PFC Controller Circuit With Improved Input Current Sensing
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Solution Overview
Problem
Conventional power factor correction (PFC) converters in off-line power supplies face inefficiencies in input current sensing, which affects their ability to maintain current in phase with AC voltage, leading to suboptimal power factor correction and increased power consumption.
Innovation Solution
A controller is introduced that generates a switch control signal by combining output voltage error signals with instantaneous input voltage and current sensing signals, using a gain modulator and comparator to form a switch modulation signal, allowing for improved input current sensing and regulation, thereby reducing power consumption and enhancing operational efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current sensing resistor is used to sense input current in conventional PFC converters, then the input current can be monitored, but the sensing accuracy is insufficient leading to suboptimal power factor correction
Solution Approach 1:
The patent introduces an intermediary current source that draws current from the output node of the gain modulator, where this current is representative of the instantaneous input current sensing signal. This intermediary current source enables more accurate current sensing by utilizing the existing voltage at the output node, which already contains information about both the input voltage and current, without requiring additional sensing resistors that would increase power consumption.
Solution Approach 2:
The voltage at the output node of the gain modulator serves multiple functions: it represents the instantaneous input voltage sensing signal, the instantaneous input current sensing signal, and the output voltage error signal all combined. By utilizing this multi-functional voltage signal, the patent achieves improved current sensing accuracy while avoiding the need for separate sensing circuits that would increase power consumption.
2Productivity
If conventional current sensing methods are used, then the circuit structure is simple, but the operational efficiency of the PFC converter is reduced
Solution Approach 1:
The patent merges the current sensing function with the existing gain modulator and output voltage regulation circuitry. The controller combines the output voltage error signal with the instantaneous input voltage sensing signal using a gain modulator, and then uses a current source to draw a current representative of the input current from the same output node. This merging of functions improves operational efficiency without significantly increasing device complexity.
Solution Approach 2:
The patent implements a feedback mechanism where the voltage at the output node of the gain modulator, which contains information about the input current, is used to control the timing of the switch control signal through a comparator. This feedback loop enables precise control of the input current to maintain it in phase with the AC voltage, thereby improving operational efficiency while using the existing controller structure.
3Reliability
If the input current is not precisely controlled, then the circuit operation is simpler, but the power factor correction performance deteriorates
Solution Approach 1:
The patent uses a feedback mechanism where the voltage at the output node of the gain modulator is fed to a comparator that compares it with a ramp signal to generate a switch modulation signal. This feedback loop ensures that the input current is precisely controlled to track the input voltage waveform, improving power factor correction performance. The feedback utilizes existing signals in the control circuit, minimizing additional complexity.
Solution Approach 2:
The patent replaces traditional mechanical or resistive current sensing methods with an electronic signal processing approach. Instead of using a current sensing resistor that converts current to voltage, the system uses a current source that draws current representative of the input current from the gain modulator output node, and uses electronic comparison with a ramp signal to control switching. This substitution improves measurement precision and power factor correction performance while maintaining reasonable circuit complexity.
Data Source
AI summary
A power factor correction controller for a switching power supply is disclosed. The controller is configured to generate a switch control signal for modulating an input current to form an output voltage across an energy storage element. A gain modulator is configured to combine an output voltage error signal with an instantaneous input voltage sensing signal. A current source is configured to draw a current signal from an output node of the gain modulator, wherein the current signal is representative of an instantaneous input current sensing signal. Thereby a voltage at the output node is representative of the instantaneous input voltage sensing signal, the instantaneous input current sensing signal and the output voltage error signal. A comparator is configured to compare the voltage at the output node to a ramp signal to form a switch modulation signal that controls timing of the switch control signal.