Replacing a white LED in a night-light with a red LED

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I have a P.I.R. motion detector  (from Ebay) that turns on six white LEDs.
If I remove one or more of the LEDs the remaining LEDs still glow. If I try
to replace one of the original white LEDs with a common red LED, the red LED
glows and the other five white LEDS do not.
The answer is bound to illuminate my ignorance, but I can take it.
What is the answer?



Re: Replacing a white LED in a night-light with a red LED


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Boom-tish, etc.




Re: Replacing a white LED in a night-light with a red LED
finger to keyboard and composed:

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Are they all connected directly in parallel, without load sharing
resistors? If so, then the red LED probably has a lower forward
voltage drop, hence it shunts the white ones.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Re: Replacing a white LED in a night-light with a red LED

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Yes
If so, then the red LED probably has a lower forward
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Yes

Thank you



Re: Replacing a white LED in a night-light with a red LED

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Most common red LEDs have a typical voltage drop of about 2.0 volts.
Most common white LEDs have a typical voltage drop of about 3.5 volts.
Depending on the circuit configuration (I'm assuming the LEDs are in
parallel fed from a common series voltage dropping resistor), the red LED
having a lower voltage drop than the white ones is not leaving enough
voltage across the white LEDs for them to turn on, hence no light emission
from them.
With the red LED out of the circuit, measure the voltage across the white
LEDs.  Then replace one of the white LEDs with the red one and re-read the
voltage across the LEDs.  If the voltage has dropped considerably (see
typical figures above), there's your answer.

Cheers,
Alan



Re: Replacing a white LED in a night-light with a red LED
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"> With the red LED out of the circuit, measure the voltage across the white
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That is indeed the answer.
Thank you



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