DIACs, SIDACs

1. What are DIACs and SIDACs Thyristors?‌

‌DIAC‌ (Bidirectional Trigger Diode) is a double-junction, bidirectionally conductive semiconductor device designed to conduct current when the AC voltage exceeds a specific breakdown voltage. It is often used as a trigger device to control phase delay in power electronic systems. Its structure is similar to an NPN transistor without a base connection, with high impedance characteristics until the voltage reaches a critical value and exhibits a negative resistance effect.

 

‌SIDAC‌ (Bidirectional Silicon Symmetric Switch) has similar functions to DIAC, but has higher breakdown voltage and current capacity, and is usually used in higher power pulse triggering or surge suppression circuits. Both are subclasses of Thyristors and are widely used in AC control scenarios.

 

2. What are the ‌Technical Characteristics of DIACs and SIDACs Thyristors?‌

‌DIAC Characteristics‌:

Bidirectional symmetrical triggering, the breakdown voltage (V_BR) is a fixed value;

 

No polarity restriction, can respond to positive and negative half-cycle signals;

 

Turns on quickly after triggering, generating steep pulse signals, suitable for precise phase control.

 

‌SIDAC Features‌:

Supports higher voltage (up to hundreds of volts) and larger current;

 

Maintains high current, often used for protection circuits or high-voltage pulse generation.

 

3. What are DIACs and SIDACs Thyristors Used for?‌

‌DIAC Typical Applications‌:

As a trigger device for Triacs or SCR, used in phase control circuits such as dimmers and motor speed regulation;

 

Cooperates with RC circuits to generate delayed pulses to achieve power regulation of AC loads.

 

‌SIDAC Typical Applications‌:

High-voltage surge protection (such as lightning protection);

 

Scenarios that require high-voltage pulses, such as ignition systems and capacitor discharge circuits.

 

4. ‌Linkage with Other Devices‌

DIAC is often used in conjunction with Triacs, the former providing trigger pulses and the latter performing on-off control of the main circuit. For example, in a dimming circuit, DIAC delays the triggering of Triacs through an RC network to adjust the average power of the load.

 

SIDAC is more commonly used in scenarios that require high-voltage transient triggering, such as overvoltage self-locking functions in protection circuits.

 

5. ‌Classification and Manufacturers of DIACs and SIDACs Thyristors‌

DIACs and SIDACs belong to the ‌bidirectional switching devices‌ in the Thyristors category, which are different from the unidirectional SCR (silicon controlled rectifier).

 

Major manufacturers include Littelfuse, STMicroelectronics, etc., and product specifications cover different voltage/current levels.