Flyback Converter Primary-Side Drain Voltage Sampling
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Solution Overview
Problem
Existing DC-DC power converter systems face challenges in accurately determining output voltage on the secondary side without introducing additional complexity or cost, particularly in isolated topologies where feedback networks often require optocouplers or additional transformer windings.
Innovation Solution
A method and circuit that measure the drain voltage on the primary side of a flyback power converter with a single synchronized sample event, using a trigger pulse and delay to calculate the output voltage based on transformer turns ratio and other characteristics, eliminating the need for optocouplers and auxiliary windings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optocouplers are used in feedback networks, then output voltage feedback is achieved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the feedback function from the secondary side and implements it on the primary side by measuring the drain voltage of the primary switch. This eliminates the need for optocouplers and auxiliary windings, reducing device complexity while maintaining feedback accuracy through synchronous sampling of the drain voltage waveform
Solution Approach 2:
The drain voltage measurement serves multiple functions: it provides output voltage feedback, indicates switching timing, and characterizes the flyback converter operation. By using the existing drain voltage node for multiple purposes, the patent eliminates dedicated feedback components, reducing overall device complexity
2Measurement precision
If optocouplers are used in feedback networks, then output voltage feedback is achieved, but cost increases
Solution Approach 1:
The patent removes expensive optocouplers from the feedback path and replaces them with a primary-side drain voltage measurement approach. This extraction of the feedback function to the primary side eliminates the need for isolation components, significantly reducing manufacturing cost while maintaining feedback accuracy
Solution Approach 2:
The patent uses inexpensive primary-side circuit elements (switch drain node, timing circuit) to achieve feedback functionality that traditionally required expensive optocouplers. The solution replaces high-cost isolation components with low-cost primary-side measurement and timing circuitry
3Loss of information
If additional windings are added to the transformer, then feedback information is obtained, but device complexity and cost increase
Solution Approach 1:
The patent extracts the feedback information from the transformer secondary side and obtains it on the primary side through drain voltage measurement. This eliminates the need for additional transformer windings, reducing transformer structure complexity while maintaining access to output voltage information through the measured drain voltage waveform
Solution Approach 2:
The patent uses the primary switch and its drain voltage node to provide feedback information that would otherwise require additional transformer windings. The existing primary-side components serve the dual purpose of power switching and feedback information provision, eliminating the need for auxiliary feedback windings
Data Source
AI summary
The disclosure is directed to techniques to determine the output voltage on the secondary side of a power converter. These techniques maintain isolation between the primary and secondary by measuring a voltage on the primary side with a single sample event synchronized to a power cycle of the power converter. A measuring circuit may determine a drain voltage of a primary side switch that controls current to the primary side coil. The measuring circuit may sample the drain voltage at a predetermined delay time from a trigger pulse based on a control signal to the primary side switch. The output voltage may be calculated based on the sampled drain voltage and other characteristics of the flyback converter circuit, such as transformer turns ratio, primary side input voltage and other characteristics. The output voltage calculation does not require auxiliary windings or isolation components, such as an opto-coupler.