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I am having trouble understanding why the BC junction is considered to be reversed biased in these two models. The way I see it, the base looks to be in a higher potential than the collector junction given the polarity in the PNP model.

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    \$\begingroup\$ In the PNP model, everything is reversed from the NPN model. The collector is more negatvie than the base, but the CB diode is the other way round. \$\endgroup\$ – Neil_UK Oct 20 at 7:31
  • \$\begingroup\$ @Neil_UK I looked at the two-diode mode analogy of the BJT and it makes more sense. I would like to clarify that since the collector is more negative than the base, electrons would start flowing through the base from the collector. Hence, even though the BC diode would indeed be reversed-biased, since positive current flow is opposite of electron flow, that is the reason why in circuit models of the BJT, there is current flowing from the base to the collector? (in PNP transistor) Is that right? I hope I made any sense. \$\endgroup\$ – user263783 Oct 20 at 7:40
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    \$\begingroup\$ Current only flows between base and collector when the transistor is saturated, with a Vce < 0.2 V. In normal linear operation, Vce > 1 V, and only a leakage current flows between base and collector. \$\endgroup\$ – Neil_UK Oct 20 at 9:38
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    \$\begingroup\$ It's hard to imagine more misleading drawings than 1) a transistor as two back to back connected diodes in series 2) A drewing of transistor's currents and voltages with a transistor + two batteries, one connected between C and B and the other connected between B and E. There's nothing wrong with them. One can really find the dieodes with an ohmmeter and surely something can happen in the "modes of operation" circuit. But those drawings skip the fact that base is bery thin, much thinner than the usual thermal Brown motion length of the carriers in usual temperatures. \$\endgroup\$ – user287001 Oct 20 at 12:41
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    \$\begingroup\$ (continued) That thermal motion causes the current through base mostly goes between C and E, only a small part goes through the base terminal wire if there's at least a few hundred mV between C and E. That's the foundation of amplification in transistor. \$\endgroup\$ – user287001 Oct 20 at 12:46

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