Thermal runway in a transistor biased in the active region is due to :...
Thermal runway in a transistor biased in the active region is due to change in reverse collector saturation current due to rise in temperature .
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Thermal runway in a transistor biased in the active region is due to :...
Thermal Runaway in a Transistor Biased in the Active Region
Introduction
Thermal runaway refers to the condition where the temperature of a device increases continuously and uncontrollably, often leading to its failure. This phenomenon can occur in transistors when they are biased in the active region.
Explanation
When a transistor is biased in the active region, it means that it is operating as an amplifier, allowing a small input signal to control a larger output signal. In this region, the transistor is typically in a stable state, with a certain level of collector current flowing through it.
However, when the temperature of the transistor increases, it can lead to a change in the reverse collector saturation current (ICBO), which is the current flowing between the collector and the base when the emitter current is zero. This change in ICBO with temperature is the main cause of thermal runaway in a transistor biased in the active region.
Reasoning
As the temperature of the transistor increases, the reverse collector saturation current (ICBO) also increases. This is due to the increase in the number of thermally generated charge carriers in the transistor. These additional charge carriers can contribute to an increase in the collector current, causing the transistor to heat up even more.
The increase in ICBO leads to an increase in the base current (IB), as the base-emitter junction behaves like a forward-biased diode. The increased base current further increases the collector current (IC), leading to an even higher temperature. This positive feedback loop can result in thermal runaway, where the temperature of the transistor rises rapidly and uncontrollably.
Conclusion
In summary, the correct answer to the question is option 'D' - Change in reverse collector saturation current due to the rise in temperature. The increase in reverse collector saturation current (ICBO) with temperature in a transistor biased in the active region is the main cause of thermal runaway. This increase leads to a positive feedback loop, causing the transistor to heat up continuously and potentially fail.