LEDs can be ran off multiple voltages, but a series resistor is required to limit the current in the circuit. Too much current in an LED will destroy the device. As with all diodes, LED’s will only allow current to flow in the direction from the anode to the cathode.

Electromagnetic radiation can be expressed in terms of energy, wavelength, or frequency.

LED V/I characteristics

Despite some of the most popular power supply voltage options being 12V or 24V DC, it’s important to remember that (most) individual LEDs are actually 3V DC devices.

you can use 9v battery for 12v Led . Just only the brightness is less than 12v battery . if you need only Light purpose then you can use 9 volt instead of 12 volt supply.

In most applications, LEDs are driven by a DC power supply, but AC offers several significant advantages. LEDs are usually considered to be DC devices, operating from a few volts of direct current.

Resistor = (Battery Voltage – LED voltage) / desired LED current. So assuming a 12-volt power source and a white LED with the desired current of 10 mA; The formula becomes Resistor = (12-3.4)/. 010 which is 860 ohms. Since this is not a standard value I would use an 820-ohm resistor.

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.

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.

Basics: Picking Resistors for LEDs

The equipment will cease to function in short order either by the resistor itself burning up, or by the heat it generates burning up an adjacent component or possibly the circuit board its mounted on or even foil pattern on the circuit board, or maybe all three.

In such a circuit, when the switch is closed, the micro-controller input is at a logical high value, but when the switch is open, the pull-down resistor pulls the input voltage down to ground (logical zero value), preventing an undefined state at the input.

Level Shifters

12v to 5v converter using a voltage divider: You can run two LEDs in series across the resistor R2 while taking input from 12V lead-acid battery or a 12v adaptor as an input. Components required: One 12v battery, 1.8k resistor, 1.3k resistor, connecting wires. This circuit is a voltage divider schematic.

Connect the 7805 IC in the Veroboard. Now connect 470uf and one 0.1uf capacitor parallelly with pin 1,2. Now similarly connect 220uf, 0.1uf capacitor parallay with pin 2,3 as connected in the diagram below.

The input voltage should be at least 1.5V greater than the rated output voltage. Components required: One 9v battery/ 9V power supply, a 10k ohm resistor, 2.7K ohm resistor 10uF capacitor, 0.1uF capacitor, IC LM317, a Heat-sink, some wires, and soldering iron.