Thursday September 21, 2017

Simple LED Circuit

Updated 5/27/2009: The schematic will look very complicated, but once you get used to some of the electronic component notations it will get easier. For those that are new to schematics, I have created a pictural representations of what the schematic is saying. I hope this helps everyone that is new to electronic diagrams.

led diagram

When building the circuit just make certain that you have the LED oriented properly (anode to cathode) as in the schematic since LEDs are polarity-sensitve. Resistors are not polarity-sensitve (you can place them either direction) and as long as they are in series with the circuit they can be placed anywhere. Technically it's probably more correct to place the resistor between the negative (ground) of the battery terminal and the negative (cathode) of the LED since that's the way current flows, but since it's in series the resistor will drop the voltage either way. You can use a different voltage power source, just substitute the voltage in the equation above to find the resistor value you'll need.

Here's another helpful tool that will help you hook up one or many LEDs -- LED Calculator

For example, if you had a 12v PC Power Supply, 3.2v voltage drop, 20mA LED and 1 LED, here's the design

QUESTION: Can I hook up a 24v, 12v... or *gasp* 120v power supply?
**CAUTION** If you've never worked with electronics before, don't attempt hooking LEDs up to anything but small low-voltage "toy" batteries.  Especially power supplies or wall transformers that are hooked into your home power outlets.  Electricity is neat, but if you don't know what you're doing then it can be very dangerous and in some cases deadly.

Again I strongly recommend learning on small cheap low voltage batteries first.  It is certainly *possible* to work with higher voltages but often transformers will be needed to step the voltage down, bridge rectifiers needed to convert to D/C voltage, voltage regulators and filter capacitors to get a consistent voltage.  If you're scratching your head wondering what those things are then you definitely SHOULD NOT work with high voltages at this point.

QUESTION: Can I hook more than one LED up when only supplying 3v or 6v DC power supply?
Sure you can, but they will be affected depending on if you hook them up in series or in parallel.  If you're hooking up multiple LEDs in series the voltage drops as you add more LEDs will eventually exceed the supply voltage and no more LEDs will light after a certain point.  If hooking up in parallel and adding more and more LEDs you'll start dropping the current supplied to the LEDs and they will dim. Check out the Wiring Multiple LEDs tutorial.

QUESTION: Do I need resistors if I'm using a 3v DC power supply?
If they are 3.2v LEDs then no, you would not need any resistors connected to them.  The resistor is there to balance out the voltage equation so that the LED receives the proper amount of voltage.  In this case, a 3v power supply is lower than 3.2v LED, but if you read the datasheet for the LED it would likely operate at voltages under 3v.  It will depend on the LED but the datasheet should tell you the minimum operating voltage to light the LED.

What is a datasheet?  It's one of the single most important documents when building electronic circuits.  Almost all electronic components have a datasheet that describe the electricle characteristics of the device like max and min voltage, how much current the device sinks, functions of the pins if it's an IC, etc.

QUESTION: What wattage resistor would I need for a higher voltage DC power supply?
That depends on the voltage of the power supply, the datasheet specs for your LED and also another equation to calculate power.  For the purpose of this tutorial we will remain basic and stick with talking about powering off of low voltage "toy" batteries where the standard 1/4w resistors will work just fine.

As I mentioned previously, this was just a very basic circuit so that I could begin putting my breadboard to good use. It doesn't get much simpler than this =) Still, it was nice to see the LED light up in all its glory and I now know I didn't buy dud LEDs a few months ago. Good luck!

Where To Go From Here?
How to Use Solderless Breadboards - Learn how to use solderless breadboards by building the simple LED circuit from this tutorial.

Wiring Multiple LEDs
- Building off the simple LED circuit, learn how to wire up additional LEDs

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help me
Posted 09/27/11 5:53AM by vasim786
hello friend..i have 12 volt battery..then how can i calculate current(i) and r ohm..i know v=ir but i have only value of voltage..i m nt student of electronic.pls guide me
Wiring LED
Posted 08/17/11 1:25AM by Sylvi418
I use plenty of LED Bulbs for my car inside and parking lights 4 LED in series.

I am from Srilanka

Posted 07/31/11 4:20AM by venemvette
what if i want to use a 1.8v led what resistor do i need
voltage drop
Posted 04/29/11 4:41PM by Anonymous Techdoser
currently I have a circuit that drops from 11.8vdc to 8.6vdc when 26 standard bulbs are turned on. Will replacing these standard bulbs with 12v leds bulbs reduce the voltage drop
simple throw-away led lights....
Posted 03/10/11 1:12AM by Anonymous Techdoser
What happens if the led diode is 3.2V and the battery is only 3V? Obviously it does not draw the extra .2V, but what effect does that have on the circuit? I am just using 10mm leds with a 3V lithium battery. I tested on out and it stayed lit for 2 weeks. If I only need them for 1 day, can I use more then one light per battery? If so, do I need to be concerned with resistors, capacitors etc? Or can i simply attach them all directly to the one battery? My physics books are beginning to look like ancient languages and do not typically explain such easy things. :) Please help!
Solar Blinking LED
Posted 12/24/10 9:39AM by pulsar2121
I liked your article here. I am trying to get an LED to blink 60 times a minute. The LED is from a garden light. It uses a 1.2V rechargeable AA battery. I also want to connect it to the garden light's solar panel and daylight sensor. What do you think would be a good circuit for this application.
cant undersant how it's (6v-3.2v)
Posted 09/15/10 2:50AM by Amartya_karan
sir i cant understand why it will be (6v-3.2v)
i know the ohm's law. but i cant understand why you doing this (6v- 3.2v)
please give me the full method.
info on LED
Posted 05/12/10 5:24AM by mmkkhh
i feel much happy to read the comment as above which have give me much info. thanks
more info , , i will welcome ,, ,khurshid
Converting av to dc to be used to power LED's
Posted 03/15/10 9:00PM by Anonymous Techdoser
Is there a 'simple' way to convert 24vac to dc voltage to drive a LED? I fully understand the need to use the correct resistor value to reduce 24 volts to the required 2.2 volts. But how to change the darn voltage to dc???The whole package must fit inside a door bell button.
Re: without a resistor
Posted 11/20/09 5:53AM by AceBHound
Yes, that's correct -- you can hook 2 leds up without a resistor since the voltage drop will be greater than the power source voltage. You could even try 3 leds in series and as long as the LEDs can still operate around 2v they'll light (though dimmer than if they were getting the full 3-3.2v each). If you add too many LEDs though, you won't meet minimum voltage requirements and they won't light. Have fun!
without a resistor
Posted 11/18/09 1:31PM by spaceshipman
so am I right that if I hook up 2X 3V LEDs in series to a 6V battery I wont need a resistor? I'm also a beginner!
To Math Confusion
Posted 09/01/09 1:48PM by Anonymous Techdoser
The 18A that the PSU puts out is not the component in the calculation that you should be using. What you are looking for is the consumption of the LED which is typically 20mA or .02A. Thus your calculation should be (12V-3.2V)/.02A = 440ohms. The resistor that you would need is a 470 ohms resistor. They are color coded as : Yellow, Violet, Brown, Gold.

Note you should verify the voltage of the LED as every color has its' own voltage. Also verify the mA used by the LED.
Try this One
Posted 08/30/09 7:45AM by Anonymous Techdoser
use the same circuit with a lemon or two. Stick a piece of copper wire in one end and a galvanized nail in the other. You should have enough current to light the led. Trick add more lemons(batteries)to make it brighter. Then try other foods around the house. Why do some work and others don't. What even works better as a load is one of those little digital clocks from the dollar store. It takes very little current to make one of those start working and it is useful also. McGuyver will be proud of you.
Math Confusion
Posted 07/27/09 10:39AM by Anonymous Techdoser
Okay, going back to the simple circuit above... 6V - 3.2V / .02A = 140ohms. So, if, for some reason, I wanted to power an LED off of a PSU at 12V/18A... 12V-3.2V / 18A = 0.5ohms. That can't possibly be right! What have I done wrong, please?
larger batterys and several LEDs
Posted 06/12/09 9:08AM by Anonymous Techdoser
i would like to set up a string of some where around 200 leds and have them chase 4 or 5 light up at a time down the string i'm assuming ill have to use a car battery to get the voltage and ampreage that i need to do this successfully but am un sure of how to sequence them to work properly. i would like to see 5 on 5 off 5 on 5 off and so forth down the string
Power rating
Posted 05/25/09 7:02PM by Anonymous Techdoser
These are the two most basic equations to electricity (they are useful to anyone and everyone, not just engineers and electricians):
Power/watts(P) = Volts(V) * Current/Amps(I)
Volts(V) = Amps(I) * Ohms(R)
Typically written as:

In the example a 6V bat is being used with a 3.2V LED, and a 330 ohm resister. This is all you need to know.

To get the resister power, we need the resister voltage and current.

ResisterV = BatV - LoadV = 6 - 3.2 = 2.8V

ResisterI = (I=V/R) = 2.8V / 330ohms = 0.0085 or 8.5mA

Now Resister Power = 0.0085A * 2.8V = 0.0238W
Less than a tenth of a Watt is required.

What if you choose the max rated power of 20mA with the 140ohm resister what is the power then?
To extend to 10LED with 9V
Posted 05/25/09 6:30PM by Anonymous Techdoser
I assume you've identified that your led's forward voltage is 3.2V (they are not all the same, i'm working with IR LEDs right now that are 1.2V). If you have 3.2V LEDs then you can put two in series with the resister (for 1.2V LEDs, you could use 5-6 in series). However, for more you must make a parallel path with another resister and two LEDs.

But you are right, for the resister look at the total series chain for voltage drop. (9 - 3.2 - 3.2) / 20mA --> 2.6V / 0.02A = 130 ohms (plus some margin for life time if needed).

You may not use a common resister for two parallel pairs of LEDs. If one pair has a slightly smaller forward voltage total, then one side or the other will take more amperage and could keep one side off, and possibly blow out the other side.
Ok... help me extend this.
Posted 03/13/09 6:15PM by Anonymous Techdoser
I have a 9v battery and want to light a series of LEDs (up to 10).

9v-3.2v = 5.8
5.8/20mA = 5.8/.02A = 290 ohms?

But how does a series of LEDs affect it?

If I hooked up 3 LEDs... you can't just keep subtracting. (9 - 3.2 - 3.2 - 3.2).

Yes, I'm an idiot. I got a D in physics electromagnetism 20 years ago.
question about power rating on resistor?
Posted 02/25/09 10:12AM by Anonymous Techdoser
How do you know what power resistor to use? I mean 1/4 watt, 1/8 watt, 1/2 watt, etc.? I just bought a breadboard myself and this question has come up several times already. Any help would be greatly appreciated.
I can't get it!
Posted 01/05/09 9:36AM by Anonymous Techdoser
The title says it all.
Doesn't matter.
Posted 05/23/08 2:02PM by Anonymous Techdoser
The resistor can be on either end... The only thing that matters is that the polarity is right on the LED. Put the resistor anywhere you want. If the LED lights up voilla, if it doesn't reverse the pins and it will.
Simple LED Circuit
Posted 04/15/07 4:34AM by deltaboy12000
LED's cathode is identified by:
1. the short lead of the LED
2. the flat side of the case of the LED
3. the large internal metal side of the LED.

If further understanding of LEDs is wanted look up N-type and P-type material. This is very advanced reading but it the science as to why LEDs only "work" when forward biased. Also in the digital world keep in mind its sometimes required to reverse bias a diode...
Just a small note.
Posted 10/21/06 2:42PM by TruthByDenial
If your led doesn't light up.
or you are confused.

∙Make sure your battery isn't dead
∙Flip the LED ( It only conducts current one way.)
∙You're resistor is fine, as long as its directly connected to positive wire.
I figured it out, before I found this site.
Posted 10/21/06 2:39PM by TruthByDenial
One of the few things that I found Interesting is that, from negative to positive, You would have this

{Wire (-) Connects to LED (-)}
{The other leg of LED, LED (+) connects to one leg of resistor. (There is no way to put a resistor in backwards)}
{The other leg of the resistor plugs into wire (+).

So it goes. - wire, LED, Resistor, + wire.
Hope this helps as I have just figured it out, and I'm just starting to learn about electricity and circuitry
Resistor Direction
Posted 10/12/06 8:28PM by PUREMUNY
Please help. I am trying to hook up a 2.4v LED light to a 2 AA battery pack. Which direction does the resistor go? Which end of the LED? Positive or negative on the battery pack. Thanks
Posted 05/03/06 12:03AM by Anonymous Techdoser
I can't figure it out so I decided to maek a necklace out of all my resistors!!! It is so kewl LOL!!11!
Posted 05/01/06 5:01PM by Anonymous Techdoser
Posted 04/24/06 8:49AM by Anonymous Techdoser
Two probably errors:
-Battery polarity is backwards (fix: switch battery leads to circuit)
-Diode is placed in reverse bias, backwards (fix: take out diode, flip it or turn 180 degrees, replace diode.)

One possible error:
-Something (breadboard, resistor, diode, battery) is broken or out of power.

Note: Diodes require 0.7V to bias properly (light up).
Posted 04/16/06 3:13PM by Anonymous Techdoser
maybe you've got your resistor in backwards?
I can't figure it out!!
Posted 04/16/06 3:12PM by Anonymous Techdoser
I've read the instructions like a millions times and I can't get it to work!!! LOL!! This schematic is too complicated.