SCRs
1. SCRs Overview
SCR is a three-terminal electronic device based on a four-layer semiconductor structure (PNPN) with controllable rectification characteristics. It can achieve unidirectional conduction control of current through a gate signal. Due to its high efficiency, small size, and long life, it is widely used in rectification, voltage regulation, inversion, and contactless switching in the field of power electronics.
2. What are the Types of SCRs?
SCR can be divided into the following main types:
Single-way Thyristor (SCR)
It is composed of four layers of semiconductors (PNPN), which only allows current to be conducted in one direction. After conduction, it needs to be turned off by reducing the voltage or cutting off the load.
Bidirectional Thyristor (TRIAC)
It is composed of two anti-parallel SCRs, supports bidirectional conduction, and is suitable for AC control.
GTO
It is forced to shut down through a gate signal and is suitable for higher frequency switching scenarios.
Light-controlled Thyristor
It is triggered by a light signal and is often used for high-voltage isolation control.
3. How do SCRs Work?
Conduction Condition: When a positive voltage is applied between the anode and cathode and a trigger current is injected into the control electrode, the SCR enters the on state.
Maintaining Conduction: After conduction, even if the trigger signal is removed, the SCR remains on until the current is lower than the holding current or the voltage is reversed.
Shutdown Mechanism: Shutdown is achieved by reducing the current below the holding value or applying a reverse voltage.
4. Technological Development of SCRs
Technological improvements in recent years have mainly focused on the following directions:
Low Trigger Voltage Optimization: Improve device structure (such as MLSCR, LVTSCR) or use auxiliary trigger technology (such as substrate trigger, double trigger) to reduce the trigger voltage and adapt to low-voltage circuit requirements.
High-frequency Application: Develop fast thyristors (Fast SCR) and optimize bidirectional thyristors (TRIAC) to improve high-frequency switching performance.
Integrated Design: Combined with CMOS technology, improves device response speed and anti-latch capability.
5. What are SCRs Used for?
Power Supply Control: used for rectification, voltage regulation, and inverter circuits, such as switching power supplies and UPS systems.
Motor Speed Regulation: speed control of DC/AC motors by adjusting the conduction angle.
Lighting Dimming: stepless brightness adjustment in stage lighting and household dimmers.
Electrostatic Discharge Protection (ESD): protects sensitive circuits using the high robustness of thyristors.
6. Selection and Precautions for SCRs
Parameter Matching: attention should be paid to the matching of parameters such as trigger voltage, holding current, reverse breakdown voltage, and circuit requirements.
Heat Dissipation Design: heat sinks or forced heat dissipation measures are required in high-power applications.
Anti-interference Design: to avoid false triggering, the control pole signal can be optimized by shielding or filtering circuits.