If you have a 12V source and a 3V LED, why not put three or four of them in series, instead of all of them in parallel with huge power-wasting resistors for the rest of the voltage. If your max current is 1 amp but you're only driving it to 1 milliamp, why not use a smaller, cheaper LED?
LED Resistor Calculator. To calculate the resistor needed for a simple LED circuit, simply take the voltage drop away from the source voltage then apply Ohm's Law. In other words where: V S is the source voltage, measured in volts (V), V LED is the voltage drop across the LED, measured in volts (V),
The resistor would get 0.6 volts at 12 mA. So at 12 mA since the graph for brightness looks linear with respect to current, they'll be at 60% brightness.
Value of Resistor = (VSupply - VF) ÷ IF. Where: VSupply = Supply voltage. VF = Forward Voltage. IF = Forward Current. The following formula can be used to calculate the value of power rating of the resistor. Power Rating of Resistor = IF2 × Value of Resistor. Finding the Value of Resistor to Connect with an LED.
The ballast resistor can be calculated using the formula: R = V −V LED I = 12− 2 0.03 = 333Ω R = V − V L E D I = 12 − 2 0.03 = 333 Ω. The resistor must have a resistance of 333 Ω. If the precise value is not available, choose the next higher resistance value to keep the current below the LED limits.
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do 12v leds need resistors
