计算器
LED Resistor Calculator
Calculate the correct resistor value for any LED circuit — single LED, series, or parallel configurations with E24 standard values, power budget, and circuit diagrams
Parameters
Red: 1.8V – 2.2V (typical 2V)
Recommended Resistor
510 Ω
E24 standard value (exact: 500.0 Ω)
Voltage Drop
10.00 V
across resistor
Actual Current
19.6 mA
through each LED
Resistor Power
196 mW
use ≥ 1/4W rated
Efficiency
16.9%
LED power / total
Power Budget
LED Power40 mW
Resistor Loss196 mW
Total System Power236 mW
Circuit Diagram
LED Forward Voltage Reference
| Color | Typical Vf | Vf Range | Typical Current |
|---|---|---|---|
| Red | 2 V | 1.8 – 2.2 V | 20 mA |
| Orange | 2.1 V | 2 – 2.2 V | 20 mA |
| Yellow | 2.1 V | 2 – 2.2 V | 20 mA |
| Green | 2.2 V | 2 – 3.2 V | 20 mA |
| Blue | 3.2 V | 3 – 3.4 V | 20 mA |
| White | 3.2 V | 3 – 3.4 V | 20 mA |
| UV | 3.3 V | 3.2 – 3.6 V | 20 mA |
| Infrared | 1.5 V | 1.2 – 1.6 V | 20 mA |
Formulas
Resistor Value
R = (V_supply − V_f) / I_ledWhere V_f is LED forward voltage and I_led is desired current
Series LEDs
R = (V_supply − n × V_f) / I_ledAll LEDs share the same current; voltages add up
Power Dissipation
P = (V_supply − V_f)² / RHeat dissipated by the resistor — choose a rated wattage above this
Max Series LEDs
n_max = floor(V_supply / V_f)Maximum LEDs possible in series (with no voltage headroom)
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