COT Isolated Converter Secondary-Side Feedback
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Solution Overview
Problem
Conventional isolated converters face challenges in quickly stabilizing load voltage due to delays in feedback signal transmission from the secondary side to the primary side, and they struggle to control output voltage and current effectively in continuous current mode, especially with synchronous rectifiers.
Innovation Solution
The implementation of a constant on-time (COT) isolated converter that directly detects output voltage and current on the secondary side, using a processor and coupling elements to transmit control signals to the primary side, eliminating the need for compensation circuits and encoder/decoder units, allowing for fast regulation of output voltage and current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional feedback control with TL431 and VM compensation circuit is used, then loop gain and bandwidth are compensated to reduce load voltage ripple, but signal transmission delay occurs and load voltage cannot be stabilized quickly
Solution Approach 1:
The patent extracts the feedback control function from the primary side to the secondary side by placing the controller on the secondary side, eliminating the need for photo-coupler signal transmission and VM compensation circuit. The controller directly detects output voltage and current on the secondary side, removing the time delay associated with cross-side signal transmission and compensation circuits.
Solution Approach 2:
The patent implements direct feedback control on the secondary side where the controller continuously monitors output voltage and current, compares them with reference values, and adjusts the synchronous rectifier switches in real-time. This direct feedback mechanism eliminates the delay inherent in conventional primary-side control with photo-coupler signal transmission.
2Device complexity
If processor and coupling elements are used to transmit control signals, then signal encoding and decoding are eliminated, but device complexity changes
Solution Approach 1:
The patent removes the encoder and decoder units from the control system by placing the processor directly on the secondary side. The processor communicates with the primary side through simple coupling elements (resistors or capacitors) that transmit control signals without requiring complex encoding or decoding operations, thereby reducing overall device complexity while maintaining high signal transmission efficiency.
3Loss of energy
If synchronous rectifier is used in secondary side, then rectification efficiency is improved, but continuous current mode control becomes difficult
Solution Approach 1:
The patent places the controller on the secondary side to directly monitor the output current and implement continuous current mode control. The controller detects the current through the synchronous rectifier switches and adjusts their duty cycles in real-time to maintain continuous current flow, making CCM control straightforward while preserving the high efficiency benefits of synchronous rectification.
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 solution enables rapid stabilization of output voltage and current, improves efficiency by eliminating the need for compensation circuits, and allows independent regulation of output voltage and current on the secondary side without signal encoding or decoding, enhancing the converter's responsiveness and efficiency.
Implementation Method 1
a coupling element, positioned between the primary side and the secondary side, to transmit the control signal from the secondary side to the primary side
Data Source
AI summary
The present invention discloses a constant on-time isolated converter comprising a transformer with a primary side and a secondary side. The primary side is connected to an electronic switch and secondary-side is connected to a load and a processor. The processor is connected to a driver on primary side through at least one coupling element and to the electronic switch. The processor receives an output voltage or an output current across the load generating a control signal accordingly. The driver receives the control signal through the coupling element and accordingly changes the ON/OFF state of the electronic switch, regulating the output voltage and the output current via the transformer, where the duration of the ON/OFF state of the electronic switch is determined between the moment control signal changes from negative to positive and the moment it changes from positive to negative to achieve a high-speed load transient response.