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Re: Window Switch LED replacement in a Coupe Q

Peter Schultz queries:
>     Electrical Engineer question of the day:
>     Why did Audi put a resistor AFTER the LED (attached to the Cathode) in the 
>     circuit.  Doesn't before the resistor (current limiting) make more sense???
>     Is that why these LEDs burn out at such an apparently high rate???
In a series circuit, the relative positions of the LED and resistor make no 
difference to the operation of the circuit.  Sometimes the position of the 
resistor is chosen to minimize the exposure of the supply voltage to minimize 
the chances that a short circuit would cause a fuse to blow.

No, the relative positions of the LED & resistor do not cause the LEDs to 
burn out.  Chances are more likely that the current limiting resistor value 
is too low, leading to excessive current and power dissipation.  I've never 
had to replace an LED before ... I always figured that there was simply a 
bad connection that would need to be resolved.  Did you test the LED that 
you removed?  If so, was it an open circuit?  

Steve Buchholz
San Jose, CA (USA)