Flyback Transformer Inductance Calibration for Accurate Switch Control
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Solution Overview
Problem
Existing flyback converters face inaccuracies in output voltage due to the difference between nominal and actual inductance of the transformer windings, leading to control errors and inefficiencies, especially when using simple microcontrollers for current measurement.
Innovation Solution
A method to calculate the inductance of the primary winding by measuring the switch-on time and maximum current, using DC voltage and maximum current value, allowing for precise control of the power and clamp switches to achieve zero voltage and current switching without additional secondary-side measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If nominal inductance values from data sheets are used for control calculations, then device complexity is reduced, but measurement precision and control accuracy deteriorate due to tolerance deviations of +/- 5% or larger
Solution Approach 1:
The patent applies preliminary action by performing an inductance measurement and storage operation before the actual converter operation. The control unit measures the primary winding inductance during an initialization phase and stores this calibrated value for subsequent control calculations, thereby eliminating the need for complex real-time measurements while achieving high precision control.
Solution Approach 2:
The control unit performs self-calibration by automatically measuring its own primary winding inductance without requiring external measurement equipment. The control unit uses its existing current sensing capabilities to measure the current through the primary winding and calculate inductance based on the applied voltage and measured current, making the system self-sufficient.
2Measurement precision
If additional measurement components are added to achieve accurate current measurement, then measurement precision improves, but device complexity and manufacturing cost increase
Solution Approach 1:
The control unit is designed with multi-functionality, serving both as the control processor and as the measurement instrument. The same control unit that manages switch timing also performs inductance measurement and current sensing, eliminating the need for separate measurement devices and reducing overall system complexity while maintaining high measurement precision.
Solution Approach 2:
The control unit uses its own internal resources to perform measurements. By utilizing its existing current sensing circuitry and processing capabilities, the control unit measures the primary winding inductance and monitors current without requiring external measurement equipment, thereby reducing device complexity while achieving accurate measurements.
3Ease of manufacture
If simple microcontrollers are used for control, then manufacturing cost is reduced, but measurement precision and control accuracy worsen due to inability to perform accurate current measurements
Solution Approach 1:
The simple microcontroller performs preliminary inductance measurement and stores the calibrated value in its memory. This one-time calibration enables the microcontroller to use accurate inductance values in subsequent control calculations without requiring complex real-time measurement capabilities, thereby maintaining both low cost and high precision.
Solution Approach 2:
The control unit implements feedback by continuously monitoring the current through the primary winding using its existing sensing capabilities. This feedback information is used to verify and maintain accurate control based on the pre-measured inductance value, ensuring that simple microcontrollers can achieve precise control through intelligent use of available data.
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 method reduces the tolerance of inductance measurement to +/- 1%, enabling accurate control and efficient operation of flyback converters with active clamp circuits, using low-cost microcontrollers and maintaining efficiency at higher frequencies and voltages.
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 (i.e. it is switched on) transfer the stored electrical energy to the secondary side
Implementation Method 2
Switching the clamp switch in the forward phase to the conducting state and, thus, discharging the clamp capacitor to transfer the previously stored leakage energy of the transformer from the primary winding to the secondary winding of the transformer
Data Source
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AI summary
The invention provides a method for obtaining an inductance of a primary winding (L1) of a transformer of a flyback converter comprising a power switch (Sw) electrically connected in series with the primary winding (L1) of the transformer. The method comprises applying (M1) a DC voltage (Vin) to an input of the flyback converter, switching (M2) the power switch (Sw) from the non-conducting state to the conducting state and measuring a switch-on time until the power switch (Sw) switches from the conducting state to the non-conducting state as a result of the current (ip) flowing through the power switch (Sw) in the conducting state reaching a maximum current value (Îp), and computing (M3) the inductance of the primary winding (L1) of the transformer using the measured switch-on time, the DC voltage (Vin) and the maximum current value (Îp). Further, a control unit for controlling the flyback converter is disclosed.