GTO and SCR :confused:

[meowth08]

GTO: Gate Turn-Off Thyristor
SCR: Silicon Controlled Rectifier

They have the same equivalent circuit.
Two BJT: One NPN and one PNP.

SCR's turning on is dependent on gate voltage.
GTO's turning on is also dependent on the gate voltage.

SCR's turning off is independent of the gate voltage.
But how come that the GTO's turning off (note that GTO has the same schematic with SCR)
is dependent upon the applied gate voltage?

 

[panic mode]

no, it's not the same, here is something to read:
https://en.wikipedia.org/wiki/Gate_turn-off_thyristor

 

[meowth08]

hello,

i mean they have the same equivalent circuit.
https://en.wikipedia.org/wiki/File:GTO_thyristor_equivalent.svg

 

[panic mode]

there are many models depending what they are supposed to represent. they are not real circuits, just equivalent representations within context of particular description. in this case you have simplest possible model. note, all models have their limitations (such as range of gate voltage) and can only be used within their limits. limits of this model can be used to represent basic operation of standard SCR and GTO. how simple or detailed model you get to use depends on application.

 

[crutschow]

It's difficult to accurately model the fact that an SCR cannot be turned off from the gate input with a simple transistor model, thus they use the same model for both the GTO and SCR. You could, for example, add a diode in series with the gate input of the model to prevent the SCR from being turned off by the gate, but that would add an additional diode drop to the gate's forward voltage value.

 

[tvtech]

Hi Guys

The last GTO Thyristors I saw were used in the old Sony 191/192 series TV's. As far as I know, they are obsolete parts and not worth investigating/studying.

As far as I can recall, GTO's became way too expensive to manufacture. And were hence dropped worldwide.

Nice idea though In the case of 191/192 tv's....an absolute nightmare for Techs..
Because the GTO's were obsolete already in 2001..we were given an alternate circuit to use by Head Office. ONLY Genuine Phillips BUW11A transistors did the job....with modifications....and procedures for start up etc...almost like starting up a Nuclear Reactor...

If you did not follow the Mod procedures and steps to the letter as a Tech repairing the set...all blew up. Badly. Short cuts always ended in tears and MUCH more work than was initially needed.

Suffice to say, all bailed out. I think I fixed the last 191/192 I believe here in SA. How long it lasted with the Mod I don't know. Some lasted yonks. Others failed quickly. It all depended on how thorough you were with repairing the original blow up with GTO's before the Mod.

Those were the days. Thank God TV's don't use GTO's anymore.

But DAMN....the Sony Trinitron had the very best picture back then when working properly. That is why I put in the extra effort

Regards,
tvtech