John Fields
Guest
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 Posted:
Tue Feb 22, 2005 6:10 am Post subject:
Re: How can I increase voltage from 3.2v to 3.5v? |
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On 21 Feb 2005 15:55:22 -0800, craget@ntlworld.com (crag) wrote:
| Quote: | Hi guys, I want to change the power/eject led's in my xbox. The
current led's are green/red bi-coloured and I want to change them for
blue/red bi-colour. I measured the voltage on the green led and it's
3.2v but the working voltage for the blue is 3.5v. although 3.2v does
light the blue it's not very bright. What's the most simple way to up
the voltage .3 of a volt? thanks for any help.
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Measure the current going into the blue LED and decrease the value of
the current limiting resistor until the rated current is flowing
through the LED.
If know the supply voltage, the nominal LED current, and the nominal
LED voltage you can determine the value of the resistor from:
V supply - Vled
R = -----------------
Iled
For example, if you have a 5 volts supply and the LED is rated for
20mA with a nominal voltage of 3.5V,
5V - 3.5V
R = ----------- = 75 ohms
0.02A
The power the resistor will dissipatewill be
P = (V supply - Vled) * Iled
So, for this example, that would be
P = (5V - 3.5V) * 0.02A = 0.03W
So a standard 75 ohm +/- 5%, 1/4 watt resistor would be fine.
--
John Fields |
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