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Re: [TCML] Sidactors in a can of worms

Finn -
Coincidentally, earlier this week I was corresponding with Littlefuse about their "new" SIDACs, and how they compare with the "old" Teccor devices.
First, tech data on the new SIDACs is difficult to find on the Littlefuse website. I had to contact Littlefuse's Tech Support to find out where the data is.
Take a look at: http://www.littelfuse.com/data/en/Product_Catalogs/TN_Chap8_TDGEC1031.pdf.
Section 8-7 titled is "SIDACtor Construction and Operation", and this description seems to match the voltage-triggered switch operating mode we want for SISG use.
Also, see the thyristor application notes at:
which also contains some information on SIDACs.
The older Teccor literature described several different applications for the K-series SIDACs, including voltage-sensing triggers. The new Littlefuse documentation seems to focus primarily on surge supression. Also, the datasheets for the "new" parts are fundamentally different from the older Teccor datasheets. The Teccor data showed min and max "Vbo" (Voltage, break-over) values for each model. the new Littlefuse data shows a single "Vs" (Voltage, switching) value.
My question to Littlefuse: is the "Vs" value the nominal, or the maximum switching voltage? For a pure surge-supression application, the "maximum" switching voltage is probably more important.
I'm still waiting for a reply ......
Herr zapp

--- On Fri, 2/20/09, Finn Hammer <f-h@xxxx> wrote:

From: Finn Hammer <f-h@xxxx>
Subject: [TCML] Sidactors in a can of worms
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>, "piranha" <piranha@xxxxxxxxxx>
Date: Friday, February 20, 2009, 7:56 AM

I got the Sidactors yesterday, Thanx Terry, and immediately took action to
measure their break over voltage.
Something soon seemed odd, they looked like TVS'es to me, not sidactors at

When I applied voltage across them from my current limiting bench supply, a
HP6255a, the devices did respond to break over voltage, but failed to break over
to a near short, as advertised by Teccor, and as previously experienced by the
KxxxxF1 series that we have been using up to now.
What I saw was a device that plainly clamped the voltage to the break over
level, and kept it there.

This is the behavior that I`d expect from a Zener and a TVZ, but not from a

Of course, there might be a limitation of my measuring approach that I had
overlooked, holding current came to mind, so I decided to lash up a birds nest
SISG, to test out the new types against a known good one, the K2500F1, which has
shown a consistent break over voltage of 135V per section.

The K2500F1 single section worked as expected and produced this oscilloscope
In this screen,
Top trace, cyan CH2, is gate voltage, 15.2V
This is a bit low since generated from a 24V TVZ, but the current is low too,
as seen on 3rd trace.

2nd. trace, magenta CH3, is current into gate, measured with Tektronix P6022
current clamp and passive terminator.
1.36A into gate.

3rd. trace, green CH4, is current in tank circuit, 17.8AP-P measured with
Pearson Current Monitor #101

4th trace, Yellow CH1, is voltage across tank cap., 135V
Screen says 62V but probe is MX9003 differential by Metrix in 200:1

So far so good.
But when I plug any of the following sidactors into this circuit, all I can
record is that the voltage across the cap rises to, and stays at, break over
voltage of device.
What I don`t see is any rapid discharge of tank capacitor, no voltage rise on,
or current into gate, and thus no oscillations.
So as far as I can see, these Sidactors are not what they are advertised to be,
but instead TVS, Zener whatever derivatives unsuited for SISG duty.

I`m at my wits end with this, because -frankly- I feel out of my depth claiming
this in the face of a major manufacturer like Teccor.

I guess I's time to write them, but I'd just bring it up here first.

Cheers, Finn Hammer

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