Yeah thanks, I remember that chip now. Should do the trick nicely. A quick 
look at the data sheet shows turn off time may be a little slow and depends 
on output load, so for an LED multiplexing application would need to keep 
that in mind but I'm sure it would be easy to allow for.

On 3 Nov 2004 at 20:49, Marcel van Lieshout wrote:

> Perhaps these can help: http://www.voti.nl/shop/catalog.html?IC-UDN2981-DIP
> 
> Marcel
> 
> Brent Brown wrote:
> > On 3 Nov 2004 at 17:15, Dominic Stratten wrote:
> >
> >> I need to drive a blue 7 segment LED display with a PIC. The problem is 
> >> that
> >> it uses a 7.4 volt nominal supply.
> >
> > Me too, in the near future...
> >
> >> PIC PIN --> RESISTOR --> NPN TRANSISTOR BASE
> >> NPN TRANSISTOR COLLECTOR --> RESISTOR --> PNP TRANSISTOR BASE
> >> NPN TRANSISTOR EMITTER --> GND
> >> PNP TRANSISTOR EMITTER --> +7.4 volts
> >> PNP TRANSISTOR COLLECTOR --> SEGMENT OF DISPLAY
> >> (OPTIONAL - PNP TRANSISTOR BASE --> RESISTOR --> +7.4 volts)
> >
> > Yeah that sounds right. Like others have said, the "optional" resistor is
> > important for turning the tansistor off.
> >
> > The parts count is pretty high, but not easy to get around. If you use N 
> > and P
> > channel MOSFET's (logic level) instead of BJT's then you can do away with
> > the series base resistors. The next option would be a chip that has a 
> > bunch
> > of high side drivers, can't recall what's available right now. 
> 
> _______________________________________________
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist

-- 
Brent Brown, Electronic Design Solutions
16 English Street, Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/txt: 025 334 069
eMail:  brent.brown@clear.net.nz


_______________________________________________
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist