Thermal Management MCQ (EMJ32304)

A transistor has the following parameters: - R_thJC = 1.5°C/W - R_thCS = 0.1°C/W - Ambient temperature Ta = 35°C - Power dissipated Pd = 15W What heatsink thermal resistance is required to keep Tj ≤ 100°C?

• 1.5°C/W

• 1.95°C/W

• 2.5°C/W

• 2.75°C/W

Given: - R_thJC = 1.2°C/W, R_thCS = 0.2°C/W, R_thSA = 2.0°C/W - Ta = 40°C, Pd = 10W Find the junction temperature.

• 80°C

• 100°C

• 96°C

• 114°C

If a heatsink is replaced by a better one, reducing R_thSA from 3.5°C/W to 1.5°C/W, how much cooler will the case temperature be for Pd = 12W?

• 12°C

• 18°C

• 24°C

• 36°C

Which of the following best describes the purpose of the thermal pad?

• Increases junction temperature

• Improves electrical conductivity

• Reduces contact thermal resistance

• Cools ambient temperature

A transistor dissipates 6W, and the junction temperature is 100°C. If ambient is 35°C, what is the total thermal resistance?

• 10°C/W

• 8.5°C/W

• 6°C/W

• 12.5°C/W

If Tj = 105°C, Ta = 40°C, and Pd = 7W, find total thermal resistance.

• 9.3°C/W

• 7.8°C/W

• 6.5°C/W

• 4.8°C/W

To maintain Tj below 90°C, Pd = 5W, R_thJC = 1.3°C/W, R_thCS = 0.1°C/W, and Ta = 35°C. What is the max R_thSA allowed?

• 1.8°C/W

• 2.5°C/W

• 3.0°C/W

• 4.5°C/W

Which component contributes most to thermal bottleneck?

• R_thJC

• R_thCS

• R_thSA

• Ambient temperature

What happens if R_thSA increases due to improper heatsink mounting?

• Device operates cooler

• Power dissipation increases

• Junction temperature rises

• Ambient temperature drops

Which of the following statements is TRUE?

• A lower R_thSA always guarantees lower power dissipation

• R_thCS includes fan cooling

• The case temperature is always lower than junction temperature

• Ambient temperature has no impact on junction temperature