Em 27/8/2012 20:42, Mark Hanchey escreveu:
> On 8/27/2012 1:55 PM, alan smith wrote:
>>   Friend has me thinking about this...if you take 110VAC and half wave r=
ectify it, your going to end up with around 150VDC peak, so with the correc=
t resistor(7k-8K) it should drive a standard LED OK?  Guess I've never real=
ly thought about driving it directly from AC.  Yes..I know, its non-isolate=
d so its at the AC potential and a shock hazard.  Without a capacitor, you =
will see flicker on it as well of course.
>>
>>
> This is one of those things that can be done but shouldn't be done.=20
> Really to do it right the cost is pretty high compared to just using DC.=
=20
> Capacitors at the rated voltages are not cheap, at least for the good one=
s.
> A .47uf , 250V cap and a 1K, 1W resistor in parallel with each other and=
=20
> the LED connected in series across that connection  will work for=20
> powering LED.  I have seen bridge rectifiers built out of LED for low=20
> voltage demonstrations.
>
> Mark
>


I think the resistor value should be much lower, and in series with the
capacitor to reduce the inrush current. If you need a bleeding resistor,
then choose something like 220k.


Isaac

--=20
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