Timeline for Current sources and voltage sources connection
Current License: CC BY-SA 4.0
11 events
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Jun 15, 2022 at 4:17 | comment | added | Circuit fantasist | @LvW, More precisely speaking, the followers try to be voltage sources. In common mode, they succeed since they are not loaded; in differential mode, they do not succeed, since they are hard loaded. The collector currents represent their reaction to the load and are used as output signals after they are converted into voltages. | |
Jun 14, 2022 at 20:53 | comment | added | LvW | ".....two emitter followers connected to a common load": However, each of the followers sees also the small input resistance (1/gm) of its "partner" (in parallel to the common load) - therefore, I think, each of the followers does NOT act as a "voltage source" because the load resistance is equal to the source resistance. This leads to the factor 1/2 in the gain expression (1/2)gRc.. | |
Jun 14, 2022 at 19:03 | comment | added | Circuit fantasist | @LvW, As you know very well, the humble long-tailed pair consists of two emitter followers connected to a common load - a resistor. The role of this resistor is not so much to be a load but rather a "pull down" element (there is a need of such an element because both transistors are "pull-up" elements). If we connect the emitters of two different transistors (PNP and NPN), we can provoke a "voltage conflict" without a "pulling" resistor. | |
Jun 14, 2022 at 18:47 | comment | added | Circuit fantasist | @LvW, The voltage conflict principle can be observed when connecting "reacting" voltage sources with dynamic internal resistances. A typical example is the emitter follower where a transistor responds to any attempt to change its emitter voltage. In your example, the voltage sources are "passive". | |
Jun 14, 2022 at 18:40 | history | edited | Circuit fantasist | CC BY-SA 4.0 |
Added related link
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Jun 14, 2022 at 18:39 | comment | added | LvW | I must admit that I have problems to follow the "voltage conflicts" example. Lets assume that we connect two batteries (each with an internal source resistance) in parallel. The current will be zero for equal values and will simply follow Ohms law for the difference V1-V2. As far as the long-tailed pair is concerned: Does each transistor really act as a (non-ideal) voltage source? The small source resistance of T1 is connected to a load which has app. the same value (Rload is NOT much larger than 1/gm). | |
Jun 14, 2022 at 18:34 | history | edited | Circuit fantasist | CC BY-SA 4.0 |
About mutual helping heterogeneous sources
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Jun 14, 2022 at 18:22 | history | edited | Circuit fantasist | CC BY-SA 4.0 |
Structuring
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Jun 14, 2022 at 18:12 | history | edited | Circuit fantasist | CC BY-SA 4.0 |
About using voltage and current conflicts
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Jun 14, 2022 at 17:41 | history | edited | Circuit fantasist | CC BY-SA 4.0 |
More about transistor behavior
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Jun 14, 2022 at 17:14 | history | answered | Circuit fantasist | CC BY-SA 4.0 |