Rikard Bosnjakovic wrote: >On 2/28/07, Forrest W Christian wrote: > > > >According to the datasheet for my leds, each segment can eat up to >30mA. Given the worst case (all segments lit), this would be 210mA, or >1.05W at 5 volts. The sheet also says that there's generally a 2 >v-drop for each segment so I'm unsure if the dissipation is as above >or (5-2)*0.21 = 0.63W. > > Actually Pd is roughly Ic*Vce(sat). The Collector-emitter drop at saturation is typically less than .5V, so your total pd would be .21*.5 or around 1/10W. I would worry more about Ic, which is rated typically around 200ma continuous, 300ma peak. But... in reality you probably won't hit this due to the duty cycle. Remember, if you're muxing, your continuous rating can be derated since the transistor won't be on 100% of the time. Peak ratings may need to be respected more. So, all you really need is a pile of GP PNP transistors. I have an Atlas DCA ( http://www.peakelec.co.uk/acatalog/jz_dca55.html ) which makes sorting the junkbox a lot easier - but again, I've recently been re-building my collection. -forrest -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist