On May 18, 2008, at 7:38 PM, Jinx wrote:
>> Err... on a TO-92 case, the base is the middle one, right?
>
> Not always, but generally. Although if you're used to working with
> particular parts it may be that those *do not* have b in the middle,
> so then "generally" would not be true
>
>> How do you know which is the emitter and which is the collector?
>
> You could check against this
>
> http://www.fairchildsemi.com/ds/2N/2N3904.pdf

The point is that a transistor will work with E/C connections  
reversed, but it works poorly that way.  Which is approximately what  
you're seeing...

With an open-collector pin like you have, I'd be inclined to use a  
PNP transistor in a high-side driver configuration (and reversed  
logic in the SW.)  (4.3V)/(4.7k+4.7k) = 0.9mA of base current, which  
is less than I'd like when turning on an NPN transistor (it SHOULD be  
sufficient, but it's out of the "comfortable" range.)

BillW


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