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I've been playing with voltage swings in a basic emitter-follower circuit. If I swing the input too large in the negative cycle, the base-emitter junction is reverse-biased and the transister goes into cutoff mode. I can see the clipping in the output and this makes sense to me. With the collector, however, I've noticed that I can swing higher and not see symmetrcial clipping. Eventually I do see the clipping.

Is there a rule of thumb, like with the base-emitter junction, for managing base-collector junction? May I use VC-VB=0.6/0.7 V for this relationship too?

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Take a look at my emitter-follower answer - it shows the assumptions made for that circuit. electronics.stackexchange.com/questions/8656/… – W5VO♦ Jan 22 '11 at 8:41
How poor my memory is! Thanks for pointing that out. – Dr. Watson Jan 23 '11 at 3:04

2 Answers

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If you drive the base positive enough (assuming an NPN) what happens is the transistor 'saturates', and the collector voltage will dip to just a couple tenths above the emitter. In this mode, the base-collector junction is actually forward biased, instead of reverse biased as is usually the case.

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BJT is usually asymmetrical.

There is no rules AFAIK, they all different there - so you need to test each type you need.

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