V
V
mA
Typical: 10-20mA for standard, 350mA+ for high power
Circuit Diagram
Recommended Resistor
Actual Current
20.0 mA
Power Dissipation
60 mW
Resistor Rating
0.125W min
Voltage Headroom
3.0V
Formula
R = (Vsupply - VLED) / ILED
For series LEDs: VLED = Vf × number of LEDs
Why LEDs Need Resistors
LEDs are current-driven devices. Without a current limiting resistor, they will draw excessive current and burn out almost instantly. The resistor drops the excess voltage and limits current to a safe level.
Key Parameters
- Forward Voltage (Vf): Voltage drop across LED when lit
- Forward Current (If): Operating current (typically 10-20mA)
- Max Current: Don't exceed or LED will fail
- Power Rating: Resistor must handle the heat
Series vs Parallel
- Series: Same current through all LEDs, higher voltage needed
- Parallel: Lower voltage, but unequal current distribution
- Best Practice: Series with individual resistors per LED string
Typical LED Forward Voltages
| LED Color | Forward Voltage | Typical Current | Notes |
|---|---|---|---|
| Infrared | 1.2-1.6V | 20-100mA | Not visible |
| Red | 1.8-2.1V | 10-20mA | Most efficient |
| Orange | 2.0-2.2V | 10-20mA | - |
| Yellow | 2.0-2.2V | 10-20mA | - |
| Green | 2.0-3.0V | 10-20mA | Wide range |
| Blue | 3.0-3.5V | 10-20mA | Higher Vf |
| White | 3.0-3.5V | 10-20mA | Blue + phosphor |
| UV | 3.0-4.0V | 20mA | Eye hazard |