Voltage controller

This varied voltage output is used for dimming street lights, varying heating temperatures in homes or industry, speed control of fans and winding machines and many other applications, in a similar fashion to an autotransformer.

Because they are low-maintenance and very efficient, voltage controllers have largely replaced such modules as magnetic amplifiers and saturable reactors in industrial use.

[3][4][5] In an on-and-off controller, thyristors are used to switch on the circuits for a few cycles of voltage and off for certain cycles, thus altering the total RMS voltage value of the output and acting as a high speed AC switch.

The rapid switching results in high frequency distortion artifacts which can cause a rise in temperature, and may lead to interference in nearby electronics.

[6] In phase angle control, thyristors are used to selectively pass only a part of each AC cycle through to the load.

A Voltage controller thyristor based dimmer rack
An electrical schematic for a typical SCR-based light dimmer
An example of phase angle control. Blue represents the actual supply voltage of 120 V and red represents the switching on and off of the thyristor to get a controlled voltage of 60 V, achieved by cutting off the supply at certain angles and switching it on at the phase angle.
An example of a Voltage controller with heat sink attached in left. Min and max settings in the front