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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 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 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.
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.
An example of PWM [clarification needed] in an idealized inductor driven by a voltage source modulated as a series of pulses, resulting in a sine-like current in the inductor. The rectangular voltage pulses nonetheless result in a more and more smooth current waveform, as the switching frequency increases. The current waveform is the integral ...
A TRIAC resembles an SCR in that both act as electrically controlled switches. Unlike an SCR, a TRIAC can pass current in either direction. Thus, TRIACs are particularly useful for AC applications. TRIACs have three leads: a gate lead and two conducting leads, referred to as MT1 and MT2.
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 ...
The rate at which it does this is set by the slope, which functions similar to a generator's droop speed control. This slope is programmable and can be set to a high value (to have the STATCOM regulate voltage like a traditional fixed reactive device) or to near zero, producing a very flat line and reserving the STATCOMs capacity for dynamic or ...