Directly Coupled Inductor Current Sensing in DC-DC Converters
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Solution Overview
Problem
Current DC-DC converters face limitations in reducing size due to the need for multiple output inductors and filter capacitors, leading to inefficiencies in current sensing, increased power and space consumption, and complex designs that hinder further miniaturization.
Innovation Solution
The implementation of a directly coupled inductor with a single current amplifier and a resistive ladder network for current sensing, allowing for accurate current measurement and reduced physical footprint without sacrificing efficiency, using a switching scheme where no two switches are activated simultaneously to minimize inductance and current ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If indirectly coupled inductors are used to reduce physical footprint, then the size of DC-DC converter is reduced, but current sensing accuracy deteriorates and additional series resistance increases
Solution Approach 1:
The patent inverts the conventional indirectly coupled inductor approach by using directly coupled inductors with a different switching scheme. Instead of using indirect coupling with complex sensing requirements, the invention uses direct coupling with alternating switch activation, achieving both compact size and accurate current sensing through this fundamental reversal of the coupling approach.
Solution Approach 2:
The patent changes the switching parameter by ensuring no two switches are activated simultaneously, which is different from conventional approaches. This parameter change in the switching scheme enables accurate current sensing through the DCR of directly coupled inductors while maintaining compact physical footprint, resolving the contradiction between size reduction and sensing accuracy.
2Measurement precision
If multiple output inductors and filter capacitors are used, then current sensing efficiency is improved, but power consumption and device complexity increase
Solution Approach 1:
The patent merges the current sensing function into the power conversion circuit itself by utilizing the DCR of directly coupled inductors. Instead of separate sensing circuits for multiple inductors, the invention combines the sensing function with the inductor structure, using the inductors' inherent resistance for current measurement, thereby reducing overall device complexity while maintaining sensing efficiency.
Solution Approach 2:
The directly coupled inductors serve multiple functions simultaneously: power conversion and current sensing. By making the inductors universal components that perform both power transfer and sensing functions through their DCR, the patent reduces the need for separate sensing circuits, thereby reducing device complexity while maintaining current sensing efficiency.
3Loss of energy
If indirectly coupled inductors with loops are used, then flux canceling effects are achieved, but series resistance increases and efficiency decreases
Solution Approach 1:
The patent extracts the harmful loop structure from the inductor design. By eliminating the closed-loop configuration of indirectly coupled inductors and using open-ended directly coupled inductors instead, the invention removes the source of additional series resistance while maintaining the flux canceling effect through the switching scheme, thereby improving efficiency without excessive structural complexity.
4Device complexity
If DCR sensing is used in prior art circuits, then current sensing is simplified, but accurate sensing cannot take place due to simultaneous current flow
Solution Approach 1:
The patent applies periodic action by alternating the activation of switches in a structured sequence where no two switches are on simultaneously. This periodic switching creates distinct time intervals where current flows through specific inductors, enabling accurate DCR sensing during these intervals. The periodic nature of the switching scheme resolves the timing conflict that prevented accurate sensing in prior art.
Solution Approach 2:
The patent implements feedback by using the voltage developed across the DCR of directly coupled inductors during switch transitions to sense current accurately. The switching scheme is designed to create measurable voltage signals during specific phases, and this feedback information is used to determine current levels, enabling accurate sensing that overcomes the limitations of prior art DCR sensing approaches.
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 enables efficient current sensing, reduces the physical footprint of DC-DC converters, and minimizes current ripple, allowing for smaller designs while maintaining high efficiency and accurate current measurement using industry-standard DCR sensing.
Implementation Method 1
a first inductor coupled to a output filter and a load
Implementation Method 2
a output capacitor coupled to the first and second inductors, the output capacitor operating as a lowpass filter
Data Source
AI summary
A DC-DC converter includes a directly coupled inductor with coil elements and power-switching phases. Each phase includes a high-side and low-side switch, where the high-side switch couples a voltage source to a coil element and the low-side switch couples the coil element to a ground voltage. Each switch is configured to be alternately activated and no two switches are activated at the same time. A current sensor for the DC-DC converter includes a single current amplifier having inputs and an output. The output provides a current sensing signal. The current sensor also includes a single RC network coupled to one of the power-switching phases and a first input of the current amplifier. The current sensor also includes a resistive ladder. The ladder includes, for each of the other power-switching phases, a resistor coupled in parallel to the RC network resistor and to a second input of the current amplifier.