Synchronous Rectifier Control for Parasitic Inductance Detection Errors
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Solution Overview
Problem
Synchronous rectification in LLC converters can introduce significant current variations that amplify parasitic inductance effects, leading to erroneous detection and operation.
Innovation Solution
Implementing a control method that regulates the detected voltage at the detection node of the synchronous rectifier using ON-time recorder, target-voltage generator, and driver circuits to manage parasitic inductance, ensuring efficient operation by adjusting the ON-time of the synchronous rectifier based on detected voltage and target voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If synchronous rectification is employed to improve conversion efficiency, then conversion efficiency is improved, but parasitic inductance effects are amplified leading to erroneous detection
Solution Approach 1:
The patent introduces an intermediary control circuit between the synchronous rectifier and the detection node. This control circuit includes a current source, integrator, and comparator that work together to generate a compensating signal. The intermediary circuit processes the detection signal and generates a corrected voltage signal that eliminates the erroneous detection caused by parasitic inductance, allowing the synchronous rectifier to maintain high efficiency while achieving accurate detection.
2Loss of energy
If synchronous rectification is used to reduce power loss, then conduction losses are reduced, but current variations amplify parasitic inductance effects
Solution Approach 1:
The control circuit performs preliminary anti-action by generating a compensating signal before the erroneous detection occurs. The current source generates a current proportional to the detection current, the integrator integrates this current to generate a compensating voltage, and the comparator adjusts the control signal to counteract the parasitic inductance effects. This preliminary correction ensures that the synchronous rectifier operates with minimal conduction losses while the harmful parasitic effects are preemptively neutralized.
3Device complexity
If detection node voltage is directly used for control, then control simplicity is maintained, but erroneous detection occurs due to parasitic inductance
Solution Approach 1:
The control circuit implements feedback by continuously monitoring the detection node voltage and adjusting the control signal accordingly. The comparator compares the integrated voltage with a reference voltage and generates a feedback signal that adjusts the current source output. This feedback mechanism ensures that the control circuit maintains simplicity while achieving accurate detection by continuously correcting for parasitic inductance effects based on the actual detection signal.
Data Source
AI summary
A synchronous rectification controller controls a synchronous rectifier with a control node and a detection node. The synchronous rectification controller comprises an ON-time recorder and a differential driver. The ON-time recorder records a previous ON-time in response to a detected voltage at the detection node, and determines first and second regulation periods in an ON time of the synchronous rectifier based on the previous ON-time. The first regulation period occurs prior to the second regulation period. The differential driver drives the control node to regulate the detected voltage to first and second target voltages during the first and second regulation periods, respectively. The first and second target voltages are different from each other.