TRIAC Firing angle control

[MAGNOTRAN]

Hi. I am having difficulty controlling the firing angle of the TRIAC in a dimmer control circuit and not certain which parameter in SPICE model of the specific TRIAC is used to increase/decrease the TRIAC gate turn on voltage. When CKT is physically built using SC141B TRIAC, it works fine on the bench and you can control the gate turn on voltage from fully on to fully off by adjusting the potentiometer and thereby chop the sinusoid voltage that appears across the SCR or the lamp but the simulation shows very little response to potentiometer adjustment as though there is no control and TRIAC goes into immediate conduction with minimal capacitor voltage. The expected TRIAC voltage should be like chopped sinusoid  but as the attached waveform shows it is on immediately and there is barely any control. Please check and let me know how to correct. Symptom is the same with many of the TRIAC models I tried in my Multisim Ver-11. Thanks.

[MAGNOTRAN]

Adding the waveform.

[MAGNOTRAN]

Any suggestions or assistance will be greatly appreciated.

[Tayyab_R]

Hi MAGNOTRAN,

The reason there is a problem is because a lot of the Triac models do not function as expected. These models were removed in the newer version of the software. The one which you can use to simulate a triac is the MAC12HCDG. I replaced the Triac in your circuit with this one and it seems to function.

Hope this helps.

[MAGNOTRAN]

It made a slight difference (noteable TRIAC response change in the 0 to 5% value of the potentiometer and no continued TRIAC firing range control in the 10-100% range). Could you advise which parameter in the model controls the TRIAC gate voltage? Thanks very much.

[Tayyab_R]

Hi,

I am not really sure if changing the model is a good idea but you can double-click on the component and go to the Value tab. Click on Edit model to take a look at the model. It explains the different parameters for the model.

Hope this helps.