"Dave" wrote in message
news:EYVTf.6018$J43.3427@edtnps90...
"David C. Partridge" wrote in message
...
I'd think that any PNP power xistor with an adequate voltage rating would
do - this is just a pass xistor wired as an EF isn't it?

David

I know very little of transistors other than their basic function, so I
don't know the answer to your question above.

As I noted, it's being used to (down)-regulate negative DC voltage. What
might the reason have been to opt for this transistor over a regulator?
There is a +5VDC regulator right next door in the same circuit.

Can I use the regulator in place of the transistor?



Maybe, maybe not. The 2V difference probably isn't critical, but we don't
know how much current is being drawn. The 7815 is only good for around an
amp with a big heatsink, (some variants 1.5 A), the 2SB527 is good for 2A.
You could try one and measure the current, I doubt the current draw will be
anywhere near 2A. You'll probably want a decent heatsink though, and to get
closer to 13V you could bung 3 series diodes in the output of the regulator
output to give 15-2.1=12.9V. Take care to use diodes rated higher than the
current though, 1n400x might not be adequate. Again, they're only good for 1
Amp.

As for a replacement transistor, just about any power transistor of similar
(or better) rating and similar physical size will do, it isn't critical in
this application. You could use something in a TO220 package like a TIP42c
which is a popular transistor here in the UK.

http://www.fairchildsemi.com/ds/TI%2FTIP42C.pdf

Dave