Constant On-Time Isolated Converter Secondary Control
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Solution Overview
Problem
Conventional isolated converters with zero/pole compensation circuits face delays in load voltage stabilization due to the processor's location on the primary side and difficulty in controlling in continuous current mode with synchronous rectifiers, leading to inefficient voltage regulation.
Innovation Solution
The implementation of a constant on-time (COT) isolated converter with a processor on the secondary side that directly detects output voltage and current, using a coupling element to transmit control signals to the primary side, eliminating the need for compensation circuits and enabling fast load transient response without the use of encoders or decoders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a processor on the primary side with zero/pole compensation circuit is used, then the system can stabilize load voltage, but there is delay in load voltage stabilization due to signal transmission through photo-coupler and compensation circuit
Solution Approach 1:
The patent introduces a secondary side processor as an intermediary that directly detects load voltage and generates control signals. This eliminates the need for signal transmission through photo-coupler and compensation circuit, thereby reducing delay while maintaining voltage stabilization capability
Solution Approach 2:
The processor function is extracted from the primary side and relocated to the secondary side. This allows direct detection and control of load voltage without involving the primary side signal transmission path, eliminating the delay caused by photo-coupler and compensation circuit
2Loss of energy
If a synchronous rectifier is used on the secondary side, then rectification efficiency is improved, but it becomes difficult to control in continuous current mode (CCM)
Solution Approach 1:
The secondary side processor directly detects the load voltage and generates feedback control signals. This direct feedback mechanism enables precise control of the synchronous rectifier in continuous current mode, overcoming the control difficulty while maintaining high rectification efficiency
Solution Approach 2:
The secondary side processor independently generates control signals for both the primary side electronic switch and the secondary side synchronous rectifier. This self-service capability enables coordinated control of both switches, facilitating continuous current mode operation while preserving rectification efficiency
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 allows for immediate regulation of output voltage and current, enhancing stability and efficiency by directly transmitting feedback from the secondary side to the primary side, thus avoiding the complexities of gain and phase margin compensation.
Implementation Method 1
a coupling element to transmit control signals 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.