Each of the following items consists of two statements, one labeled as ‘Statement (I)’ and the other as ‘Statement (II)’. Examine these two statements carefully and select the answers to these items using the code given below.

Statement (I): Thermal runaway is not possible in a FET.

Statement (II): As the temperature of FET increases, the mobility of carriers decreases.

Concept:

1) The thermal runway is not possible in FET because as the temperature of the FET increases, the mobility decreases, i.e. if the Temperature (T) ↑, the carries Mobility (μn or μ­p) ↓, and Ips↓

2) Since the current is decreasing with an increase in temperature, the power dissipation at the output terminal of a FET decreases or we can say that it’s minimum.

So, there will be no Question of thermal Runway at the output of the FET.

• The thermal runaway takes place in a BJT.
• Thermal Runway in BJT is a process of self-damage of BJT because of overheating at the collector junction due to an increase in Ic with Ico
• If T↑, then Ico (Reverse separation current) ↑, which results in an increase in the collector current, i.e. Ic ↑.
• Power dissipation at the collector junction increases in the form of heat which again raises the temperature and cycle continues.
• If the above cycle becomes repetitive then the collector junction gets overheated and thereby thermal runway takes place.