Constant On-Time Flyback Converter Primary Side Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional flyback converters face challenges in switch-on time control due to complexity in detecting primary side information, leading to delayed switch-on and reduced efficiency, and are limited by signal transmission errors, making them unsuitable for high switching frequency applications.
Innovation Solution
A constant on-time flyback converter design where the primary controller calculates and controls the switch-on time, allowing direct access to primary side information and eliminating the need for secondary controller-mediated signal transmission, thereby reducing computational complexity and avoiding transmission errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the secondary controller computes and transmits switch-on time instructions through the isolator, then the converter can operate with isolated control, but the signal transmission introduces errors and requires additional blanking time that limits high switching frequency applications
Solution Approach 1:
Instead of having the secondary controller compute and transmit the switch-on time instruction to the primary controller, this patent inverts the control flow by having the primary controller directly generate the switch-on time instruction based on primary side detection. This eliminates the need for secondary controller computation and signal transmission through the isolator, thereby removing transmission errors and blanking time requirements, enabling high switching frequency operation.
2Reliability
If the secondary controller detects primary side information through resistors and parasitic capacitors, then the converter can achieve isolated detection, but the RC time delay effect causes synchronous rectifier delay and reduces efficiency
Solution Approach 1:
This patent extracts the detection function from the secondary controller and relocates it to the primary controller. The primary controller directly detects primary side information such as switch node voltage and current through dedicated detection circuits, eliminating the need for resistors and parasitic capacitors on the secondary side. This removes the RC time delay effect entirely, allowing the synchronous rectifier to operate without delay and maximizing efficiency.
3Reliability
If the secondary controller computes switch-on time based on transmitted signals, then the converter can maintain isolated control architecture, but the computational complexity increases and direct primary side information access is lost
Solution Approach 1:
The primary controller performs self-service by directly detecting primary side information and autonomously computing the switch-on time instruction without requiring complex computations from the secondary controller. The primary controller uses its own detection capabilities to obtain switch node voltage and current, then calculates the appropriate switch-on time based on these local measurements, simplifying the overall control architecture while maintaining isolated operation.
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 design simplifies switch-on time control, enhances efficiency by eliminating detection delays, and enables operation in high switching frequency scenarios, expanding the converter's application range.
Implementation Method 1
A primary coil on a primary side of a transformer of the flyback converter is directly connected to an input voltage during the switch on stage. When the current in the primary coil and the magnetic field in the transformer's magnetic core increases, the energy is stored in the magnetic core.
Implementation Method 2
During the switch off stage, the current in the primary coil is zero, and the magnetic field in the magnetic core begins to decrease. A positive voltage is induced at the secondary coil. The diode on the secondary side is in a positive bias state and conducts.
Data Source
AI summary
When a constant on-time flyback converter is in the switch-on stage, the gate voltage of the switch and the input voltage of the flyback converter adopt the primary side of the transformer to control. The gate voltage is controlled by the second control signal generated by the controller. The flyback converter is then turn off to enter the switch off stage. When the flyback converter is in the switch off stage, the secondary side controller on the secondary side of the transformer, based on the output voltage and output current of the secondary side, sends a first control signal to the primary side controller to control the main switch to turn on. Thus, the flyback converter enters the switch-on stage. Therefore, the calculation complexity is reduced, and there is no need to set a blanking time, such that the flyback converter can be used in high switching frequency applications.