[SOLVED] Can PWM be applied to MOC3011.

Hi all,

I know this question is not new in this board. But I could not find the correct solution.

Q. Can we applied PWM signal to MOC(any non-zero cross).The other side of the MOC is connected to a AC Heater, how much AC voltage is not the concern?

Basically the idea is to control the heater heat level.

Thanks

Usually, PWM for heating control is performed as full wave switching, using a zero crossing detector. This is basically required by EMC regulations. The pulse witdh is restricted to multiplies of 20 ms in this case, which isn't a problem with e.g. 1 to 20 sec pulse period. For fast heating zones, a delta-sigma modulator switching at full wave gives a more smooth heating control.

Thankyou FvM

Can you explain delta-sigma modulator switching in short.

Thankyou

prmurthy said:

Q. Can we applied PWM signal to MOC(any non-zero cross).The other side of the MOC is connected to a AC Heater, how much AC voltage is not the concern?
Basically the idea is to control the heater heat level.

Click to expand...

Yes, you can, and the usual AC voltage (230 v 50 Hz) is not a problem
using a proper current limiting resistor (datasheet).
Of course you need also a TRIAC !!!

But I don't recommend this method, rather use zero-cross MOC and make
a "very long time PWM" (say 20 half period of the AC voltage = 200 msec).
A heating system has big time constant..

zuisti said:

But I don't recommend this method, rather use zero-cross MOC and make
a "very long time PWM" (say 20 half period of the AC voltage = 200 msec).
A heating system has big time constant..

Click to expand...

I am not intended to use ZC MOC like MOC3041 etc. I am intended to use MOC3011 which works well with 230V ac and it is non-ZC. Of course I will be using a TRAIC without which rest is meaningless.

I have one more question in mind now does it chops the phase which results a voltage drop ?? or something else?? could not actually get into the point well.


Thankyou

---------- Post added at 15:03 ---------- Previous post was at 15:01 ----------

@ FvM

this is what I got from internet.

"Delta-sigmaMain article: Delta-sigma modulation
In delta-sigma modulation as a PWM control method, the output signal is subtracted from a reference signal to form an error signal. This error is integrated, and when the integral of the error exceeds the limits, the output changes state."

It sounds like a PI controller.

Thankyou

Well, if you want to use the PWM in any event:

You need an independent zero crossing detector wich starts a delay timer (monostable, 0.01...9.99 msec).
The timers's end signal fires the TRIAC via the MOC. The greater the delay, the less the output power.

But so you will get a big pulse noise (EMI problems). therefore I said that the ZC method is better.

A non ZCD opto triac is able to do phase angle control, not chopping. You can switch on at very time, but not switch off. If you consider how a TRIAC works, you'll surely get the reason. Phase angle control is commonly used for lighting (dimmer). As said, EMC rules require to use full-wave switching for loads other than lamps or motors. You don't need to care for it with a DIY design, but you should for a product.

A SD modulator uses an integrator, but it's not a controller, it doesn't measure a process value, it's just a forward correction scheme. 1st order SD, as usefull in case of a heating fullwave switcher, is a very simple algorithm. You have an accumulator (the integrator) increased by the control value every time step (a fullwave period). If the accumulator value is above a threshold, you switch output for one period and substract a respective value from the accumulator. The error resulting from the 1 bit quantization of the output signal will level over time.

Thankyou
Zuisti and FvM,

Got your points. I am just working differnet options. Presently which uses on/off control. I have created a software PWM. But the results are not good and I have swing in the temperatures from the set point.

I will close the thread here.

Thankyou for your supports.