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car enterior LED light bulb problem

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bursach

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Hi everybody!
I`ve got one problem with my enterior light in my car.
I replaced standard light bulb 10W with smd LED bar, but it still working when door is closed, but much weaker then door is open.
The car engine is off.
I measured voltage in standby, door is closed, there is a 12.6V in bulb place without bulb, but when I put this LED bar, voltage dropp approximately to 7.6V, still door closed, and some weak shine is present.
Is there any simple undervoltage circuit, that I can use for this problem, it will cut off any voltage under 10V?
I`ve noticed, that is almost similiar problem in other cars. This car is opel kadett.
Renault Twingo has the same problem, but if your engine is start, and you driving in high rpm, the LED is shining brightly, door is closed....
Thanks in advance.
 
Car interior light-using LEDs

Bursach: I don't know if you had already solved this 2006 problem! I owned different japanese cars and there are simple "push to open" switches on the doors which are all wired parallel to a single dome bulb(12v). One end of the sw is grounded. In other words,any of the switches can send a negative to a common bulb. The positive side of the bulb goes to the ignition switch so that it is off when the key is removed. If the switches on the doors are used for some other purposes, then that is where it is possible that you are getting some "grounding" via another circuit. Or maybe, electronics is used and the sw does not fully open. when you are using the regular bulbm the current leakage is not strong enought to light up the bulb but for LEDS, ah,it will glimmer. i know what you mean , if only we can introduce some cut off. Well, one sure way isto put a tiny relay in there, where the tiny leakage will not be enought to close it. But that is bulky. Get a zener diode which is like a hurdle bar. Get a one watter of say 11 volts, anything below will not cross it to the LEDS. You may try voltage regulators of the 78xx family. Try the 7810. It ha thre terminals. Left is in, center is ground, right is out. Jow if you want to increase it voltage output, series a resistor between the center pin and ground. At a certain voltage below the output voltage, the voltage regulator shuts down. You may alsowant to try to parrallel a resistor on the LED. LEDS work on 2-3 volts and normally a resistor is series to drop the voltage. You can lower the series resistor to get more volatge across and parallel a resistor on the LED to split the current flow.

Good Luck.

BK
 
Bravo: thanks for your fast response.
I have tried this with paralel and series resistors but no effect.
Zener diode is for overvoltage protection, it will pass everything bellow its nominal voltage. I`ve been thinking about it also, but maybe I will use reley as you recommended to get this device work properly.
 
Using a zener diode as a voltage threshold

Hi Bursach. First, I misread the date of your first post. Now I got it, your post is recent and what I saw was your joining date in 2006! Let me if you got it right about using the zener didoe. yes, a zener diode is usually used as a "brute" voltage regulator and will ground or short out anything about its rated value. It is placed on the line to ground. What I meant there was to use it in series with the supply line to the LEDS, kathode facing the + line and the anode to the LED. It will then pass only the voltage at its rated value or over. Thus, it the voltage when the LED shows dim light is say 8 volts, it won't go through if you are using an 11 v zener. I would measure the voltage when that thing happens and base the value of the zener on that voltage. You don't really want a very low value as it won't blocka strong enought voltage to dim the LED still. I suggest 11 v cuz I am assuming that when a door opens, a full 12v is delivered. Of course, you need to step down the 12 v to the LED but that is a matter of resistors in series. Normally, the door switches supplies the negative side. Just reverse the zener or put it on the positive side from the ignition switch to the LED.

BravoKilo
 
Ok BravoKilo, no problem, I will try with zener in series to LED bar.
Will let you know if it helps. I think, as I understand it will.
Thanks! :):)
 
but when I put this LED bar, voltage dropp approximately to 7.6V, still door closed, and some weak shine is present
The source impedance seems awfully high for a circuit that drives a lamp.
 
This with zener diode in series works, but ...
zener should be only 1V , to work fine.
I`ve got a power supply and I measure a voltage needed for proper working.
Have not got this zener 1V, so I`ve experimented with 5v6. Led bar is a full shine for about 18V, zener in series. Which means I need 1V zener and it will work perfectly with 13V or higher. Of course voltage regulator 7812 or similiar is recommended.
 
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