Triac speed controllers

The use of semiconductor switches (thyristors) for controlling electric motors instead of contact switching of windings or, moreover, rheostatic speed control significantly improved their performance:

• increased reliability - both control systems and the engines themselves;
  
• the level of acoustic noise and all types of interference and radiation has decreased - in power networks and radio frequency;
  
• the possibility of arbitrarily precise speed control appeared, and in comparison with rheostatic ones, power losses practically disappeared;
  
• the dimensions, weight and price of electronic components have decreased, the aesthetics have improved.
  

The next step in improving the control of electric motors was the transition to switches that are symmetrical in terms of the polarity of inclusion - triacs. Operating directly on alternating current, they allow you to use one semiconductor device instead of two or save a power rectifier bridge. Simplification of circuitry and design solutions further increases the reliability, reduces the size and cost of devices. Triac speed controllers can be parts of fan coil units, ventilation and other systems, as well as independent electronic devices in their own cases - both surface-mounted and built into electrical panels or building structures. There are also household models in the dimensions of standard wall switches.