Active Clamp Flyback Control Using Computed Clamp Timing
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Solution Overview
Problem
Existing flyback converters with active clamp circuits require additional electrical components on the secondary side for current measurement, making it costly and complex to use simple microcontrollers for controlling the clamp switch.
Innovation Solution
A control unit computes a waiting time for switching the clamp switch based on the inductance of the primary winding, maximum current value, winding ratio, and output voltage, eliminating the need for secondary-side measurements and allowing the use of low-cost microcontrollers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional electrical components are added on the secondary side for current measurement, then measurement precision is improved, but device complexity increases and manufacturing cost increases
Solution Approach 1:
The patent extracts the current measurement function from the secondary side and relocates it to the primary side by measuring the current through the primary winding. This eliminates the need for additional measurement components on the secondary side while maintaining the ability to determine when the secondary current reaches zero, thereby reducing device complexity without sacrificing measurement precision.
Solution Approach 2:
The control unit is designed to perform multiple functions: it controls both the power switch and the clamp switch, measures primary winding current, computes waiting time based on transformer parameters, and determines secondary current status indirectly. This multi-functionality eliminates the need for separate measurement components and simplifies the overall control system.
2Measurement precision
If additional electrical components are added on the secondary side for current measurement, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent removes the need for secondary-side measurement components by extracting the measurement function to the primary side. This reduction in component count directly lowers manufacturing costs while maintaining the necessary measurement precision through alternative measurement and computation methods.
Solution Approach 2:
The patent uses simple, low-cost components such as a basic current sensor on the primary side and a microcontroller that performs computations based on stored transformer parameters. This approach replaces expensive secondary-side measurement hardware with cheaper computational methods, reducing overall manufacturing cost.
3Ease of operation
If waiting time is computed using inductance, maximum current value, winding ratio, and output voltage, then ease of operation is improved, but loss of time increases
Solution Approach 1:
The transformer parameters (inductance, winding ratio) are predetermined and stored in the control unit before operation. The maximum current value is also predetermined. When operation begins, the control unit simply retrieves these stored values and computes the waiting time using the formula, eliminating the need for real-time measurement and complex calculations during operation, thus improving ease of operation while keeping the actual waiting time minimal.
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
Enables zero current and voltage switching without additional measurements, simplifying the control of flyback converters and reducing costs.
Implementation Method 1
The clamp capacitor of the active clamp circuit is configured to store leakage electrical energy of the transformer and when the clamp switch is in the conducting state transfer the stored electrical energy to the secondary side
Implementation Method 2
The control unit is configured to compute the waiting time using an inductance of a primary winding of a transformer of the flyback converter, the maximum current value, a winding ratio of the transformer and an output voltage of the flyback converter
Data Source
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AI summary
The present invention provides a control unit (1) for controlling a flyback converter comprising a power switch (Sw) and an active clamp circuit (3) having a clamp switch (Sa), wherein the control unit (1) is configured to switch the clamp switch (Sa) from the non-conducting state to the conducting state when a waiting time (toff,HS) has elapsed after switching the power switch (Sw) from the conducting state to the non-conducting state, switch the power switch (Sw) from the conducting state to the non-conducting state when a current (ip) flowing through the power switch (Sw) being in the conducting state reaches a maximum current value (Îp), and compute the waiting time using an inductance of a primary winding (L1) of a transformer of the flyback converter, the maximum current value (Îp), a winding ratio (n) of the transformer and an output voltage (Vout) of the flyback converter.