This led calculator determines the resistor value for a single led, leds in series or in parallel and can handle calculations for many situations. Below the form you can read more on the subject, discover the formulas employed and some example calculations.


Led resistor type:*
Supply voltage:*
Voltage drop across led:*
Desired current for led:*

How does this led calculator work?

This is a useful tool when working with led resistor values, either for single cases, series or parallel constructions. The led calculator can handle led resistor calculations for different types and arrays so that it requires you to input specific fields depending on what you need to estimate. Just choose the calculation you want to perform, press Calculate button then the tool will do the math. The form above is based on the following led resistor formulas depending on the calculation performed:

For your convenience the following legend will be used in the formulas:

Supply voltage = Sv

Voltage drop across led = Vd

Desired current for led = Dc

Estimated limiting resistor = ELR

Estimated resistor wattage = ERW

Safe pick = SP

Single led calculation

  • ELR = (Sv– Vd)/(Dc/1000).
  • ERW = (Sv – Vd)*(Dc/1000).
  • SP = (ERW*100/60)

Example in the case of a single led, with a supply voltage of 20volts, at a drop across led of 5volts and a desired current of 12miliamps. The result is:

- Limiting resistor = 1250 Ω

- Resistor wattage = 0.18 W

- Safe pick (resistor’s power rating) = 0.3 W

- Nearest highest 10% resistor = 1.5 KΩ

Leds in series calculation

  • ELR = (Sv – Vd *No. of leds in series) / (Dc / 1000).
  • ERW = (Sv – Vd *No. of leds in series) * (Dc / 1000).
  • SP = (ERW * 100 / 60)

Example for 5 leds in series with a supply of 40volts and a drop voltage of 10volts with a desired current of 25miliamps per led. The result is: “Please note that your leds need more voltage than supply can manage. You either have to lower the amount of leds or check the given supply voltage!” Therefore we need to increase the supply. Let’s try the same case at a voltage supply of 200volts:

- Limiting resistor = 6000 Ω

- Resistor wattage = 3.75 W

- Safe pick (resistor’s power rating) = 6.25 W

- Nearest highest 10% resistor = 6.8 KΩ

Leds in parallel calculation

ELR = (Sv – Vd) / (Dc *No. of leds in parallel / 1000).

ERW = (Sv – Vd) * (Dc*No. of leds in parallel / 1000).

SP = (ERW * 100 / 60)

Example: Let’s take the case of 4 leds connected in parallel, with a supply voltage of 120volts, at a voltage drop of 30volts. There is desired a 50miliamps current per led. The result is:

- Limiting resistor = 450 Ω

- Resistor wattage = 18 W

- Safe pick (resistor’s power rating) = 30 W

- Estimated nearest highest 10% resistor = 470 Ω

26 Mar, 2015 | 0 comments

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