Why are there no SCRs with a ground input trigger or MOSFET SCRs?
Is a negative voltage SCR half of a TRIAC? Never made separately?

 

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Why are there no SCRs with a ground input trigger or MOSFET SCRs?
Is a negative voltage SCR half of a TRIAC? Never made separately?

The FET doesn't have a conduction path from gate to source. Only a capacitor.

 

Evidently, there are:

https://www.ibiblio.org/kuphaldt/electricCircuits/Semi/SEMI_7.html

They are described at the end of the article. Also a quite good article on the subject of SCR's.

And yes you could use a TRAIC to switch a negative DC voltage. (You would have to provide a means of turning it off tho.)

 

The FET doesn't have a conduction path from gate to source. Only a capacitor.

Is that a bad thing?
An SCR with the input resistance of a MOSFET? Sounds good.

 

The FET doesn't have a conduction path from gate to source. Only a capacitor.

Is that a bad thing?
An SCR with the input resistance of a MOSFET? Sounds good.

Evidently, there are:

https://www.ibiblio.org/kuphaldt/electricCircuits/Semi/SEMI_7.html

They are described at the end of the article. Also a quite good article on the subject of SCR's.

And yes you could use a TRAIC to switch a negative DC voltage. (You would have to provide a means of turning it off tho.)

\Link doesn't work. "RC5 not supported", or something like that. I have TLS enabled.

(edited to add ...)

ibiblio is difficult to navigate. Is that SCR thing under "projects". Searching is not intuitive.

 

Is that a bad thing?
An SCR with the input resistance of a MOSFET? Sounds good.

\Link doesn't work. "RC5 not supported", or something like that. I have TLS enabled.

(edited to add ...)

ibiblio is difficult to navigate. Is that SCR thing under "projects". Searching is not intuitive.

Just get a "sensitive gate" scr. Much lower trigger and hold currents.

 

Just get a "sensitive gate" scr. Much lower trigger and hold currents.

How about a ground input SCR instead of a positive voltage trigger? Does anybody make one?

 

How about a ground input SCR instead of a positive voltage trigger? Does anybody make one?

I think the body diodes get in the way with the ones you have shown. Always on with a negative supply voltage.

 

How about a ground input SCR instead of a positive voltage trigger? Does anybody make one?

Here

 

Diodes go in the desired direction. On N channel devices the cathode goes toward the Drain. On P channel devices the cathode goes toward the Source.

I think the body diodes get in the way with the ones you have shown. Always on with a negative supply voltage.

I will have to include them. Thanks.

 

Diodes go in the desired direction. On N channel devices the cathode goes toward the Drain. On P channel devices the cathode goes toward the Source.

View attachment 118328 View attachment 118327

I will have to include them. Thanks.

And since scr and thyristors are commonly used with AC circuits, the body diode screws things up on the negative cycle.

 

There's another option, but don't know how low powered they are produced in. It's called a GTO, gate turn-off thyristor. https://en.wikipedia.org/wiki/Gate_turn-off_thyristor

 

I suspect that IGBT's are winning out over SCR's and triacs. Dealing with the commutation issue can be a b****.

The same thing happened with bubble memory and CCD memory when dynamic RAM came in.

 

I suspect that IGBT's are winning out over SCR's and triacs. Dealing with the commutation issue can be a b****.

Aren't IGBT's just a BJT with a capacitve gate instead of a base? And they still have the intrinsic diode issue.

 

Aren't IGBT's just a BJT with a capacitve gate instead of a base? And they still have the intrinsic diode issue.

It is more like a darlington where the input side is a MOSFET and the output side is a BJT. ill have to draw it out when I have a minute to see if the body diode is an issue in the igbt.