SLUAAQ7A August   2023  – April 2025 UCC256404

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Theory of LLC Topology Design
  6. 3Burst Mode Operating Control Mechanism
  7. 4Potential ZCS Issue When Exiting Burst Mode
  8. 5Design to External Circuit for Solving ZCS Issue at Burst Transition Period
  9. 6Design to Accurate External Circuit for Solving ZCS Issue at Burst Transition Period_(Option)
    1. 6.1 Test Result of External Circuit for Solving ZCS Issue at Burst Transition Period
  10. 7Summary
  11. 8References
  12. 9Revision History

4 Potential ZCS Issue When Exiting Burst Mode

The ZCS happening can occur when the burst packets are too close to each other. This is can happen when there is less off time before coming out of burst mode and the switching node is still ringing which can cause the low side to turn on with current spikes. Figure 4-1 shows how the ZCS problem occurs as burst packets get closer to each other.

  1. When burst off period is small, the first pulse of the burst packet can turn on under ZCS condition
  2. Minimum burst off can be designed for switching node to be damped and when first pulse of the burst packet can turn on without ZCS
ZCS Issue Mechanism at Burst Operating ConditionFigure 4-1 ZCS Issue Mechanism at Burst Operating Condition