Soft start using triac

Thread Starter


Joined Oct 10, 2022
Hi everyone,

I want to develop a soft start system for the receiver. In real system, it is a power supply in the laboratory with a variable resistance value - hence programming the resistance R3 as a variable value determined by the voltage source.

The system to perform a soft start for the receiver, which causes a large current peak when switching on the voltage, is based on a triac, i.e. when the triac sees that the current flowing to R3 is 12A, it cuts off the sine wave at this point, which makes that the intensity will never reach a greater value.

Besides the soft start model, I am attaching the contents of trctriac.lib and TRIAC_Teccor.asy which I have implemented into the circuit in the form of a triac element.

Please help me develop an algorithm for setting the changeable angle. I thought about defining angle alpha using the arcus function, e.g. atan(I(R3))=12, but that was beyond my skills.

Best regards,



Joined Nov 6, 2012
This looks like a Homework assignment.

I wouldn't do it this way, simply because Triacs are so NOISY.
( but they can be cheap and effective )

It doesn't look like you've tried to come up with a solution.
Try looking at how a cheap "Light-Dimmer" works.