On 11/28/2014 8:50 AM, Scott Dorsey wrote:
gareth wrote:
These LED replacements for 240V mains lamps; if one were to
open them, would one find a high voltage regulator suitable for
some of our valve experiments and repairs?

You might find a little constant current supply, but my guess is that
you'd just find a big dropping resistor. That configuration would
result in most of the power being wasted as heat, but it would still
produce less heat than an incandescent and be brighter.

If you want a high voltage regulator, a TIP50 transistor and a high
voltage zener (or a string of low voltage zeners) will fix you right
up. The TIP50 is comparatively easy to damage, but if you don't hook
it up backwards or something it will be very, very reliable. Not
expensive.

Think of the TIP50 as a 5080 replacement with a lot more gain and
better transconductance in the bargain.

If you want a high voltage switcher, on the other hand, look at the
Linear Technology chips intended for LCD backlight inverters. There
are some great Jim Williams applications notes.
--scott


No, these have electronic power supplies in them. Otherwise they would
dissipate huge amounts of heat. Think about it. LED's run at about 3V.
That means a 9W LED requires about 3 amps of power. 3 amps at 240V is
720W - or about 711W of power wasted. They would be way less efficient
than any other type of bulbs. Plus LED's run on DC and would not work
as efficiently on 50Hz AC.

However, they also are generally pretty well potted and almost
impossible to take apart without destroying them. And even if you could
get one apart, its design is single-purpose and generally won't do well
in a different application.

--
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