IGBT module overcurrent protection is critical for ensuring reliable system operation. This article systematically analyzes two mainstream overcurrent protection solutions: VCE(sat) detection and direct current sensing, focusing on their applications in SHYSEMI's IGBT modules and the implementation of IGBT driver protection technology.
1.Two Technical Paths for Overcurrent Protection Circuits.
Based on the current sensing method, IGBT overcurrent protection is divided into two categories:
VCE(sat) Detection Method
During normal operation, the IGBT's saturation voltage drop is approximately 3V (low-voltage dropout products can reach 1.5V). During overcurrent, VCE rises by 1-2V. This method offers a simple circuit with no additional losses, but it lacks sufficient response to IGBT short-circuits. It is a commonly used protection solution for Shenhuaying's IGBT modules.
Direct Current Sensing Method
Comprehensive protection is achieved by detecting the main circuit current, including:
- Current transformer detection: Suitable for high-current AC circuits
- Resistor voltage drop detection: Suitable for low-current AC and DC circuits, but power consumption must be considered.
2.In-Depth Analysis of VCE(sat) Sensing Technology
Core Circuit Architecture
A combination of diode isolation and Zener diode detection is used. When the IGBT is off, the diode reverse-biases to isolate the high voltage. When on, VCE ≈ 3V, and the diode conducts. When VCE rises above 5V (in case of overcurrent), the Zener diode breaks down and outputs a protection signal.
Gate Clamping Protection Circuit
A typical circuit includes a clamping diode (ZD2) and a snubber capacitor (C1). During overcurrent, the gate voltage is clamped to 6V, causing the IGBT to operate in the amplification region and reduce current. The snubber capacitor prevents high-voltage spikes from inductive loads.
Integrated Solutions
Integrated driver chips, such as the EXB841, include complete VCE(sat) detection functionality:
- Dedicated isolation diode (D7) and detection voltage regulator (ZD1)
- Independent power supply ensures detection reliability
- Provides -5V negative gate voltage to enhance shutdown reliability
The internal equivalent circuit schematic diagram of EXB841
Please note: The VCE(sat) protection threshold is affected by device characteristics, and parameters must be adjusted according to the specific IGBT driver protection design.
3. Technical Implementation of Direct Detection Solutions
Current Transformer Solution
Current is detected using a pulse step-up transformer, with only 1-2 turns on the primary side to reduce losses. A signal conditioning circuit is required to improve interference immunity. This solution is suitable for Shenhuaying's high-power IGBT modules.
Resistor Sampling Solution
Using a sampling resistor to detect current voltage drop offers a simple circuit and is applicable to both AC and DC applications. Note:
- Sampling resistor power loss design
- Small signal amplification circuit anti-interference processing
- Temperature drift compensation measures
4.Solution Comparison and Application Recommendations
Recommended for Shenhuaying IGBT module applications:
- Industrial inverters: Use VCE (sat) + resistor sampling combined protection
- New energy sector: Preferred current transformer solutions
- Precision medical equipment: Recommended resistor sampling combined with digital protection algorithms
Conclusion
Overcurrent protection design requires a comprehensive consideration of system cost, accuracy requirements, and reliability requirements. Shenhuaying IGBT modules offer comprehensive protection interfaces, combined with advanced IGBT driver protection technology, providing users with comprehensive solutions from the chip level to the system level. Proper protection circuit design not only improves system reliability but also maximizes the performance advantages of IGBT.