Coupled-Inductor Phase Current Sensing for Power Supplies
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional phase-current sense circuits in power supplies suffer from inaccuracies due to temperature and current-induced changes in inductance and series equivalent resistance, leading to time-constant mismatches that cause distortion in sense voltage, affecting feedback loop performance and over-current protection activation.
Innovation Solution
A coupled-inductor structure with a primary winding and an auxiliary winding configured for magnetic coupling, where the sense voltage is generated based on the leakage inductance, reducing the impact of temperature and current variations, and allowing for a smaller phase inductor and higher over-current protection threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional phase-current sense circuits are used, then the circuit structure is simple, but the sense voltage accuracy deteriorates due to time-constant mismatches caused by temperature and current variations
Solution Approach 1:
An auxiliary winding is introduced as an intermediary element magnetically coupled to the phase inductor. This auxiliary winding generates a sense voltage that is magnetically coupled to the phase current, serving as a mediator between the phase current and the control circuit. The sense voltage from the auxiliary winding accurately reflects the phase current without being affected by the time-constant mismatches that plague conventional direct sensing circuits.
Solution Approach 2:
The patent replaces the conventional electrical sensing approach (direct voltage measurement across sense impedance) with a magnetic coupling approach. Instead of measuring electrical parameters directly in the phase current path, the system uses magnetic field coupling through the auxiliary winding to obtain an accurate representation of the phase current, substituting electrical measurement with magnetic interaction.
2Speed
If conventional sense circuits with larger phase inductors are used, then the over-current protection threshold can be set higher, but the response time to load variations becomes slower
Solution Approach 1:
The auxiliary winding acts as a magnetic intermediary that provides a low-inductance path for sense voltage generation. This allows the system to achieve fast response times (characteristic of smaller inductors) while maintaining the ability to detect high over-current conditions (capability of larger inductors), as the auxiliary winding's magnetic coupling reflects the phase current accurately without the sluggish response of large inductors.
3Speed
If the phase inductor size is reduced to improve response time, then the response speed increases, but the inductance becomes insufficient for proper current limiting
Solution Approach 1:
The patent segments the inductance function into two separate components: the phase inductor (optimized for fast response with smaller inductance) and the auxiliary winding (which provides the magnetic coupling for accurate current sensing). This segmentation allows each component to be optimized independently - the phase inductor for speed and the auxiliary winding for sensing accuracy - resolving the contradiction between response speed and inductance magnitude.
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 configuration results in faster response times to load variations, reduced settling times, and improved accuracy of sense voltage tracking, minimizing the risk of premature or delayed over-current protection activation, thus enhancing the stability and reliability of the power supply.
Implementation Method 1
an auxiliary winding magnetically coupled to a phase inductor of a power supply
Data Source
AI summary
In an embodiment, a coupled-inductor structure includes first and second windings. The first winding is configured to conduct a phase current, has a first node configured for coupling to a phase node of a power supply, and has a second node configured for coupling to an output node of the power supply and to a first node of a sense impedance that is configured to generate a sense signal representative of the phase current. And the second winding is configured for magnetic coupling with the first winding, has a first node coupled to the first node of the first winding, and has a second node configured for coupling to a second node of the sense impedance. For example, the first winding may be a phase inductor of a switching power supply, and the impedance may be a capacitor that generates a sense voltage representative of the phase current.