What are Diacs (Diodes for Alternating Current)

Diacs are bidirectional semiconductor devices designed to conduct current only after a defined voltage threshold is exceeded in either polarity. They remain in a high-impedance state under normal operating conditions and transition abruptly into conduction when the applied voltage reaches the device’s breakover characteristic. This symmetrical switching behavior makes diacs well-suited for use in alternating current control circuits.

In power electronics, diacs are primarily used as triggering elements for thyristors such as triacs. Their sharp breakover action provides a repeatable and polarity-independent trigger point, enabling consistent phase-angle control in AC systems. The device structure and doping profile determine the electrical characteristics that govern when and how the diac switches between its blocking and conducting states.

Key Specifications

• Breakover Voltage: The breakover voltage defines the magnitude of applied voltage, in either polarity, at which the diac transitions from its non-conductive state to its conductive state. This parameter directly determines the trigger point in AC control applications and influences the phase angle at which downstream switching devices are activated.
• Breakover Current: The breakover current specifies the current level associated with the onset of conduction once the breakover voltage is reached. It reflects the internal switching behavior of the diac and affects how decisively the device turns on and initiates current flow into the connected control circuitry.

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