Hi everyone,
I am constructing a dimmer circuit for heating purposes and i am looking for appropriate ZCD technique to fire the triac . Have any one tried to do such a thing ?

 

You only need zcd and opto-coupler when using a microcontroller..

 

You only need zcd and opto-coupler when using a microcontroller..

Can you please clarify ?

 

In order to fire the triac at zero or some delay after zero, you need to have a Zero crossing detector circuit, so your micro knows when its zero mains voltage, then it can fire the triac at any delay to create a dimmer.



Are you using an Arduino or Pic...?

 

If you use a zero crossing detector you will only be able to control the temperature by dropping half cycles. The other approach using thyristors is to make the phase of the firing pulses relative to the powerline voltage continuously variable. Is dropping half cycles the method you want or would you like the phase to be continuously variable.

What is it that you are planning to control the temperature of, and will the control circuitry be floating on the AC line or earthed?

 

In order to fire the triac at zero or some delay after zero, you need to have a Zero crossing detector circuit, so your micro knows when its zero mains voltage, then it can fire the triac at any delay to create a dimmer.

Are you using an Arduino or Pic...?

'
I used the this technique and the pulses get crazy around the zeros , have you got any idea of why that happens ?


Do you mean this technique ?

 

Use an Opto-coupler Not a 741!!!

 

If you use a zero crossing detector you will only be able to control the temperature by dropping half cycles. The other approach using thyristors is to make the phase of the firing pulses relative to the powerline voltage continuously variable. Is dropping half cycles the method you want or would you like the phase to be continuously variable.

What is it that you are planning to control the temperature of, and will the control circuitry be floating on the AC line or earthed?

I am doing this circuit to control water temperature. I looking for controlling the voltage along the whole period not just the half of the power. Is triac suitable for that or it just controls the half of the power as you mentioned ?

 

In order to fire the triac at zero or some delay after zero, you need to have a Zero crossing detector circuit, so your micro knows when its zero mains voltage, then it can fire the triac at any delay to create a dimmer.


View attachment 193298
Are you using an Arduino or Pic...?

I am using an Arduino , But if possible can you please let me know why this type of ZCD would work with triac while the compactor technique will not ?

 

The triac can be used for applications in which full cycles are dropped and for continuously variable firing angle it can be turned on for a fraction of a cycle.

The circuit below is what I used to reduce the power going into my on-demand water heater for my shower. The water source is a tank near the surface of my lawn so the incoming watertemperature varies a lot between summer and winter, hence the Summer/Winter switch.



The circuit below is what I used to couple the line timing information and the triac drive signal to an earthed microcontroller. The purpose is to allow every nth half cylcle to be passed along to the motor. The circuit worked great but the motor did not like being run at a low speed with fully current every n half cycles. The controller is small ATTINY12 using its internal RC clock.

 

Heaters never are small power installations, therefore my advice is look onto nothing but "zero-cross" circuits.

 

I am using an Arduino , But if possible can you please let me know why this type of ZCD would work with triac while the compactor technique will not ?

Using an Opto-coupler is better to detect Zero crossing not an op amp..remember that half the Voltage across the Heater is a Quarter of the Wattage!!

W= VxV/R.

 

I used the this technique and the pulses get crazy around the zeros , have you got any idea of why that happens ?

An opamp has a kind of metastable state when two voltages are identical on their input pins. Your slow moving AC voltage and the zero volt signal are identical for quite a while, causing this instability.