Dual-Switch Flyback Converter With Dynamic Primary Current Compensation
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Solution Overview
Problem
Dual-switch flyback converters face challenges in implementing effective primary side regulation due to the dependency of de-magnetizing voltage on input and load voltages, which complicates the compensation of peak current differences between primary and secondary windings.
Innovation Solution
A dual-switch flyback converter design that incorporates two primary side sensing approaches: measuring or deducing the peak current in the primary winding and accounting for the clamping diode current, allowing for accurate secondary side current determination through a controller that calculates the difference in charge release during the freewheeling phase, enabling variable compensation for improved primary side regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If primary side regulation is implemented in a dual-switch flyback converter, then cost and complexity are reduced by eliminating secondary side sensing, but measurement precision deteriorates because the peak current difference between primary and secondary windings cannot be compensated with a fixed correction
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed correction approach to a dynamic correction approach. The correction value is no longer static but varies based on real-time operating conditions. Specifically, the patent uses duty cycle information and current measurements to dynamically adjust the correction applied to the primary current measurement, enabling accurate secondary current estimation despite the variable peak current difference caused by de-magnetizing voltage dependencies on input and load voltages.
Solution Approach 2:
The patent changes parameters by introducing variable correction factors based on operating conditions. Instead of using a constant correction value, the system adjusts correction parameters according to duty cycle and current measurements. This allows the regulation system to adapt to varying input voltages and load conditions, maintaining measurement precision while keeping the control circuit on the primary side.
2Device complexity
If fixed correction is used to compensate peak current difference in primary side regulation, then device complexity is reduced, but measurement precision deteriorates because the de-magnetizing voltage dependency on input and load voltages causes variable current difference
Solution Approach 1:
The patent transforms the static fixed correction into a dynamic correction mechanism. The correction value is continuously adjusted based on duty cycle and current measurements, allowing the system to compensate for the variable peak current difference that arises from de-magnetizing voltage dependencies on input and load voltages.
Solution Approach 2:
The patent implements feedback by using duty cycle information and current measurements to continuously adjust the correction applied to primary current measurements. This feedback loop ensures that the correction remains accurate under varying operating conditions, maintaining measurement precision without increasing overall device complexity.
3Measurement precision
If secondary side sensing is used for current regulation, then measurement precision is improved, but device complexity and cost increase due to required high-voltage insulation and auxiliary circuitry
Solution Approach 1:
The patent uses an intermediary approach by measuring primary current and using duty cycle information as intermediaries to indirectly determine secondary current. Instead of directly sensing secondary current, the system uses the relationship between primary and secondary currents combined with duty cycle measurements to calculate the secondary current, avoiding the need for secondary side sensing circuitry and high-voltage insulation.
Solution Approach 2:
The patent replaces the physical secondary side sensing mechanism with an electrical calculation approach. Instead of using a physical sensor on the secondary side that would require high-voltage insulation, the system uses electrical measurements from the primary side combined with duty cycle information to compute the secondary current, substituting a simpler electrical system for a more complex mechanical/physical sensing system.
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 achieves accurate primary side regulation of the output current at the secondary side without requiring load sensing at the secondary side, enhancing the efficiency and reliability of the converter by accounting for input voltage variance.
Implementation Method 1
a transformer comprising a primary side for connection to an input supply and a secondary side for connection to a load; a first switching circuit at the primary side adapted to allow the primary side to accumulate power from the input supply in a charging phase and to allow the secondary side to release a portion of the accumulated power to the load in a freewheeling phase
Implementation Method 2
a first sensing circuit to sense the primary side current in the charging phase
Implementation Method 3
a second sensing circuit to derive a parameter which depends on the leakage current
Data Source
AI summary
A dual-switch flyback converter in which the output current, in operating regions where a constant output current is required, can be regulated from the primary side. The output current is regulated constantly regardless of the input and output voltages by compensating the peak current in the primary winding with the average current in the clamping diode, or the conduction duration of the clamping diode.