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Electronics and Communication Engineering - Electronic Devices and Circuits - Discussion

Discussion Forum : Electronic Devices and Circuits - Section 2 (Q.No. 36)
Electronic Devices and Circuits
36.
For BJT transistor. The maximum power dissipation is specified as 350 mW if ambient temperature is 25°C. If ambient temperature is 60°C the maximum power dissipation should be limited to about
100 mW
250 mW
450 mW
600 mW
Answer: Option
Explanation:

350 - 2.5 (60 - 25) ∼ 250 mW.

Discussion:
11 comments Page 1 of 2.
Charlene said:   9 years ago
Where did you obtain the 2.5 value? Thanks for your response!
(2)
Janu said:   8 years ago
How it's possible?

Please explain the answer.
(1)
Keerthi said:   5 years ago
@Shadan.

Nice explanation, Thanks.
(1)
Chellakumar said:   9 years ago
How do you put 2.5 in above sum where did you get this value?
Ajit said:   9 years ago
2.5mW/1degree. Celsius is the derating factor of BJT.
Mojojo said:   8 years ago
I think it should be 450mW.

If temperature increases, the resistance decreases in semicon. Thus, the current should increase also. So it should be 350 + 2. 5 (60 - 25) = 450mW.

Am I right?
Shadan said:   7 years ago
Since Temperature here rises from 25to 60so We find temperature difference,
60-25=35Degree celcius =35*2.5 mW (because )1degree celcius. = 2.5 mW,
= 87.5mW.

350-87.5=262.5 approx taking 250.
Raj said:   6 years ago
There is current increasing but voltage deceasing, so power dissipation decreasing.
Zoro said:   5 years ago
You may see on Shockley's equation that Tc is positive But variations of reverse saturation current is more significant than thermal voltage variations in diodes. Based on temp effects diode has a negative linear temperature coefficient usually (-2.5mW Ge or -2.0mW Si)
Yam said:   2 years ago
How it's possible?

Anyone, Please explain the answer.
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