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circuit or diagram to car led bulb error

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Member level 4
May 19, 2006
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On my car I change my original lamps to LED, but need have an resistor in parallel to simutate my bulb...

don't is possible make an circuit to simulate the bulb without an simple resistor? I seen many buld on ebay with some circuits, but I can't find anyone...

someone kown how I can start developer an circuit to this case?

best regards.

You're apparently talking about a method to cheat a lamp surveillance circuit in your car. It would be helpful to measure it's characteristics before developing anything. What's are sense current, resistance threshold and timing behaviour? When is it active?

There are two ways to look at this..

If you are replacing outside lights like directionals, they have the possibility of blinking too fast due to load being changed & may produce a code, depending on what kind of vehicle you have.
If your talking about marker lights daytime running lights, 3rd break lights, you will be ok.

If your replacing instrument cluster bulbs, you run the possibility of frying the instrument cluster & throwing a code.
I have two vehicles that run nothing but LEDs with the exception of the headlights.

If you could provide what lights your wanting to swap out, it would be helpful.
Keep in mind that an alternator can output from 12-15 volts.
If your using a single led, thats a lot of heat to dissipate.
If you want to cheat and get a guaranteed to work bulb, you can check out LED Lights & Accessories - SUPER BRIGHT LEDS
However nothing feels better than having the satisfaction that you did it yourself.
Keep in mind that there are different kinds of LEDs out there.
Some at 20mA , 24mA, 30mA, and some made out of the U.S. have strange numbers.
Also, your viewing angle makes a difference.
25 Degree are popular for outside of the vehicle, but not the interior, like instrument gauge lights, you will need a wider angle.

FvM- makes a valid point..

What lights are you replacing ?


I can't explain me correctly sorry... I like replace rear break lights and driving lights, but if I use an simple LED with an resistor to controll led corrent, appear an error on painel.

I try use an bulb like this **broken link removed** and error disappear...

what circuit this lights have to cancel the error?

best regards

What kind of LED are you using?
What are the specifications on the LEDs that you are using ?
mA, Voltage .

The led lamps in your link have a 240 ohm SMD resistor between the two inputs (black square with 241 written on it), this is why they can fool the car system that checks for a lamp resistance.


On break light I have bulb with 21W (I think), so P=VI <=> I = 21/12 = 1.75A, U=RI <=> R = 6.8Ohm, for I simulate my light I need an resistor with 6.8R@21W, with a simple 240R SMD resistor it burn, or not???

because that I think witch this bulbs (in picture) have some circuit on it...

I like design an generic circuit for an LED with drop = 2.5V @ 20mA

best regards

The leds in the picture have a proper driver for constant current to the leds and a resistor that consumes 12/240=50mA that seems to be used as dummy load to fool the car surveillance circuit into thinking that there is a lamp connected.
The 240 ohm resistor is connected in parallel to the led circuit, it is completely irrelevant with the led operation, both the led circuit and the resistor get 12v.

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yes I understand this... (problem can stay on my ingles)

how I can make this driver? what is calculations?

don't is this case but for example if I have an LED with 50W?

best regards

The drivers that these leds use are some kind of IC drivers that can provide a constant current, you can't do the same thing with just a resistor because it would produce too much heat so I can't give you any calculation, you have to find a proper driver chip.
For example I have used in the past a chip but it can work only up to 6v **broken link removed**
you want something similar for 12v


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