Current require for LED in scan mode

khongai

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« on: September 21, 2007, 09:03:50 09:03 »

Hi friends,

I want to design 1 message display board.

How can i calculate the requirement current for LED?


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fagari

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Re: Current require for LED in scan mode

« Reply #1 on: September 22, 2007, 07:45:52 07:45 »

it's depend yours circuit design and source code.

Example :
if you use standart led, normaly max current is max 20-30 mA but use small pulse time max current is about 100 mA.

I use 39 Ohm current resistor and 5 V supplay voltage and 50 us drive time for bright Led.


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maiasj

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Re: Current require for LED in scan mode

« Reply #2 on: September 22, 2007, 01:43:40 13:43 »

Loot at the LED's datasheet for the max. current for DC supply and then multiply for the dutycicle. Ex: LED DC Imax = 20 mA, DS = 10%, so max. current is 200 mA.


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freddy

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Re: Current require for LED in scan mode

« Reply #3 on: September 22, 2007, 04:11:04 16:11 »

Quote from: maiasj on September 22, 2007, 01:43:40 13:43

Loot at the LED's datasheet for the max. current for DC supply and then multiply for the dutycicle. Ex: LED DC Imax = 20 mA, DS = 10%, so max. current is 200 mA.

Attention when you start and stop the multiplexing... or the LED with 200mA... Shocked

A solution for unwanted critical situation is to make by hardware a simple control (like a capacitor) to stop
the unwanted continuos drive of transistor that's drive the LED.


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