Switched Mode Power Supply Controller Demagnetization Timing
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Solution Overview
Problem
Flyback converter topologies in switched-mode power supplies face efficiency limitations due to power losses in rectifying diodes, particularly at higher powers and small output voltages, which are not effectively addressed by existing methods.
Innovation Solution
A method and controller for determining the demagnetization zero current time in a switched mode power supply using the volt-second balance theorem, allowing for synchronous rectification and reducing the need for additional PWM circuits, thereby minimizing power losses by controlling the switch on the secondary side from the primary side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a rectifying diode is used on the secondary side of the transformer, then the circuit structure is simple, but power loss increases due to forward voltage drop
Solution Approach 1:
The patent changes the operating parameters of the power switch on the secondary side by controlling its switching timing based on the demagnetization current characteristics. The controller adjusts the switching parameters (turn-on and turn-off timing) to achieve synchronous rectification, thereby reducing the forward voltage drop losses associated with using a rectifying diode while maintaining circuit simplicity.
Solution Approach 2:
The patent introduces dynamic control of the power switch on the secondary side by continuously monitoring the demagnetization current and adjusting the switching timing accordingly. This dynamic adjustment allows the circuit to adapt to varying load conditions and minimize power losses, transforming the static rectifying diode function into a dynamically controlled switching operation.
2Loss of energy
If synchronous rectification is implemented with a power switch on the secondary side, then power loss is reduced, but device complexity increases
Solution Approach 1:
The patent merges the control functions for the primary side power switch and the secondary side power switch into a single controller located on the primary side. This integration eliminates the need for a separate secondary side PWM circuit, reducing device complexity while maintaining the benefits of synchronous rectification. The controller uses the demagnetization current information to coordinate both switching operations.
Solution Approach 2:
The primary side controller is designed to perform multiple functions: controlling the primary side power switch, monitoring the demagnetization current, and controlling the secondary side power switch. This multi-functional approach eliminates the need for separate dedicated circuits, reducing overall device complexity while achieving synchronous rectification.
3Loss of energy
If a secondary PWM circuit is added for synchronous rectification, then power loss is reduced, but system cost increases
Solution Approach 1:
The patent combines the control functions into a single primary side controller, eliminating the need for a separate secondary PWM circuit. This merging approach reduces component count, PCB real estate, and overall system cost while maintaining the power loss reduction benefits of synchronous rectification.
Solution Approach 2:
The patent uses the demagnetization current as an intermediary signal that carries information about the transformer's magnetic state. This current waveform serves as a natural timing reference that allows the primary side controller to coordinate secondary side switching without requiring a separate PWM circuit, thereby reducing system cost.
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 approach enhances efficiency by eliminating diode forward voltage drops and reduces system costs by eliminating the need for a secondary PWM circuit, enabling quasi-resonant operation and improved power handling.
Implementation Method 1
a power switch provided in a circuit including a primary side of the transformer is closed and energy provided at an input of the converter is stored in the magnetic field of the transformer
Implementation Method 2
During the conduction phase of the demagnetization current through the rectifying diode, the diode forward voltage drop is responsible for a power loss
Data Source
AI summary
In various embodiments a method is provided for determining a demagnetization zero current time for a switched mode power supply having a transformer, a first side and a second side being galvanically separated from each other and a switched mode power supply controller, the method including: determining a first voltage being applied to one side of the transformer; determining a second voltage provided at the other side of the transformer; determining a time the first voltage is provided to a winding of the transformer; and determining, by a circuit located on the same side of the transformer as the switched mode power supply controller, the demagnetization zero current time using the determined first voltage, the determined second voltage and the determined time.