Synchronous Flyback Converter Current Sensing Without Auxiliary Winding
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Solution Overview
Problem
Existing flyback converter circuits for illuminants, such as LEDs, require complex and costly auxiliary windings for current detection, leading to imprecise current output regulation.
Innovation Solution
A flyback converter circuit with a first controllable switch and an external capacitor, a second controllable switch, and a transformer, where the second switch is switched off when the current reaches a negative value, and the discharge rate of the capacitor is measured to determine the current flowing through the second switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an auxiliary winding is used for current detection, then the current output to LEDs can be regulated, but the structure becomes complex and expensive
Solution Approach 1:
The patent extracts the current detection function from the auxiliary winding and implements it through the discharge current of the capacitor, which is naturally present in the circuit. By removing the auxiliary winding and using the existing capacitor discharge current for measurement, the patent simplifies the circuit structure while maintaining current detection capability
Solution Approach 2:
The capacitor in the circuit serves dual purposes: it functions as a timing element for the switching cycle and simultaneously provides the discharge current that carries information about the secondary-side current. This self-service approach eliminates the need for separate detection components
2Reliability
If the current output is established based on voltage from auxiliary winding, then galvanic isolation is maintained, but the current regulation precision deteriorates
Solution Approach 1:
The patent uses the capacitor discharge current as an intermediary that indirectly reflects the secondary-side current information. This discharge current serves as a mediator between the primary and secondary sides, providing accurate current information without requiring direct voltage measurement from the secondary side, thus maintaining both isolation and precision
3Loss of energy
If a synchronous flyback converter is used to discharge parasitic capacitors, then zero-voltage switching is enabled, but the control complexity increases
Solution Approach 1:
The patent implements feedback by measuring the discharge current of the capacitor and using this information to control the switching of the second switch. The discharge current provides real-time feedback about the energy state of the parasitic capacitor, enabling the controller to optimize switching timing and achieve zero-voltage switching while maintaining manageable control 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 configuration allows for precise control and regulation of output power over a large load range with a simpler and more cost-effective structure, eliminating the need for auxiliary windings and improving current output accuracy.
Implementation Method 1
the current generated in this way for the discharge of the parasitic capacitors depends on the level of the current flowing through the second switch and on the structure of the transformer (inductance L and winding ratio n)
Data Source
AI summary
The present invention relates to a flyback converter circuit (3) which has: a first controllable switch (8) with a capacitor (14); a second controllable switch (11); a transformer (7) with a primary winding (6) which is coupled to the first switch (8) and a secondary winding (10) which is coupled to the second switch (11); a controller (13) which is configured to switch off the second switch (11) when the current through the second switch (11) has reached a negative value after it has decreased to zero, the capacitor (14) being charged after the first switch (8) is switched off and discharged after the second switch (11) is switched off; and means (1) for establishing the discharge rate of the capacitor (14) in order to determine the current flowing through the second switch (11) at the time at which it is switched off.