Integrated Current Sensing Circuit for Switching Power Supplies
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Solution Overview
Problem
In integrated switching power supplies, accurately sensing input current is challenging due to high common mode voltages and noisy signals, which can lead to power supply damage and require additional expensive circuitry or impractical resistor matching.
Innovation Solution
A circuit implementation that uses an RC filter in parallel with the input inductor's DC resistance, coupled with internal current sensing circuitry within the integrated circuit, to equalize voltages and measure current with a small bias current, effectively handling common mode voltages from 3 to 50 volts and higher.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional external circuitry such as low offset amplifiers is used to sense input current, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the current sensing function from external circuitry and integrates it directly into the controller's internal architecture. The sense resistor is incorporated within the controller, and the sensing circuitry uses the controller's existing operational amplifier and voltage references, eliminating the need for external low offset amplifiers and reducing overall system complexity while maintaining measurement precision.
Solution Approach 2:
The patent merges the current sensing function with the controller's existing voltage regulation and operational amplifier resources. The same operational amplifier used for voltage feedback is utilized for current sensing through the integrated sense resistor, combining multiple functions into a single integrated circuit and reducing component count.
2Adaptability or versatility
If resistor bridge is used to bring DCR voltages within controller supply voltage range, then adaptability is improved, but manufacturing precision requirements become impractical
Solution Approach 1:
The patent changes the operating parameters of the sensing circuit by using the controller's internal voltage references and operational amplifier to directly measure voltages across the sense resistor. The circuit is designed to operate within the controller's supply voltage range (VCC and GND) by using differential voltage measurement techniques, eliminating the need for external resistor bridges and their associated matching precision requirements.
3Device complexity
If DCR of input inductor is used as current sense resistor, then device complexity is reduced, but measurement precision deteriorates due to high common mode voltages and noisy signals
Solution Approach 1:
The patent introduces a dedicated sense resistor as an intermediary element between the input inductor and the controller's sensing circuitry. This separate sense resistor provides a stable, low-value resistance specifically for current measurement purposes, isolating the sensing function from the inductor's DCR and its associated high common mode voltages and noise, thereby improving measurement precision while keeping the overall circuit simple.
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
Enables precise input current sensing with a simple and cost-effective solution, preventing power supply damage and providing accurate real-time current measurements without the need for external low offset amplifiers or impractical resistor matching.
Implementation Method 1
A circuit implementation that uses an RC filter in parallel with the input inductor's DC resistance, coupled with internal current sensing circuitry within the integrated circuit, to equalize voltages and measure current
Data Source
AI summary
An apparatus for sensing an input current through an inductor includes an RC circuit connected in parallel with the inductor across first and second input pins of an integrated circuit. A voltage monitoring circuit monitors a first voltage at the first input pin of the integrated circuit and monitors a second voltage at the second input pin of the integrated circuit. An op-amp compares the first voltage with the second voltage and generates a control output responsive to the comparison. A current sink circuit responsive to the indication controls the first voltage to substantially equal the second voltage.