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Step 3Calculate the resistor values
When you're working with LEDs, it's very important that you use the proper resistor(s) in series with the LED(s). Using the wrong resistors or not using any resistors at all will reduce the lifespan of the LED(s) or burn them out instantly.
In this step, I'll show you how to calculate the value of the resistors. Before you can calculate the value, there are three things that you need to know.
The forward voltage of the LED(s). In datasheets this is often marked as Vf. For white and warm white LEDs, this is usually 3.4 to 3.6 volts.
The forward current of the LED(s). In datasheets this is often marked as If. The forward current varies a lot from LED to LED. LEDs that has a brightness of 1000mcd to 20000mcd usually has a forward current of 20mA. However this is not always the case. You should always check the specs of your LEDs.
The supply voltage of the intire circuit. I used a 12V wall wart adaptor.
I use ledcalc.com to calculate the resistance of the resistors.
To calculate the resistor value, simply type in the forward voltage, forward current, the supply voltage and how many LEDs you want. The calculator recommends a 56 ohm resistor when using two 100mA LEDs in series with 12V supply voltage.
Note: the resistor values shown in the schematic below are for the 5-chips 100mA LEDs that I use in this project only. If you're using different LEDs than I do, you should use ledcalc.com to calculate the proper resistance.
In this step, I'll show you how to calculate the value of the resistors. Before you can calculate the value, there are three things that you need to know.
The forward voltage of the LED(s). In datasheets this is often marked as Vf. For white and warm white LEDs, this is usually 3.4 to 3.6 volts.
The forward current of the LED(s). In datasheets this is often marked as If. The forward current varies a lot from LED to LED. LEDs that has a brightness of 1000mcd to 20000mcd usually has a forward current of 20mA. However this is not always the case. You should always check the specs of your LEDs.
The supply voltage of the intire circuit. I used a 12V wall wart adaptor.
I use ledcalc.com to calculate the resistance of the resistors.
To calculate the resistor value, simply type in the forward voltage, forward current, the supply voltage and how many LEDs you want. The calculator recommends a 56 ohm resistor when using two 100mA LEDs in series with 12V supply voltage.
Note: the resistor values shown in the schematic below are for the 5-chips 100mA LEDs that I use in this project only. If you're using different LEDs than I do, you should use ledcalc.com to calculate the proper resistance.
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