0

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?

Dr. Watson
  • 794
  • 9
  • 22
  • Take a look at my emitter-follower answer - it shows the assumptions made for that circuit. http://electronics.stackexchange.com/questions/8656/emitter-follower-output/8659#8659 – W5VO Jan 22 '11 at 08:41
  • How poor my memory is! Thanks for pointing that out. – Dr. Watson Jan 23 '11 at 03:04

2 Answers2

1

BJT is usually asymmetrical.

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

BarsMonster
  • 3,267
  • 4
  • 45
  • 79
1

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.

NickHalden
  • 4,167
  • 3
  • 31
  • 40
JustJeff
  • 19,163
  • 3
  • 48
  • 75