Electronic Circuits and Projects Forum

NO.

He is doing a row scan not a column scan.Positive supply to the LED's will comes from 74HC595 & flow current to GND via row side.So you don't need additional ULN drivers.

I haven't use N-fets as he mentioned because those are very hard to find.

Use darlington on row side.

With that "cathode row" design, you could replace the 74HC595's with Micrel MIC5891 serial-to-parallel "sourcing" driver ICs but they're a bit expensive. Use two sets of Si2312BDS N-FET "sinking" row drivers (inputs connected in parallel) with outputs from each set driving the rows for a single 8x64 block.

With an "anode row" design, you could use MIC5821 or TPIC6C595 "sinking" column driver ICs and P-FET "sourcing" row drivers. Or you could use the 74HC595's driving ULN2803A's you mentioned.

Good Day Mike

Where were you all this time! I was waiting.

I had a similar issue on the current design 16 X 64 multiplex.

For a 16 rows design you are divided into two rows & do the scan in this case brightness will be 1/8.When its comes to real life adding two sets of column shift registers to the top row 8s (8, 595’s) & bottom row 8s (8, 595’s) becomes very hard.

I planed to scan 1/16 using 8, 595’s by adding some 64 PNP transistors to the each 595 outputs.

What’s your comment sir!!

My current LED arrangement is "Cathode row design" that's why when the no of rows gets bigger the hardware part goes hell of a mess.

Thinking to do my LED arrangement like "Anode row design" so all I have to place ULN with each 595 on column side & only need 16 current source transistors on row side.

I need your comments Mike.

You'll want to drive them at more than 20mA as they're only on 1/8 of the time. 60mA is common and may not damage them as quickly as 160mA. Also HE red are nice and bright with less current that standard red LEDs.
One way is PNP driving transistors.