🚀 go-pugleaf

vail@tegra.COM (Johnathan Vail) writes:
> On a related note:  I was working on a CD player and on the circuit
> board was a normal looking glass diode, cathode band and all, that lit
> up red.  It wasn't an indicator, and had a normal D number like the
> other real diodes on the board.
> 
> Was the light emitted a side effect of the diode?
> 
> Was it a special LED in this package for use to frop a certain voltage
> or something?
LEDs also make good low-voltage voltage regulators using the forward
drop.  I used one many years ago in a circuit.  The ones I had didn't
have a forward drop that was very consistent unit to unit, tho'.  
Forward voltage ranges from about 1 to 2 V as I recall, depending on
type and color.  This is great, tho', since zeners of this low value
are hard to come by.
"The forward conduction characteristic of the LED displays a much
sharper knee than ordinarily obtained from forward-biased silicon
junction diodes...Generally, satisfactory regulating action begins
when the LED is just visible in the dark."
From: "Regulated  Power Supplies", Irving M. Gottlieb, 
Howard W. Sams, 1981, 3rd ed.