"Lostgallifreyan" wrote in message
...
"Arfa Daily" wrote in
:

So, I'm still no closer to knowing how the multi-LED GU10-s or even
single LED types, are actually ballasted for 240v AC use, and whether
the claim that "these lamps put out almost no heat at all" is at least
basically true overall, in which case the ballasting arrangement must
be *very* efficient, or refers specifically to forward IR radiation in
the same direction as the light, which obviously will be minimal, or
is a fundamental marketing hype lie. Maybe I'll just buy one, and see
if I can figure out just what its guts are.


I'm not sure yet either, if it has to be really tiny. I'd allow for the
mains to low-volt part to be done in something about matchbox size, not
sure about smaller though.

The point with the 5mm LED's is that don't need much cooling, because they
don't put out much heat. If they did they'd burn because they really ARE
terrible for thermal coupling, thus proving that any claim to get high
output from such isn't a good claim. Not even the best LED's are that
efficient.

I agree that some strong output can be had but it's usually directional,
and close to monochrmatic. As soon as that energy is spread in a broad
spectrum by phosphor, you need a very strong source of shortwave light to
pump the phosphors, and the clue is a heatsink, or a diode that is clearly
made for mounting on one.

One thought, maybe not wildly helpful: I remember being suprised as a kid
by a NiCd charger that was as small as the 4 x AA battery pack. It had no
transformer. It had a rectifier and current limit resistor and did not run
hot. I guess the unhelpful part of this observation is that it didn't have
to provide one amp of current. On the other hand, power conversion needs
to
provide that amp at low volts, so as it's a lot less than an amp at 240V,
the smoothing capacitor might not need to be large. There might be
efficient circuits that don't even need one.

Points well taken, but I'm gonna reserve judgement at this time, until I can
find out how it's done. If the whole string of LEDs is in series, and they
are not super high power types requiring an amp continuous, then we could be
talking just 150mA or so. Alternatively, we could be talking pulsing the
whole string at an amp or so. I really think that I'm going to have to buy
one, and attack it with the Dremmel ... I can't think that I have ever seen
any kind of switching supply that works from low frequency AC input power,
that doesn't have a smoothing cap. It's hard to see how it could be done
without, unless you employ 'electronic' smoothing using a regulator with
feedback, as I have sometimes seen done in 'professional' equipment, but
even then, you're going to be talking circuitry that is as big as a
smoothing cap of as little as 22uF at the required 400v working, would be.

Looking at the pictures of the Cree GU10 replacements, it's hard to say if
the enclosure is a 100% ringer for the incandescent version, but even if
it's not, it still looks pretty tight to get any kind of 'conventional'
switcher squeezed into.

Arfa