DIAC (Diode a.c. Switch)

DIAC (Diode a.c. Switch)
DIAC (Diode a.c. Switch)

Electronic circuits commonly use the two-terminal semiconductor DIAC (Diode a.c. Switch). It is designed to turn on alternating current (a.c.) at the breakover voltage. Triacs and SCRs (Silicon-Controlled Rectifiers) are used with the DIAC to manage power to loads like lamps, motors, and heaters. Electronic circuit builders must understand the DIAC’s definition, purpose, and applications.

Some gadgets can switch alternating current on and off. That’s where DIACs help. The current can flow in either direction, making these little electrical components useful in AC switching circuits. This post will teach you all about these electrical unsung heroes. We’ll explain DIACs’ operation, their differences from other diodes, and their common uses. This simple yet comprehensive book will help you understand and use DIAC devices, whether you’re new to circuit design or brushing up. We’ve barely scraped the surface with 100 words, so read on for the complete DIAC download!

DIAC Definition

The bidirectional thyristor DIAC is a diode a.c. switch. The two-terminal diode can conduct current in either direction when voltage thresholds are satisfied. It conducts electricity in positive and negative alternating current cycles due of its avalanche breakdown. The DIAC’s symmetric construction and behavior make it excellent for initiating controlled conduction in both a.c. polarities.

DIAC goal

The DIAC controls and triggers alternating current in electronic circuits reliably. It switches power to a load like a bulb or motor based on input voltage. The DIAC is mostly employed in phase control applications that need accurate power regulation. By precisely triggering the DIAC at the desired moment in the a.c. waveform, load power may be adjusted.


DIACs are used in electronic circuits and systems. It’s utilized in dimmer switches to alter lamp brightness. The DIAC is used in phase-angled firing circuits, electronic ignition, motor speed control, and temperature modulation. The DIAC also triggers counters, timers, and oscillators. This versatile alternating current controller is used in automation, home appliances, and telecommunications.

What Is a DIAC?

  • The Diode a.c. Switch (DIAC) is a tiny electrical component that switches alternating current (a.c.) signals two ways. Power control circuits use it to trigger SCRs and triacs.
  • After reaching its breakover voltage, a DIAC is a two-terminal semiconductor diode that conducts current in both directions.
DIAC (Diode a.c. Switch)
DIAC (Diode a.c. Switch)
  • It is an open circuit with high resistance until the applied voltage reaches the breakover voltage.
  • Since its resistance drops rapidly, the DIAC conducts current in both directions. The current will continue until the voltage drops below its holding current.
  • Two crossed diodes representing bi-directional DIAC are common symbols.
  • DIAC triggers power switching devices like triacs and SCRs to turn on and off in circuits. This controls power flow.
  • The holding current of DIACs is usually 1mA when turned on. This keeps them on and conducts AC.

In short, a DIAC controls power handling devices in circuits by sharply switching from non-conducting to conducting states based on breakover voltage. Simple but crucial for power applications.

How Does a DIAC work?

A DIAC (Diode for alternating Current) conducts electricity at a specified voltage. Explaining how it works.

  • A DIAC has two back-to-back diodes. Two semiconductor junctions conduct at different voltages.
  • At very low voltages, DIAC conducts nothing. Imagine a boulder blocking electricity.
  • The DIAC conducts when its voltage surpasses a semiconductor junction’s breakdown voltage. Voltage runs like a river around a boulder in the DIAC.
  • Current will flow via the second semiconductor junction as voltage rises. The DIAC now lets current flow freely like a floodgate.
  • After the voltage drops below the holding current, the DIAC stops conducting and inhibits electrical flow until the threshold voltages are exceeded.
  • Depending on the voltage provided, a DIAC turns on and off, allowing current to flow in both directions at the breakover voltage threshold.

DIACs control and switch alternating current flows. Light dimmer circuits, touch-activated lamp switches, and AC power control applications employ it. Thank a DIAC next time you dim a light!

Utilizations of DIAC

Some major DIAC applications and uses. Their major function is to switch AC with negative resistance.

AC power control—DIACs switch AC loads on and off like triacs. Lamps, heaters, tiny motors, and more can be controlled. They switch at every AC waveform zero crossing.

Triggering triacs in AC circuits is a popular DIAC usage. Each half AC cycle, the DIAC sends a high-voltage pulse to turn the triac. Useful for light dimmers, motor speed controllers, etc.

Overvoltage protection—DIACs safeguard delicate devices against voltage spikes. Below breakover voltage, they are nonconductive yet short high-voltage transients to ground, preventing harm. Aids device protection.

DIACs create pulses to turn thyristors and transistors on and off in timing and wave-shaping circuits. This produces precise motor, switch, and measurement device pulses.

Connecting a DIAC to an RC network creates simple, inexpensive relaxation oscillators with exact timing. The DIAC provides oscillator feedback loop hysteresis.

The DIAC is a simple yet flexible component for controlling and safeguarding AC-powered gear, from AC power switching to triggering triacs and transistors, protecting against voltage spikes, and generating pulses and oscillation signals. With a rudimentary understanding of DIAC applications, you can use them efficiently in your next circuit design.

Advantages of Using a DIAC

  • This simple two-layer, two-terminal thyristor device has many benefits for circuit construction employing a DIAC (Diode for Alternating Current). Look at the main reasons to include a DIAC.
  • Switches both ways. One of the key benefits of a DIAC is that it can turn a circuit on and off both ways. Its bidirectional switching makes it ideal for triggering circuits like TRIAC-based AC switches or thyristor-based circuits, notably in AC power control applications.
  • Highly sensitive gate. DIACs are sensitive and easy to trigger into conduction due to their low breakover voltage. Even modest voltage spikes activate it.
  • Cost-effective and small. DIACs are cheaper than other thyristors and take up less PCB area.
  • Safe from noise. The DIAC does not conduct due to electrical noise. It improves circuit noise immunity by requiring a clear signal to switch on.
  • Operating longevity. A DIAC’s solid-state components and no moving elements provide dependable switching over millions of running cycles.

If you need a bidirectional triggering device or a basic silicon bilateral thyristor switch for AC circuits, a DIAC is a cheap and simple option. DIACs offer noise immunity, sensitivity, compactness, and reliability.

DIAC Selection Factors

When picking a DIAC (diode alternating current switch) for your circuit design, consider these specs and features:

Breakover voltage—The minimal voltage the DIAC needs to conduct current. Use a DIAC with a breakover voltage that matches your input voltages. Common voltages are 30V, 32V, 48V.

Peak DIAC breakover current—The maximum current when activated. Choose a DIAC rated for your application’s peak currents.

Commutation voltage—The DIAC’s stopping voltage after triggering. Commutation voltage should be much below supply voltage.


Here’s all about DIACs. This breakdown covers the basics of what they perform, how they work, their major properties, and application in circuits. Although small, these devices control alternating current in numerous electronic applications. After this introduction, you can confidently use DIACs in your designs and experiment with AC power regulation. Discover power electronics! Always double-check connections and voltages when breadboarding for safety.

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