On Fri, 28 Nov 2014 08:50:09 -0500, 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

The regulators in LED lamps are constant current types, not constant
voltage. They also have some sort of step-down circuit because the LED
needs a lot more current than what you would want to draw from the AC
lines. Common power LED currents are in the neighborhood of 350 and 700
mA.

Some very small LED lamps, Christmas light size, use capacitors to limit
the current.

Jim Mueller



--
Jim Mueller

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