When the junction temperature of a transistor increases, its ______ increases.

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ALP CBT 2 Electronic Mechanic Previous Paper: Held on 21 Jan 2019 Shift 1
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  1. Emitter voltage
  2. Collector current
  3. Collector voltage
  4. Collector resistance

Answer (Detailed Solution Below)

Option 2 : Collector current
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Detailed Solution

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When the junction temperature of a transistor increases, it increases the collector current causing a further increase in temperature and this process is called Thermal runway.

So, option (2) is correct.

Notes:

Thermal resistance between collector-base junction develops due to thermal run-way.

\(\theta = \frac{{{T_j} - {T_A}}}{{{P_D}}}\left( {K/watt} \right)\) 

Where,

θ = Thermal resistance

Tj = collector Junction Temperature

TA = Ambient temperature

PD = Power dissipation along collector junction.

Thermal resistance increases due to increase in Junction temperature.

Thermal run-away can be avoided if:

\(\frac{{\partial {P_c}}}{{\partial {T_j}}} \le \frac{{\partial {P_D}}}{{\partial {T_j}}} = \frac{1}{\theta }\) 

Where,

\(\frac{{\partial {P_c}}}{{\partial {T_j}}}\)  is rate at which heat is released.

\(\frac{{\partial {P_D}}}{{\partial {T_j}}}\) is rate at which heat is dissipated.

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