Bridgeless PFC Current Sampling Circuit With Single-Resistor Switching
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Solution Overview
Problem
Conventional bridgeless PFCs require two current sampling circuits, leading to increased circuit complexity, high-frequency switching losses, and occupation of limited high-frequency input/output pins of the controller.
Innovation Solution
A single sampling resistor is used in conjunction with first and second current sampling modules, each comprising a transformer, sampled current phase switching units, and main current freewheeling units, allowing for separate sampling circuits in each half cycle without requiring high-frequency PWM control signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two current sampling circuits are used to sample different current paths in positive and negative half cycles, then current sampling accuracy is improved, but circuit complexity increases
Solution Approach 1:
The patent combines two separate current sampling circuits into a single integrated sampling circuit that can handle both positive and negative half cycles. The single sampling circuit includes switching elements that are controlled to connect different current paths to the same sampling resistor based on the AC cycle phase, thereby reducing component count while maintaining sampling capability for both half cycles
Solution Approach 2:
The single current sampling circuit is designed with multi-functional switching capability to serve dual purposes: sampling current during positive half cycles and sampling current during negative half cycles. The switching elements enable the same sampling circuit to adaptively connect to different current paths depending on the operating phase, making one circuit perform the function of what would traditionally require two separate circuits
2Speed
If high-frequency PWM control signals are used to control switches in sampling circuits, then switching speed is improved, but switching losses increase
Solution Approach 1:
Instead of using continuous high-frequency PWM control signals, the patent employs periodic control where the switching elements are activated only during specific phases (positive or negative half cycles) at lower frequencies. The switching frequency is synchronized with the AC input frequency rather than using high-frequency PWM, thereby reducing switching frequency while maintaining adequate current sampling performance during each half cycle
3Measurement precision
If two current sampling circuits are implemented, then current sampling accuracy is improved, but occupation of high-frequency IO pins increases
Solution Approach 1:
The patent merges the control functions for both half-cycle sampling into a single controller interface. The single current sampling circuit requires only one set of high-frequency IO pins for control signals, whereas two separate sampling circuits would require two independent control interfaces and double the number of high-frequency pins. The switching elements are controlled through a unified control scheme that shares the available IO resources
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
Reduces circuit complexity, minimizes switching losses, and frees up high-frequency IO pins of the controller, enhancing overall design flexibility.
Implementation Method 1
The first transformer T1 includes a first primary winding N11 and a first secondary winding N12 coupled with the first primary winding N11
Data Source
AI summary
A current sampling circuit for a bridgeless power factor corrector is provided. The current sampling circuit comprises a sampling resistor, a first and second current sampling modules. In the first and second current sampling modules, primary windings of transformers are respectively serially connected to a first and second fast switches of the bridgeless power factor corrector. In a positive half cycle of the AC power, a second sampled current phase switching unit is turned on to form a second sampling circuit, and a first main current freewheeling unit is turned on to form a freewheeling path of a first transformer. In a negative half cycle of the AC power, a first sampled current phase switching unit is turned on to form a first sampling circuit, and a second main current freewheeling unit is turned on to form a freewheeling path of a second transformer.