Laske vastusarvo, LED-virta ja vastuksen teho matalajännitteisille DC-LED-piireille.
Resistor resultUse the voltage of the battery, adapter, or logic rail.
Use the datasheet value when you have it.
Small indicator LEDs often run at 2 to 20 mA.
Count the LEDs that share one resistor in a string.
The default values model a 5 V supply, one red LED, and 20 mA target current.
Round up to a real resistor value, or keep the raw value.
Extra wattage margin keeps the resistor cooler.
Each parallel string should use its own resistor.
Use 0 for a mechanical switch or no extra driver drop.
Read the bands from left to right: first digit, second digit, multiplier, then tolerance.
This is the standard international resistor color code for digit and multiplier bands.
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The resistor only sees the voltage left after the LED string and any switch or driver drop.
The display uses milliamps, but the formula converts current to amps before calculating resistance and power.
E12 and E24 rounding choose the next higher standard resistor value, which usually lowers LED current slightly.
LED color gives a rough forward voltage only. Use the datasheet value when the exact current matters.
A resistor can have the right ohm value and still overheat if its wattage rating is too low.
Parallel LEDs may not share current evenly. For this simple circuit, give each parallel string its own resistor.
Many modern LEDs are visible below 20 mA. A lower current saves power and reduces heat.
The selected resistor may not equal the ideal value, so use the actual current result before choosing a part.
This calculator is for simple low-voltage LED circuits. High-power LEDs usually need a current-regulated driver.
A 5 V supply, 2 V LED, and 20 mA target current gives a 150 ohm resistor and about 0.06 W of resistor heat.
A 9 V battery, 1.8 V red LED, and 5 mA target current rounds to 1.5 k ohm in the E12 series.
Three 3.2 V LEDs drop 9.6 V, leaving 2.4 V for the resistor at the selected current.