Re: LED display design

On Fri, 29 Jul 2005 00:18:53 +0200, Mochuelo wrote:

> On 27 Jul 2005 22:00:02 -0700, "captsomer" <destinyyacht@xxxxxxxx>
> wrote:
>
>>I need to build a sign. It will have 7 letters and I want to use LED's
>>to backlight it. I'm going to need to light about 40 of them. I have
>>tinkered around with LED's in the past and I have a basic knowledge,
>>but I thought I'd ask others for thier opinion before I spend all of
>>this time and money.
>>
>>This circuit needs to be powered by 110 VAC. The LED's are 3.6v @ 20mA.
>>Should I use a lower voltage power supply? Are there schematics for
>>projects like this on the web that might come close to what I'm doing?
>>Series or paralell?
>
> Do you need isolation? (If you were using bulbs, you probably would
> not have it, either). If you don't need it, there is a cheap
> alternative with very few capacitors, resistors and diodes. Let me
> know if you want to go this way.

Easy. Two series strings of 20 LEDs each, with about a 2.4K, 2W resistor
all in series, in antiparallel. (i.e., one string with the cathodes up,
the other with the cathodes down, and the two strings in parallel right
across the 110V line). This is assuming LED current of ~20 mA.


L1 -------------+-------+
| |
[2K4] [2K4]
| |
--- ---
\ / / \
--- ---
| |
. .
. . <- 40 total, 20 per string
. .
| |
--- ---
\ / / \
--- ---
| |
L2 -------------+-------+


Cheers!
Rich

.

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