PWM multiple 7-segment LEDs

[Ioannis]

The sink is always better choice than sourcing.

Then N-channel MosFets along with NPN transistors are much better than P equivalent ones and more choices available.

And finally, even if a PIC can source or sink 20, 30 or 50mA per pin, there is a maximum TOTAL dissipation for the whole chip, so that you cannot source at the same time on all pins a max of 50mA on each pin!

You will melt the chip!

So, yes. I am for the sink topology too.

Ioannis

[Ioannis]

Now, if you look at datasheet, p236, for the 946 chip.

Output Low is 0.6 Volt at only 8.5mA but,

Output High Vdd-0.7 Volt at 3.0mA

So, yes. It is better to sink than source.

Ioannis

[richard]

for my money i would do it the traditional way or if multiplexed display is not bright enough use a bunch of tpic6b595's



note schema is not complete but you get the idea, i was going to try it in proteus then i remembered how crap proteus is at simulating multiplexing
so i gave up

[tumbleweed]

With that many displays I assumed they would be multiplexed as in richard's post #17.
Surely a lot less supply current, and you wouldn't need nearly as many pic's to drive them... maybe get away with one or two 44-pin packages.

[Demon]

for my money i would do it the traditional way or if multiplexed display is not bright enough use a bunch of tpic6b595's...

Thanks, I'm off to google that chip (no idea what it is). I've also seen talk about using a 74HC595 (never met that creature either).


EDIT: Google says TPIC6B595 can sink up to 150mA at 50V. JLCPCB carries them at $1.54.

Google says 74HC595 has a 70mA total limit, so there goes that chip. JLCPCB has them at $0.11 too.

[Ioannis]

The 74HC595 is a shift register. How can this help on 7-seg LED's ?

Dedicated chips like Maxims or the TPIC6B595 I think is the way to go.

Ioannis

[Demon]

The 74HC595 is a shift register. How can this help on 7-seg LED's ? ...

Some people use them to drive 7-segment LEDs. They don't have digit control, only segment control, so you need one per digit.




It turns out my supplier for 7-segment LEDs also print and assembles PCBs. It wouldn't be cost effective to ship my LEDs back, so I might very well do the jump to the MAX7219 if I have to buy more LEDs.

I'm keeping all my options open for the time being, but the MAX7219 does offer one really neat feature; an intensity control. That TPIC6B595 is a close 2nd for common anode LEDs.

[richard]

You should also look at HT16K33 , that can read in switches and buttons too
ditto for
tm1637 and 1638