Re: Require a source driver

hybrid_snyper wrote:

Donald wrote:

ehsjr wrote:

Donald wrote:


ehsjr wrote:


hybrid_snyper wrote:


Hi all,

im building at LED matrix to display scrolling text. I have constructed
as simulation in Multisim and I have discovered that i am unable to
provide enough current to source the LED anodes. Would any body be able
to suggest a device i could use to provide enough current to source a
row of 95 LEDs. For an idea of what i am building have a look at this
link.

http://www.acm.uiuc.edu/sigarch/tutorials/ledarray/

thanks


You could use a power darlington like a TIP120. On a nice
heatsink, it can provide up to 5 amps, and your 95 LEDs at
20 mA each need under 2 amps total. You'll need to limit
the current through each of the LEDs so they don't burn out.

Ed



Ed,

2 amps is all LEDs on at one time.

The link provided shows a multiplexed system.
So, one row of X LEDs x 20ma + 10% overhead is the total current
required.


He wants 95 leds in a row. "Would any body be able
to suggest a device i could use to provide enough current
to source a row of 95 LEDs." I must be missing something.
His link shows a total of 32 LEDs - 4 rows of 8. Maybe he
wants to source a *matrix* of 95 LEDs, not a *row* of
95?

Ed


hybrid_snyper,

What is the configuration are you looking at.

5 columns x 95 rows = 95 LEDs, or do you have another configuration in
mind.
Only 5 LEDs would be on at a time. This would require 95 low side
transistors and 5 high side buffers.

Good Luck

donald


In spite of my typo [19->95], the OP did say "im building at LED matrix".

Is hybrid_snyper still out there.

donald


Yes, sorry i have not been feeling to good these past few days.

I'm building a LED matrix the DOC i posted is just test circuit to
which I am going to build-up with more 5x7 LED arrays. The LED matrix
is made of 95 columns and 7 rows. I'm not multiplexing the rows put
rather feeding data into rows and scanning the columns at a high
frequency with a decade counter made up from 4017s. The matrix will be
controlled from a PIC. Columns will be scanned in such a way that the
data will change with each clock of the counter. So data1 displays in
column 1; CLK; data2 displayed in column 2. Obviously this syncing will
be software controlled in the MCU.

With the direction of John B, i have looked at the MX6952
http://datasheets.maxim-ic.com/en/ds/MAX6952.pdf , this seems to be
able to provide the functionality that i need, and will save on some
coding in the MCU. This IC appears to allow me to daisy chain to
support more 5x7 LED arrays. i was originally wanting to use 19 LED
arrays, now i will use 20 which means i can daisy chain 5 MX6952 to
run the matrix. My software will just have to output the 16-bit words
for each character to the MX6952. just got to think on how i can scroll
this text, but that will come later.

Thank you all for your input on this, im learning something new with
every post, even that I have bad grammar, seem to type faster than my
train of thought ;o)

One last note.

Is this a one off (2 or 3) or will you building many units.

Cost of each unit could be reduced by using more software and less hardware.

Good Luck
donald

PS: Please post pics of what you end up with.
.

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