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ramz
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Join Date: Jan 2008
Posts: 4

Driver

01/15/2008 5:06 AM

hi can you help me about current driver of 5 x 7 LED dot matrix to stable the brightness.
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techno
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Canada - Member - Our strength is our diversity

Join Date: Jan 2007
Location: Canada
Posts: 1024
Good Answers: 40
#1

Re: Driver

01/15/2008 10:41 AM

Try adding a zener diode to the circuit

Seems to me, the more LED's that are 'on' in parallel, the lower the total resistance and the lower the voltage drop across the LED's creating less light. You need to compensate by having the current limiting resistor change its value to keep the voltage drops constant (and thus the current in each diode constant)

A Zener diode will effectively do this, in series with the LED's.

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ramz
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Posts: 4
#2
In reply to #1

Re: Driver

01/15/2008 11:26 PM

so you mean before we connect to LED,we should connect the zener diode first?
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Anonymous Poster
#3
In reply to #2

Re: Driver

01/16/2008 7:38 AM

<A Zener diode will effectively do this, in series with the LED's.>
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techno
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#5
In reply to #2

Re: Driver

01/17/2008 10:28 AM

The zener should be between the LEDs and the ground or return path.

You need a Low voltage adjustable zener such as this one http://focus.ti.com/docs/prod/folders/print/tlv431.html

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charlie_r
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Join Date: May 2007
Location: 39°10' N 91°52' W
Posts: 237
Good Answers: 15
#4

Re: Driver

01/16/2008 7:48 AM

You may need to go to a pulsed circuit, that will drive only one LED at a time.

POV (persistence of vision) will make it look like all your LEDs are lit simultaneously.

Or you could use this circuit on each column or row:


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Anonymous Poster (1); charlie_r (1); ramz (1); techno (2)

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