Secondary Switch Hold-Time Control for Zero-Voltage Switching

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Solution Overview

Problem

Existing power converters face challenges in achieving zero voltage switching (ZVS) without primary to secondary communication, limiting efficiency improvements.

Innovation Solution

Dynamically controlling a secondary switch using a ZVS on-time calculator that calculates the secondary switch hold time based on measurable quantities like forward pin voltage and output voltage, eliminating the need for primary to secondary communication.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If conventional switching control is used in power converters, then the device complexity is low, but switching losses increase and efficiency decreases

Engineering Contradiction:

Improveswitching lossesVSAvoidcontrol circuit complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The secondary switch automatically generates the hold time signal based on local voltage measurements (forward pin voltage and output voltage) without requiring external control signals from the primary side. The circuit serves itself by using its own operational parameters to generate the timing control, eliminating the need for complex primary-to-secondary communication while achieving zero voltage switching

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The invention dynamically adjusts the secondary switch hold time based on real-time voltage parameters. By measuring the forward pin voltage and output voltage, the system calculates and adapts the hold time duration to maintain zero voltage switching conditions across varying operating conditions, thereby reducing switching losses without fixed complex control logic

Inventive Principle:

Principle #35Parameter changes

2Productivity

If zero voltage switching is implemented without primary to secondary communication, then efficiency improves, but the ability to achieve ZVS is limited

Engineering Contradiction:

Improvepower conversion efficiencyVSAvoidZVS achievement reliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The secondary switch control implements local feedback by continuously monitoring the forward pin voltage and output voltage. This feedback mechanism allows the circuit to automatically adjust the hold time to maintain zero voltage switching conditions without requiring communication from the primary side, ensuring reliable ZVS achievement while improving efficiency

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The secondary switch is turned on before the primary switch turns off, preparing the circuit for zero voltage switching. By anticipating the switching event and pre-positioning the secondary switch based on voltage measurements, the system ensures smooth transitions and reliable ZVS without waiting for primary side signals

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS20250337336A1Dynamically controlling a secondary switch to achieve zero voltage switching

Publication Date: 2025.10.30 POWER INTEGRATIONS INC

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 calculate a required secondary switch hold time. By measuring a forward pin voltage when the primary switch is conducting, the required secondary switch hold time may be determined without the need for primary to secondary communication.