Buck PFC Controller On-Time Calculation
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Solution Overview
Problem
Conventional buck PFC AC-DC converters experience input current distortion when the input voltage is less than the output voltage, particularly for low power applications, and require complex current measurement systems to maintain efficiency and compliance with standards like BSI EN61000 series.
Innovation Solution
The proposed solution involves a buck PFC AC-DC converter that calculates the on-time of switches based on measured input voltage, using an open-loop system without precise current sensing, with the on-time proportional to the square of the input voltage or directly proportional to it, and employs NMOS FETs and a reverse bias diode to generate output voltage from an inductor-capacitor node, allowing operation without complex feedback schemes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional buck PFC uses precise current measurement systems, then input current distortion is reduced, but device complexity increases
Solution Approach 1:
The patent extracts and eliminates the complex current measurement system from the buck PFC design. Instead of using traditional precise current sensors and measurement circuits, the invention uses only voltage measurement combined with calculated on-time control, thereby removing the harmful complexity while maintaining low input current distortion through the simplified control approach
Solution Approach 2:
The patent introduces voltage measurement as an intermediary substitute for direct current measurement. By measuring input voltage and using it to calculate the switch on-time, the system achieves current control indirectly without requiring complex current sensing, thus reducing device complexity while maintaining performance
2Power
If buck PFC operates when input voltage is less than output voltage, then voltage conversion is achieved, but input current distortion increases
Solution Approach 1:
The patent applies preliminary action by calculating the switch on-time in advance based on the measured input voltage before the switching operation occurs. This pre-calculated on-time, determined by the formula T_on = k*V_in/(V_in-V_out), ensures proper current waveform generation even when input voltage is less than output voltage, preventing input current distortion before it can occur
Solution Approach 2:
The patent dynamically adjusts the switch on-time parameter based on the input voltage level. By changing the on-time parameter according to the relationship T_on proportional to V_in/(V_in-V_out), the system adapts to different operating conditions including cases where input voltage is less than output voltage, thereby maintaining low input current distortion across the full operating range
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 approach reduces input current distortion and maintains efficiency, meeting standards for low power applications by using an open-loop system that calculates switch on-time based on input voltage, resulting in a smoother output current waveform without the need for precise current sensing, thus optimizing performance and compliance.
Implementation Method 1
an inductor that is coupled to the switch; a capacitor coupled to the inductor, wherein the output voltage is output from a node between the inductor and the capacitor
Implementation Method 2
a measuring circuit that receives and measures the input voltage
Data Source
AI summary
An apparatus for generating an output voltage from an input voltage is provided. The apparatus comprises a switch that receives the input voltage, an inductor that is coupled to the switch, a capacitor coupled to the inductor with the output voltage being output from a node between the inductor and the capacitor, a measuring circuit that receives and measures the input voltage, and a controller that is coupled to the switch and to the measuring circuit. Additionally, the controller receives the measured input voltage and calculates an on-time for the switch based on the measured input voltage and actuates the switch for the on-time.