🚀 go-pugleaf

>In article <1020006@hpdmd48.boi.hp.com> rrr@hpdmd48.boi.hp.com (Rudi Rynders) writes:
>
>    Given an incandescent lamp with a dimmer switch. The lamp is on.
>...
>    switch up, no matter how slow, the light always comes on rather
>    suddenly and much brighter than in the reverse process .
>
>>This is not a physics problem, it is an electrical engineering problem.

Yes, but it has to do with the circuit triggering the triac.
The manufacturer was cheap.  Very simplified, the triac is
triggered from a `diac', a bidirectional 5-layer breakdown diode,
a variable resistor, and a capacitor.  The R-C circuit charges from
the line, and when the voltage exceeds the breakdown voltage of the
diac, the capacitor discharges through the gate of the triac and
the triac turns on.

If the diac has not triggered recently, the capacitor holds a
residual charge from the previous half cycle, opposite in polarity
to the voltage necessary to trigger.  To overcome this charge
(which is refilled every half cycle) it is necessary to advance
the control (decrease the resistance) such that the current cycle
can charge the capacitor enough to trigger the diac->triac pair.

However, once the diac has fired, there is much less residual
charge on the capacitor, so now the capacitor can charge to the
trigger voltage much sooner in each cycle, so the lamp is now
on brightly.

The cheapest cure is to use an asymmetrical trigger diac.  This
costs a few cents more than the symmetrical ones.

See a triac manufacturer's application notes for more info.

I hope this is not too confusing.
	geoff steckel (gwes@wjh12.harvard.EDU)
			(...!husc6!wjh12!omnivore!gws)
Disclaimer: I am not affiliated with Sun Microsystems, despite the From: line.
This posting is entirely the author's responsibility.