Enter the values in the below fields
This Led resistor calculator can be used to find values of the resistors by giving the input for Supply Voltage(VS), forward voltage(VF) and forward current(IF). Connecting a LED directly to the power supply will overheat it and eventually burn it out. To avoid this, a current limiting resistor has to be used to limit the current flowing to the LED from the power supply or battery. The resistor can be connected in two ways, either it can be connected in series or in parallel.
The supply voltage from the power source or battery should not be lesser than the forward voltage of the LED. The forward current of the LEDs may range from 10mA to 30mA, if you are not sure about the forward current of the LED you are going to use in the circuit, type 20mA in the calculator. To get long lasting life for LEDs, run them on 20% lesser current rating than the actual forward current. For example, If a LED has a forward current of 25mA, run it on 20mA current rating.
How to use this Led resistor calculator
The Forward Voltage LEDs of will differ based on their colours, the values are shown below. Use this values in the Led resistor calculator.
Blue and White – 3.6 Volts
Green, Yellow, Amber – 2.1 Volts
Orange – 2.2 Volts
Red – 2 Volts
Infrared – 1.7 Volts
The formulas to find different values of this LED resistor calculator are mentioned below
LED resistor value R = ( VS– VF) / IF (mA).
If multiple LEDs are connected in Series, the formula to find resistor value is R = (VS– (VF* LED count) ) / IF(mA)
If multiple LEDs are connected in Parallel, the formula to find resistor value is R = ( VS – VF ) / ( IF (mA) * LED count)
The above-mentioned formulas can only be used if the LEDs used in the circuit are of same colours if you are using different coloured LEDs connected in parallel, a separate resistor has to be used for each LEDs.
VS– Supply Voltage
VF– Forward Voltage of LED
IF – Forward Current of LED
Power dissipated by the resistor, PDR =( PTOTAL – PLED)
Power Consumed by LED, PLED = (PTOTAL – PDR)
Total Power Consumed by the circuit, PTOTAL = (PDR + PLED)
How to calculate Resistor Wattage?
The Resistor Wattage can be calculated by (IF)2 * resistor value.
IF=20mA and resistor=300 ohm then, (20)2 * 300 = 120mW. Then the result has to be doubled as 120mW*2 = 240mW to avoid overheating of the resistor. But in real-time resistors has some default wattage rating 1/2W, 1/4W, 1W etc. So the nearest higher wattage value should be selected. In this case, 1/4W(250mW) resistor has to be used for 240mW.
How to find LED terminals?
Anode and cathode are the two terminals present in the LED. Anode is the positive terminal with a longer lead and cathode is the negative terminal with a shorter the lead.
See also Power supply circuits