Re: multi white led circuit
- From: ehsjr <ehsjr@xxxxxxxxxxxxxxxx>
- Date: Sat, 10 Jun 2006 00:05:26 GMT
jay wrote:
I am wanting to make a light source for a video projector.
I would like to use 640 leds in a space of about 6"x9"
Considering using a power supply from a computer or direct ac
can I use the following circuit for that many leds?
A .47mf 250V capacitor in series with a row of 20 leds, 32 rows with
a 1K 1W metal oxide resistor across a 120V AC line
Any help here would be greatly appreciated
Your scheme will work with modification, but it's
not safe, and you really don't get an advantage using
a cap. If you are bound and determined to do it:
1N4004 Led1 LED20
Ac ---+---[R]---|<----|<--- ... ---|<---+
| |
+---[R]--->|---->|--- ... --->|---+
1N4004 Led1 Led20 |
Ac -------------------------------------+
16 strings of the above. Resistors will
be 120 - Vf*20/I ohms. I'd get 100 1.8K 2 watt
resistors and put 2 in series for each string
to spread the heat a bit. You'll save $5.04
using resistors vs capacitors, and have 20 left
over by buying 100 resistors for $10.00 vs 32
capacitors for $15.04 (Mouser). And no ugliness
of shorted capacitors or high current surges.
The IN4004 diodes are needed in either case.
Finally, 3600 ohms will accomodate a good range
of Vf. At Vf = 4, 11 mA; at Vf = 2.8, 17 mA.
Your Leds will have Vf > 2.8, < 4.0
Ed
.
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