Everything You Need to Know About SIDAC Thyristors
Everything You Need to Know About SIDAC Thyristors
Blog Article
What Are SIDACs?
SIDAC (Silicon Diode for Alternating Current) is a thyristor-like device with a high breakdown voltage. Its primary function is to serve as an over-voltage protection component or pulse trigger in circuits. SIDAC typically conducts only when the voltage reaches a certain threshold, allowing current to flow in both directions (forward and reverse) until the current decreases to a specific level, at which point it returns to its non-conductive state.
The XC3S4000-4FGG676C uses a PNPN four-layer structure, similar to an SCR (Silicon Controlled Rectifier), but unlike SCRs, SIDAC can conduct in both positive and negative directions. It features high voltage breakdown capability, low on-state resistance, and excellent resistance to pulse noise.
Working Principle of SIDACs
When the externally applied voltage gradually increases and approaches the breakdown voltage of the SIDAC, the internal electric field of the device intensifies, causing the carriers within the PNPN structure to accelerate, creating a strong electric field region. When the voltage reaches or exceeds the designed breakdown voltage, the SIDAC suddenly conducts, allowing current to flow freely in both forward and reverse directions. This conduction is triggered by the injection and ionization of carriers inside the device, similar to the avalanche breakdown phenomenon.
Once conducting, the SIDAC remains in the conducting state until the current passing through the device drops below its holding current. At this point, the SIDAC returns to its non-conducting state. During conduction, the impedance of the SIDAC significantly decreases. Additionally, the bidirectional conduction characteristic of the SIDAC allows it to operate effectively in AC circuits, as it can conduct in both positive and negative half-cycles of the voltage.
SIDAC Trigger Circuits
A XC3S4000-4FGG676C trigger circuit is a voltage-controlled mechanism using a SIDAC (Silicon Diode for Alternating Current), commonly applied in overvoltage protection, dimming control, and pulse triggering circuits. A typical SIDAC trigger circuit consists of a power supply, a current-limiting resistor, a capacitor, and a SIDAC. The basic circuit layout involves the current-limiting resistor and capacitor connected in series across the power supply, with the SIDAC connected in parallel to the capacitor.
During operation, as the supply voltage gradually increases, the capacitor charges through the current-limiting resistor. Over time, the voltage across the capacitor rises. When this voltage reaches the SIDAC's breakdown voltage (e.g., 40V), the SIDAC suddenly conducts, discharging the capacitor rapidly and creating a steady current flow across the SIDAC. This limits the circuit voltage to the breakdown voltage, protecting subsequent components from overvoltage damage.
For instance, with a current-limiting resistor of 10kΩ, a capacitor of 100µF, and a SIDAC with a breakdown voltage of 40V, the SIDAC triggers when the supply voltage exceeds 40V, reducing the capacitor voltage quickly to 40V and ensuring safe circuit operation.
Moreover, the trigger timing in a SIDAC circuit can be adjusted by varying the values of the current-limiting resistor and the capacitor.
SIDACs and DIACs
SIDAC and DIAC are both bidirectional triggering devices commonly used in circuits for overvoltage protection and triggering applications. They both conduct it when the voltage reaches a certain threshold and allow current to flow in both directions. Additionally, both devices have bidirectional breakdown characteristics, maintaining a low-impedance state after triggering until the current drops below the holding current.
However, there are differences between SIDAC and DIAC in terms of their breakdown voltage and applications. DIAC typically has a lower breakdown voltage, usually between 30V and 40V, and is mainly used to trigger SCRs or TRIACs. SIDAC, on the other hand, has a higher breakdown voltage, typically ranging from 50V to 300V, and is used in overvoltage protection or higher-voltage triggering applications. Moreover, SIDAC has a PNPN four-layer structure similar to an SCR, while DIAC has a three-layer PNP or NPN structure.
Why Are SIDACs Important?
SIDACs are commonly used in circuits that require overvoltage protection and high-voltage triggering. Due to their high breakdown voltage and bidirectional conduction characteristics, SIDACs effectively protect electronic devices from damage caused by excessive voltage. For instance, in power protection circuits, when the voltage exceeds a preset threshold, SIDACs rapidly conduct, keeping the voltage within a safe range and preventing equipment failure. Additionally, SIDACs are widely applied in pulse triggering, dimming circuits, and high-voltage triggering devices, offering reliable voltage control and triggering mechanisms.
FAQs
Can SIDACs be used in AC and DC circuits?
Yes, XC3S4000-4FGG676C can be used in both AC and DC circuits due to their bidirectional conduction capabilities. However, they are more commonly employed in AC applications, particularly for overvoltage protection and triggering purposes.
What are the advantages of using SIDACs?
SIDACs offer high-voltage protection, bidirectional operation, and reliable performance in high-voltage and high-frequency applications. They are particularly useful in circuits that require rapid switching to prevent damage due to overvoltage conditions.
How is a SIDAC structured?
A SIDAC features a PNPN four-layer structure, similar to a silicon-controlled rectifier (SCR), which enables its bidirectional conduction and high-voltage operation.