What Is a DIAC?
A DIAC, or diode for alternating current, functions in AC circuits to distribute current in both directions once a specific voltage threshold is exceeded. Also known as a trigger diode, it comprises two parallel-connected diodes facing opposite directions, enabling it to control switching operations effectively in AC power supplies. Its use extends to triggering devices like triacs for applications in lighting dimming and heating control, leveraging its bidirectional current flow for smooth operation. The simplicity of its two-terminal design facilitates less complex circuit configurations, enhancing design efficiency and longevity over mechanical switches.
Applications of DIACs
DIACs serve various roles in electrical systems, including:
Lighting Dimming
They play a crucial role in adjusting lighting brightness, where their triggering action ensures smooth transitions in luminosity.
Heating Control
In heating systems and ovens, DIACs contribute to temperature regulation by controlling the activation of heating elements for consistent heat distribution.
Electric Motor Control
DIACs are instrumental in managing AC electric motors, particularly in adjusting rotation direction and speed, in conjunction with triacs and SCRs for precise current control.
Operating Principle of DIACs
DIACs are characterized by their PNPn semiconductor structure, activating to conduct AC signals beyond a threshold voltage in both positive and negative cycles. This bidirectional capability ensures seamless operation across AC power supply fluctuations, with current flow maintained until the input voltage falls below the threshold.
Selecting DIACs
When choosing a DIAC, consider the following factors.
Breakover Voltage
Select a DIAC with a breakover voltage that matches the application requirements, ensuring it can initiate conduction at the desired voltage level.
Rated Current
The DIAC should support the maximum current demand of the circuit without compromising performance, as indicated by its current rating.
Rise Time
For applications requiring swift switching, the DIAC’s rise time, or the speed at which it enters a conduction state, becomes critical.
Leakage Current
Opt for DIACs with minimal leakage current to enhance efficiency, especially in applications where precision is key.
Package Type
Choose an appropriate package type based on the physical constraints and installation requirements, with common options including DO-35, TO-92, and TO-220.