24 Feb
2010
24 Feb
'10
2:14 a.m.
Chuck Guzis wrote:
There's some fellow on the web who's been
making various line/mains-
operated lights using only a resistor in series with a single LED.
Weird--I would have at least paralleled the LED with another
resistor. I'll try to find his web page, if anyone's interested.
I have on occasion run single LEDs from line voltage by paralleling the LED
with a diode, then putting the pair in series with a C and R. C is calculated
to provide most of the voltage drop via capacitive reactance, a small R is
still present to limit inrush current. The diode limits the reverse voltage and
permits bidirectional current flow so the cap sees AC.
Power consumption and heat dissipation are reduced compared to a solution using
only R, and a power resistor is not needed.
I haven't tested the circuit over many on/off cycles though, to find out
whether perhaps the peak in-rush current reduces LED life.