Resonant Hybrid Flyback Control With Blanking for Fast Transients
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Solution Overview
Problem
Resonant hybrid flyback converters face issues with early turn-off of the low-side switch due to the inclusion of both magnetizing and reflected secondary currents, which complicates control and can be slow for fast transients, necessitating improved control methods.
Innovation Solution
Implementing a hysteretic control mechanism using a blanking signal that inhibits switch commutation based on sensing primary and secondary currents, with a control circuit determining peak values and deriving a blanking signal to manage switch operation dynamically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the low-side switch on-time is dynamically adapted to the current operating point based on output voltage, then the output window can be achieved, but the response is too slow for fast transients
Solution Approach 1:
The patent implements feedback control by sensing the primary current and comparing it against reference values to dynamically adjust the low-side switch on-time. The control circuit continuously monitors the primary current waveform and adapts the switch timing based on the detected current peaks, enabling fast transient response while maintaining reliable output voltage regulation.
Solution Approach 2:
The patent applies dynamic control by making the low-side switch on-time variable rather than fixed. The control circuit adjusts the on-time duration in real-time based on the detected primary current characteristics and operating conditions, allowing the converter to respond quickly to transients while adapting to different load and line conditions.
2Speed
If hysteretic control is applied to the low-side switch based on magnetizing current, then fast transient response is achieved, but the control complexity increases due to the need to distinguish magnetizing current from reflected secondary current
Solution Approach 1:
The patent introduces an intermediary approach by using the primary current sense waveform as a mediator between the complex current composition and the control decision. The control circuit analyzes the primary current waveform characteristics (peaks, slopes, magnitudes) to indirectly determine the appropriate switch timing without needing to separately measure or distinguish between magnetizing and reflected secondary currents, thus simplifying the control logic.
Solution Approach 2:
The patent replaces complex mechanical or circuit-based current separation methods with electronic signal processing. The control circuit uses electronic analysis of the primary current waveform to extract the necessary timing information, substituting physical current separation mechanisms with computational methods that are easier to implement and control.
3Device complexity
If the low-side switch on-time is kept fixed, then the control is simple, but the reflected secondary current triggers early turn-off reducing the output window
Solution Approach 1:
The patent applies self-service control where the primary current waveform itself provides the timing information needed for optimal switch operation. The control circuit detects the primary current peaks and uses this information to automatically adjust the low-side switch on-time, allowing the system to self-regulate the output window size based on actual operating conditions without complex external control signals.
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
Enables robust hysteretic control across varying load conditions, ensuring efficient zero-voltage and zero-current switching, enhancing converter performance and stability.
Implementation Method 1
a resonant tank circuit includes the primary-side inductance
Implementation Method 2
induce an oscillation-based power transfer via a resonant tank circuit and a galvanic separation
Implementation Method 3
a transformer, comprising a primary winding and a secondary winding
Implementation Method 4
a rectifying circuit
Data Source
Figure 1
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AI summary
Disclosed is a resonant hybrid flyback converter (1). The converter comprises an input capacitor (102) and an output capacitor (111); a high-side, HS, switch (104, Q1) and a low-side, LS, switch (105, Q2); a transformer, comprising a primary winding (106, Lr; 108, Lm) and a secondary winding (109); and a rectifying circuit (110, D). The input capacitor (102), the HS switch (104, Q1) and the LS switch (105, Q2) form a first circuit loop, the LS switch (105, Q2), the primary winding (106, Lr; 108, Lm) and the resonant capacitor (107, Cr) form a second circuit loop; and the rectifying circuit (110, D), the secondary winding (109) and the output capacitor (111) form a third circuit loop. The converter (1) further comprises a first sensing circuit, configured to sense a primary current (304, IHB) through the primary winding (106, Lr; 108, Lm) and the resonant capacitor (107, Cr); a second sensing circuit, configured to sense a secondary current (307, ISEC) through the rectifying circuit (110, D) and the secondary winding (109); and a control circuit (103). The control circuit (103) is configured to determine a positive peak value (305, IMAGpos) for the primary current (304, IHB) in accordance with a closed-loop control of an average of the secondary current (307, ISEC) and a setpoint value (IsECYef) for said average; determine a negative peak value (306, IMAGneg) for the primary current (304, IHB) in accordance with a current-limited and voltage-limited commutation of the switches (104, Q1; 105, Q2); derive a blanking signal (308) that temporally covers a non-zero secondary current (307, ISEC) period; and drive the switches (104, Q1; 105, Q2) in turns in accordance with a dead time (tdead) for the commutation of the switches (104, Q1; 105, Q2), and a hysteretic control of the primary current (304, IHB) between the positive peak value (305, IMAGPOS) and the negative peak value (306, IMAGneg). The hysteretic control is inhibited by the blanking signal (308). The use of the blanking signal enables a hysteretic control of resonant hybrid flyback converters irrespective of the particular load condition.