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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 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.
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.
In the following example crowbar circuit, the LM431 adjustable zener regulator controls the gate of the TRIAC. The resistor divider of R 1 and R 2 provide the reference voltage for the LM431. The divider is set so that during normal operating conditions, the voltage across R 2 is slightly lower than V REF of the LM431. Since this voltage is ...
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 ...
One example is the TRIAC, which is comparable to two thyristors connected back-to-back (in other words, reverse parallel), but on a single piece of silicon. Two LEDs can be paired this way, so that each protects the other from reverse voltage. A series string of such pairs can be connected to AC or DC power, with an appropriate resistor.
A simple example of holding current is in a Spark gap. In the most basic of circuits, if the current falls below the holding current even briefly, the circuit is turned 'OFF' (becomes blocked). However, complex circuits and devices may have different delays built-in between the time the current falls below this level and the time the device ...
Switch statements come in two main variants: a structured switch, as in Pascal, which takes exactly one branch, and an unstructured switch, as in C, which functions as a type of goto. The main reasons for using a switch include improving clarity, by reducing otherwise repetitive coding, and (if the heuristics permit) also offering the potential ...