Content last revised on February 9, 2026
ETK81-050: Integrated 500V 80A Thyristor/Diode Module for Inrush Current Control
The Fuji Electric ETK81-050, a member of their Thyristor/Diode Module family, is an integrated power module engineered to simplify the design and enhance the reliability of three-phase power conversion front-ends. By combining a three-phase diode bridge rectifier, a soft-start thyristor, and an NTC thermistor into a single compact package, this module offers a streamlined solution for managing power rectification and fault protection. It is specified with a repetitive peak reverse voltage of 500V and an average forward current of 80A. This device directly addresses the critical engineering challenge of mitigating high inrush currents during the charging of DC link capacitors, thereby reducing component count and preventing startup failures.
Application Scenarios & Value
Streamlining Front-End Design in Motor Drives and Power Supplies
For 200V-class AC drives requiring a compact and reliable solution for inrush current limitation, the ETK81-050 offers an optimal, integrated approach. In a typical engineering scenario involving the design of a Variable Frequency Drive (VFD), engineers face the challenge of managing the substantial inrush current that occurs when initially charging the large DC link capacitor. Unchecked, this current can trip circuit breakers, damage upstream components, and reduce the lifespan of the capacitors themselves. The ETK81-050's integrated soft-charge thyristor provides a controlled charging path, effectively limiting the current peak without the need for bulky external power resistors and bypass relays. This integration not only shrinks the required PCB footprint but also simplifies the entire soft-start circuit, leading to a more robust and cost-effective final design. This module's capabilities are equally valuable in applications such as AC servo drives, uninterruptible power supplies (UPS), and other industrial inverter systems where reliable startup is paramount.
Key Parameter Overview
Functional Specs for Rectification, Control, and Thermal Management
The electrical and thermal characteristics of the ETK81-050 are tailored for integrated power conversion front-ends. The parameters are grouped by function to clarify their role in system design.
| Parameter | Value | Notes |
|---|---|---|
| Rectifier Diode Section (Absolute Maximum Ratings at Tc=25°C) | ||
| Repetitive Peak Reverse Voltage (VRRM) | 500 V | Defines the maximum reverse voltage the diodes can block. |
| Average Forward Current (ID) | 80 A | Maximum continuous DC current the rectifier can handle. |
| Peak Surge Forward Current (IFSM) | 850 A | Indicates the diode's robustness against non-repetitive current surges. |
| Soft-Start Thyristor Section (Absolute Maximum Ratings at Tc=25°C) | ||
| Repetitive Peak Off-State Voltage (VDRM) | 500 V | Defines the maximum voltage the thyristor can block in its off-state. |
| Average On-State Current (IT(AV)) | 50 A | Maximum continuous current handling capability of the thyristor. |
| Thermal and Isolation Characteristics | ||
| Operating Junction Temperature (Tj) | -40 to +125 °C | Specifies the operational temperature range of the semiconductor junctions. |
| Thermal Resistance (Rth(j-c)) | 0.25 °C/W (Diode) / 0.40 °C/W (Thyristor) | Crucial for heatsink design, indicating how efficiently heat is transferred from the chip to the case. |
| Isolation Voltage (Visol) | 2500 V | Specifies the AC voltage the module can withstand between its terminals and the baseplate for 1 minute. |
Download the ETK81-050 datasheet for detailed specifications and performance curves.
Application Vignette
System-Level Advantages in Variable Frequency Drive Design
In a standard 240V three-phase VFD, directly charging a large DC link capacitor can cause inrush currents that are many times the nominal operating current. This traditionally requires complex external circuits with power resistors and bypass relays, which consume valuable space, generate unwanted heat, and introduce additional points of potential failure. The ETK81-050 module's architecture offers an elegant, all-in-one solution. During startup, the thyristor is triggered to charge the capacitor bank through a small current-limiting resistor. Once the DC link voltage reaches a safe, predefined level, the main system contactor can close, bypassing the soft-start path for full-power operation. This integrated approach leads to a significant reduction in PCB footprint, lower assembly costs, and fundamentally higher system reliability. Furthermore, the built-in NTC Thermistor provides a direct feedback mechanism for the VFD's control unit to monitor temperature, ensuring the drive operates within its Safe Operating Area (SOA) and enabling proactive thermal management.
Frequently Asked Questions
What is the primary advantage of integrating the thyristor with the diode bridge in the ETK81-050?
The primary advantage is significant design simplification and enhanced reliability. This integration eliminates the need for a separate, bulky pre-charge circuit composed of power resistors and bypass relays, which reduces component count, assembly complexity, and potential points of failure in power systems like VFDs.
How does the built-in NTC thermistor contribute to system protection?
The integrated NTC thermistor enables real-time monitoring of the module's substrate temperature. This data can be utilized by the system's microcontroller to implement precise over-temperature protection (OTP), preventing thermal runaway and ensuring the module operates within its specified thermal limits, thereby extending the operational life of the entire drive system.
For engineers developing compact and reliable motor drives or power supplies, the ETK81-050 offers a clear path to simplifying front-end design without compromising on safety or performance. To evaluate this module for your specific design requirements, please review the detailed datasheet or contact our technical support team for further information.