LED circuit

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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.^[1] The switch may be replaced with another component or circuit to form a continuity tester^[2] 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.^[3]

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.^[4][5] The resistor value is computed by subtracting the forward bias voltage from the supply voltage, and then dividing by the desired operating current.^[6]

This basic circuit is used in a wide range of applications, including many consumer appliances.^[7]

[edit] Resistance formula

The formula to use to calculate the correct resistance for resistor to use is:

where:

• 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)

[edit] See also

• Throwies
• Ohm's law

[edit] References

1. ^ Singmin, Andrew (1997). "3. Building a Project Using a Basic LED Circuit", Beginning electronics through projects. Oxford [England]: Newnes, p. 29. ISBN 0-7506-9898-5. “As you can see in Figure 3-1, there are just four components in an LED circuit. They are • a battery, • a switch, • an LED, and • a resistor.” 
2. ^ Cave, John; Caborn, Colin; Mould, Ian (2000). Design and Technology. Cheltenham: Nelson Thornes Ltd, p. 116. ISBN 0-17-448277-9. “A fuse or filament bulb placed to complete the circuit will show whether the bulb or fuse is good.” 
3. ^ Isabelle L. Hurbain; Michael Gasperi; Philippe E. Hurbain (2007). Extreme NXT: Extending the LEGO Mindstorms NXT to the Next Level (Technology in Action). Berkeley, CA: APress, p. 269. ISBN 1-59059-818-0. “…the 1N4148 is a small diode used to protect the LED from reverse voltage. …You can also use another LED in place of the 1N4148,…” 
4. ^ Meade, Russell L. (2004). Foundations of Electronics: Circuits & Devices Conventional Flow. Clifton Park, NY: Thomson Delmar Learning, p. 1051. ISBN 1-4018-5976-3. “The value of the current limiting resistor connected in series with the LED depends on the amount of supply voltage.” 
5. ^ applied electronics - Page 270
6. ^ Walsh, Ronald A. (2000). Electromechanical design handbook. New York: McGraw-Hill, p. 6-242. ISBN 0-07-134812-3. “The light-emitting diode is normally fed from a supply voltage source that is higher than the LED can sustain without burnout.” 
7. ^ Catsoulis, John (2003). Designing embedded hardware. Sebastopol, CA: O'Reilly. ISBN 0-596-00362-5. “This simple LED circuit (or variations of it) drives the LEDs on your PC's front panel, your VCR and DVD player, your cell phone, and a host of other appliances.”