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I know this question has been asked a lot of times and there are a lot of tutorials but please bare with me for one second. I understand the basic concept but based on my simulated results, one thing is not matching my expectation. Please see circuit below.

enter image description here

I expect that when I increase the base voltage very high, the collector voltage will decrease to 0, as it does. But why doesn't this put the transistor into cutoff/saturation? Why doesn't the current decrease to zero? No matter what Vbe is, all Vce curves go to zero.

Here is a link to the VCE curve: https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/info/comp/active/BiPolar/bpcur.html

[EDIT] Also, note that the 2N3904 has a saturation collector-emitter voltage of 0.2. So really, as soon as the voltage decreases below 0.2, it should decrease.

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    \$\begingroup\$ Saturation doesn't mean the collector current goes to zero. It means whatever is supplying current to the collector can't provide enough current to keep the transistor forward-active. (Also think about this: if collector voltage is 0, then voltage across R1 and D1 is 5 V, so there must be current flowing through those parts. Where else can it go but through the BJT then?) \$\endgroup\$ – The Photon Feb 27 '16 at 5:02
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    \$\begingroup\$ To say it another way, saturation in BJT's means the BJT doesn't control the collector current any more, instead the bias circuit (Vdd, R1, D1 in this case) controls the current. \$\endgroup\$ – The Photon Feb 27 '16 at 5:04
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    \$\begingroup\$ And that is why it flattens out. Thanks a lot. Can you post an answer? \$\endgroup\$ – user2316667 Feb 27 '16 at 5:18
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Saturation doesn't mean the collector current goes to zero. It means whatever is supplying current to the collector can't provide enough current to keep the transistor forward-active. (Also think about this: if collector voltage is 0, then voltage across R1 and D1 is 5 V, so there must be current flowing through those parts. Where else can it go but through the BJT then?)

When the BJT is in saturation, it doesn't (as far as back-of-the-envelope calculation models are concerned) control the collector current any more. Whatever is biasing the collector (Vdd, R1, and D1 in this case) controls the collector current.

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