The Natural Philosopher wrote:
On 05/10/2020 11:12, wrote:
On Monday, 5 October 2020 10:02:15 UTC+1, charles wrote:
In article , Dave W
wrote:

Triacs conduct in both directions when the gate is held +ve, so give
full-cycle operation.

er, no. Triacs are diodes. To get full cycle conduction you need a pair of
triacs.

Yes, triacs do conduct in both directions and can be triggered with
either polarity as well. In other words, all combinations of positive
and negative voltage on the main terminals and trigger terminal are
able to trigger conduction using a single triac. The sensitivity can
however vary depending on the particular combination.

John

Yes, The silicon controlled rectifier is the unidirectional one: Triacs
are almost a pair in parrallel.


Lots of interesting and educational stuff.

Id not have thought of building a timer out of capacitance decay.

I had a look at the YouTube video, and read the comments and someone there
had also traced the circuit and (I think) explained it.

Having heard how hot that resistor can get, Im glad mine is mounted in a
relatively large enclosure.

Perhaps I should add some ventilation!

--
Chris