How to calculate the required current limiting resistance value for LED?

Calculating the required current limiting resistance value for LED is a key step in ensuring the safe operation of LED. The following is the calculation process:

1. Determine the forward voltage and current of the LED:
Firstly, it is necessary to know the forward voltage V_F and forward current I_F of the LED. These parameters can usually be found in the LED data manual.

2. Determine the power supply voltage:
Determine the power supply voltage (V_ {\ text {supply}}}) to power the LED.

3. Calculate the current limiting resistance value using Ohm's law:
According to Ohm's Law, the resistance value R of a current limiting resistor can be calculated using the following formula:
     [ R = \frac{V_{\text{supply}} - V_F}{I_F} ]
Among them:
(V_ {\ text {supply}} \) is the power supply voltage (in volts V).
V_F is the forward voltage of the LED (in volts V).
I2 is the forward current of the LED (unit: Ampere A).

4. Calculate the power capacity of the current limiting resistor:
-The power capacity P of the current limiting resistor can be calculated using the following formula:
     [ P = I_F^2 \times R ]
Among them:
I2 is the forward current of the LED (unit: Ampere A).
-R is the resistance value of the current limiting resistor (unit: ohms Ω).

5. Choose the appropriate resistor:
-Select a suitable current limiting resistor based on the calculated resistance value and power capacity. Usually, to ensure that the resistor is not damaged due to overheating, a higher power rating than the calculated power value is chosen.

Example

Assuming there is an LED with a forward voltage of 2V, a forward current of 20mA (0.02A), and a power supply voltage of 5V. We can calculate the resistance and power capacity of the current limiting resistor according to the following steps:

1. Calculate the resistance of the current limiting resistor:
   \[ R = \frac{5V - 2V}{0.02A} = \frac{3V}{0.02A} = 150\Omega \]

2. Calculate the power capacity of the current limiting resistor:
   \[ P = (0.02A)^2 \times 150\Omega = 0.0004A^2 \times 150\Omega = 0.06W \]

3. Choose the appropriate resistor:
According to the calculation results, a current limiting resistor with a resistance of 150 Ω and a power capacity greater than 0.06W should be selected. Usually, a 1/4W (0.25W) resistor is chosen to ensure sufficient power capacity.

By following the above steps, it is possible to ensure that the LED operates within a safe current range while avoiding damage to the current limiting resistor due to overheating.