Analog Circuits Questions and Answers – Heat Sink for Power Transistor-2

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This set of Analog Circuits online quiz focuses on “Heat Sink for Power Transistor-2”.

1. Which of the following heat sink is used for low power application?
a) Stamped heat sink
b) Machining heat sink
c) Aluminum heat sink
d) Bolded-Fin heat sink
View Answer

Answer: a
Explanation: Stamped heat sinks are made of metal that are stamped to form a particular shape. These are cheaper compared to extruded heat sinks. These are used for low-power applications and hence these are low in performance.
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2. The performance of heat sink does not depend upon ___________
a) Choice of material
b) Protrusion design
c) Surface treatment
d) none of the mentioned
View Answer

Answer: d
Explanation: The performance of the heat sink depends on the factors like the choice of material, protrusion design, surface treatment and air velocity. The material is preferred to have high conductivity and heat absorption. The shape and design also effect heat flow as well as coolant flow in the sink.

3. What is a heat spreader?
a) An older version of a heat sink
b) Another name for heat sink
c) Device to transfer heat from device to the sink
d) A connector for coolant to flow
View Answer

Answer: c
Explanation: A heat spreader conducts heat between a heat source and a heat sink. Most commonly, a block of material with high thermal conductivity is used as a heat spreader.

4. Heat dissipation from heat sink take place primarily by ___________
a) Conduction
b) Convection
c) Radiation
d) All of the mentioned
View Answer

Answer: d
Explanation: Heat dissipation from heat sink take place primarily by convection since there is no actual contact between heat sink and transistor. Heat dissipation also takes place by Radiation but it is comparatively low.

5. Heat sinks are provided with peripheral fins to ___________
a) Provide good appearance
b) Increase heat absorption
c) Increase surface area of heat dissipation
d) Provide material stability
View Answer

Answer: c
Explanation: Heat sinks are provided with peripheral fins to increase surface area of heat conduction. Increase in dissipation also increase absorption but more correct option is c.
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6. Heat sinks are usually provided with black anodized finish to ___________
a) Enhance heat dissipation by radiation
b) Enhance heat dissipation by convection
c) Prevent electrical connection
d) Remove dust accumulation
View Answer

Answer: a
Explanation: Heat sinks are usually provided with black anodized finish to enhance heat dissipation by radiation. Anodizing thickens and toughens the naturally occurring protective oxide layer on the metal surface. It provides dielectric isolation between cooling components and the electronics in the device.

7. Which substance is used to maintain electrical insulation between a heat sink and transistor?
a) plastic
b) fiber
c) ceramic
d) mica
View Answer

Answer: d
Explanation: Many transistors have metal cases which are connected to a lead and thus it becomes necessary to insulate the heat sink from the transistor. Insulating kits of a mica sheet and a plastic sleeve are used.

8. De-rating factor is usually expressed in ___________
a) W/°C
b) °C/W
c) W/s
d) kW/K
View Answer

Answer: a
Explanation: De-rating factors for determining the power dissipation rating is usually given at any temperature above 25°C. The de-rating factor is specified in W/°C.

9. Cavities embedded in heat source is also known as ___________
a) Low sink
b) Sink hole
c) On-sink
d) Inverted sink
View Answer

Answer: d
Explanation: Cavities embedded in heat source is also known as an inverted sink.
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10. By dividing volumetric thermal resistance by required thermal resistance we will obtain ___________
a) Power dissipation of heat sink
b) Volume of heat sink
c) Maximum temperature of heat sink
d) Volume of surrounding air
View Answer

Answer: b
Explanation: By dividing volumetric thermal resistance by required thermal resistance we will obtain volume of heat sink.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn