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Below are a few neat Javascript calculators that calculates the proper resistor value needed for the current limiting resistor used when powering LEDs. You will need to know some specs of the LED you are using (forward voltage, LED driving current), including the supply voltage you plan to drive the LED with.  Enter these in the spaces below then hit "Calculate Resistor Value" to determine the proper resistor value. The power (wattage) draw by the LED will also be calculated for you.
 

Total LEDs (in series)	LED Forward Voltage	Maximum LED Current (mA)	Supply Voltage	Calculated Series Resistor

 

MORE LED RESISTOR CALCULATORS Single LED Supply Voltage   VOLTS Voltage Drop Across LED (Forward V)   VOLTS Maximum LED Current   MILLIAMPS Calculated Limiting Resistor   OHMS Nearest higher rated 10% resistor   Calculated Resistor Wattage   WATTS Safe pick is a resistor with power rating of   WATTS LEDs in series Supply Voltage   VOLTS Voltage Drop Across LED (Forward V)   VOLTS Maximum LED Current   MILLIAMPS # of LEDs connected in series     LEDs Calculated Limiting Resistor   OHMS Nearest higher rated 10% resistor   Calculated Resistor Wattage   WATTS Recommended resistor power rating of   WATTS LEDs in parallel Supply Voltage   VOLTS Voltage Drop Across LED (Forward V)   VOLTS Maximum LED Current   MILLIAMPS # of LEDs connected in parallel   LEDs Calculated Limiting Resistor   OHMS Nearest higher rated 10% resistor   Calculated Resistor Wattage   WATTS Recommended Resistor power rating of   WATTS OTHER LED CALCULATORS http://ledcalculator.net/ http://led.linear1.org/led.wiz http://led.linear1.org/1led.wiz http://electronics2000.co.uk/calc/calcled.php http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator http://ledcalc.com/ http://www.csgnetwork.com/ledsingresistancecalc.html http://home.cogeco.ca/~rpaisley4/LEDcalc.html   F.A.Q. coming soon...   Earthmen Productions © Dec-00-May-21 Go to Top of Page Go to Main Menu            [The link bar feature is not available in this web]