Constant On-Time Isolated Converter 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 operate efficiently in continuous current mode with synchronous rectifiers, requiring complex compensation circuits and encoding/decoding technologies.
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 encoding/decoding, and allowing independent 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 loop gain and bandwidth are compensated to reduce ripple signal, but signal transmission delay occurs and load voltage cannot be stabilized quickly
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 through the voltage divider. This eliminates the photo-coupler transmission delay and allows immediate voltage stabilization without signal transmission latency.
Solution Approach 2:
The patent implements direct voltage feedback on the secondary side where the controller detects the output voltage in real-time and immediately adjusts the PWM duty cycle accordingly. This closed-loop feedback mechanism eliminates the delay inherent in primary-side detection and photo-coupler signal transmission, enabling faster load voltage stabilization.
2Reliability
If processor and photo-coupler are used to transmit feedback signal from secondary side to primary side, then voltage regulation is achieved, but device complexity increases due to encoding/decoding requirements
Solution Approach 1:
The patent extracts the voltage regulation function from the primary side and relocates it entirely to the secondary side. The controller on the secondary side directly detects output voltage and controls the synchronous rectifier switches, eliminating the need for photo-couplers, encoding/decoding circuits, and complex compensation networks on the primary side.
Solution Approach 2:
The patent uses the transformer's magnetic coupling as an intermediary for power transmission while eliminating the need for additional signal coupling components. The secondary side controller directly controls the switching based on local voltage detection, using the transformer itself as the coupling medium rather than requiring separate signal transmission paths with photo-couplers.
3Loss of energy
If synchronous rectifier is used on secondary side, then rectification efficiency is improved, but continuous current mode control becomes difficult
Solution Approach 1:
The patent implements self-service control where the secondary side controller autonomously detects the output voltage and directly controls the synchronous rectifier switches based on the detected voltage and current conditions. This eliminates the need for complex primary-side control circuits and enables continuous current mode operation through direct local control of the rectifier switches.
Solution Approach 2:
The patent employs dynamic control of the synchronous rectifier switches on the secondary side, where the controller adjusts the switching timing and duty cycle in real-time based on detected voltage and current conditions. This dynamic control enables continuous current mode operation and adapts to varying load conditions, overcoming the limitations of fixed control schemes.
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 fast load transient response and efficient regulation of output voltage and current without the need for complex compensation circuits or encoding/decoding, improving stability and efficiency by directly controlling the electronic switch based on real-time feedback.
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 20 to the controller 22 in the primary side
Data Source
Figure 1
Figure 2
Figure 3A
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.