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TRIAC. For other uses, see Triac. 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. TRIACs are a subset of thyristors (analogous to a relay ...
A silicon controlled rectifier or semiconductor controlled rectifier is a four-layer solid-state current -controlling device. The name "silicon controlled rectifier" is General Electric 's trade name for a type of thyristor. The principle of four-layer p–n–p–n switching was developed by Moll, Tanenbaum, Goldey, and Holonyak of Bell ...
The thyristor is a four-layered, three-terminal semiconductor device, with each layer consisting of alternating N-type or P-type material, for example P-N-P-N. The main terminals, labelled anode and cathode, are across all four layers. The control terminal, called the gate, is attached to p-type material near the cathode.
Like an SCR, when a voltage pulse is present on the gate terminal, the device turns on. The main difference between an SCR and a Triac is that both the positive and negative cycle can be turned on independently of each other, using a positive or negative gate pulse. Similar to an SCR, once the device is turned on, the device cannot be turned off.
A crowbar circuit is an electrical circuit used for preventing an overvoltage or surge condition of a power supply unit from damaging the circuits attached to the power supply. It operates by putting a short circuit or low resistance path across the voltage output (V o), like dropping a crowbar across the output terminals of the power supply.
The control signal must be coupled to the controlled circuit in a way which provides galvanic isolation between the two circuits. Many SSRs use optical coupling. The control voltage energizes an internal LED which illuminates and switches on a photo-sensitive diode (photo-voltaic); the diode current turns on a back-to-back thyristor ( TRIAC ...
Phase-fired control (PFC) is often used to control the amount of voltage, current or power that a power supply feeds to its load. It does this to create an average value at its output. If the supply has a DC output, its time base is of no importance in deciding when to pulse the supply on or off, as the value that will be pulsed on and off is ...
Zero-crossing control (or burst-fire control) is an approach for electrical control circuits that starts operation with the AC load voltage at close to 0 volts in the AC cycle. [ 1 ] This is in relation to solid-state relays, such as TRIACs and silicon controlled rectifiers. [ 1 ] The purpose of the circuit is to start the TRIAC conducting very ...