How Does a Dimmer Switch Work on a Circuit?

How Does a Dimmer Switch Work on a Circuit?

** There are a few different types of dimmers used today. The two most popular (or mostly used types in residential wiring) are the TRIAC type dimmer that functions by delaying when the applied voltage waveform is allowed to be applied to the light that you want to control. 

Various answers you have already received describe how a TRIAC-type dimmer works. The simple description is all the voltage is dropped across the TRIAC until it is turned on, then the voltage is applied to the light. This is similar to a light switch in that when the switch is in the “off” position all the voltage dropped across it in this position and no voltage across the light. 

When to position the switch in the on position, all the voltage is then applied across the light and it turns on. The TRIAC is a switch that may be turned on and off very rapidly allowing you the vary how much voltage is applied to the light and thus affect the amount of light given off by the lamp.

The second type of dimmer typically used in residential systems is the FET-controlled dimmer. This type of dimmer is typically used with low voltage (12 volts as an example) systems using an electronic transformer (usually capacitive coupled transformers). 

This type of dimmer also controls the voltage level that makes it to the lamp but the TRIAC type holds the voltage off the then turns on and allows the voltage waveform to access the light. The FET dimmer allows the voltage waveform to access the light first and then later the FET dimmer forces the voltage to turn off the lamp. 

(Actually, it turns off the current flow which in turn causes all the voltage to appear across the FET switch).

** The control element is a triac, which is a solid-state switch that is normally off. The dimmer has a timer circuit that switches it on. You dim the light by delaying when the triac is triggered: the later, the less power is delivered to the light. Once triggered, the Triac conducts until the current drops below a minimum that allow it to switch itself off. Since AC passes through zero twice a cycle, the triac conducts from trigger to the end of each half-cycle. Full brightness triggers near the beginning of each half-cycle, which allows the current to flow for almost the entire time.

In incandescent lights, the filament gets cooler, which makes it both dimmer and redder. Dimmable LED lamps to get dimmer, but the color doesn’t change.