Constant On-Time Isolated Converter for Fast Load Transient Response
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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 isolated voltage divider design with TL431 and VM compensation circuit is used, then the system stability is improved through zero/pole compensation, but the load voltage stabilization speed deteriorates due to signal transmission delay
Solution Approach 1:
The patent extracts the voltage detection function from the primary side controller and relocates it to the secondary side, where the controller directly detects the output voltage without needing to transmit feedback signals through the primary side. This eliminates the signal transmission delay and removes the need for complex compensation circuits, achieving fast load voltage stabilization while maintaining system stability.
2Reliability
If processor and photo-coupler are used to transmit feedback signal from secondary side to primary side, then the isolated voltage divider design is achieved, but the control response speed deteriorates due to delay in signal transmission
Solution Approach 1:
Instead of transmitting the feedback signal from the secondary side to the primary side through photo-couplers (conventional approach), the patent inverts the control architecture by placing the controller on the secondary side that directly detects and controls the output voltage. The primary side controller simply generates PWM signals based on this control, eliminating the need for slow feedback signal transmission and achieving fast control response while maintaining isolated feedback design.
3Loss of energy
If synchronous rectifier is used in secondary side, then the rectification efficiency is improved, but the control in continuous current mode becomes difficult
Solution Approach 1:
The patent implements direct voltage feedback control on the secondary side, where the controller continuously monitors the output voltage and adjusts the synchronous rectifier switching accordingly. This feedback mechanism simplifies the control in continuous current mode by directly regulating the output voltage based on real-time detection, making the control strategy straightforward while maintaining high 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 enables rapid stabilization of output voltage and current, improves efficiency by eliminating the need for compensation circuits, and allows independent regulation of the secondary side, enhancing the converter's responsiveness to load transients.
Implementation Method 1
a transformer is used to convert the high voltage AC power to low voltage DC power
Implementation Method 2
transmits it from the secondary side through the photo-coupler to the controller in 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.