Circuit Diagram for a 12V LED Lamp

What color LED it makes a difference. One LED or how many 3mm 5mm What is you power source? These are vital things to answer. More info required. It does not compute!

Have you tried a resistor and ohms law??

Here you go, one very basic electrical diaghram for a LED. The resistor will depend on the particular LED used and the desired light intensity from say LED. As a fellow member stated, you can use Ohms law to determine the value of the resistor.

You can also Wiki LED for more links and information.

To my fellow forum members.... Sorry for the crude drawing I was lazy and used MS Paint.

You make look easier than it is you have to allow for the voltage drop across the LED

that is you take the supply voltage subtract the LED's forward voltage (this is where the color comes in) then decide on the current to be used and then select then the resister. V=IxR I=V/R R=V/I. That sums it up.

I 'm curious, why do you need to include a resister in the 12V LED circuit, if the LED is rated at 12 volts already?

Some LED's have a built in resister to allow for 12V usage. Made for car alarm indicators, those funny little red lights that wink at you.

By lamp, I assume you mean a desk lamp or something similar. In that case, you need more than one LED. Here's one:

Let's assume that each LED's forward voltage drop is 1.2Vdc (makes it easier for me). This means that if I string ten LEDs in series, I won't need a resistor since 10 x 1.2vdc = 12vdc. If your LEDs are 1.5Vdc, you'll need eight in series and no resistor.

If they are, say, 2.1Vdc, it's going to be a bit different. 6 x 2.1vdc = 12.6Vdc, which is a little more than your supply. It might still work albeit a little dimmer.

If you use five, 5 x 2.1Vdc = 10.5Vdc. That means your resistor will have to drop 1.5Vdc. You'll need to know the forward current of your LEDs in order to calculate your resistor's value. Now take out your calculator and start pushing buttons.

LED's are current mode devices. You must always use a current limiting device i.e. a resistor or some other means. To operate one without such would be like trying to use a zener diode without any current limiting device. The knee on the forward voltage curve is too sharp and also temperature dependent. Your example of 10 LED's in series from a 12 volt source is marginal. You would be better off to split it into two strings of five.

Quite.

Yeah, I give up after a while. Time to let out the magic smoke. Perhaps a car battery with welding cables would be expedient.

A lot of people now use LED drivers in the place of resistors, esp in battery powered uses due to the wasted power in resistors.

LED drivers here

http://www.google.com/search?hl=en&q=%22led+driver%22+%2Bmodule&btnG=Google+Search

hi dear,

i want ur suggesion that i want to make a breaklight for my bike and i want to use approximately 50 led than sir how can i make it if u have a some diagrams or for any destination suggesion so give me it i m thankfull to u.

thanking u sir forever

r r suthar

Si tienes el código del LED, ve sus valores de consumo, voltaje directo "V_f(Vdc)", máximo consumo de corriente "I_f(mA)", la resistencia aproximadamente del LED será (R=V_f/I_f), la potencia también esta en el manual, P_d(mW) = [P=V_fxI_f] (aprox), como te habrás dado cuenta la formula es lineal, si tu LED es de 12 Voltios DC no requieres ninguna resistencia si tu fuente es de 12 voltios, la resistencia propia del LED actúa como limitador de corriente, solo ten cuidado de no ponerlo al revés no puede exceder el Voltaje Reverso "V_r", que también esta en el detalle técnico, identifica bien el ánodo y el cátodo, el LED es un diodo emisor de luz y como diodo lo puedes identificar con un multitester.

Si tienes mas de un LED puedes colocarlos de forma paralela o seriales, si son (paralelas: suma las corrientes), si son (seriales: suma los voltajes), por cada LED.

Mi espanol es...er rusty .

But if I interpret it correctly, you have made a slight error. The value of the resistor is:

R = (12 - V_f)/I_f.

If your LED string is already equal to 12Vdc, then, yes, you won't need a resistor (R = 0Ω). If it's less than 12V, then you'll need to use the formula to calculate for the resistor value.

Otherwise, I agree with the rest of your posts.

Vulcan, do you actually use LED's in the way you describe? I have used LED's for 30 years and never heard such a recommendation. Just out of curiosity I checked a couple with a current limited supply and as expected the voltage difference between really dim and over current is only a couple of tenths of a volt. It just defies all recommendations I have ever read in LED data sheets and in order to assure that my designs had a margin of safety for the parts I have never attempted to use LED's without resistors (excepting special pulsed applications which are beyond the scope of this application). What kind of designs have you done where you used LED's in this manner?

Yes, I have done this. Only problem is that the LEDs available in those days were very much inferior to the ones we have today.

I was a lot younger then and I naively thought I could build a lamp out of LEDs (red ones at that but it was experimental). I stringed 8 LEDs in series, put a 12Vdc power source across it and it worked!

But the light intensity was dismal. I haven't tried it since (about 25 years ago) but I think the same principle applies. I guess the advantage I had back then was that I never read that document you mentioned about the proper application of LEDs.

Would the thing have lasted? I didn't try. The LEDs weren't hot but, after seeing the result, I reused the parts for other projects. I am, however, willing to try it again using the super-bright LEDs now available.

Well I just used a 2000mcd super bright LED that I bought about a month ago for a project and it measured a much smaller difference between the very dim (1.65v) point and the too much current (1.9v) point of operation than an older LED from 30 years ago. That would indicate that the no current limit method is even less appropriate than it might have been with older LED's. I could never let a design go out where the margin between doesn't work and burns out is only a couple of hundred millivolts and I didn't just try something once years ago I have used LED's in over 40 successful designs. I'm going to have to stick by my contention that this is a very bad way to attempt to use LED's and one I have never seen used in hundreds of good designs. Good luck to anyone who may attempt to go that route. I would seriously recommend that you don't and that you seek other design application recommendations from the manufacturers if you don't believe me.

That's okay. We agree to disagree. In the interest of "proper" design, however, you're right. Better to build it to last than to build it in minimalist fashion.

For your info, I've also built circuits in the succeeding years and I've always had to put resistors in series with single LEDs. It's just that I've never had reason to put a whole bunch of them together like I did before (I used LEDs for indication, not illumination).

This post has made me curious. I've got an LED flashlight here and I'm tempted to open it up. 'Been with me for two years and it's still as bright as the day I bought it. It's got eight LEDs and two AA batteries. I don't think it's series connected though. Maybe parallel. 'Let you know later.

Can't get the darn flashlight (torch to some of you) open. Okay, actually, I'm afraid to open it. I tried using couple of rubber bands (to wrap around it and provide a good surface for twisting). No luck.

Next I tried using electrical pliers but I just scratched the nice aluminum surface. Then I tried using a small pipe wrench, scratched it again.

Sorry kids. I just ruined a nice LED flashlight in the name of...curiousity. It still works, by the way. That was nice, a child-proof flashlight .

Vulcan, You were right at the bottom end of the LEDs emission curve. One less LED and they would have been a lot brighter and hotter and you might have gotten a progressive failure of one after the other cooking themselves into conduction, which can lead to them all cooking.

Some LEDs have current limiting built in so they can be operated on a wider range than the original ones which had a sharp knee.

Modern super brights? I have never used one

A room at this location, 5m x 3.5m in size, is lit with 10 x 1.1W proprietary LED cluster lamps, each containing 12 super-bright white LEDs.

Try it!

Estas en lo correcto Vulcan, tu formula del calculo de la Resistencia en función al voltaje, pero la pregunta no especifica si tiene una fuente de voltaje de 12 voltios o esta usando un LED de 12 voltios. - Los voltajes de LED comunes están entre (1.65 a 2.60 Vdc) "los comerciales", con corrientes de (35 a 50 mA), según aplicación y color. - Lo que nos esta pidiendo es un diagrama que creo que ya cumplimos.

Lea, lea, leer …

Usted tiene razón. Él no dijo que el suministro de energía era 12V o si esto fuera el LED que era 12V. Kingbright vende LEDs con resistencias incorporadas, sólo descubrí. Dos modelos que vi eran para 5V y el otro para 12V.

Translation:

Read, read, read…

You're right. He didn't say that the power supply was 12V or if it was the LED that was 12V. Kingbright sells LEDs with built-in resistors, I just discovered. Two models I saw were for 5V and another for 12V.

Hope my Spanish was correct .

Just run up to the LUMILED web site, there you will find the circuit design guild for LED systems.

Each type of lamp, HER, GaN, AlInGaP, all have different Vf conditions. The circuit construction is based upon the type of LED you are using.

Some GaN chips run at 4.5 V while AlInGaP run in the 1.5 to 3 V range.

Most of the time you should run a timing circuit. It is all in the design guild that you can down load. Easy....

SC

LED need 0.7V to turn on. After that most of them should have MAX current of 20mA. Some high output one would use higher current, they usually come with heatsink. Read manufacturer datasheet for max current rating for your LEDs.

The easiest way to find out max current/brightness is try. Using a variable voltage source and amp/volt meter, connect LED to source. Increase voltage from 0 till LED turn on. Keep increasing and note brightness until you can't notice any change. Note the current C1/voltage V1. Reduce voltage until you see it start to dim. Note current C2/voltage V2. C2 or V2 is safe for long time use. (C2+C1)/2 or (V1+V2)/2 is good for max brightness. Remember different color LED will have different current/voltage due to different internal resistance. Also always try to connect LEDs with resistor first before connecting them in parallel with each other. Connecting other way (including in series) will result in different brightness in each LED. Again due to slight internal resistance different.

Pineapple.

LED turnon voltage varies with the color and process. None are at 0.7 volts

Figure 1. Standard red, green, and yellow LEDs have forward voltages in the range 1.4V to 2.6V, depending on the desired brightness and the choice of forward current. For forward currents below 10mA, the forward voltage varies only a few hundreds of millivolts.

http://www.maxim-ic.com/appnotes.cfm/appnote_number/3070

As a rule of thumb I use 20ma at 2 volts . You can do the ret of the math.

Another possibility is using a switching regulator modified as a current source as they are used for LED backlight applications. You find them at linear.com or at ti.com together with schematics and application notes.

The advantages are:
1. No energy is wasted by resistors because the efficiency is very good (80...95%).
2. You can vary the number of LEDS in the chain according to your application at the same efficiency.
3. The LEDS are overload-protected as they are driven with constant current.

The disadvantages are:
1. Some more parts
2. Higher price.

Regards Uwe

There is an awful lot of comment on the subject of LED's and it may interest those involved to know that it is possible to energise an LED from a fraction of 1 Volt with the device I have developed. In fact all that is required is the forward volt drop of a single silicon diode, that diode can be a power type capable of handling 10 amperes. the benefit is that you can then see via the photons produced by the LED , electrical current flow or more exactly a portion of this flow. This can aid the troubleshooting of electrical circuits where this device is fitted. The sensitivity of the LED to milliamp current flow is little diminished yet capable of withstanding much higher currents and without the need of any ballast resistors.

LED's are essentialy current devices but have a varying requirement for a minimum forward voltage before they start conducting, this doorstep voltage is determined by the bandgap in elecron volts or radiant colour of the diode junction. My device standardises the Vf requirement to a minimun of 0.35 volts (ANY COLOUR TYPE) making it a very simple current detector with a negative impedance in the order of 200 to 0.2 Ohms over the range of 3mA to 10 Amperes.

Is anybody interested to know more of how current flow and its polarity can be made visible and detectable with simplicity and very high degrees of reliability?

Its has vast potential in all aspects of any electrical system for retriving information and making conditions obvious to the eye.

Hello All, Im from philippines I have a project right now i try to add LED on my motorcycle which has 12V battery and try this one 2 White LED and 1 Resistor(1K ohms i think 1/4watts) at first the LED are OK,after a couple of hours one LED was busted. why the one LED got busted? thanks a lot

Hi There!

I don't know how u connected the led's .Try one 330 ohms resistor (1/4 watts)on both the led's in series combination.I assume the forward voltage on each white led is 3.3 volts.All the best

Mohammed Zubair

Canada

Try a 3V zener in series with the LEDs, no resistor. Measure it as you vary voltage, have fun.

Not sure if this thread is still active, but I thought I would let you know the circuit diagram for LED lamp powered by 12v battery that I have working at home. Although the design I have on my web site actually uses two 5v array LED circuits:

http://www.bobzone.webatu.com/clouds/LED%20lamps.htm

The reason for this is because when I used a 12v circuit, the LED's would reduce brightness and eventually switch off when battery falls below 11.5v beyond the current limit of resistor. To compensate for this the circuit is powered by 5v via a power regulator 7805 and 10 Ohm resistor to limit current, allowing the battery to provide sufficient power as low as 9v needed for the regulator to work.

The LED's are high brightness type I obtained from a cheap camping lamp complete with round unit, having to change only the .5 watt resistor with a 10 watt type due to heating with constant use. With each LED wired in parallel the current use is more than a 12v series circuit, but using a car battery with 5v circuit the brightness remains constant for longer periods.

Just thought I'd let you know as the circuit works fine and bright enough to read with in a dark room, and my intention is to fit them throughout my home in conjunction with a solar charger for battery.