Regarding the working of the triac

[nileshthakare2]

Hi

i have some problem in triac circuit.My triac is continuously in on condition.if anyone knowns about the problem with my circuit please help me.i have attach link of my schematic design.(https://obrazki.elektroda.pl/52_1312605496.jpg)

thanks
nilesh)

 

[bigdogguru]

Have you contacted the Forum Member KerimF?

He is by far the most knowledgeable concerning TRIACs.

 

[siongboon]

I believe it could be C7.
Try removing the component and see if it works.

Best Regards,
Siong Boon

**broken link removed**

 

[mister_rf]

Try to connect this way:

 

[mister_rf]

Not a good idea to feed a PWM signal into a triac.
A triac will turn on when there is a pulse or voltage on it's gate and then not turn off until the voltage drops to zero. So unless you can synchronise your PWM to the mains, or slow it down so that it is in the same order of magnitude as a mains cycle there is no point, so it will look to be full on all the time.
The normal way to dim some stuff with a triac is to use phase angle control, but that implies to delay gate pulse for a time after the zero crossing and then fires the triac.

 

[nileshthakare2]

Hi ,
Thanks for my help.


Sory i have change all circuit only supply changes is remaining in schematic(**broken link removed** have used 15Vac not 12Vac and other circuit are the same.I want to heat the coil for only 45degree Celsius of water.For that I used 230 v supply which is step down up to 15 V and then this 15 V is given to triac. so i want to control only 15v supply by the pwm but for 25% of pwm duty cycle it gives 13 volt across the coil and for 0% it gives 0V so i think for 25-50-75% duty cycle it requires different voltage across the coil. but voltage drop is too low so i think something wrong in the circuit so i want help because i am not find any problem with the circuit.If i remove the coil and join the bulb then for different duty cycle its luminance varying.So i think triac is working fine but somewhere resister had some problem. If you find any problem then please told me.As per mister_rf says
"So unless you can synchronise your PWM to the mains, or slow it down so that it is in the same order of magnitude as a mains cycle there is no point, so it will look to be full on all the time." SO i will try to implement this then i hope its working fine.

Thanks for replying
Nilesh

 

[mister_rf]

Because heater resistance have a lot of inertia, it's common to drive them in "burst" mode.
Using a zero-crossing opto coupler you just need to let the current flow for n-periods of line voltage (a burst of sinusoidal wave). So in this way no needs to synchronize your microcontroller with zero crossing. That’s a similar way to operate at a very low PWM frequency, e.g. 0.1-1 Hz.(Because only the frequency of pulses varies, it is really pulse frequency modulation :-D )
Read here:

https://www.edaboard.com/threads/193673/

 

[nileshthakare2]

Hi
Thanks for replying i have going to implement as per your saying.

thanks
Nilesh