Secondary Switch Hold-Time Control for Primary ZVS
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Solution Overview
Problem
Existing power converters face challenges in achieving zero voltage switching (ZVS) for the primary switch without relying on primary to secondary communication.
Innovation Solution
The method involves controlling a secondary switch by calculating its required hold time, which is determined by measuring the forward pin voltage or the ratio of discharge time to charge time during a switching cycle, allowing ZVS of the primary switch without primary to secondary communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If primary to secondary communication is used to achieve zero voltage switching, then switching losses are reduced, but device complexity increases
Solution Approach 1:
The patent extracts the ZVS control functionality from the primary side to the secondary side. The secondary controller independently determines the secondary switch hold time using only secondary side measurements (forward pin voltage or charge/discharge time ratio), eliminating the need for primary to secondary communication while achieving primary switch ZVS.
Solution Approach 2:
The secondary controller performs self-service by autonomously calculating the required secondary switch hold time based on local measurements. It uses the forward pin voltage measurement or the ratio of discharge time to charge time to determine the hold time without external assistance from the primary controller, thereby achieving ZVS without communication infrastructure.
2Device complexity
If secondary switch hold time is calculated using forward pin voltage measurement, then ZVS is achieved without primary to secondary communication, but measurement precision requirements increase
Solution Approach 1:
The patent implements feedback by continuously monitoring the forward pin voltage during the secondary switch hold time. The secondary controller uses this voltage feedback to verify that ZVS conditions are met and to dynamically adjust the hold time calculation, ensuring accurate ZVS achievement despite measurement challenges.
3Device complexity
If secondary switch hold time is calculated using charge and discharge time ratio, then ZVS is achieved without primary to secondary communication, but time measurement precision requirements increase
Solution Approach 1:
The patent utilizes the periodic nature of the charge and discharge cycles in the flyback converter. By measuring the ratio of discharge time to charge time over multiple periodic cycles, the secondary controller can average out timing variations and achieve more precise hold time calculation, reducing the impact of single-cycle measurement errors.
Data Source
AI summary
Zero voltage switching with a secondary switch (e.g., a synchronous rectifier) is described herein. The method allows a secondary side controller to dynamically calculate during a switching period a required secondary switch hold time to effectuate ZVS of a primary switch. By measuring a charge time and a discharge time during a switching period, the required secondary switch hold time may be determined without the need for primary to secondary communication.