These dual pfet's (irf7304) have been working for me as high side row drivers in a multiplexed 8x8 RGB led configuration. That would be 480ma max, but haven't been using all white much either.
It's going to take me a little while to digest this. I'll get back to you later today.
About the 70mA, that is what I have suspected too, but I do not understand why, maybe 80% of all projects I have seen, they drive the leds directly with the 74HC595, and on each port only having a weak resitor, something about 80-180 ohms.
But in this case, the 74HC595 was sinking the current and not powering.
But still, the Icc/Ignd is 70mA, so I suppose that the effect would be the same.
About the transistors, there are some cheap 500mA (90 Euro cent) transistor array to sink the current wich would be controled by the 74HC595.
Then, I would have only to get some transistors to power the rows.
I think, correct me if i'm wrong, this would be the easiest, cheapest way, and I would have less components on the board.
This is the solution I thought of, with everything I have read on forums/other projects/some datasheets, because sinking is easier than powering, and even a lot cheaper.
If can get my hands on some cheap 1A NPN transistors, I could drive an entire row of 40 leds, using each, 20mA. If I use 15mA, I could use a 800mA transistor, and the leds, I think, would be still bright enough. once again, please correct me if I'm wrong.
Another option, would be to use cheap 200mA transistor array to power the rows (or some transistors) and sink them with some cheap transistor array.
This second option, I think it would be more expensive than the first one, because I have to sink 800mA max. In the first option I would only have to sink 200mA.
Which would you recommend?
Another option, would be to use cheap 200mA transistor array to power the rows (or some transistors) and sink them with some cheap transistor array.
This second option, I think it would be more expensive than the first one, because I have to sink 800mA max. In the first option I would only have to sink 200mA.
Which would you recommend?
About the PN2222, i have seen a lot of different ones... some that are capable of 600mA, others of 800mA, and others of 1A. search for this transistor in the site tme.eu, and there they say that that transistor supports 1A. Because of these different numbers, I'm confused, and thats the reason I also asked here in the forum, hoping that you would also come across these numbers.
About beeing easier to sink than to drive, and a lot cheaper, is just what I found googling around.
Taking this in consideration, and as we have more columns than rows, the cheapest way would be sinking on top (columns), and sourcing at the side (rows).
I prefer IC's too, but power IC's, for sourcing this, are way too expensive. With discrete elements, I could do this, for each 8 rows, for less than 1Euro, and with IC it would be for +/- 3Euro.
My LED matrix is a common anode, So I have to source the, normaly, the rows, and actualy, it is also what would be the cheapest. But with common anodes matrix, I could also source at the columns, because it is just a matter of wiring. I have read that common anodes/cathodes, in the Led Matrixes, are, in fact, only to tell us if the rows are of the matrix are anodes or cathodes.
About the rows, I think your are mistaken. In each row, we have 40 columns, and these 40 leds need to be sunk. it would be arround 800mA.
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