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# when using resistors for leds does it even matter what i use?? Answered

or is it depending on the voltage cuz i know more than 4.5 will kill a normal led or a big one idk about the small ones or the EXTREMELY small surface mount ones. but all i want to know is the normal and big ones

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Nope, any resistor at all will do. It's not about managing the voltage and current in the circuit, it's all about making the LED feel valued and empowered. Resistors are like little pets for the LED, providing companionship and unconditional love. Most LEDs are happy just to have a resistor at all, and don't care what kind it is.

hahaha you're my hero.

I am also available for weddings and bar mitzvahs.

True, and if they really hit it off, the LED will release a magical blue smoke to show its love for the pet resistor.

Of course it matters ! The colour of the LED affects the forward voltage drop - 4.5 volts won't turn on some White LEDs.

The resistor is chosen from a formula.

R= (supply volts- diode forward drop) / LED current.

The watt rating of the resistor *may also play into it as well as other considerations. For instance, an led that conducts a large forward current will likely burn out a resistor that is rated for too low a power dissipation at the dropping voltage..

So, as Steve suggests, first we calculate the nominal resistance, then we plug in the nominal forward current (the current thru the led) and drop voltage (the voltage that the resistor is expected to dissipate) to find the necessary power rating for the resistor by

Pr= Iled  x Vr

where Pr is the minimum power rating of the resistor (choose a value above the calculated value)

where Iled is the forward current thru the led (and resistor)

and Vr is the voltage across the resistor