The correct answer is: C. Emitter is forward biased
Thermal runaway is a self-reinforcing positive feedback loop that can occur in transistors. It is caused by a combination of factors, including the transistor’s internal resistance, the current flowing through it, and the temperature of the transistor’s junction.
When the emitter is forward biased, current flows from the base to the emitter. This current causes the transistor to amplify the input signal, which in turn causes more current to flow through the transistor. This can lead to a runaway condition, in which the transistor’s temperature increases rapidly, causing the current to increase even further, and so on.
Thermal runaway can damage the transistor or even cause it to catch fire. It is important to design circuits that prevent thermal runaway from occurring. One way to do this is to use a resistor in series with the base of the transistor. This resistor will limit the amount of current that can flow through the base, and help to prevent the transistor from overheating.
Another way to prevent thermal runaway is to use a negative feedback loop. In a negative feedback loop, the output of the circuit is used to control the input. This helps to keep the output of the circuit stable, and prevents it from oscillating or going into thermal runaway.
Thermal runaway is a serious problem that can damage or destroy transistors. It is important to understand the causes of thermal runaway and to take steps to prevent it from occurring.
Here is a brief explanation of each option:
- A. Collector is reverse biased: This is not the correct answer because thermal runaway occurs when the emitter is forward biased.
- B. Transistor is not biased: This is not the correct answer because thermal runaway can occur even when the transistor is biased.
- C. Emitter is forward biased: This is the correct answer because thermal runaway occurs when the emitter is forward biased.
- D. Junction capacitance is high: This is not the correct answer because thermal runaway is not caused by high junction capacitance.