Timeline for Confusion about the meaning of re and rπ
Current License: CC BY-SA 3.0
10 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Apr 9, 2018 at 17:06 | comment | added | LvW | Clear answer: No - causality works only with Vbe as the controlling quantity (and Ic as the controlled variable). | |
| Apr 9, 2018 at 17:05 | comment | added | analogsystemsrf | Look at the slope of the emitter-base junction at 1uA or 10uA or 100uA or 1mA or 10mA. That is the gm or 1/gm. | |
| Apr 9, 2018 at 15:48 | vote | accept | user1999 | ||
| Apr 9, 2018 at 15:48 | comment | added | user1999 | Just one more last question: When Vbe changes Ic changes so we can find the transconductance. So Vbe controls Ic in general... But is the opposite correct? In active region, if one causes a change in Ic(maybe by temperature or resistance change) would Vbe change according to the transconductance relation? Is causality valid both way? (I also ask because re is dVbe/dIe sounds like change in Ic causes a change in Vbe) | |
| Apr 9, 2018 at 15:44 | comment | added | user1999 | I see I mixed up the concepts. | |
| Apr 9, 2018 at 15:43 | comment | added | LvW | Yes - looking into a certain node gives the input resistance (which is the resistance between that node and GROUND). But your question was if re is a kind of resistance between E and B (internal emitter resistance or something like that). And the answer is : NO ! A resistor describes the voltage-current ratio between two nodes. However, looking into the E node, tlhis is not the case because the voltage between B and E is Vbe, but the current goes through the node C. | |
| Apr 9, 2018 at 15:39 | history | edited | LvW | CC BY-SA 3.0 |
added 151 characters in body
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| Apr 9, 2018 at 15:38 | comment | added | user1999 | I'm not into the subject quite new but I think I see what you mean in that sense it is not a resistance. I think some engineers invented the "resistance looking into" thing to make re a resistance. I just saw a user ak-94's answer here: electronics.stackexchange.com/a/157638/161776 I didn't think of it like that before. | |
| Apr 9, 2018 at 15:37 | history | edited | LvW | CC BY-SA 3.0 |
added 151 characters in body
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| Apr 9, 2018 at 15:28 | history | answered | LvW | CC BY-SA 3.0 |