+-----------+-------- +5V
| |
4.7K Ohm Collector
| .
D33D1 --- 220ohm ------+-------- Base Q1, PNP Silicon
.
Emitter ----- 47 Ohm ---+--- RS-232 OUT
|
3.3 K Ohm
|
-12V (Regulated)
Sure you don't have collector and emitter switched on that diagram? If
you don't, you're using it "backwards"; lots of BJTs will work if you
swap C and E, but not as well as they will the right way around. (The
usual simplistic diagrams of BJTs make them look symmetric in this
regard, but as I understand it the diagrams are a simplification and
the actual geometry is not as symmetric as the diagrams make it look.)
Also, you're getting close to the RS-232 undefined voltage area there,
unless your RS-232 ground is not at the same voltage the +5 and -12
lines are referenced to; assuming Q1 drops half a volt and is otherwise
perfect, the open-circuit swing is between -12 and +4.27 (approx.), the
+ve end of which is close to the -3-to-+3 (IIRC) undefined area.
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