Re: Making an X-10 lamp module immune to dimming

[isw <isw@xxxxxxxxxxx>]

In article <ldmdnSt8M_e4q9DVnZ2dnUVZ_g2dnZ2d@xxxxxxx>,
 "Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote:

> "isw" <isw@xxxxxxxxxxx> wrote in message
> news:isw-D9C27F.22374307062008@xxxxxxxxxxxxxxxxxxxxxxxxx
> > In article <F7udnWa4cqAYo9fVnZ2dnUVZ_rCtnZ2d@xxxxxxx>,
> >  "Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote:
> >
> >
> > --snip--
> >
> > > I am still a bit confused about one thing.  When the AC waveform crosses
> > > over, does current through the device drop to zero and the triac stops
> > > conducting simply because there's no current at that point on the sine
> wave?
> >
> > Precisely.
> >
> > > Does the triac have to be "retriggered" at that point and after each
> > > subsequent recrossing or does it start firing again as soon as current
> > > begins to flow again in the opposite direction?
> >
> > It will not conduct again until the proper amount of gate current is
> > applied, while there is a voltage across the device.
> >
> > > I have another question.  When taking apart the lamp module, I noticed
> that
> > > the tiny triac has an enormous aluminum heat sink.  What process
> generates
> > > the high heat developed?
> >
> > Mostly, it's the voltage drop across the chunk of silicon that forms the
> > triac, although some of it may be due to the tiny wires that connect the
> > chip to the external leads.
> >
> > A transistor is a three-layer device (NPN, say); a SCR is a four-layer
> > device (NPNP), and a triac comprises five (NPNPN or the other way
> > around). Interestingly, because of the way thyristors work, even though
> > they have more layers than transistors, the voltage drop across one when
> > conducting is lower.
> >
> > But still, whatever that drop is, multiplied by RMS current that is
> > flowing, creates heat.
> >
> > If you think about it, the worst case is when the device is "half on",
> > because the voltage drop is much larger. One reason to use a triac or
> > SCR instead of a transistor is because they sort of "automatically" go
> > through that halfway state very rapidly. Another is that the voltage
> > drop when conducting is lower.
>
> That explains a few things, especially why dimmers get very hot when dimming
> at some levels but not others.  What I am trying to say is that the heat
> output curve looks very unlike a resistive dimmer in the same circuit.

That's right. No matter how fast the device switches on, making the
transition at the peak of the half-cycle is going to take longer than
when it's near one end or the other. Hence, more heat is generated.

Isaac