* Question
What are the main technical parameters of thyristors?
* Answer
A thyristor, also known as an SCR (Silicon Controlled Rectifier), is a semiconductor device used for controlling high-power electrical energy in industrial, automotive, and power conversion systems. To select and apply a thyristor effectively, engineers must understand its key technical parameters, which define its performance, reliability, and application limits.
1. Repetitive Peak Off-State Voltage (V<sub>DRM</sub> or V<sub>RRM</sub>)
This parameter represents the maximum voltage the thyristor can withstand in the off-state without conducting.
It defines the device’s voltage blocking capability in both forward and reverse directions.
Exceeding this voltage may lead to avalanche breakdown and permanent damage.
Engineers typically choose a thyristor with a rated off-state voltage at least 20–30% higher than the circuit’s maximum operating voltage.
2. On-State Current (I<sub>T</sub>)
The on-state current indicates the maximum continuous current the device can conduct once triggered.
It is closely related to the device’s thermal capacity and cooling conditions. Exceeding this limit causes excessive junction temperature, which may result in thermal runaway or device failure.
3. Gate Trigger Current and Voltage (I<sub>GT</sub>, V<sub>GT</sub>)
These values define the minimum current and voltage required at the gate to switch the thyristor from off to on.
Lower trigger parameters indicate higher gate sensitivity, beneficial for low-power control circuits.
In high-noise environments, slightly higher trigger thresholds help avoid false triggering.
4. Holding Current (I<sub>H</sub>) and Latching Current (I<sub>L</sub>)
Latching Current (I<sub>L</sub>): The minimum anode current needed to keep the thyristor conducting immediately after triggering.
Holding Current (I<sub>H</sub>): The minimum current required to maintain conduction once the device is fully on.
If the current falls below I<sub>H</sub>, the thyristor automatically turns off.
These parameters are crucial for low-current control circuits and phase control applications.
5. Rate of Voltage and Current Change (dv/dt and di/dt)
These dynamic parameters describe how quickly voltage or current can change across the device without unintended switching or damage.
dv/dt (voltage rate): A high rate of rise may trigger the device unintentionally.
di/dt (current rate): A steep current rise during turn-on may damage the junction due to localized heating.
Proper snubber networks and gate resistors are used to limit these transients.
6. Thermal Resistance and Junction Temperature (R<sub>θJC</sub>, T<sub>J</sub>)
These parameters determine how efficiently heat is conducted from the junction to the case or heatsink.
Maintaining the junction temperature below the specified T<sub>J(max)</sub> is vital for ensuring device longevity and stability.
Good thermal management extends the operating life of the thyristor, especially in high-current or high-frequency circuits.
7. Turn-On and Turn-Off Time
These timing parameters describe the switching response speed.
Turn-on time includes the delay and rise time for conduction after gate triggering.
Turn-off time (t<sub>q</sub>) indicates how long the thyristor needs to recover its blocking capability after conduction stops.
Shorter switching times are important for AC phase control and high-frequency converters.
Summary
The main technical parameters of a thyristor—covering voltage, current, gate sensitivity, dynamic characteristics, and thermal limits—determine its performance and suitability for specific applications.
Selecting the right device involves balancing power capacity, switching speed, and thermal design to ensure reliable operation under real-world electrical stresses.
For high-quality and reliable power semiconductor components, sourcing from trusted distributors like Win Source ensures authenticity, performance consistency, and global supply support.
COMMENTS