[TCML] The difference btwn a SIDAC and a SIDACtor.

[Finn Hammer <f-h@xxxx>]

All.
I`ve had a good sleep, and have perhaps been  dreaming about these 
little chips.

First thing is to define the difference between. SIDAC and SIDACtor:

SIDAC is simply voltage controlled: at break over voltage, it switches 
to a near short, with a low voltage, 1-2V,  across device.

SIDACtor is controlled in 2 steps.
1st. step is voltage controlled, at break over voltage, it transforms 
into a TVS diode, and clamps voltage to break over voltage value.
2nd. step is current controlled. If current trough TVS device, at break 
over voltage, exceeds 800mA, the device switches to a near short, with a 
low voltage 1-2V across device.

This difference explains why my test setup failed to produce breakdown 
all the way to the low voltage state: I had a 68kohm resistor between 
tank circuit and smoothing capacitor. I also think it disqualifies NST 
rectified systems from working. 800mA into a short elevated to several 
kilovolts is no small thing.

In my SISG scheme, where I bypass most of the SIDAC/SIDACtor's with a 
SCR, the current can easily be supplied from the tank capacitor, (When 
the SCR is trigged, the action is much like kicking the stool away from 
under the feet of a poor sod with a rope around his neck) and since the 
break over voltage rating of the one remaining SIDACtor in each section 
is very low, a successfully triggered section cannot be over volted.

But I am ultimately depending on the crowbar action of the 
SIDAC/SIDACtor string: Some of the stacked sections are bound to get 
triggered later than others, and these sections rely on the breakdown of 
the full string of SIDACtor's to protest the IGBT from over voltage. At 
least that is my cautious point of view. Therefore the voltage rise 
across one SIDACtor, from the point of the first breakdown into the TVS 
stage, and up to the point where the current breaks it down to SIDAC 
action has to be read out on the speck sheet or measured..

I will get back to this in a later installment.

Cheers, Finn Hammer

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