reversing transistors

[rhdwave]

Just wondering what would happen if you reversed the alignment of a 3906 transistor? That is, if you socketed it correctly then took it out and reversed the emitter and collector

[R.G.]

The reverse connection is well documented. It works with these changes in characteristics:

1. The reverse "collector" voltage rating is lowered to the reverse Vbe value. On modern silicon transistors this is about 5-7Vdc. More than about 7Vdc on the collector to emitter will break over the transistor.
2. The hfe in this situation is very much lower than the hfe in normal operation. It can be down in the units (i.e. 1,2,3...).
3. The "collector"-"emitter" resistance in the resistive area is lowered. Transistors are (were... back when NPNs were used as switched) used reverse mode for switching.

All of this falls out of the asymmetrical doping of modern transistors. Back when transistors were made by cooking indium pellets on a "base" chunk of germanium, the junctions on both sides were pretty much alike, and you could use it either way. Many older germanium devices have symmetrical characteristics and can be used equally well (or poorly, depending on how you look at it) either way. The Vbe breakover on many older Ge devices is upwards of 20-30V. But you can make better gain, frequency response, etc. by making the base-emitter junction smaller and thinner than the collector, and all modern silicon devices are made that way to get higher gain, better frequency response and other characteristics.

[mountainking]

You can also read what Jack Orman has to say on his site: http://www.muzique.com/lab/reverse.htm

[rhdwave]

Okay, thanks very much for the replies