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



In article <VtCdnaFcKJIC0NfVnZ2dnUVZ_rPinZ2d@xxxxxxx>, ROBERT_GREEN1963@xxxxxxxxx (Robert Green) writes:

| As I looked at the mod schematic, I realized that the switching was
| occurring without any polarity reversal of the trigger.

No, you were right the first time.  The direction of the gate current is
reversing in step with the line, keeping the triggering in the more sensitive
quadrants.  The unmodified module uses its own DC supply to drive the gate
current independent of the line polarity.  Using the more sensitive quadrants
(or, in general, using two quadrants with the same sensitivity) keeps the
triggering times as symmetrical as possible minimizing the DC component in
the output.

| I am assuming that
| the pulse has to be given after each ZC because the triac has turned itself
| off because of a lack of current flow.

You assume correctly.

| I worded that badly.  I should have said that the support circuitry in the
| mod detects the ZC and then feeds that to the optoisolator which then pulses
| the triac with power that is independent of the existing module circuitry.

Again, you were right the first time.  This optoisolator has extra circuitry
to synchronize with the zero crossing.  Although the output of the module's
IC is synchronized to the line, once it is integrated and passed through a
threshold detector there is no guarantee that the resulting transition will
be anywhere near a zero crossing of the supply.  The MOC3042 insures that
the switching will happen only near the zero crossing.  Note that we are
talking about the single transition from off to on when the module is so
commanded, not a transition that happens twice per cycle.  Whether this
is important is up to you.

| I assume that's done because of the line voltages involved and to prevent
| any unintended interaction of the modification circuitry with the module's
| circuits.

I suspect you are correct.  The zero crossing synchronization is just an
extra (but nice) feature that comes for free with a part that happens to
do just what is needed for the modification.

				Dan Lanciani
				ddl@danlan.*com


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