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Is a 1 ohm resistor really needed? Answered

I will be making an LED display. After calculating using the online calculator, I am told that I will need 1 ohm resistors for my series of LEDs.

I am thinking that 1 ohm is really not a lot and if I can skip it. Thanks!!

Tags:LEDs

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user
Re-designBest Answer (author)2010-03-23

Yeah skip it.  Unless you get a high precision resistor (expensive) you won't get 1 ohm anyway.  Leds are not quite that sensitive so they would take a little over voltage anyway, but this should be fine.

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user
stella_7277 (author)Re-design2010-03-23

I will skip it then. Less work on the soldering too!! YAY!! Thanks!!

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user
steveastrouk (author)stella_72772010-03-23

No, but the brightness will become temperature sensitive.

Steve

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user
AndyGadget (author)2010-03-24

3 LEDs in series off 9V - OK for a quick lash-up but I wouldn't advise it for a 'serious' project.

Your 3V LEDs will either be a typical value (Vf typ) or a maximum value (Vf max), depending on how it was written in the spec. you read.  The ones you have may not be 3V exactly.

A 9V battery has a discharge curve something like THIS, so your 9V battery is actually only 9V for a short time.

If I was doing this I would put the LEDs in parallel, each with its own resistor.  From the calculator, you would need a 330R for each.  This would make the circuit much less reliant on the exact supply voltage and volt drop of the LED.  The downside is that it consumes more power and uses more components.  Swings and roundabouts, but you would probably find that my design gets more out of a battery because the brightness would fade much more slowly as the battery discharged.

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mathews (author)2010-03-23

What are the details for the power supply and LEDs?

What is the voltage of the supply?

What are the voltage drop and current consumption of the LED?

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stella_7277 (author)mathews2010-03-23

Voltage is 9V
Forward Voltage is 3
Diode Forward current is 20M.A (assuming from the LED calculator site http://led.linear1.org/led.wiz)

It gives me a series of 3 LEDs with 1 ohm resistor.

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