Resistor Calculation for LEDs: Step-by-Step Guide

1️⃣ Why Do LEDs Need a Resistor?

An LED (Light Emitting Diode) requires a resistor to:

✔ Limit the current to prevent burnout
✔ Ensure consistent brightness
✔ Match voltage supply with LED voltage drop

Without a resistor, the LED can overheat and fail due to excessive current.

2️⃣ LED Resistor Calculation Formula

To find the correct resistance value (R), use Ohm’s Law:

$$R = \frac{U_{\text{source}} - U_{\text{LED}}}{I_{\text{LED}}}$$

Where:
✔ $R$ = Resistor value in Ohms (Ω)
✔ $U_{\text{source}}$ = Power supply voltage (V)
✔ $U_{\text{LED}}$ = LED forward voltage (V)
✔ $I_{\text{LED}}$ = LED operating current (A)

3️⃣ Example Calculation

Scenario:

You want to connect an LED with the following specs:
✅ LED forward voltage = 2V
✅ LED current rating = 10mA (0.01A)
✅ Power supply = 5V

Step 1: Calculate Resistance

$$R = \frac{5V - 2V}{0.01A} = \frac{3V}{0.01A} = 300Ω$$

📌 Choose a standard resistor value: The closest standard resistor is 330Ω (E12 series).

4️⃣ Power Rating of the Resistor

To prevent overheating, calculate the resistor’s power dissipation:

$$P = U_R \times I_{\text{LED}}$$ $$P = 3V \times 0.01A = 0.03W$$

📌 Choose a resistor with at least double the power rating. In this case, a 0.125W (1/8W) resistor is sufficient.

5️⃣ Choosing the Right Resistor for Different LED Voltages

6️⃣ Multiple LEDs in a Circuit

Series Connection:

✔ Add the forward voltages together
✔ Use the same current rating

$$R = \frac{U_{\text{source}} - (U_{\text{LED1}} + U_{\text{LED2}} + ...)}{I_{\text{LED}}}$$

Parallel Connection:

✔ Each LED needs its own resistor
✔ Use the same voltage drop for calculation

7️⃣ Conclusion: Key Takeaways

✔ Always calculate the resistor value before connecting an LED
✔ Choose the nearest standard resistor value
✔ Check power rating to avoid overheating
✔ Use proper wiring for multiple LEDs

By following these calculations, you ensure LED longevity and stable performance in your circuits! 🚀