Newsgroups: sci.electronics.design,sci.electronics.components,sci.electronics.misc
Subject: Re: Touch dimmer circuit
References:  <[email protected]>
"Ban"  writes:

> As said in a reply, it's hard to dimm flourescent lights. I have seen it
> done with special tubes having a net of wires around, but I don't know how
> the electronics were done for this purpose.

The methods for dimming fluorescent lights is described at
http://www.misty.com/~don/f-dim.html
There are few different methids for doing that.
More links to the topic can be found at
http://www.epanorama.net/lights.html 
(tht page is a source for information on any electronics related to lighting)

For dimming fluorescent lights the most traditional ways have been
giving the preheat to the ends of fluorescent lamps always on 
(having separate transformer to generate low heating voltages
for those ends) and then dimming the current going through the tube
using more or less normal light dimmer.

Other nowadays more common method for doing the fluorescent light dimming
is buying an electronic ballast with built-in dimmign functionality.
Those units take depending on the model either an external potentiometer
wired to two control pins or 1-10V control voltage. For example
Helvar (http://www.helvar.com/) makes such electronic ballasts for
fluorescent lamps. 

> If the lamps were 12V halogens, you can dimm an electronic transformer with
> a dimmer suitable for this purpose (conducting from zero-crossing and cut
> off when the desired phase angle is reached). 

This is true. Other possible method for dimming is buy an electronic
transformer which is specifically designed to be dimmed with normal
light dimmers and use it with a normal light dimmer. There are such
electronic transformers on the market which cna be dimmed with normal
light dimemrs (it is usually said in the package or the unit itself).

WARNING: Trying to dim an electronic transformer not designed to be dimmed
with a normal light dimmer can damage both the light dimmer and
the electronic transformer.

> 12V conventional transformers
> can be driven by a dimmer suitable for inductive loads (like motors). 

That's true. Conventional 12V transformers with halogens wired
to them will dim quite nicley with a dimmer which can handle inductive
loads.

> In both cases the dimmer should have a current limiter incorporated, which is
> not usually contained in the dimmers designed for a resistive load only.

How many of the light dimmers have a current limiter incorporated ?
Haven't seen much such units. And how those functions are implemented
into dimmers ?

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/