SLUAB45 October   2026 UCD3138

 

  1.   1
  2.   Abstract
  3. 1Issue Description: Abnormal SR Voltage Stress Under Output Short-Circuit
    1. 1.1 Abnormal Phenomenon: SR Voltage Stress Exceeds the Limit in Short-Circuit Testing
    2. 1.2 Root Cause Analysis: Timing Mechanism of Turn-Off Stress Caused by Negative Current
  4. 2Solution: SR Stress Optimization Based on the UCD3138 Automatic Mode Switching Capability
    1. 2.1 Key Technology: Principle of the UCD3138 Automatic Mode Switching Capability
    2. 2.2 Solution Implementation: Dynamically Adjusting the Control Timing of the SR On-Time With Mode Switching
  5. 3Experimental Verification: Effectiveness Testing of the Optimization Solution
    1. 3.1 Result Comparison: SR Stress Reduced From 69V to 29.6V
    2. 3.2 Waveform Analysis: Dynamic Switching of the SR On-Time and Early Turn-Off
  6. 4Conclusion
  7. 5References

1 Issue Description: Abnormal SR Voltage Stress Under Output Short-Circuit

The LLC resonant converter is widely used due to its high efficiency and soft switching characteristics, and its synchronous rectification (SR) technology can further improve the overall efficiency. However, under extreme failure conditions such as output short-circuit, the SR may be at risk of over-voltage damage due to abnormal operating conditions. This chapter will analyze in particular the phenomenon and root cause of this issue.