Flyback Converter On-Time Extension for Voltage Measurement
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Solution Overview
Problem
Flyback converters face challenges in accurately measuring input and output voltages due to voltage distortion, such as ringing, which requires a minimum on-time for voltage settling and measurement, potentially leading to errors in sensing and control, especially under high input voltages or light-load conditions.
Innovation Solution
A system that extends the on-time of the primary switch if it does not exceed a threshold within a specified period, ensuring accurate voltage measurement on reference windings, and uses this measurement to control switching frequency and duty cycle, while disabling voltage measurement when consecutive measurements exceed a threshold, indicating peak charging conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the primary switch on-time is extended to allow voltage settling and measurement, then measurement precision is improved, but productivity deteriorates due to increased on-time requirements
Solution Approach 1:
The system dynamically adjusts the primary switch on-time based on operational conditions. When voltage measurement is required, the on-time is extended to meet the threshold; during normal operation, the on-time returns to its optimal value for power conversion efficiency. This dynamic adaptation resolves the contradiction by making the on-time extension conditional rather than permanent.
Solution Approach 2:
The system implements periodic voltage measurements at specific intervals rather than continuous measurement. The extended on-time is applied only during designated measurement periods, allowing the system to maintain high measurement precision when needed while minimizing the impact on overall productivity by returning to efficient operation between measurements.
2Productivity
If the on-time threshold is lowered to improve productivity, then power conversion efficiency is improved, but measurement precision deteriorates due to insufficient voltage settling time
Solution Approach 1:
The system performs preliminary voltage settling by extending the on-time before the actual measurement is taken. This preliminary action ensures that the voltage has fully settled and stabilized on the reference winding before the measurement begins, guaranteeing measurement precision even when the overall on-time threshold remains low for productivity.
Solution Approach 2:
The system maintains continuous monitoring of voltage conditions and uses the extended on-time only when measurement is required. During normal operation, the system continues efficient power conversion with shorter on-times, ensuring that the useful action of power conversion remains continuous and efficient while occasionally interrupting for measurement when necessary.
3Measurement precision
If voltage measurement is continuously performed, then measurement precision is maintained, but device complexity increases due to additional control logic
Solution Approach 1:
The system extracts the voltage measurement function from continuous operation and performs it only at specific intervals when the extended on-time is applied. By separating the measurement function from continuous power conversion, the system maintains measurement precision while significantly reducing the complexity of control logic required to manage continuous measurement and adjustment.
Solution Approach 2:
The system uses its own extended on-time period to perform self-diagnosis and voltage measurement without requiring external intervention or additional dedicated measurement circuits. The primary switch itself provides the extended on-time needed for measurement, allowing the system to serve its own measurement needs and reducing overall device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures accurate sensing and control of flyback converters, reducing errors and optimizing power conversion efficiency by ensuring sufficient on-time for voltage settling and measurement, and dynamically adjusting based on load and input conditions.
Implementation Method 1
the voltage on the auxiliary winding is proportional to the input voltage... the voltage on the secondary winding is proportional to the input voltage
Data Source
AI summary
The disclosed embodiments provide a system that operates switched-mode power supplies, such as flyback converters. The power supplies may comprise isolated or non-isolated power converters. During operation, the system senses an on-time of a primary switch in the power converter. Upon detecting that the on-time does not exceed an on-time threshold within a first pre-specified period that spans one or more switching cycles, the system extends the on-time during a subsequent switching cycle to at least meet the on-time threshold. The system may then measure the voltage on one or more reference windings of the power converter during the on-time of the subsequent switching cycle, wherein the reference winding may comprise, e.g., an auxiliary winding of the primary winding of the power converter or a secondary winding of the power converter (e.g., in the case of isolated power converters utilizing a transformer).