Led in paralel resistor.

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svarc

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hello there. i am using 10 red 5mm led's in parallel at 20mA on 5V with single 15ohm 2W resistor but the resistor is heating up like crazy (pls dont ask me why i am using only one resistor for all led's). i measured the voltage drop on this type of led its exactly 2V. is there anything else that i should know that's making my resistor to heat up?
Maybe my power calculation is wrong. Total led current consumption 10x0.02A=0.2A so P=0.2A x 5V=1W so i am using a resistor with double the calculated wattage.
Thanks in advance and best wishes.
 

LED forward voltage = 2V. So drop across resistor = 3V. Current through resistor (and thus LED's) = 3/15 A = 0.2A. Power dissipated by resistor = 3V * 0.2A = 0.6W
So, the resistor is fine.

What type of resistor are you using? Sometimes, even when the power dissipation is within limits, the resistor can get very hot. eg. Ceramic resistors can heat up to more than 100'C even when power is within limits.

Hope this helps.
Tahmid.
 

Maybe these won't be a problem, since you are within the power limit (that too, by quite a lot). If you are concerned about the heat, you could parallel a few resistors to spread the heat among them. However, 0.6W dissipation by a resistor rated at 2W, shouldn't be a problem, barring heat.
 

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