Ltspice Advice

[eTech]

Hi eT - what happened to R3 the 22ohm from trig to ground. It seems it should be there as that is what the actual circuit has.

I've added it back in.

If you have the .asc I can try it.

Attached Dimmer6.zip

This is connected to the 339 circuit we have been discussing as that circuit feeds the SG which in turn drives the triac so if it is borderline then what may be the cause of the pulse.

Oh...you mean the relay chattering thing?
I didn't realized this thread was related to that.

I was unsure you were aware of how the power control circuit in this thread worked. It seemed you were expecting a change of lamp voltage but really the lamp "on time" is what is being controlled by the CTL pulse.

Anyway...I've attached the .asc file

eT

 

[Quantised]

Hi eT

Thanks for the .asc file. I have changed it a little to reflect the actual circuit by moving the lamp. In reality the lamp should be replaced by a transformer that drives a charger circuit for a 12v battery, about 15 amps in at 120v 60Hz and around 100 amps out at 15v DC when at full chat. But the lamp is fine as it the small load that I want to study.

When the control signal demands a very low power I think the circuit is on the edge of instability and triac then suddenly fires.

The power control seems to be duration of the triac pulse and not the voltage - pure guess on my part but as you say that is how the ctl works although I am still struggling to get it to work. The new circuit is called dimmer7 inside the zip file.

Dimmer6.zip

 

[Quantised]

Bit of a eureka moment really.

Went over the board and changed the model to be the same as the actual circuit and also measured the actual ctl pulse at varying load levels.
The pulse was synchronised to mains freq and when high power is drawn the pulse is short - like 1ms and grows as the load is decreased to around 7ms.

So with the new circuit I tried this pulse style and it works perfect, change the pulse duration and the power changes, great.

Also R3 is stable now at 22R but R6 needs to be 700R for the sim to run.

I tried a range of parametric studies on the snubbers, load, R3 etc but found no point where it was unstable.

So now wait and watch the scope to see if the ctl spikes and causes the pulsed triac firing.