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Re: [TCML] Sidactors in a can of worms

Quarkster skrev:
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.

It is true that the SIDACtor V/I curves resemble the SIDAC curves, and the above reference says:
The SIDACtor device operates much like a switch. In the off state, the device exhibits leakage currents (IDRM) less than 5 ?A, making it invisible to the circuit it is protecting. As a transient voltage exceeds the SIDACtor device?s VDRM, the device begins to enter its protective mode with characteristics similar to an avalanche diode. When supplied with enough current (IS), the SIDACtor device switches to an on state, shunting the surge from
the circuit it is protecting
notice that they say: supplied with enough current, Is, it turns on to the low voltage drop stage.
Then check a datasheet:
where you will see that the Is=800mA.

It was with this in mind that I discharged a capacitor into a coil, to supply up to 10's of ampere, but the breakdown did not happen.

I notiched one thing: When I touched the leads from the lab supply to the SIDACtors in the DO-214 package, with a voltage above their rating, they would respond with a fierce spark, and then settle in on the preakover voltage. Perhaps they simply are so fast, that they catch the spike in a jiffy, and after that, are able to controll the situation with relatively transparent (to the supply) avalance action. The rise time of the DC supply is not fast enough to pose a threat, so the sidactor simply manages to controll the situation with avalance action.

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.
In fact the *old time* sidacs are still listed as available on the site, look for sidacs under swiching thyristors, and even the much fabled F1 package (to202) but looking at the listed datasheet, only DO-214, DO-15and TO-92 packages are available.

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 ...... Regards,
Herr zapp

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