Author Topic: How will I know how many ohms I have to resist with 11 leds in Phat PSP?  (Read 10129 times)

Offline Blizzrad

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In a circuit like this, having an even distribution of current among the LEDs (which also results in even brightness) is dependent on them having identical electrical characteristics. Red LEDs might have a forward voltage around 2v, while blue might be around 3.3v. Because the red LED requires a significantly lower voltage before it starts conducting, the electrons will take the easiest path through the red LED and the blue LED will never be lit. This also means that the red LED will have twice the rated current flowing through it because the circuit has only one current limiting resistor and depends on the LEDs to distribute the current evenly.

You may still notice differences in brightness levels when using several of the same color LEDs in this configuration due to manufacturing differences and other variables. Wiring the LEDs in series (unfortunately not possible with your 5v supply) or giving each parallel branch it's own resistor will even out the current distribution (when the LEDs are in series the current flowing through each of them will always be the same, as current must be equal throughout all points of a series circuit).
« Last Edit: March 19, 2009, 08:11:28 AM by Blizzrad »

Offline Blazinkaos

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No sea there is different types of voltage currents i thinks that what its called there series, parallel, read this site it was a quick find it may help you understand the difference unless someone else knows a better one.
http://library.thinkquest.org/10796/ch14/ch14.htm

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Offline SEA DAWG

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Correct me if I am wrong with the two statements:

1.
I would want to be able to wire my leds in series, but I cannot because the forward voltage would be to high for the Psp (unless I used just one with one resistor, but I can't due to lack of space).

2.
Thus I need to wire it up in a parallel circuit so I only have to use one resistor.

Offline Blazinkaos

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You cant do series with the voltage you have so parallel is best for this.
« Last Edit: March 23, 2009, 10:53:35 AM by Blazinkaos »

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Offline DiscEngine

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How much voltage would you need to do series then.
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Offline SEA DAWG

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Ok sweet thx sooo much guys!

For 2 blue leds, 6.8 volts (3.4 max forward voltage for both)

Offline Blazinkaos

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see you would need that much voltage to do series...

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