Buck-Boost Converter Overcurrent Detection With One Shunt Resistor
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Solution Overview
Problem
Existing buck-boost switching converters require two shunt resistors for overcurrent detection, which occupy space, dissipate power, and increase package size and pin count, particularly in discontinuous current mode.
Innovation Solution
A controller and control method that utilizes a single shunt resistor and a low-pass filtering circuit to detect overcurrents by averaging the resistor current, eliminating the need for one of the shunt resistors and reducing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two shunt resistors are used for overcurrent detection in buck-boost switching converters, then accurate overcurrent detection is achieved, but device complexity, package size, and power consumption increase
Solution Approach 1:
The patent merges the functions of two separate shunt resistors into a single shunt resistor by utilizing the capacitor's voltage to represent the second current. The control circuit processes the voltage from one shunt resistor and the capacitor voltage together to detect both inductor current and output current, eliminating the need for a second physical shunt resistor while maintaining detection accuracy
Solution Approach 2:
The patent introduces a capacitor as an intermediary element that stores energy and provides a voltage signal proportional to the output current. This capacitor acts as a mediator that enables the single shunt resistor to indirectly measure both currents through voltage processing, avoiding the need for direct current sensing with two resistors
2Measurement precision
If two shunt resistors are used for overcurrent detection, then accurate measurement is achieved, but the package size and pin count increase
Solution Approach 1:
The patent combines the current sensing function into a single shunt resistor configuration, reducing the number of external components and their associated packaging requirements. The integrated approach using one shunt resistor and the existing capacitor reduces the overall package footprint and pin count while maintaining dual-current measurement capability
3Measurement precision
If two shunt resistors are used for overcurrent detection, then comprehensive current monitoring is achieved, but power consumption increases
Solution Approach 1:
The patent consolidates the power dissipation of two shunt resistors into a single shunt resistor. Since power loss in shunt resistors is proportional to the square of the current and the resistance value, reducing from two resistors to one directly reduces the total power dissipation while maintaining the ability to monitor both inductor and output currents through integrated voltage processing
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 costs, space, and power consumption while maintaining accurate overcurrent detection, with rapid response times and reduced false positives.
Implementation Method 1
a low-pass filtering circuit configured to couple to the shunt resistor and to generate a filtered electrical quantity based on the voltage at the shunt resistor
Implementation Method 2
the shunt resistor is subject to a voltage and is traversed by a resistor current
Data Source
AI summary
A controller for a buck-boost switching converter, which includes an inductor and a shunt resistor and is coupled to a load which draws a load current, includes a control circuit which performs charge and discharge cycles of the inductor. A first comparator stage generates a first signal which is indicative of a direction of the resistor current during the charge and discharge cycles. A low-pass filtering circuit generates a filtered electrical quantity based on a voltage on the shunt resistor during the charge and discharge cycles. A second comparator stage generates a second signal indicative of a comparison between the filtered electrical quantity and a reference electrical quantity. A detection stage detects the occurrence of an overcurrent in the load based on the second signal.