Primary-Side QR Flyback Converter Without Line Sensing
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Solution Overview
Problem
High-power-factor (Hi-PF) quasi-resonant (QR) flyback converters face challenges in achieving low total harmonic distortion (THD) and efficient operation without using costly line-sensing circuitry and analog divider circuitry, which are necessary for meeting stringent market requirements such as EU COC Ver.5 and US DOE Feb.2014 specifications.
Innovation Solution
A primary-side controlled QR flyback converter design that generates a sinusoidal input current, eliminating the need for line-sensing circuitry and analog divider circuitry by using a shaper circuit, bias circuit, and error detection circuit to regulate the DC output current and voltage using only primary-side available quantities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If line-sensing circuitry is used to sense instantaneous rectified AC mains input voltage, then power factor and total harmonic distortion performance is improved, but power loss increases by 10-15 mW which may exceed total power consumption limits
Solution Approach 1:
The patent removes the line-sensing circuitry from the converter system entirely. Instead of sensing the instantaneous rectified AC mains voltage, the system uses only quantities available on the primary side that do not require additional sensing components. This extraction of the problematic line-sensing element eliminates the 10-15 mW power loss while maintaining compliance with power consumption specifications.
Solution Approach 2:
The patent makes the control circuit universally adaptable to different input voltage conditions without requiring voltage-specific sensing. By using primary-side quantities that are inherently available during normal operation, the same control circuitry handles all operating conditions, eliminating the need for separate line-sensing functionality.
2Manufacturing precision
If analog divider circuitry is used for primary side regulation, then output current regulation accuracy is improved, but silicon area increases and cost increases
Solution Approach 1:
The patent removes the analog divider circuitry from the integrated circuit. Instead of using dedicated divider components that occupy significant silicon area, the system achieves regulation accuracy through alternative primary-side control methods that do not require these extracted components.
Solution Approach 2:
The patent creates a simplified control approach that copies the essential regulation function without requiring complex analog divider circuitry. By using primary-side quantities and simplified control logic, the system replicates the regulation accuracy function with minimal silicon footprint.
3Manufacturing precision
If analog divider circuitry is used for primary side regulation, then output current regulation accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts and removes the complex analog divider circuitry from the system. By eliminating this complex component, the overall device complexity is reduced while maintaining regulation accuracy through alternative primary-side control methods.
Solution Approach 2:
The patent changes the control parameters from requiring complex analog division operations to using simpler primary-side quantities. This parameter change simplifies the circuit implementation while maintaining the necessary regulation accuracy for output current control.
Data Source
AI summary
A method controls a power switch and senses a primary current through a transformer primary winding coupled to the power switch and deactivates the switch responsive to the sensed primary current reaching a current sensed reference. A demagnetization mode is initiated responsive to deactivating the power switch. During this mode a first capacitance is charged with a first charging current to generate the current sensed reference. The first charging current is based on a bias signal. A second capacitance is charged with a second charging current to generate the bias signal. The second charging current is based on a compensation signal. A third charging current generates a comparison signal, the third charging current based on the current sensed reference. The compensation signal is based on a difference between the comparison signal and an internal reference and the power switch activated based on a secondary current in a secondary transformer winding.