stupid question about SCRs

[batres]

Hello everybody,

I feen entirely stupid about this simple problem, but I figured I would be even more stupid if I didn't ask the people that actually know what they're doing.

I have been working with Multisim for a couple of months and right now I am working on the SCR stuff. I have this VERY simple circuit that is supposed to trigger an SCR using a pulse generator. According to my understanding, when I am using AC voltage and I trigger my SCR using a pulse, the damn thing should start operating right away and stop til that cycle of the sine wave has finished. However, when I trigger this one, for some reason all I get is a little pulse on my "load" (some resistor I've put after the SCR), which is not exactly what I expected.

This is really driving me crazy, since I've done this many times in real life, but when it comes to the simulator, I can't seem to get it right for the life of me.

Help pliz

[lacy]

There is a problem with the circuit file. The Labview instrument XLV1 that you are using for an input will not work for me.It is either not saved with the file or something. If you could just give me the frequency of the pulse and whether or not it is a sinusoidal, square or triangle waveform then I can simulate your circuit properly.

[lacy]

Until I am able to sinulate your circuit I will tell you what I know about this. Based upon looking at your circuit and reading your post, I would think that your pulse signal is out of phase with your AC Voltage If they are not exactly in phase the SCR won't trigger at the proper point in the AC cycle and therefore only a small portion of the cyle will be transfered to the load. This would account for the small blip you are probably seeing on the scope. The further out of phase the two signals the less power get to the load. How to get the signals in phase? I don't know the answer to that at this point since I can't simulate the circuit.

[batres]

Hello,

I thought that the VI would be available on any installation of Multisim but I guess I was wrong.

Anyway, you can use the standard signal generator to create a square signal with a frequency of 60Hz, a value of 5% on the duty cycle, and an amplitude of 5. To get my phases to "match" I changed the phase of the voltage source, so the pulse falls somewhere in the middle of the positive sine (which should cause the SCR to trigger and remain closed till the sine reaches a value of 0).

Thanks

[lacy]

I believe you to be correct. This doesn't seem to be working in Multisim and I do not have any idea as to why. When you trigger it the output should start following the half cycle of the waveform until zero and then the SCR should switch off. It appears that the gate trigger is turning it on and off instead of the anode voltage as it would be in the real component.

Maybe the NI Support Team can address this as to why this is happening. To me this is a basic function of SCR's and it should be working in the simulator. I have tried other SCR's in the database and get the same results.