Flyback Converter Cord Resistance Compensation
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Solution Overview
Problem
Existing flyback converters face challenges in maintaining constant output current due to variations in primary inductor inductance, propagation delays, and parasitics, leading to inaccuracies in peak current detection and increased costs from the use of optical couplers and secondary side control circuits.
Innovation Solution
A flyback converter with primary side control, utilizing a comparing circuit and adaptive current limiter to adjust the peak current and switching frequency, eliminating the need for secondary side control and optical couplers, and incorporating a cord correction circuit to compensate for voltage losses in the charger cord.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If secondary side control with optical coupler is used, then output current regulation accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the control function from the secondary side to the primary side, eliminating the need for optical couplers and secondary side control circuits. The primary side control circuit directly regulates the switching transistor based on feedback from the auxiliary winding, achieving accurate output current regulation without complex isolation components.
Solution Approach 2:
The patent introduces an auxiliary winding as an intermediary element that provides feedback information about the output current to the primary side control circuit. This auxiliary winding acts as a mediator that transfers information about output conditions back to the input side, enabling accurate regulation without direct secondary side control.
2Adaptability or versatility
If primary inductor inductance varies, then manufacturing adaptability is improved, but output current accuracy deteriorates
Solution Approach 1:
The patent employs feedback from the auxiliary winding to continuously monitor and adjust the switching transistor duty cycle based on actual output current conditions. This feedback mechanism compensates for variations in primary inductor inductance, maintaining accurate output current regulation despite manufacturing tolerances in the inductor.
3Ease of operation
If propagation delays and parasitics are present, then real-world operability is improved, but peak current detection accuracy deteriorates
Solution Approach 1:
The patent uses the auxiliary winding to provide advance feedback about the output current status before the main switching cycle completes. This preliminary information allows the control circuit to anticipate and compensate for propagation delays and parasitic effects, maintaining accurate peak current detection despite real-world operational conditions.
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
The solution ensures a constant output current with improved accuracy and reduced costs, insensitivity to temperature, input line voltage, and component variations, while maintaining reliable and efficient power supply operations.
Implementation Method 1
a transformer that converts an input voltage into a different output voltage
Implementation Method 2
When a main power switch in the converter is turned on, a current starts flowing through the primary winding of the transformer. After current ramps up through the primary winding to a peak magnitude and is then cut, a collapsing magnetic field around the primary winding transfers energy to a secondary winding.
Data Source
AI summary
A cord correction circuit in a primary-side-controlled flyback converter compensates for the loss of output voltage caused by the resistance of the charger cord. In one embodiment, a correction voltage is subtracted from a feedback voltage received from a primary-side auxiliary inductor. A pre-amplifier then compares a reference voltage to the corrected feedback voltage. In another embodiment, the correction voltage is summed with the reference voltage, and the pre-amplifier compares the feedback voltage to the corrected reference voltage. The difference between the voltages on the input leads of the pre-amplifier is used to increase the output voltage to compensate for the voltage lost through the charger cord. The flyback converter also has a comparing circuit and a control loop that maintain the peak level of current flowing through the primary inductor of the converter. Adjusting the frequency and pulse width of an inductor switch signal controls the converter output current.