Alternistor = trade name for traic?

[N_Cook]

No other difference? alternistor = triac ?
its just that a number of apparently unrelated companies use the term
alternistor for what otherwise seems to be traic

[Phil Allison]

"N_Cook"

> No other difference? alternistor = triac ?

** Nope.

> its just that a number of apparently unrelated companies use the term
> alternistor for what otherwise seems to be traic

** The term refers to a special type of triac that has a very high dv/dt
rating - so high, that in most applications there is no need for a RC
snubber.

With ordinary triacs, a fast rising voltage wave or a high frequency wave
will cause the device to trigger itself on.

Not so with an alternistor.


.... Phil

[Lee]

They seem to be a special case version though:

http://www.littelfuse.com/data/en/Data_Sheets/E4AlternistorTriac.pdf

Also, Wiki says: "A TRIAC which can only operate in quadrants I through
III, and cannot be triggered in quadrant IV, has improved turn-off
(commutation) characteristics.
These devices are made specifically for improved commutation when
controlling a highly-inductive load, such as a motor or solenoid, an
application where normal TRIACs have problems due to high
voltage/current angles"

[N_Cook]

Lee <cyber...@ukonline.net> wrote in message
news:b06j83...@mid.individual.net...

I'd managed to miss that distinction along the way. It seems odd that RS,
probably the largest industrial electronic components supplier in the UK ,
makes no mention of them alongside or within their triac listings.

[Dave M]

--

Phil is correct. Also called Snubberless Triacs by some manugacturers.
Another thing I can add is that the construction of an alternistor is that
of two inverse-parallel connected SCRs. This arrangement has been long
known to avoid the triggering problems associated with using a triac to
control highly inductive loads, such as motors.

Dave M

[N_Cook]

N_Cook <div...@tcp.co.uk> wrote in message
news:knl9o3$l4r$1...@dont-email.me...

googling
alternistor "600 volt" site:co.uk
throws up no UK suppliers for 600V alternistors
luckily no one ever uses a snubber in this use, usually just a triac, so
replaced with an ordinary 600V triac and turns on and off ok, presumably
maker had a stock of alternistors , so used them instead of a triac there

[Phil Allison]

"Nutcase Kook"

>
> googling
> alternistor "600 volt" site:co.uk
> throws up no UK suppliers for 600V alternistors

** But "snubberless triac " works a treat.

http://uk.rs-online.com/web/p/triacs/2512909P/

http://uk.futureelectronics.com/en/technologies/electromechanical/circuit-protection/power-thyristors/Pages/7452774-BTA25-800BW.aspx?IM=0

http://www.amazon.co.uk/BTA12-600BW-Triac-Snubberless-TO-220AB-Package/dp/B00BRYZKX0

http://www.rapidonline.com/electronic-components/bta12-600bw-12a600v-snubberless-triac-47-3260

http://uk.farnell.com/stmicroelectronics/btb24-600bwrg/triac-snubberless/dp/1611394

And many, many more...

Yaaawnnnnnnn.


.... Phil

[Lee]

> googling
> alternistor "600 volt" site:co.uk
> throws up no UK suppliers for 600V alternistors
> luckily no one ever uses a snubber in this use, usually just a triac, so
> replaced with an ordinary 600V triac and turns on and off ok, presumably
> maker had a stock of alternistors , so used them instead of a triac there
>
>

Depends whether you count Digikey as a UK supplier (they have UK pricing
and supply to the UK) - they list them anyway.

[N_Cook]

Lee <cyber...@ukonline.net> wrote in message

news:b08vu5...@mid.individual.net...

Digikey seemed to list alternistors but not 600V ones.
The failed one has no T1-gate resistance in the 10s to low hundreds of ohms,
is that a (sometimes) characteristic of alternistors ? otherwise no gas
venting through the epoxy fill or other signs of distress

[Dave M]

--

http://uk.farnell.com and http://uk.rs-online.com both list 600V units.
Search for either Alternistor or Snubberless Triac. They will show up in
the search results. Just select the appropriate voltage and current rated
device you need.


Dave M

[Ian Field]

"Dave M" <dgmina...@mediacombb.net> wrote in message
news:romdnUAe9O-ypgPM...@giganews.com...

The alternistor is one I'd forgotten until it was just mentioned.

Is that the "magic ingredient" in electronic florescent starters?

The triac in those basically replaces the bi-metal contacts in the glow tube
that break the current for a large back emf from the iron ballast.

[Ian Field]

"N_Cook" <div...@tcp.co.uk> wrote in message

news:knnqap$tr$1...@dont-email.me...

Its a long shot - but check out the ST semiconductor range of triacs for
electronic florescent starters, they have to withstand the back emf from the
iron cored ballast, and presumably a pretty sharp dV/dT.

[Phil Allison]

"Lee"

>
> Also, Wiki says: "A TRIAC which can only operate in quadrants I through
> III, and cannot be triggered in quadrant IV, has improved turn-off
> (commutation) characteristics.
> These devices are made specifically for improved commutation when
> controlling a highly-inductive load, such as a motor or solenoid, an
> application where normal TRIACs have problems due to high voltage/current
> angles"

** The wiki quote is a bit misleading - cos there are two specs for dV/dt.

1. The regular spec referring to the "withstanding" condition where the
triac is in the off state.

2. The other called " Commutating dV/dt" - referring to the condition where
the triac has just stopped conduction because the load current has fallen
below the holding threshold, about 15mA to 50mA for most devices. At this
critical point in time, the device will retrigger if the voltage rises too
fast. The back emf from an inductor can easily do so.

The commutating figure is generally much lower that the regular one, up to
100 times lower - eg the triac ( or SBS ) used in the MOC series of
opto-couplers has a regular dV/dt of 10V/uS, falling to a mere 0.1V/uS while
commutating off.

A simple RC snubber across the main triac normally solves the problem.

BTW: If properly designed, the triac/SBS in a MOC goes off as soon as the
driven triac begins to conduct so the commutating dV/dt issue never arises.


... Phil