# LED parallel circuits and how they function?

• Kevv
In summary: To reduce power dissipation, you might want to consider using a series resistor instead of parallel ones. With a series resistor, the current through the LED is reduced by the total resistance of the circuit. For example, if you are using a 100Ω resistor in series with an LED, and the current through the LED is 10mA, the power dissipation will be 1W."
Kevv
First off, I'm looking at adding in a few LED's into my iPhone 4s (I'm very limited on space, but there is a pretty open area.) I have found a connection point that gives off 2.8v and is commonly used for lighting up LED's with the screen.

I plan to add in a red, green and blue 0603 (or even 0402) SMD LED in a parallel set up, but I don't know how the voltage would work out. Should I expect for all 3 of the lights to use different resistors and that they won't be affected by the circuit? (Using this to figure out resistance: http://www.muzique.com/schem/led.htm )

I've done lots of small scale soldering before so SMD is no big deal to me, but I would assume that I should also use SMD resistors. What exactly should I pay attention to in the resistors?(I'm new here :D)

You have only 2.8V, you don't have enough voltage to put all three is series, putting two in series and one stand alone, then using resistor might end it have one LED giving different light intensity unless you adjust the resistor to give even intensity. The easiest way is to have three individual LED/resistor circuits. With this, you want to do a quick calculation on the power dissipation in the resistor. Make sure the power does not exceed the specification of the 0603 or the 0402 SMD resistor.

yungman said:
You have only 2.8V, you don't have enough voltage to put all three is series, putting two in series and one stand alone, then using resistor might end it have one LED giving different light intensity unless you adjust the resistor to give even intensity. The easiest way is to have three individual LED/resistor circuits. With this, you want to do a quick calculation on the power dissipation in the resistor. Make sure the power does not exceed the specification of the 0603 or the 0402 SMD resistor.

I planned on putting them parallel, I was able to realize I did not have enough voltage for a series arrangement. I didn't think about putting the blue one on one circuit and then the red and green on another, but the red and green together would be about 3.6V needed to light both.

What exactly is the power dissipation? I haven't gone too far into electrical engineering to fully understand the terms.

Say your LED drop 1.8V as you indicated, you have a 2.8V supply, so the resistor in series is going to drop 1V. Say you want to draw 10mA through the LED to give you the brightness you want, so you put a 100Ω resistor in series with the LED. The power dissipated in the resistor is $\;W=IV\;$ where I=10mA and V=1V. So the power dissipation is 0.01W. Use this as the guide line. In your case, you should keep the power below the specified maximum power dissipation allow for the resistor used. Preferably 1/3 or less the specified power of the resistor.

yungman said:
Say your LED drop 1.8V as you indicated, you have a 2.8V supply, so the resistor in series is going to drop 1V. Say you want to draw 10mA through the LED to give you the brightness you want, so you put a 100Ω resistor in series with the LED. The power dissipated in the resistor is $\;W=IV\;$ where I=10mA and V=1V. So the power dissipation is 0.01W. Use this as the guide line. In your case, you should keep the power below the specified maximum power dissipation allow for the resistor used. Preferably 1/3 or less the specified power of the resistor.

Alright, thank you very much for your help :).

## 1. What is a parallel circuit?

A parallel circuit is a type of electrical circuit where there are multiple paths for the current to flow. This means that the components in the circuit are connected side by side, rather than in a single series.

## 2. How do LED parallel circuits function?

In an LED parallel circuit, each LED has its own individual branch or path. This means that if one LED fails, the others will still continue to function. The voltage across each LED remains the same, but the current is divided among the branches.

## 3. What are the advantages of using LED parallel circuits?

One major advantage of using LED parallel circuits is that they provide redundancy. If one LED fails, the rest will continue to function. Additionally, the brightness of each LED remains consistent as the voltage is divided among the branches. Parallel circuits also allow for more flexibility in designing and adding components to the circuit.

## 4. How do you calculate the total resistance in a LED parallel circuit?

To calculate the total resistance in a LED parallel circuit, you can use the formula 1/Rtotal = 1/R1 + 1/R2 + ... + 1/Rn, where Rtotal is the total resistance and R1, R2, etc. are the resistances of each individual branch. This formula takes into account the inverse relationship between resistance and current in parallel circuits.

## 5. Are there any disadvantages to using LED parallel circuits?

One potential disadvantage of LED parallel circuits is that they require more wiring and components compared to series circuits. This can make them more complex and difficult to troubleshoot if there are any issues. Additionally, if the voltage is not evenly divided among the branches, some LEDs may be brighter than others, leading to an uneven lighting display.

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