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LTSpice Question

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Papabravo

Well-Known Member
Start by making sure that each component has a reference designator with a letter and a number e.g. R1, R2, ... for resistors.

Second make sure each component has a value e.g 100, 2.7K, .. for resistors
 
Ok that be done,

I have a circuit that worked, I am now trying to insert a SCR in the place of a Opto and Triac, thats when the message comes up.

All to the left of R13 works but I want to switch a 12V d.c. load of about 50W.

Andrew

This being a newb is real tough
 

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Papabravo

Well-Known Member
Ok that be done,

I have a circuit that worked, I am now trying to insert a SCR in the place of a Opto and Triac, thats when the message comes up.

All to the left of R13 works but I want to switch a 12V d.c. load of about 50W.

Andrew

This being a newb is real tough
Tried to load your file, but got a dialog box that said
"Couldn't find symbols
LM339A
SCR_Teccor

Correct me if I'm wrong or off base, but isn't using an SCR to switch a DC load problematical because you can't turn it off? Unlike an AC circuit the current does not make periodic zero crossings. If I were you I would consider a PNP high-side Switch like say a VN340 or similar
 
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Hi,

I get the same when transferring the file to another PC. I then go find the files and load them into the relevent directories. Is there any way to embed the files in the .asc file?

Cheers
Andrew
 
Hi,

that could be my problem then, I tried with a Mosfet and got the same response. Is it best to use the opto which has a zero crossing circuit?

Cheers
Andrew
 

Papabravo

Well-Known Member
Hi,

that could be my problem then, I tried with a Mosfet and got the same response. Is it best to use the opto which has a zero crossing circuit?

Cheers
Andrew
I don't think so. The only way to reduce a DC current to zero is to interrupt the flow of current. See the following page:
 

Roff

Well-Known Member
I found the source of your original problem.
In the file Teccscr.lib, you need to either remove all the text lines at the top of the file (leave the "**********" above the first subcircuit), or you can put an asterisk in front of each line. In either case, save the file before re-running the sim.
You should do this even if you get rid of the SCR in your circuit, in the event that you want to use this file again.
 
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Papabravo

Well-Known Member
Did I miss something? Where was the file Teccscr.lib? Did you actually find it on the web?
 

Roff

Well-Known Member
Did I miss something? Where was the file Teccscr.lib? Did you actually find it on the web?
No, you didn't miss anything. I already had it in my SUB folder. I had downloaded it from Teccor several years ago. it looks like the file has changed somewhat since Littelfuse acquired them. It appears that the first file listed here is basically the same thing, without the troublesome header.

BTW, "any" was a word that appeared several times in the header. Hence the error, "Multiple instances of 'Any'". I had a hell of a time finding it. I finally started gutting the circuit, re-simming until the error went away.
 
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Hi guys,

thanks for the effort it is appreciated. Problem fixed on my side too now.

I tried numerous options last night, I can get to switch a.c. but switching d.c. is proving to be entirely another matter.

Pappabravo, could not find a model for the VN340 so was unable to try it. Are there any standard devices in the standard libraries that will work?

Cheers
Andrew

PS: Will I still need the MOC3081?
 

ericgibbs

Well-Known Member
Most Helpful Member
Hi guys,

thanks for the effort it is appreciated. Problem fixed on my side too now.

I tried numerous options last night, I can get to switch a.c. but switching d.c. is proving to be entirely another matter.

Pappabravo, could not find a model for the VN340 so was unable to try it. Are there any standard devices in the standard libraries that will work?

Cheers
Andrew

PS: Will I still need the MOC3081?

hi Andrew,
You can switch ON an SCR to control 'dc', BUT you cannot switch it OFF without removing the load connection to the SCR or shorting the SCR out.

Switching 'dc', no ZCD is required , so no MOC is required.

Use a power MOSFET not an SCR.:)
 
Hi,

OK progress. Used an N channel Mosfet and the circuit switches but out of phase I think. Heater appears on when it should be off?

Tried a P channels Mosfet and it never turns off.

Why would the current be a negative value?

Cheers
Andrew
 

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  • AndrewSCR.asc
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ericgibbs

Well-Known Member
Most Helpful Member
Hi,

OK progress. Used an N channel Mosfet and the circuit switches but out of phase I think. Heater appears on when it should be off?

Tried a P channels Mosfet and it never turns off.

Why would the current be a negative value?

Cheers
Andrew

hi,
Look at this P MOS option.
 

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  • AAesp02.gif
    AAesp02.gif
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ericgibbs

Well-Known Member
Most Helpful Member
hi,

This a N MOSFET option.
 

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    AAesp03.gif
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  • AndrewFET2.asc
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