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Often I come up with the following reasoning when it comes to why collector has larger area than the emitter:

For less power dissipation collector area should be more. In other words, when area is more, resistance is less for a given current and hence power dissipation is less.

Usually base area < emitter area < collector area

But this argument confuses me because the collector and emitter passes almost the same amount of current. What is the point of saying collector needs to dissipate more power hence it needs to have greater area. If Ic and Ie are almost the same why wouldn't both regions dissipate the same power?

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  • \$\begingroup\$ Indeed, emitter current > collector current. Can you cite that reference. Something may be out of context here. \$\endgroup\$ – Trevor_G Oct 28 '17 at 17:39
  • \$\begingroup\$ emitter current > collector current. Is that the reason? But Ic and Ie are so close to each other. Is that tiny difference have such big impact on the area sizes designated? \$\endgroup\$ – atmnt Oct 28 '17 at 17:48
  • \$\begingroup\$ No I was just expanding on what you say. Where did you get the quote form in your question though? \$\endgroup\$ – Trevor_G Oct 28 '17 at 17:53
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    \$\begingroup\$ Ok so it only says "all should be large enough" for less power dissipation. \$\endgroup\$ – atmnt Oct 28 '17 at 17:55
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    \$\begingroup\$ Yup. especially when you consider the collector is the foundation layer of the transistor that the base and emitter are built on top of. If you make the foundation bigger the whole house gets bigger. \$\endgroup\$ – Trevor_G Oct 28 '17 at 17:56

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