[sdiy] Left over transistor in a transistor array

[Magnus Danielson]

David Ingebretsen skrev:
> I found a circuit I want to build which uses a CA3046 transistor array. One transistor is unused and in the schematic, the base and emitter are left disconnected and the collector is tied to -15 volts.
> 
> What is "good" practice for the pins of an unused transistor in an array like this? 

I think you should be aware of the following little piece of text from 
the CA3046 datasheet:

NOTE:
1. The collector of each transistor of the CA3045 and CA3046 is isolated 
from the substrate by an integral diode. The substrate (Terminal 13) 
must be connected to the most negative point in the external circuit to 
maintain isolation between transistors and to provide for normal 
transistor action.

It should be noted that pin 13 is the emitter of one of the transistors 
(with base at pin 12 and collector at pin 14).

Thus, hook pin 13 to -15V or whatever is the lowest in your design. If 
this is how you need to wire a transistor up anyways, then use that 
transistor for that function.

So, I think you *DO* care.

Cheers,
Magnus