Dual-Edge Tracking Synchronous Rectifier Control for Resonant Converters
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Solution Overview
Problem
Resonant converters face issues with switching noise and output stability due to negative currents at synchronous rectifier switches, which can lead to failure and impact overall performance, especially when switching frequencies change rapidly.
Innovation Solution
The implementation of dual-edge tracking synchronous rectifier control techniques, where SR switches are controlled based on rising and falling edges of primary side switch signals and voltage across SR switches, generating predictive drive signals to prevent early or late turn-off times, ensuring constant or variable conduction times depending on resonance operation modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If synchronous rectifier switches are controlled with fixed timing, then the control circuit is simple, but negative currents occur causing switching noise and output instability
Solution Approach 1:
The patent implements feedback control by monitoring the voltage across synchronous rectifier switches and using this information to dynamically adjust the turn-off timing of the switches. The control circuit measures the actual voltage conditions and feeds this information back to the timing control mechanism, enabling the system to adapt to varying operating conditions and eliminate negative currents while maintaining output stability.
Solution Approach 2:
The patent transitions from fixed timing control to dynamic timing control by making the turn-off time of synchronous rectifier switches variable based on real-time voltage measurements. The control circuit adjusts the switching timing dynamically according to the measured voltage across the switches, allowing the system to adapt to changing operating conditions such as varying switching frequencies and load conditions.
2Adaptability or versatility
If switching frequency changes rapidly, then the converter adapts to varying load conditions, but negative currents increase causing severe switching noise
Solution Approach 1:
The control circuit continuously monitors the voltage across synchronous rectifier switches and uses this feedback to adjust turn-off timing in real-time. This feedback mechanism ensures that even when switching frequency changes rapidly to adapt to varying load conditions, the control system can compensate by adjusting the timing to prevent negative currents, thereby reducing switching noise.
Solution Approach 2:
The patent implements preliminary action by predicting the optimal turn-off time based on measured voltage conditions before negative currents can develop. The control circuit uses the measured voltage across the switches to anticipate the optimal timing for turn-off, preventing the occurrence of negative currents before they can cause switching noise, rather than reacting after the problem occurs.
3Ease of operation
If SR switches turn off early or late, then timing control is simple, but output stability deteriorates and control circuit may fail
Solution Approach 1:
The patent uses feedback control to monitor the voltage across synchronous rectifier switches and automatically adjust the turn-off timing to optimal values. This feedback mechanism eliminates the need for manual timing adjustments and prevents both early and late turn-off conditions by continuously adapting the timing based on actual voltage measurements, thereby improving control circuit reliability.
Solution Approach 2:
The control circuit performs self-adjustment by automatically modifying its own timing control based on voltage measurements taken from the synchronous rectifier switches. The system uses its own output voltage information to regulate its switching timing, enabling self-correction of timing errors without external intervention, thus maintaining reliability while keeping the control mechanism relatively simple.
Data Source
AI summary
This disclosure provides control techniques for a resonant converter. In one control technique, for switching speeds that are below the resonant frequency of the primary stage of the converter, the switches of the synchronous rectifier (SR) portion (SR switches) of the resonant converter are controlled based on a rising edge of the corresponding primary side switch and the turn off time of a corresponding SR switch. In general, for below resonance operation, each corresponding SR switch will be turned off prior to the falling edge of each corresponding primary side switch, while each corresponding SR switch will be turned on at the rising edge of the each corresponding primary side switch. The conduction time of respective SR switches is generally constant for below resonance operation. In another control technique, for switching speeds that are above the resonant frequency of the primary stage of the converter, the SR switches are controlled based on the falling and rising edges of the voltage across the each corresponding SR switch. In general, for above resonance operation, each corresponding SR switch will be turned off after the falling edge of each corresponding primary side switch, while each corresponding SR switch will be turned on after the rising edge of the each corresponding primary side switch.