PFC Converter Inductor Current Detection Circuit
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Solution Overview
Problem
Existing PFC converters face challenges in accurately detecting inductor current, including power loss and increased cost, particularly when using current detecting resistors or transformers, and struggle to effectively correct the power factor while minimizing losses.
Innovation Solution
A PFC converter design that employs on-period and off-period current detecting circuits using current detecting resistors or transformers to sample current values at specific points, allowing for one-point sampling to calculate the average inductor current, thereby reducing power loss and cost while accurately detecting the inductor current, including its DC component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current detecting resistor is used to detect inductor current, then the current can be detected, but power loss increases
Solution Approach 1:
The patent employs periodic sampling of the inductor current at specific moments (when the switching element turns on or off) rather than continuous detection. This periodic action allows the use of a current detecting resistor without causing continuous power loss, as the resistor only draws power during brief sampling intervals rather than continuously.
2Loss of energy
If a current transformer is used to detect inductor current, then power loss is reduced, but the DC component of current cannot be detected
Solution Approach 1:
The patent segments the current detection process into two distinct parts: (1) using a current transformer to detect the AC component of the inductor current, and (2) using a current detecting resistor to detect the DC component during specific switching periods. By segmenting the detection function between these two methods, the system achieves both low power loss and accurate DC component detection.
3Measurement precision
If multiple current detecting circuits are used to detect both AC and DC components, then detection accuracy is improved, but device complexity increases
Solution Approach 1:
The patent makes the current detecting resistor serve multiple functions: it detects the DC component of the inductor current during switching periods, and its output is also used in conjunction with the current transformer signal to obtain the complete current waveform. This multi-functionality eliminates the need for separate detection circuits for AC and DC components, reducing overall device complexity while maintaining detection accuracy.
4Measurement precision
If continuous current detection is performed, then accurate power factor correction is achieved, but power consumption increases
Solution Approach 1:
The patent implements periodic sampling of the inductor current at critical switching moments rather than continuous detection. This periodic action provides sufficient information for accurate power factor correction while dramatically reducing the power consumption of the detection circuit, as the detecting resistor is only active during brief sampling intervals rather than continuously throughout the operating cycle.
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 enables low-cost, low-loss power factor correction by accurately detecting inductor current, reducing power consumption, and simplifying the current detecting circuit, while using a single current transformer to minimize size and cost.
Implementation Method 1
a current detecting resistor R that detects a current flowing through the diode bridge B1
Implementation Method 2
Insert a current transformer into a current path or perform detection using a current transformer in which an inductor is on the primary side
Data Source
AI summary
A low-cost PFC converter capable of detecting an inductor current including a DC component and performing appropriate correction of a power factor with low loss includes a diode bridge that rectifies an AC voltage input from an AC input power supply Vac, a series circuit including an inductor and a switching element, a rectifying and smoothing circuit that is connected in parallel to the switching element and that includes a diode and a smoothing capacitor, and a digital signal processing circuit that performs on/off control on the switching element so that an input current input from the AC input power supply Vac has a similar waveform with respect to an AC voltage. A current flowing through the inductor during an off period of the switching element is detected using a current detecting resistor, and a decreased voltage of the current detecting resistor is sampled at the middle of the off period of the switching element, thereby detecting an average value of the input current.