The original bulb, as well as the four LED array replacement, is the spindle shaped, symmetrical type and can be placed in the socket in any direction. That's why I assumed that it had a rectifyer built in.

 

Hi Svinto, is this what you have? WLED-x4 (194 type) Wedge Base bulbs Specifications

Your right, the white and red ones are non-polarized. Makes your life easier!
They work on a wider voltage range too.

If your like me you probably have a wallwart sitting around that will work. I never throw out a working power supply when what ever it went to dies

Glad this is going to work out well for you, Cary

 

eric, out of curiosity how would you determine what portion of the reverse voltage each LED carries in a long series string? Is it just variations in the reverse breakdown voltage that causes it?

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Interesting, I didn't think 50 Hz flicker would be visible?

 

boutyhunter, you have to understand a little more about how human vision works. Frequency is not the only determining factor in perception, the difference between the two points is. In the case of a motion images, film uses as low as 24 frames per second, but even in a high action movie the difference between each frame is very small. Same thing with a lightbulb, a common incandescent bulb flickers at twice the line frequency, this flicker is very subtle though, and isn't noticeable to the human eye. An LED fed AC will only be on for half of the AC cycle, so it dims on, then off for 1 half cycle and full off for the other, depending on what the person is looking at or doing this can be very pronounced. As far as what the maximum frequency and modulation depth a person will notice is HIGHLY dependent on the individual. I personally notice flicker most in my peripheral vision, because that's primarily what it's for, to detect movement. I've had CRT monitors with a full screen refresh rate of 75+hz and in my peripheral vision I can still see the screen flicker when my head is moving.

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If you say so, but it's been my experience that people notice their LED backlights flickering when their current sources used to drive them have a low frequency motorboat type oscillation. As long as the oscillation frequency doesn't drop too low, no complaints.

 

Not even remotely comparable, as the oscillation frequency slows on that type of circuit the modulation depth would increase as well. You measured the frequency change, you probably weren't even thinking of the modulation depth change. As the modulation depth increases, the detectable frequency decreases, you already had a decreasing frequency, but the modulation depth probably increased much faster. You attributed the change to frequency drop not modulation depth, because you were looking at it with human eyes. We can see contrasting objects very well, but are almost completely incapable of measuring the absolute brightness of a light source.

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hi SC,
Its akin to the variation in Vfwd of LED's of the same colour.
As you know, connecting unmatched [Vfwd] LED's in parallel and powered via a common resistor can result in early/catastrophic failure of the 'lowest' Vfwd and the next one in the group and so on.

So the variation in Vrev breakdown and reverse leakage current of the LED's can cause a failure in a series reversed voltage biased LED string.
The leakage current thru the string can create a state where the reverse voltage across any one LED exceeds the rated Vrev.

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Eric " Good enough is Perfect "
I will NOT answer PM's requesting technical help, please use the Forum
PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/

 

It is this type Super Bright LEDs ? Festoon Light Bulbs which I have just learned is called a festoon bulb in English. And I sure do have a pile of orphan wallwarts ... Thanks again everyone for the help!

 

Hello
I really need help about led's because i have burnt out my brand new 24 white led's by applying them 12 volts dc they were all in parallel i tried to use a 5 volts regulator but that produces excess of heat so plz help me in calculating the series resistor for the led's
i want to use 12 led's in series or paralles suggested by you people
Plzzzzzzzzzzz Reply

 

Unless the LEDs are superbly matched (which can only happen if they are fabricated on a single die) the reverse voltage distribution will vary a lot across each diode, far worse than the variations seen in VF. The reverse biased diode is essentially "off" which means it's a very high impedance and just leaking a tiny amount of current up until it reaches the voltage where it breaks down (avalanches) which will destroy it. The leakage currents back through diodes is not tested at all and can vary a lot. In cases where you MUST allow reverse voltages across a string, it's recommended to use resistors in parallel to force the voltage to share more equally across each diode. It's best practice to NEVER apply a reverse voltage which could exceed the breakdown of any single diode.

 

If you apply 12V: use a resistor of about 910 Ohms in series with EACH LED, wire all LED/resistors in parallel from 12V to ground. That will give you about 10 mA per LED.

You could wire the LEDs in series with sets of three ONLY and have a resistor of about 300 Ohms in series with each set of three LEDs. Wire all of the sets of three LEDs/resistor in parallel from 12V to ground.

 

Avalanche conditions do not instantly destroy a diode, otherwise Zener diodes wouldn't exist. It just suddenly dawned on my as well that the entire argument is moot. The array that I created was 40 series with two series in anti-parallel. The diodes were never reverse biased over their rated reverse voltage because the anti- parrallel string was conducting during the second half of the AC cycle.

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LEDs and Zener diodes are totally different animals. Zeners are designed to have large junction areas, LEDs are easily blown by over voltage (been there done that). The point is that any PN junction which is driven to a voltage above it's rated will be damaged unless the current is limited to a value which is low enough to prevent damage. That safe value of current will depend on the junction design, but any P-N junction will be destroyed if driven above rated voltage from a low impedance source where the current is not controlled.

 

Thank You bountyHunter
But the main Problem is
i am confused about the voltage and current requirement for the led so
plz give me some information about the voltage and the current ratings of some different led's
and some math to calculate resistance
i am waiting for reply
once again thanx