Flyback Regulator Primary Side Sensing Sampling
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Solution Overview
Problem
Existing isolated flyback power supplies using primary side sensing for regulation face limitations in accuracy and speed due to dependence on transformer characteristics, leading to inadequate output regulation and increased size and cost with the use of optoisolators for electrical isolation.
Innovation Solution
A power supply regulator system that includes an error circuit, sample and hold circuit, and controller circuit to accurately sample and hold the primary winding voltage during diode conduction, generating an error signal to adjust pulse patterns for precise output voltage control, independent of transformer characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optoisolators are used to maintain electrical isolation for output sensing, then electrical isolation is maintained, but the power supply size increases, cost increases, and regulation speed decreases
Solution Approach 1:
The patent extracts the sensing function from the isolated side and relocates it to the primary side by monitoring the voltage across the primary winding during the off-period. This eliminates the need for optoisolators and secondary-side sensing circuitry, directly resolving the contradiction by maintaining electrical isolation while reducing size and cost.
Solution Approach 2:
The patent uses the transformer's inherent characteristics as an intermediary to transfer output voltage information back to the primary side. By monitoring the reflected voltage on the primary winding during the off-period, the system indirectly senses the output voltage without breaking electrical isolation, thus avoiding optoisolators while maintaining regulation capability.
2Reliability
If traditional primary side sensing is used during off-period, then electrical isolation is maintained, but regulation accuracy and speed are inadequate due to dependence on transformer characteristics
Solution Approach 1:
The patent performs the voltage sampling action at a precisely predetermined moment - immediately when the switching device turns off and before significant voltage drops occur in the secondary circuit. This preliminary sampling captures the reflected voltage before it is degraded by diode and winding losses, thereby improving measurement precision while maintaining electrical isolation.
Solution Approach 2:
The patent implements dynamic sampling that adapts to the switching cycle timing. By capturing the primary voltage at the specific dynamic moment when the switching device transitions off and the diode begins conduction, the system optimizes the measurement window to minimize the influence of transformer characteristics and circuit losses, improving regulation accuracy.
3Reliability
If sampling is done during off-period when primary winding is decoupled, then electrical isolation is maintained, but voltage drops in secondary winding and diode reduce measurement accuracy
Solution Approach 1:
The patent rushes through the critical measurement window immediately at the start of the off-period, before the secondary circuit voltage drops become significant. By capturing the primary voltage signal in this brief window and holding it for processing, the system skips over the period when voltage drops would corrupt the measurement, thereby maintaining both electrical isolation and measurement accuracy.
Solution Approach 2:
The patent uses a sample-and-hold circuit that captures and preserves the voltage measurement taken at the optimal moment. This held value serves as a cushion against subsequent voltage drops in the secondary circuit, allowing accurate regulation decisions to be made even though sampling occurs during the off-period when secondary voltage degradation begins.
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
The system achieves faster and more accurate output regulation with reduced dependence on transformer specifics, enabling efficient operation across a variety of transformers while minimizing errors from voltage drops in the secondary winding and diode.
Implementation Method 1
This techniques works due to inherent characteristics of transformer. These inherent characteristics cause the voltage on the primary winding during this period to be approximately equal to the output voltage of the power supply, times the ratio of turns in the primary and secondary windings.
Data Source
AI summary
A regulator for an isolated flyback power supply using primary side sensing. The regulator may include an error circuit configured to generate an error signal representative of the difference between a target value and a measured value, a sample and hold circuit, and a controller circuit. The controller circuit may be configured to cause the sample and hold circuit to sample the value of a derived signal that is derived from a connection to the primary winding at a time when the primary winding is decoupled from the energy-supplying circuit and the diode is conducting current, and to hold the sampled value at least until the diode stops conducting current. The controller circuit may also be configured to cause the held value to be the measured value used by the error circuit.