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About Triacs

Triacs are three-terminal silicon devices that are configured in an inverse parallel arrangement to provide load current during both halves of the AC supply voltage. They have two anodes (A1 and A2) for conducting current in both directions. They also have two gates (G1 and G2), each of which triggers a corresponding anode. As a rule, the gate trigger voltage is the same polarity as the voltage through the triac. For example, if the voltage from A1 to A2 is positive, then the gate trigger voltage is also positive. Once triggered, triacs continue to conduct current as long as there is current flow, even if there is no longer voltage at the gate terminal. Typically, triacs are used to control motor speed. Because load current (armature speed) flows during both halves of the applied AC voltage, motors rotate smoothly at all rotational speeds.

Products & Services Related to Triacs

Diacs

Diacs are bi-directional diodes that switch AC voltages and trigger silicon controlled rectifiers (SCRs) and triacs. Except for a small leakage current, diacs do not conduct until the breakover voltage is reached.

Sidacs

Sidacs are bidirectional silicon switches that provide greater power handling capabilities than standard diacs. These four-layer (PNPN) semiconductor devices are triggered by thyristors and act as open circuits that are capable of withstanding a specific rated voltage until triggered.

Silicon Controlled Rectifiers (SCR)

Silicon controlled rectifiers (SCR) are four-layer (PNPN) thyristors with three terminals: an input control terminal (gate), an output terminal (anode), and a terminal common to both the input and output (cathode). SCRs are used mainly with high voltages and currents, often to control alternating current (AC) where the change of sign causes the device to switch off automatically.

Thyristors

Thyristors are a class of four-layer (PNPN) semiconductor devices that act as switches, rectifiers, or voltage regulators.

Engineering Web: Triacs - Machine Design

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Solid-State Relays and I/O \| Machine Design Solid-state relays (SSRs) control load currents through solid-state switches such as triacs, SCRs, or power transistors.
Machine Design \| Solid-state relays (SSRs) control load currents through solid-state switches such as triacs, SCRs, or power transistors.
Gate Turn-Off Switch \| Machine Design Bilateral triode (triac): Triacs can withstand high current and are often used to control ac power.

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