Simple LED circuit diagram
In electronics, the basic LED circuit is an electrical circuit used to power a light-emitting diode (LED). It consists of up to four components connected in series: a voltage source, a current limiting resistor, a LED, and optionally a switch to open and close the circuit. The switch may be replaced with another component or circuit to form a continuity tester Two diodes may be placed in parallel in the circuit, but connected anode to cathode; the second diode may be used to protect the LED against reverse bias, which can damage the LED, or it may be another LED which is illuminated when the polarity of the voltage source is reversed.
The LEDs used will have a forward voltage specified at the intended operating current. When the voltage source Ohm's law is used to calculate the resistor that is used to attain the correct current. The resistor value is computed by subtracting the forward bias voltage from the supply voltage, and then dividing by the desired operating current.
This basic circuit is used in a wide range of applications, including many consumer appliances.
The formula to use to calculate the correct resistance for resistor to use is:
(POWER SUPPLY VOLTAGE-LED VOLTAGE DROP)/LED CURRENT RATING
Power supply voltage is the voltage of the power supply (such as a 9 volt battery)
LED voltage drop is the voltage drop across the LED (typically about 1.7 - 3.3 volts; this varies by the color of the LED)
LED current rating is the manufacturer rating of the LED (usually given in milliamperes such as 15 mA)