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A TRIAC (triode for alternating current; also bidirectional triode thyristor or bilateral triode thyristor [1]) is a three-terminal electronic component that conducts current in either direction when triggered. The term TRIAC is a genericised trademark.
Many opto-TRIACs come with zero-cross circuits built in. They are often used to control larger, power TRIACs. In this setup TRIAC turn-on delays compound, so quick turn-on times are important. The corresponding phase-angle circuits are more sophisticated and more expensive than zero-cross circuits.
A zero-crossing is a point where the sign of a mathematical function changes (e.g. from positive to negative), represented by an intercept of the axis (zero value) in the graph of the function. It is a commonly used term in electronics, mathematics, acoustics, and image processing.
A thyristor (/ θ aɪ ˈ r ɪ s t ər /, from a combination of Greek language θύρα, meaning "door" or "valve", and transistor [1]) is a solid-state semiconductor device which can be thought of as being a highly robust and switchable diode, allowing the passage of current in one direction but not the other, often under control of a gate electrode, that is used in high power applications ...
In AC circuits, SCR or triac relays inherently switch off at the points of AC zero cross when there is zero load current. The circuit will never be interrupted in the middle of a sine wave peak, preventing the large transient voltages that would otherwise occur due to the sudden collapse of the magnetic field around the inductance.
A QUADRAC is a special type of thyristor which combines a DIAC and a TRIAC in a single package. The DIAC is the triggering device for the TRIAC. Thyristors are four-layer (PNPN) semiconductor devices that act as switches, rectifiers or voltage regulators in a variety of applications. When triggered, thyristors turn on and become low-resistance ...
A phase-fired controller, like a buck-topology switched-mode power supply, is only able to deliver an output voltage not exceeding its input, minus any losses occurring in the control elements themselves.
Adjusting the brightness of light emitted by a light source is then merely a matter of setting at what voltage (or phase) in the AC half-cycle the dimmer begins to provide electric current to the light source (e.g. by using an electronic switch such as a triac). In this case the PWM duty cycle is the ratio of the conduction time to the duration ...