Help with a Triac circuit please！

[Eric911]

Hi all,
Hello guys. It has been some since the last time I posted here.
I need to build a 1-10Amp (max voltage 85Vac) source for motor.

I have found a circuit (attached) from ST datasheets that looks interesting. As figure 11 show in below link of PDF. (https://www.electro-tech-online.com/custompdfs/2012/11/CD00003856.pdf)

My issue is: how to work about the DB1? I tested this circuit, i found the pulse of trigger is not symmetric wave in positive half cycle and negative half cycle? Is anybody advise the reason? Any help is welcome, much appreciation.

thanks.

Eric

 

[dr pepper]

Dunno if its the reason but some triacs have different trigger currents depending on which phase quarter they are triggered at.
Non symetric triggering might not effect a motor much, but it would a transformer the resultant dc would get it hot.
I have a circuit tucked away somewhere I've used for a welding transformer it is very symetric, do you want me to look for it?

 

[Eric911]

Hi dr pepper,
Thanks for your reply.
Of course, if okay, pls share with me. If not, may you describe the circuit how to figure out this issue? Much appreciation.

Eric

 

[Eric911]

Hi dr pepper,
Thanks for your reply.
Of course, if okay, pls share with me. If not, may you describe the circuit how to figure out this issue? Much appreciation.

Eric

Dunno if its the reason but some triacs have different trigger currents depending on which phase quarter they are triggered at.
Non symetric triggering might not effect a motor much, but it would a transformer the resultant dc would get it hot.
I have a circuit tucked away somewhere I've used for a welding transformer it is very symetric, do you want me to look for it?

 

[dr pepper]

Having dug it up I realised that this circuit uses 2 thyristors, maybe not what you need:



This might be better for a motor:



Or this:

 

[Eric911]

Hi dr pepper,
thank you for your reply, you're a very kind hearted man.
I have rearched above of circuit. I want the triac could be worked in 132Vac to 108Vac and 150 radian. the issue is these circuit couldn't be trggered at 108V and 150 radian. This is why i select figure 11 in ST application. but i met a issue, the circuit similar as figure 11, the positive sine and negative sine of trigger pluse are not symmetry. I couldn't figure out this issue until now, so i want go more help in here.

thanks again.

Eric

Having dug it up I realised that this circuit uses 2 thyristors, maybe not what you need:

View attachment 68761

This might be better for a motor:

View attachment 68762

Or this:

View attachment 68763

 

[dr pepper]

That circuit oughta work, st wouldnt publish a lemon.

 

[Eric911]

Yes, that circuit could work. I built a PCB board, the circuit is similar as my above mention. But i met a issue in here, i found the trigger pluse is not symmetric wave in positive half cycle and negative half cycle? I want to find the reason, but still not find it. may you give any advice?

BR,

Eric

That circuit oughta work, st wouldnt publish a lemon.

 

[dr pepper]

That circuit should produce reasonable symetric triggering, as I understand it thats the purpose of the bridge with the output shorted with resistors.
Double check your circuit for faults, are all the diodes in the bridge ok?, is the diac in the trigger circuit ok, if you have a 0-30v bench supply you can test a diac, put a 1k resistor in line with it accross the supply, it should turn on depending on the diac at about 25 to 30v.
I'm splitting hairs here but you say the trigger pulse isnt symetric, do you mean the pulse at the gate of the triac?, or do you mean the o/p waveform isnt symetric?
Its possible that your circuit is ok component wise but having false triggering problems, sounds like your able to 'scope the o/p, if thats the case replace the transformer load with a incandescent light bulb and see if the waveform changes, maybe theres some ringing or noise back from the tranny messing things up.

Please post in english, everyone here does - post been deleted disregard.