LED Series Resistor Calculator

This tool is used to determine the value of current limiting resistors needed to connect multiple LEDs. Find the resistor value and power required to connect multiple LEDs with our LED Series Resistor calculator using supply and forward voltage. Enter the indicated values to identify the value of current limiting series resistor when driving a single or an array of LEDs. When you select a resistor for this purpose, choose a device with a power rating between 2 and 10 times the value calculated below in order to avoid excessive resistor temperatures.

LED Series Resistor Calculator

Supply Voltage
V
Forward Voltage
V
Forward Current
mA
Resistor Value
=Ω
Power
=W

Formula

Introduction

This video explained how to calculate the resistance value for LEDs for both series and parallel circuits.

How to calculate Resistor value for LED series and parallel circuit with Ohm's Law

Every light-emitting diode (LED) has a current that they can safely handle. Going beyond that maximum current, even briefly, will damage the LED. Thus, limiting the current through the LED with the use of a series resistor is a common and simple practice. Note that this method is not recommended for high current LEDs, which need a more reliable switching current regulator.

Calculate Resistor value for LED series

LED circuit

To calculate the resistor needed for a simple LED circuit, simply take the voltage drop away from the source voltage then apply Ohm's Law. In other words.

LED Series Resistor Calculator Formula =

R = (Vs - Vf) ÷ If

Where:

Vs= Supply voltage

If= LED current. The usual operating range of common 3 mm and 5 mm LEDs is 10-30 milliamps. If access to an LED's datasheet is impossible, 20 mA is a good guess.

Vf= LED voltage drop. The voltage drop on a LED depends on the color it emits. Here is a neat table of each color and their corresponding voltage drop:

 

resistor color and voltage

 

Frequently Asked Questions

How do you calculate the resistor in a LED series?

The value of the correct Resistor for LEDs in Series is the Supply Voltage (pressure) minus the total pressure consumed by all off the LEDs (Voltage Drop Across a Single LED times by the total Number of LEDs), that answer is then divided by the LED Current (electron flow) required by the circuit.

What size resistor do I need for LED?

LEDs typically require 10 to 20mA, the datasheet for the LED will detail this along with the forward voltage drop. For example an ultra bright blue LED with a 9V battery has a forward voltage of 3.2V and typical current of 20mA. So the resistor needs to be 290 ohms or as close as is available.

Do you need a resistor for each LED?

An LED (Light Emitting Diode) emits light when an electric current passes through it. The simplest circuit to power an LED is a voltage source with a resistor and an LED in series. Such a resistor is often called a ballast resistor. If the voltage source is equal to the voltage drop of the LED, no resistor is required.

How do I connect 220 volts to LED?

You can use a LED at 220V by having a capacitor in series in order to limit the current. The advantage is that the capacitor will not heat up! The role of the zener diode is to protect the LED from high voltages. During the positive half-cycle D1 limits the voltage on LED and R1 at 2.7 Volts.

What happens if you don't use a resistor with an LED?

When hooking up an LED, you are always supposed to use a current-limiting resistor to protect the LED from the full voltage. If you hook the LED up directly to the 5 volts without a resistor, the LED will be over-driven, it will be very bright for a while, and then it will burn out.

What voltage do LEDS use?

Typically, the forward voltage of an LED is between 1.8 and 3.3 volts. It varies by the color of the LED. A red LED typically drops around 1.7 to 2.0 volts, but since both voltage drop and light frequency increase with band gap, a blue LED may drop around 3 to 3.3 volts.

Should resistor go before after LED?

It doesn't matter! The resistor can go before – or after – the LED, and it will still protect it. the current that flows out of a battery is always equal to the current that flows back into the battery.

How do I calculate resistance?

If you know the total current and the voltage across the whole circuit, you can find the total resistance using Ohm's Law: R = V / I. For example, a parallel circuit has a voltage of 9 volts and total current of 3 amps. The total resistance RT = 9 volts / 3 amps = 3 Ω.

How do I know what voltage my LED is?

How to find voltage and current of LED 1.The easiest way is to look it up in the datasheet. 2.You could find the LED voltage by using a multimeter with diode function. 3.You could connect a battery to the LED and a potentiometer. Start with a high resistance on the potentiometer and gradually decrease it until you have an nice brightness.

What resistor do I need to reduce voltage?

To reduce voltage in half, we simply form a voltage divider circuit between 2 resistors of equal value (for example, 2 10KΩ) resistors. To divide voltage in half, all you must do is place any 2 resistors of equal value in series and then place a jumper wire in between the resistors.
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