At 08:44 AM 5/27/2005, phil B wrote: >Something that I wanted to look at but never got to >was to run the 595s at a lower Vcc to get output high >to be the LED voltage drop (lets say 2V for arguments >sake). Then the max dissipation would be 2*8*10 >(160mW) and eat less battery. I do something similar with that 40- LED board I described earlier. All the logic runs from a simple zener-regulated 5V supply but the LEDs anodes are all connected to a Nat-Semi simple switcher set at 3.3V. The LEDs illuminate when driven LO by the hc595 and are reverse-biased with somewhat less than 2 volts while off. Well within the LED specs. This display card is mounted to a piece of Lexan fitted to a cut opening in an industrial control panel. It makes for a completely water-tight and fairly good-looking display but total dissipation was a concern. Running the LEDs at that low voltage kept the temperature rise very low. Not using a switcher would have resulted in considerable heat, given that the whole thing is running from a 24Vac supply. Note that the hc595s are running from the same 5V supply as the PIC - only the LEDs are run at 3.3V. Another advantage of doing it this way is that the mosfets in the output stages of the hc595 are fully enhanced. Running the hc595 at 3.3V results in much higher RDSon and hotter chips. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 21 years of Engineering Innovation (1984 - 2005) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist