4511 CMOS with Vdd =3D 12 V & level shifters on the BCD I/P? Also, if only 12 hr clock, the MSD (hour 10's) can be treated as a single = LED string with the two segments paralleled. So you only need three 7-segme= nt drivers. Add another single LED to indicate AM/PM if needed. Stephen > -----Original Message----- > From: piclist-bounces@mit.edu On Behalf Of > Dwayne Reid > Sent: Thursday, 28 February 2019 4:25 AM > To: Microcontroller discussion list - Public. > Subject: Re: [EE] Looking for recommendation: high-side LED display drive= r >=20 > Hi there, Spehro. >=20 > I was actually heading down that path myself: having a chain of 4- > HC595 shift registers with their ground pin shifted by about plus 3 Vdc a= nd > using simple level-shift circuit on the control and data lines. The sing= le-LED > dots would use another HC595 that wasn't ground-shifted. >=20 > The advantages of doing it this way are: single-dot HC595 is at the PIC g= round > potential **and** there is minimal ground current on the level-shifted > HC595 chain. So the level-shifted power supply ground might just be a si= ngle > LED with appropriate bias resistor (to keep the LED lit). Have to work t= he > numbers but seems reasonable at first blush. >=20 > I'm going to have to look hard at the package dissipation and maximum > package current ratings for the HC595 - 28- segments split over four pack= ages > is 7 segments per package at 20 mA per segment for a total of about 140 m= A > current per package. That seems too high at first glance but the data sh= eet > should tell all. >=20 > Many thanks! >=20 > dwayne >=20 >=20 > At 08:54 AM 2/27/2019, speff@interlog.com wrote: > >Quoting Dwayne Reid : > > > > > Good day to all > > > > > > Several years ago, we purchased the assets of a L > > > >By the way, if you create negative supply (perhaps with a inverting > >boost converter) you could use a 74HC595 chain to switch the anodes > >directly (just resistor networks in series). > > > >I did something similar to this with a common anode display some years > >ago, and deliberately gave the power supply a temperature coefficient > >to match the LED tempco. > > > >--Spehro Pefhany >=20 >=20 > -- > Dwayne Reid > Trinity Electronics Systems Ltd Edmonton, AB, CANADA > 780-489-3199 voice 780-487-6397 fax 888-489-3199 Toll Free > www.trinity-electronics.com > Custom Electronics Design and Manufacturing >=20 > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .