Re: bjt emitter current rating

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Jim Lux" <jimlux@xxxxxxxxxxxxx>

By and large, yes....

But just how much base current are you going to be driving with.  If you're
operating the transistor as an amplifier (not a switch), then the base
current will be less than the Ic  (Ie = Ic+Ib, and since Ic = Ib* hFE, Ie=
Ib*(1-hFE))

However, if you're running in saturation (where Ic << Ib*hFE) it's
conceivable you could have a lot more emitter current than collector
current.  I think the datasheet limit you're going to want to look at is the
Ib max in this situation..

Looking at the data sheet for the venerable 2N3055, for instance..
http://www.onsemi.com/pub/Collateral/2N3055-D.PDF

They give Ib max as 7A..

I suppose you could have Ib=7A and Ic=15A, so Ie=22A, but I don't think that
would work.  The limiting things here stuff like bond wires, and the emitter
and collector will have similar connections (in fact, the collector
connection is usually the case, so is probably a lot tougher than the
emitter, which is a bond wire to a pin).

And, given the really crummy large signal current gain (hFE) of the 2N3055
(all of 5 at Ic=10A), I can see how one might run a lot of base current...
At that test condition, Ib=2A, so Ie=12A.... Maybe that's what limits the Ic
on that part.. Ic=15A, Ib=3A, Ie=18A???



----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Thursday, January 27, 2005 3:18 PM
Subject: bjt emitter current rating


> Original poster: "Anthony" <ant17@xxxxxxxxxxxxxxxx>
>
> hi guys i was hoping someone might be able to tell me is the emitter
> current rating of a npn transistor same as the collector rating if someone
> could shed some light on this i would be greatful
>
>