You could look at 12 or 20 bit shift registers like thesehttp://datasheets.maxim-ic.com/en/ds/MAX6920.pdfhttp://datasheets.maxim-ic.com/en/ds/MAX6921-MAX6931.pdfUse this to source current, and TPiC6B595s to sink current (or ULN2803 on output of 74HC595).If your matrix is 12x12, why do you need more than 2 8bit parts each for the rows & columns?Request a couple of samples from MAXIM.
"It's for a 12x12x12 LED cube, and I am trying to keep the muxing down, so I am turning on a layer at a time (144 LED's at most)."So you've got horizantal muxing & vertical muxing.Using a Maxim 12-bit chip to drive anode high and allegro chip to pull low, that's just 2 chips & resister per layer, with the vertical chip cycling thru the layer output enables.
The problem is mixing PWM with the multiplexing, the two need to be synchronised. An on time of 8% is not going to be too bright. 25% on time is just on the limit of what I think is acceptable.
Is there something I am missing?
QuoteIs there something I am missing?The magic of using constant current drivers where you can separate (decouple?) the led current value you want from the multiplexing timing duty cycle ?Lefty
Maybe the heat dissipates faster as the led heats up. Or maybe it's linear. Who knows?
If one goes out & buys a bag of 1000 LEDs from e-bay from China, what do you get?
for a multiplexed 5x5 matrix, each LED will only be on for 4% of the time