Contents
What resistor do I need for LED lights?
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 every 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. If the voltage source is equal to the voltage drop of the LED, no resistor is required.
How do I know what resistor I need?
To calculate the resistor you need, just add the voltage: we need 4V (2V + 2V), and we have 5V. So we need to drop 1V. For the current, just use the 20mA. In a series circuit, the amperage is the same for the entire circuit.
How many volts does a 3.3V led need?
If your LED takes 100 mA at 3.3 volts (for instance) you would need to drop 1.7 volts from 5 volts with a resistor. That means a resistor of value 1.7 volts / 100 mA = 17 ohm.
Do you need a 3.3V resistor for a switch?
For pull-down resistors on switches you need to ensure that if there is a wetting current requirement to be met, the resistor is low enough to allow that current to flow. You cannot safely power most LEDs with a 3.3V source when the source can supply more current than the LED’s capacity.
Which is resistor should I use with my led?
For a standard LED the forward voltage will typically be 2V, where as an ultra bright LED will be about 3.5V. A proportion of the battery voltage is dropped across the LED (the forward voltage) and the rest of the voltage is dropped across the resistor. This is shown in the diagram top right.
How to calculate the resistance of an led?
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… R is the resistance, measured in Ohms (Ω).