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Posted to uk.d-i-y
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Cheap R80 Reflector to Poundland Golf Ball SES LED conversion.
In article ,
writes:
On Saturday, 24 September 2016 19:52:17 UTC+1, The Natural Philosopher wro=
te:
On 24/09/16 19:02, tabbypurr wrote:
On Saturday, 24 September 2016 18:18:37 UTC+1, The Natural Philosopher =
wrote:
Actually the cheap way to drop LED voltage for mains uses is a series
capacitor. Then FW bridge rect and if you want smoothing caps, and put
the LED chips in series.
for e.g a 7W LED you need 30mA or about 7.5k impedance at 50hz.
About 0.47uF.
need to add a resistor too
=20
No, you don't.
Especially with a smoothing cap.
Without one the only Rs in circuit are the dropper cap, the diodes and the =
reservoir cap. The LEDs would then be hit with brief massive overpower at t=
imes, and the current limit of the dropper & diodes exceeded. You can build=
it like that if you want, but it's not a smart choice.
+1
Also, remember to allow for the worse case which is a switch-off when
the cap has 340V across it, followed by a switch on half a cycle later
(or n+0.5 cycles later), which gives you 680V across that resistance.
The series resistance is needed to limit peak current flow in this case.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
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