MOC3021 Light Dimmer buzz

[ehabzaky]

Dear All,

I'm using the circuit below as per the MOC3021 datasheet.



When using this circuit as a on/off switch to the load there is no problem but when used as a light dimmer by controlling the waveform I hear a buzz sound although it is working fine too.

1- What is the source of this buzz sound? I expect it is the repeated on/off of MOC3021 or Triac.
2- Is there any harm on the circuit to be used while this buzz sound is there?
3- Is there a way to eliminate it and does it worth to do so?

Regards,
Ehab

 

[smijesh]

Buzz sound generating from Triac it's mechanical vibration. It's being generated from the high current/fast rise time when the Triac fires.
It is not suggesting for continuous use, If may fail due to overheat.
To reduce the buzz sound you should use better LC scrubber circuit or change the value of capacitor or resister

Try link
https://www.edaboard.com/threads/265546/

 

[chuckey]

It could be from a ceramic capacitor. A dob of silicone goo might dampen out the noise. FWIW In my last house I installed a touch dimmer which buzzed slightly, it lasted for over 20 years until I sold the house.
Frank

 

[D.A.(Tony)Stewart]

Ceramics can be piezoelectric with high current impulses from switching. As suggested dampening the ceramics or using a plastic cap ( preferred) for the snubber especially, ought to work. Snubber caps need to be plastic line rated for immunity from shorts with lightning transients, also and I assume you made that choice.

 

[ehabzaky]

Thanks for the info.

I tried the circuit without the snubbing and the buzz sound disappeared so it is mainly due to the ceramic capacitor as explained by you.

I'm using SMD Ceramic capacitors package 1206 500v. Is there a replacement plastic SMD capacitors? Could someone send me a sample link?

Regards,
Ehab

 

[smijesh]

You cant get film capacitors with 1206 package. You can try with other package
**broken link removed**

 

[D.A.(Tony)Stewart]

more like a 2220 SMD or TH part

 

[ehabzaky]

Thanks all for your help and support. I didn't find SMD resistors so I used Polyster Film Resistor and the buzz sound gone.

I need help please to select the power rating for the resistors in the above circuit.

The 39Ohm, 360Ohm and 470Ohm what is the suitable power rating for each? I used 1206 package (0.25W) for all but I notice that the 39Ohm resistor sometimes get burned. If I used package 2512 (1W) for 39Ohm will it be enough? Also do I have to change the 360 & 470 Ohms to 2512 package (1W) or the current package 1206 (0.25W) will be suitable?

The Voltage is 240 VAC

Regards,
Ehab

 

[D.A.(Tony)Stewart]

Don't you know how to compute power loss?

 

[ehabzaky]

Don't you know how to compute power loss?

I could do for the 39 Ohm resistor and the 0.25W resistor rating was enough as per my calculations but I saw it was burnt twice on my trials. For the other 2 resistors I am not sure about the calculations as I don't have much experience here.

If somebody could help me to select the suitable power ratings for the 3 resistors, it will be great.

Regards,
Ehab

 

[D.A.(Tony)Stewart]

When did the 39 Ohm get burnt? Switching On or Off?

I would suspect it would burn out in the turn on peak V state because 0.01uF is several MOhm at 50 Hz but a transient pulse has broad spectral content, so we treat the Cap as a short circuit, thus you need to absorb many watts for a few ms only during the transient. Choose a 1W or 2W carbon resistor, not a metal or carbon film !!

The others can be 1/4W but must also be solid carbon and not carbon film to withstand surges.