Phase Dimmer Control using Triac

Thread Starter


Joined Aug 29, 2019
Hello Sir/Madam,

I am engineering student making phase dimmer control using triac
The schematic is as attached
What I have observed that many times attached circuit stop working due to failure of triac
I am not sure is it because of di/dt or dv/dt failure. In order to avoid this I have used triac of much higher rating (10A) even though current needed can be as low as 1A.
However the problem continues.

I have observed that the failure is for transformer powered halogen lamp (inductive load?) and for ceiling fans.
It works satisfactorily for incandescent lamps.

Also I am sharing one more observation that if I connect glass tube fuse link in series with the load then the fuse blows.
From the various information available I realized that I need to use choke / inductor to overcome this problem. Is that right?
I need help to
1. To find out the value of the inductor for 0.5A, 1A and 2A
2. Is this a special type of inductor? if yeswish to know make

Thank you in advance




Last edited by a moderator:


Joined Mar 10, 2018
4,057 you can download this

For sure switching L loads always a concern. Have you looked at voltages with respect to neutral,
to see if you have some very high transients, ones that snubber values not taking care of ? A DSO
can capture a transient quite easily in one shot mode. Set triggering for a V that is at ratings
of Triac and see if you get a trigger. Single shot mode.

Be very careful about doing scope measurements in AC line applications, ap notes below. You
can blow out your scope front end real easily if you don't understand the ground issues involved.

Probing%20Techniques%20for%20Accurate%20Voltage%20Measurements%2051W_60161_1_HR_Letter (1).pdf

Regards, Dana.