🚀 go-pugleaf

In article <1992Dec27.051620.22808@ee.ubc.ca> jmorriso@ee.ubc.ca (John Paul Morrison) writes:
>In article <1992Dec26.063254.23524@murdoch.acc.Virginia.EDU> alexander@kronos.pharm.Virginia.EDU (Robert Alexander) writes:
>>In article <72415@cup.portal.com> dbell@cup.portal.com (David J Bell) writes:
>>>
>>>>But a light dimmer I have installed makes the lightbulb RING alot, and
>>>>it's very annoying. The ringing gets worse when you dim the light. I'm
>>>>wondering if a "RFI free" dimmer will reduce this ringing.


>At 120 V 60 Hz, the bulb doesn't make any noise. But with the dimmer
>(triac + stuff), it does ring, and not at 60Hz (which wouldn't be bad)
>but it rings around 2-3 kHz, which is ANNOYING (since hearing is very acute
>around there).

	Either you have to have enough filter components (inductors
or capacitors) to filter higher frequencies than 60 Hz, or you
have to have a light bulb thatoesn't acoustically respond to
the various frequencies generated by the dimmer.

	One can presumably operate 12V halogen lamps on regulated
12V switching power supplies (most of which are adjustable, and
therefore allow dimming).  Going the build-it-yourself route is
expensive and not recommended for power circuitry, unless it
can't be bought.

	Or, one can use a dimmer circuit that doesn't generate
any harmonics; I refer, of course, to a variable autotransformer
(VARIAC or similar brand).

	It is possible to make regulated high-frequency AC with a
switching resonant converter, but (aside from some microwave ovens)
this kind of circuit is not commercially available in suitable
form for running incandescent bulbs.  I have run lamps with
a microwave oven (works best on neon and low-pressure gas lamps),
but this sems not entirely practical...

	Almost all dimming circuits use the simple SCR or TRIAC
switching scheme that generates significant acoustic-frequency
'buzz', and any coiled-filament bulb will convert some of this
energy to audible sound.  Perhaps trying different kinds
of bulb and selecting for least whine is the easiest route to take.

	John Whitmore