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

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Jeff Volp" <JeffVolp@xxxxxxx> wrote in message
news:08F1k.18467$102.2347@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> The delay of that pulse with respect to powerline zero crossings determine
> the brightness.  It is not clear how they adjust the phase, but it is
probably
> done by some sort of timer in the IC whose count for each half cycle is a
> function of the dim level.

If the line driving the triac is not pulsed in any way, but is constantly
powered, I thought that the output of the triac will always be 100% but
obviously it's more complex than that.  Not only is the light output chopped
each A/C cycle, but it seems that from Isaac said that they number of pulse
occurring during each A/C cycle is chopped into smaller pulses.  More
pulses, more light.  Might that be to keep the triac cooler than it would be
with longer pulses?  Why would they do it that way instead of a variable
width pulse that lengthed as the brightness was turned up?

I've been reading about triacs all night and it says at Wiki: "Triac is one
of many power-enhancing Mini-Cons who help the Autobots search the galaxy
for pure energon ore."  No, wait, that's: "It should be noted that once
avalanche breakdown has occurred, the thyristor continues to conduct,
irrespective of the gate voltage, until either: (a) the potential VG is
removed or (b) the current through the device (anode-cathode) is less than
the holding current specified by the manufacturer.

So it seems that even keeping the gate high all the time wouldn't work  It
seems that one of the mods extracted the ZC via an optoisolator and that
implies that the triac has to be pulsed in phase with the AC cycle for it to
allow current to pass.  That's not how I thought of a triac, conceptually.
When the author warns "this circuit only works if line current is fed into
pin 6 of the optoisolator. If you hook the circuit up wrong, the
zero-crossing circuit will not detect the voltage zero crossing and will not
trigger the alternistor" it seems to imply that to pass A/C current, the
triac must be synched to deal with the constantly reversing polarity of the
AC current.


--
Bobby G.