter configuration has a higher stability factor S=1+╬▓, making it more sensitive to temperature.
The leakage current ICBOтАЛ doubles for every 10┬░C rise in temperature.
Higher stability factor implies higher instability of the operating point.
Superior thermal stability
Low input impedance
High output impedance
Current gain is less than unity
Requires impedance matching for multi-stage applications
High frequency amplifiers
Impedance matching circuits
| Feature | Common Base | Common Emitter |
|---|---|---|
Stability Factor (S) | тЙИ1 | 1+╬▓ |
The stability factor S is defined as тИВICBOтАЛтИВICтАЛтАЛ. Ideally, S should be 1.
Option B (Common Emitter) is widely used for amplification but exhibits poor temperature stability compared to CB due to the ╬▓ multiplier effect on the leakage current.
A is correct тАФ The Common Base configuration possesses the lowest stability factor, making it the most thermally stable configuration among the three.
Always remember that for thermal stability, a lower Stability Factor S is better; S=1 is the ideal value which is closely approached by the Common Base configuration.