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Thyristors: Key Parameters

Introduction

Standard Gate-Turn-Off Thyristors

Thyristors, invented by GE in 1950, are four-layer three-terminal devices, as illustrated in Figure 1. These semiconductor devices play a crucial role in electronic circuits, offering controlled rectification and amplification functions. Over the years, thyristors have found extensive applications in various fields due to their unique characteristics. As depicted in the diagram, the structure consists of four alternating layers of P-type and N-type semiconductors, forming three junctions. This configuration enables the thyristor to control the flow of electrical current effectively. Understanding the intricacies of thyristor design and its applications is essential for harnessing the full potential of this pioneering electronic component.

Standard Gate-Turn-Off Thyristors1
Standard Gate-Turn-Off Thyristors1
Standard Gate-Turn-Off Thyristors2
Standard Gate-Turn-Off Thyristors3
Standard Gate-Turn-Off Thyristors4
Standard Gate-Turn-Off Thyristors4
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Amplified Gate Structure

The triggering of large Electrically Triggered Thyristors (ETTs) demands high-power gate pulses. To mitigate the trigger power requirements, modern large thyristors are equipped with internally cascaded auxiliary thyristors. These thyristors, featuring amplified gate structures, prove more effective in reducing gate current. This is because the primary triggering energy is generated from the anode voltage by the gate current amplifier, requiring reliable triggering only for the first (small) amplifying thyristor. The incorporation of cascaded auxiliary thyristors not only enhances the efficiency of gate triggering but also contributes to overall performance improvements in large thyristor applications. This innovative approach in gate design optimizes energy consumption and ensures the robust operation of these critical electronic components.

Amplified Gate Structure of Thyristors
Equivalent Circuit of Thyristors with Amplified Gate Structure
Equivalent Circuit of Thyristors with Amplified Gate Structure
Schematic Diagram of the Cathode Surface in a Thyristor

Key Parameters of Thyristors

The parameters of thyristors can be categorized into electrical, thermal, and mechanical parameters. For detailed parameter definitions, reference can be made to the literature (GBT 15291-2015 Semiconductor Devices Part 6: Thyristors), and for testing methods, the literature (JBT 7626-2013 Test Methods for Reverse Blocking Triode Thyristors) can be consulted. From an application perspective, let’s provide an overview of the key parameters that users are typically concerned about.

  1. Electrical Parameters:

    • Forward Voltage Drop (Vf): The voltage across the thyristor during forward conduction.
    • Holding Current (Ih): The minimum current required to maintain conduction.
    • Gate Trigger Current (Igt): The minimum current needed to trigger the thyristor into conduction.
    • Turn-Off Time (tq): The time taken for the thyristor to turn off after the gate signal is removed.
  2. Thermal Parameters:

    • Junction Temperature (Tj): The temperature at the thyristor’s semiconductor junction.
    • Thermal Resistance (Rth): The measure of how easily heat can flow through the thyristor.
    • Surge Current Rating (I²t): The maximum allowable energy for a surge current without causing damage.
  3. Mechanical Parameters:

    • Mounting Force: The force required to properly mount the thyristor on a heat sink or other surfaces.
    • Weight: The physical mass of the thyristor, which may be crucial in certain applications.

Understanding and considering these parameters is crucial for users to ensure proper selection and optimal performance of thyristors in various applications.

Repetitive Blocking Voltage (V DRM / V RRM)

Breakover Voltage
Breakover Voltage

In this section, we delve into one of the critical electrical parameters of thyristors: the Repetitive Blocking Voltage, often denoted as V DRM (Repetitive Direct Reverse Blocking Voltage) for DC applications or V RRM (Repetitive Reverse Blocking Voltage) for AC applications.

Repetitive Blocking Voltage (V DRM / V RRM): This parameter represents the maximum voltage that the thyristor can withstand in its off-state without breaking down. For direct current (DC) applications, it is expressed as V DRM, while for alternating current (AC) applications, it is denoted as V RRM.

Understanding this parameter is vital for ensuring the reliable operation of the thyristor in various circuit configurations. It is essential to select a thyristor with a repetitive blocking voltage rating that exceeds the maximum voltage encountered in the application. Failure to do so may lead to breakdown and potential damage to the thyristor.

Additionally, designers and engineers need to consider the margin of safety when choosing thyristors, taking into account factors such as voltage spikes, surges, and other transient conditions that may occur in the specific application environment.

Proper attention to the Repetitive Blocking Voltage is crucial for the longevity and stability of the thyristor in a given electrical circuit. It ensures that the device can consistently and safely handle the voltages it encounters during normal operation, contributing to the overall reliability of the electronic system in which it is employed.

Leakage Current (I DRM / I RRM)

Leakage current, denoted as I DRM for direct current (DC) applications and I RRM for alternating current (AC) applications, is a crucial parameter in thyristor specifications. This current represents the small amount of current that flows through the device when it is in the blocking state.

The magnitude of the leakage current is influenced by factors such as the size of the thyristor’s chip area and the operating temperature, typically rated as the junction temperature. In the case of high-temperature conditions, the rated junction temperature, the leakage current (IDRM/IRRM) generally falls within the range of 20 to 200mA.

Understanding and controlling leakage current is essential for the proper functioning and reliability of the thyristor. Excessive leakage current can lead to undesired power losses and, in some cases, affect the overall performance of the electronic circuit. Designers and engineers must carefully consider the specific application requirements and environmental conditions when selecting a thyristor to ensure that the leakage current remains within acceptable limits.

In summary, the leakage current is a critical parameter that reflects the thyristor’s ability to maintain a blocked state effectively. Keeping this current within specified limits is vital for achieving optimal performance and reliability in a diverse range of electronic applications.

Key Parameters of Thyristors

The critical rate of rise of the off-state voltage, dv/dt, is typically required to be equal to or greater than 500V/µs in most applications. This parameter is crucial for ensuring the proper performance of thyristors during switching operations.

Other key parameters include:

  1. On-State Peak Voltage (VTM): The maximum voltage across the thyristor when it is in the conducting state.

  2. On-State Average Voltage (VTAV): The average voltage across the thyristor during its conducting state.

  3. Rated On-State Average Current (ITAV): The maximum average current that the thyristor is designed to handle in its conducting state.

  4. On-State Root Mean Square Current (ITRMS): The effective (root mean square) value of the current during the thyristor’s conducting state.

  5. Surge Current (ITSM): The maximum allowable current for a short-duration surge without causing damage.

  6. Critical Rate of Rise of Anode Current during Turn-On (di/dt): The maximum rate at which the anode current rises during the turn-on process.

  7. On-State Threshold Voltage (VTO): The minimum voltage required to turn on the thyristor and initiate conduction.

  8. On-State Slope Resistance (rTO): The slope resistance during the thyristor’s conducting state.

The power loss, PTAV, in the thyristor is calculated as the product of the on-state threshold voltage (VTO) multiplied by the rated on-state average current (ITAV), plus the product of the slope resistance (rTO) multiplied by the square of the on-state root mean square current (ITRMS^2). This formula represents the power dissipation characteristics of the thyristor during its conducting state. Understanding and optimizing these parameters are essential for selecting the right thyristor for specific applications and ensuring reliable and efficient operation.

Rated On-State Average Current (ITAV)

The Rated On-State Average Current (ITAV) is a critical parameter that defines the maximum average current the thyristor can handle during its conducting state. This parameter is crucial in applications where the thyristor is regularly in the on-state, such as in power control circuits.

Formula for Power Dissipation (PTAV): The power dissipation in the thyristor during its on-state operation is given by the formula:

PT AV = VTO * ITAV * rTO * ITRMS²

where:

  • is the power dissipation.
  • is the on-state threshold voltage.
  • is the Rated On-State Average Current.
  • is the on-state slope resistance.
  • is the on-state root mean square current.

Explanation:

  • The first term () represents the power dissipated due to the voltage drop across the thyristor during its on-state. This term accounts for the energy consumed by the thyristor to maintain conduction.

  • The second term () represents the power dissipation due to the slope resistance during on-state. This term accounts for the energy lost as heat due to the dynamic resistance of the thyristor during conduction.

Optimizing ITAV is crucial for applications where the thyristor is expected to handle higher average currents. It ensures that the device can effectively manage the power dissipation and prevents overheating. Engineers must carefully consider ITAV along with other relevant parameters to select a thyristor that meets the specific requirements of their application, balancing factors such as power handling capacity and thermal management.

The Key Parameters of Thyristors ITAV1
The Key Parameters of Thyristors ITAV2

Turn-On/Turn-Off Characteristics

Gate Trigger Voltage (VGT): Gate Trigger Voltage (VGT) is the voltage required at the gate terminal to initiate the turn-on process of the thyristor. It signifies the minimum voltage needed to activate the device.

Gate Trigger Current (IGT): Gate Trigger Current (IGT) is the minimum current needed at the gate terminal to initiate the thyristor’s turn-on. It quantifies the sensitivity of the device to the applied gate current.

Gate Non-Trigger Voltage (VGD): Gate Non-Trigger Voltage (VGD) is the voltage at the gate terminal below which the thyristor remains in the off-state. It represents the voltage level required to prevent unintended triggering.

Holding Current (IH): Holding Current (IH) is the minimum current required to maintain the thyristor in the on-state after it has been triggered. It ensures the device remains in the conducting state once turned on.

Latching Current (IL): Latching Current (IL) is the minimum current necessary to sustain the thyristor in the on-state even after removing the gate trigger. It defines the current level at which the thyristor ‘latches’ into the conducting state.

Gate Control Turn-On Time (tgt): Gate Control Turn-On Time (tgt) is the time taken for the thyristor to turn on once the gate is triggered. It is a crucial parameter for precise timing in applications requiring controlled switching.

Circuit Commutation Turn-Off Time (tq): Circuit Commutation Turn-Off Time (tq) is the time required for the thyristor to turn off during circuit commutation. It influences the switching speed of the device in turn-off conditions.

Reverse Recovery Charge (Qrr): Reverse Recovery Charge (Qrr) represents the charge that must be removed during the reverse recovery process of the thyristor. It is essential for evaluating the diode-like behavior during turn-off.

Gate Junction Resistance (RGK): Gate Junction Resistance (RGK) is the resistance associated with the gate terminal. It impacts the gate control characteristics and influences the turn-on and turn-off times of the thyristor.

Relationship Curve between Gate Trigger Current and Thyristor Rated Current

Gate Trigger Voltage (VGT): Gate Trigger Voltage (VGT) is a critical parameter influencing the turn-on behavior of the thyristor. It represents the minimum voltage required at the gate terminal to initiate the turn-on process. The relationship between VGT and the thyristor’s rated current provides insights into the device’s sensitivity to gate voltage across different operating conditions.

Gate Trigger Current (IGT) and Relationship with Rated Current: Gate Trigger Current (IGT) is the minimum current needed at the gate terminal to initiate the turn-on process. The relationship between IGT and the thyristor’s rated current is depicted in a characteristic curve. This curve illustrates how the gate trigger current varies with the thyristor’s rated current, offering valuable information for selecting and configuring the device in various applications. It helps determine the appropriate gate drive requirements for reliable turn-on.

Understanding the gate trigger current in relation to the rated current is essential for designing circuits that can effectively trigger the thyristor within specified parameters. This relationship curve guides engineers in choosing appropriate gate drive circuits and ensures reliable performance in diverse operating conditions.

In summary, the gate trigger voltage and current characteristics provide a comprehensive understanding of the thyristor’s turn-on behavior, enabling engineers to optimize the device’s performance based on specific application requirements.

Temperature-Dependent Curves of Gate Trigger Current and Gate Trigger Voltage for Thyristors

Gate Trigger Current (IGT) vs. Gate Trigger Voltage (VGT) vs. Temperature:

The relationship between Gate Trigger Current (IGT) and Gate Trigger Voltage (VGT) with temperature is crucial for understanding the performance characteristics of a thyristor under varying environmental conditions. This information is often presented in characteristic curves, illustrating how these parameters change with temperature.

  1. Gate Trigger Current vs. Temperature:

    • As temperature increases, the Gate Trigger Current (IGT) typically experiences changes. This curve provides insights into how the thyristor’s sensitivity to the gate trigger current is affected by temperature variations.
    • Higher temperatures may influence the semiconductor material properties, impacting the conductivity and response to the gate trigger current.
  2. Gate Trigger Voltage vs. Temperature:

    • The Gate Trigger Voltage (VGT) also exhibits changes with temperature variations. This curve illustrates how the minimum voltage required to initiate the turn-on process at the gate terminal is influenced by temperature.
    • Temperature can affect the energy barrier at the gate, influencing the voltage required for triggering.

Understanding these curves is essential for designing circuits that can reliably trigger the thyristor across a range of temperatures. Engineers use this information to ensure that the gate drive characteristics are optimized for the expected temperature conditions in a specific application.

In summary, the Gate Trigger Current and Voltage vs. Temperature curves provide valuable insights into the thyristor’s behavior under different thermal conditions. This knowledge is instrumental in selecting and configuring thyristors for applications where temperature variations play a significant role in device performance.

Gate Trigger Current vs. Thyristor Turn-On Time Relationship Curve
Gate Trigger Current vs. Thyristor Turn-On Time Relationship Curve

Gate Trigger Current (IGT) vs. Thyristor Turn-On Time Relationship Curve:

The relationship between Gate Trigger Current (IGT) and the thyristor’s turn-on time is represented by a characteristic curve. This curve is instrumental in understanding how the gate trigger current influences the speed at which the thyristor transitions from the off-state to the on-state.

  1. Gate Trigger Current (IGT):

    • Gate Trigger Current (IGT) is the minimum current required at the gate terminal to initiate the turn-on process of the thyristor.
  2. Thyristor Turn-On Time:

    • Thyristor Turn-On Time represents the duration it takes for the thyristor to transition from the off-state to the on-state once the gate is triggered.

Characteristic Curve:

  • The characteristic curve depicts how variations in the gate trigger current impact the thyristor’s turn-on time. It provides engineers with a visual representation of the relationship between these two parameters.

  • As the gate trigger current increases or decreases, the turn-on time of the thyristor may exhibit corresponding changes. A lower gate trigger current may result in a faster turn-on time, while a higher gate trigger current may prolong the turn-on process.

Understanding this relationship is critical for engineers designing circuits that require precise control over the thyristor’s switching speed. It aids in optimizing the gate trigger current to achieve desired performance characteristics in diverse applications. The characteristic curve serves as a valuable tool for selecting the appropriate gate trigger current for specific operational requirements, ensuring reliable and efficient thyristor performance.

Turn-On Characteristics of Thyristors

Characteristic Trigger Curve of Thyristor Gate
Characteristic Trigger Curve of Thyristor Gate

Gate Trigger Characteristics Curve of Thyristors:

The Gate Trigger Characteristics Curve of thyristors is a graphical representation illustrating the relationship between the gate trigger current (IGT) and the corresponding gate trigger voltage (VGT). This curve is instrumental in comprehending the sensitivity and responsiveness of the thyristor to the applied gate signal.

  1. Gate Trigger Current (IGT):

    • The Gate Trigger Current (IGT) is the minimum current required at the gate terminal to initiate the turn-on process of the thyristor.
  2. Gate Trigger Voltage (VGT):

    • The Gate Trigger Voltage (VGT) is the minimum voltage required at the gate terminal to achieve the turn-on state.

Characteristic Curve Details:

  • The Gate Trigger Characteristics Curve provides a comprehensive view of how changes in the gate trigger current affect the gate trigger voltage and vice versa.

  • Typically, as the gate trigger current increases, the corresponding gate trigger voltage may also rise. This relationship is crucial for understanding the behavior of the thyristor during the turn-on process.

  • Engineers use this curve to determine the optimal gate trigger conditions for reliable and efficient thyristor operation in specific applications. It aids in selecting suitable gate drive circuits and ensuring precise control over the turn-on characteristics of the device.

  • The curve also helps in assessing the trade-offs between gate trigger current and voltage, allowing designers to make informed decisions based on the requirements of the application.

In summary, the Gate Trigger Characteristics Curve is a fundamental tool for engineers, providing insights into the interdependence of gate trigger current and voltage. It serves as a guide for designing circuits that leverage the unique turn-on characteristics of thyristors for diverse electronic applications.

Conclusion: Key Parameters of Thyristors

In conclusion, the key parameters of thyristors play a pivotal role in defining the performance and reliability of these semiconductor devices across a spectrum of applications. Each parameter, from the critical gate-trigger characteristics like Gate Trigger Current (IGT) and Gate Trigger Voltage (VGT) to essential operational parameters such as Rated On-State Average Current (ITAV) and Turn-On/Turn-Off times, contributes to the overall functionality of the thyristor.

Understanding the intricacies of these parameters allows engineers to make informed decisions during the selection and configuration of thyristors for specific applications. Whether considering the Repetitive Blocking Voltage, Leakage Current, or Gate Junction Resistance, each parameter contributes to the optimal operation of the thyristor in different environments and under varying conditions.

The characteristic curves, illustrating relationships between parameters and their dependencies on temperature and other variables, serve as invaluable tools for engineers. These curves empower them to fine-tune circuit designs, ensuring reliable performance and adherence to application-specific requirements.

As technology continues to advance, the continuous refinement and optimization of these key parameters pave the way for enhanced efficiency, reduced power losses, and increased reliability in diverse electronic systems. In the dynamic landscape of electronics, a profound understanding of these parameters not only fosters innovation but also ensures the seamless integration of thyristors into a wide array of applications, ranging from power control circuits to sophisticated electronic devices. The journey of harnessing the full potential of thyristors begins with a comprehensive grasp of these key parameters, guiding engineers towards innovative and efficient solutions in the ever-evolving field of semiconductor technology.

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