At 06:04 AM 6/4/2009, Isaac Marino Bavaresco wrote: >Forrest W Christian escreveu: > > I'm needing to drive 4 latching relays with 3.3V (8 total coils). > > Low-side switching is ok. The relay I'm looking at is rated for 66.7mA > > of operating current. > >Usually the data-sheet shows the worst case Vce(sat) with a high >current. The Vce(sat) for smaller currents are generally much less than >what is in the data-sheet. Good data-sheets show a graphic of Vce(sat) x >Ic x Ib. Yeah - but the uln280x are darlington transistors. You just ain't gonna get much less than 1V saturation. Forrest - I know that you asked for drivers, but how about an SPI part with integrated DMOS output transistors? We use the TPIC family a LOT here - TPIC6595 and TPIC6C595. Avoid the TPIC6B595 - we've had nothing but grief with them. TPIC6C595 is in a 16 pin DIP package and is good for 100mA continuous per output. TPIC6595 is in a 20 pin package and is good for 250mA continuous per output. You also don't need clamp diodes on the relay coils - the devices are rated for inductive use and contain circuitry to cause avalanche at about 60V peak. We've used many thousands of these with no problems. We often drive them from a tiny PIC - each of the 3 SPI control lines can be shared with switches or an analog input or two. Hope this helps! dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist