LED限流电阻计算器（欧姆定律）

计算原理

The resistor value is Ohm's law applied to the voltage the LEDs do not use: R = (Vs − n × Vf) ÷ I, with the milliamp figure converted to amps first. At the defaults of a 9 V supply, 2.0 V forward voltage, 20 mA and one LED, that is 7 V ÷ 0.02 A = 350 Ω. The tool then rounds up to the next standard value in your chosen series, 390 Ω in E12, recalculates the real current through it at 17.9 mA, and reports P = V_R × I.

Forward voltage moves the answer most, and the preset row fills it in: Red 2.0 V, Yellow 2.1 V, Green 2.2 V, Blue and White 3.2 V, IR 1.5 V, UV 3.5 V. Use your LED's datasheet where you have one. LEDs in series multiplies Vf, not the current. The resistor series only decides which stock value you are offered, with E12 (10%) giving coarse steps and E24 (5%) landing closer to the exact figure, and both round upward so actual current lands at or below your target.

One resistor, one series string. Putting LEDs in parallel behind a single resistor is not modelled, and should not be built that way, since the lowest-Vf LED takes more than its share of the current. Forward voltage is treated as a constant, but real Vf shifts with current, temperature and production batch, so measured current will differ from the figure shown. The recommended wattage is simply twice the calculated dissipation, with no allowance for a hot enclosure or a constant-current driver.

常见问题