Timeline for Adding a base resistor in a common emitter amplifier
Current License: CC BY-SA 4.0
8 events
| when toggle format | what | by | license | comment | |
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| Jul 27, 2020 at 4:49 | comment | added | linuxfan says Reinstate Monica | @lvw I agree. I thought that talking about "voltage developing" was simpler, especially for an inexperienced user, than pulling down more complicated concepts. A note in the answer would improve it, but I am not good enough to add it. Maybe you can do it? :-) | |
| Jul 26, 2020 at 19:00 | comment | added | LvW | Yes - it is absolutely no problem if one knows what he is doing...but - for my opinion - the situation is different if we try to explain something to somebody who is not so experienced...you see what I mean? | |
| Jul 26, 2020 at 15:59 | comment | added | linuxfan says Reinstate Monica | @LvW of course you are right or, maybe, not always (how about the BEMF of a DC motor?). Anyway, when concentrating on currents like in this case, or for example when a shunt resistor is used to read current, it is correct to think in terms of current developing voltage. | |
| Jul 24, 2020 at 18:34 | comment | added | LvW | Quote: "Current develops voltage when traversing resistors". I agree that during circuit analysis we ASSUME that this happens. But in reality (and physically spoken) this is wrong. No current without driving voltage. It is the E-field within a resistor (caused by the applied voltage) that allows current trough the devivce - NOT VICE VERSA! More than that - try to rethink your understanding of the transistor principle...don`t overestimate the role of the base current... | |
| Jul 24, 2020 at 17:31 | comment | added | jonk | @HelenaWells Oh, you definitely have it right that a resistor is needed somewhere inserted between voltage supply rails an the PN junction of base-emitter. Otherwise, just as you say, the full voltage will be applied to the base-emitter and the current would be exponentially large (and bad.) But that doesn't mean that the resistor placed on the base side does the same thing as a resistor on the emitter side, for an amplifier circuit. It does do the same thing in terms of limiting current through the junction, though. So you see part of the issue. Just not all of it. | |
| Jul 24, 2020 at 17:31 | comment | added | linuxfan says Reinstate Monica | Yes, a resistor in base is to limit the base current, and to raise the input impedance; a resistor at emitter also does that, but it also stabilizes. If your transistor is a switch, you can perhaps avoid emitter resistor; but if your transistor has to be even a little linear, you must stabilize it. | |
| Jul 24, 2020 at 17:28 | comment | added | Helena Wells | OK but if we don't put any base or emitter resistor doesn't this mean Ib becomes too big the junction can't handle it? | |
| Jul 24, 2020 at 17:21 | history | answered | linuxfan says Reinstate Monica | CC BY-SA 4.0 |