ELEKTRONIKA

LED ellenállás kalkulátor

Számítsa ki az ellenállás értékét, a LED áramát és az ellenállás teljesítményét kisfeszültségű DC LED áramkörökhöz.

Resistor result
LED circuit inputs
V

Use the voltage of the battery, adapter, or logic rail.

V

Use the datasheet value when you have it.

mA

Small indicator LEDs often run at 2 to 20 mA.

Count the LEDs that share one resistor in a string.

Common starting point

The default values model a 5 V supply, one red LED, and 20 mA target current.

Resistor values
E24

Round up to a real resistor value, or keep the raw value.

Power safety factor
3x

Extra wattage margin keeps the resistor cooler.

Each parallel string should use its own resistor.

V

Use 0 for a mechanical switch or no extra driver drop.

Resistor result
Selected resistor
150 ohmper string

Resistor color code

Read the bands from left to right: first digit, second digit, multiplier, then tolerance.

Bands read as 150 ohm +/-5%
1st digit
Brown
1
2nd digit
Green
5
Multiplier
Brown
x10
Tolerance
Gold
+/-5%
Color map

This is the standard international resistor color code for digit and multiplier bands.

ColorDigitMultiplierTolerance
Black0x1-
Brown1x10+/-1%
Red2x100+/-2%
Orange3x1,000-
Yellow4x10,000-
Green5x100,000+/-0.5%
Blue6x1,000,000+/-0.25%
Violet7x10,000,000+/-0.1%
Gray8x100,000,000+/-0.05%
White9x1,000,000,000-
Gold-x0.1+/-5%
Silver-x0.01+/-10%
Ideal resistor
150 ohm
Actual current
20 mA
Resistor power
0.06 W
Suggested resistor wattage
0.25 W

Circuit details

LED string voltage
2 V
Voltage across resistor
3 V
Minimum wattage with margin
0.18 W
Total current
20 mA
Resistor = (supply voltage - LED string voltage - switch drop) / target current.
Saved on this device

Recent LED calculations stay in this browser only.

No data
No saved calculations yet.

How to Size an LED Resistor

What the calculator does

Subtract the LED voltage

The resistor only sees the voltage left after the LED string and any switch or driver drop.

Use current in amps

The display uses milliamps, but the formula converts current to amps before calculating resistance and power.

Round up to a real part

E12 and E24 rounding choose the next higher standard resistor value, which usually lowers LED current slightly.

Common mistakes

Using color instead of the datasheet

LED color gives a rough forward voltage only. Use the datasheet value when the exact current matters.

Forgetting resistor wattage

A resistor can have the right ohm value and still overheat if its wattage rating is too low.

Putting parallel LEDs on one resistor

Parallel LEDs may not share current evenly. For this simple circuit, give each parallel string its own resistor.

Tips

Use less current for indicators

Many modern LEDs are visible below 20 mA. A lower current saves power and reduces heat.

Check actual current after rounding

The selected resistor may not equal the ideal value, so use the actual current result before choosing a part.

Use a driver for high-power LEDs

This calculator is for simple low-voltage LED circuits. High-power LEDs usually need a current-regulated driver.

Examples

5 V red indicator

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.

9 V battery at lower current

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 white LEDs on 12 V

Three 3.2 V LEDs drop 9.6 V, leaving 2.4 V for the resistor at the selected current.