LED circuit

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, an LED, and optionally a switch to open and close the circuit. [cite book |author=Singmin, Andrew |title=Beginning electronics through projects |chapter = 3. Building a Project Using a Basic LED Circuit |publisher=Newnes |location=Oxford [England] |year=1997 |pages= p. 29 |isbn=0-7506-9898-5 |quote = 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.] The switch may be replaced with another component or circuit to form a continuity testercite book |author=Cave, John; Caborn, Colin; Mould, Ian |title=Design and Technology |publisher=Nelson Thornes Ltd |location=Cheltenham |year= 2000 |pages= p. 116 |isbn=0-17-448277-9 |quote=A fuse or filament bulb placed to complete the circuit will show whether the bulb or fuse is good.] 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.cite book |author=Isabelle L. Hurbain; Michael Gasperi; Philippe E. Hurbain |title=Extreme NXT: Extending the LEGO Mindstorms NXT to the Next Level (Technology in Action) |publisher=APress |location=Berkeley, CA |year= 2007 |pages= p. 269 |isbn=1-59059-818-0 | quote= …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,…]

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 theresistor that is used to attain the correct current.cite book |author=Meade, Russell L. |title=Foundations of Electronics: Circuits & Devices Conventional Flow |publisher=Thomson Delmar Learning |location=Clifton Park, NY |year= 2004|pages= p. 1051|isbn=1-4018-5976-3 | quote = The value of the current limiting resistor connected in series with the LED depends on the amount of supply voltage.] [ [http://books.google.com/books?id=v9dSggu4hB8C&pg=PA270&dq=%22led+circuit%22&sig=BNso7jk9j0A5nDc9KLnY5aXNcvs applied electronics - Page 270] ] The resistor value is computed by subtracting the forward bias voltage from the supply voltage, and then dividing by the desired operating current.cite book |author=Walsh, Ronald A. |title=Electromechanical design handbook |publisher=McGraw-Hill |location=New York |year=2000 |pages= p. 6-242|isbn=0-07-134812-3 | quote=The light-emitting diode is normally fed from a supply voltage source that is higher than the LED can sustain without burnout.]

This basic circuit is used in a wide range of applications, including many consumer appliances.cite book |author=Catsoulis, John |title=Designing embedded hardware |publisher=O'Reilly |location=Sebastopol, CA |year=2003 |pages= |isbn=0-596-00362-5 | quote = 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.]

Resistance formula

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

:$mbox\{resistance\; in\; ohms\}\; =\; frac\; \{mbox\{power\; supply\; voltage\}\; -\; mbox\{LED\; voltage\; drop\}\; \}\; \{mbox\{LED\; current\; rating$

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)

=See also=
* Ohm's law
* LED Limiting Resistor Calculator [http://www.avgoservices.com/Led.html]

References