Current Sensing Circuit for Four-Switch Buck-Boost Convertor
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Solution Overview
Problem
Current current sensing circuits for four-switch buck-boost converters are inefficient due to power dissipation in sensing resistors and require multiple sensing circuits for different operating modes, increasing complexity and cost.
Innovation Solution
A current sensing circuit using a pair of normally-ON transistors and sensing circuits that detect currents through the low side switches, providing a single current sensing signal that represents both input and output currents by switching between different switch nodes during different operating modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sensing resistor is placed in series with the inductor to detect inductor current, then the current sensing function is achieved, but power dissipation increases and efficiency decreases
Solution Approach 1:
The patent extracts the current sensing function from a separate sensing resistor and relocates it to the low-side power switches themselves. By using the inherent on-resistance of the low-side switches as the sensing element, the design eliminates the need for an additional sensing resistor, thereby removing the associated power dissipation while maintaining current sensing capability.
Solution Approach 2:
The low-side power switches serve dual functions: they perform their primary switching function for power conversion while simultaneously acting as current sensing elements. This multi-functionality allows the same component to fulfill both power transmission and current measurement roles, eliminating the need for separate sensing components and reducing overall power loss.
2Adaptability or versatility
If multiple current sensing circuits are used to detect currents through different power switches for different working modes, then all currents can be detected, but device complexity and system cost increase
Solution Approach 1:
A single current sensing circuit is designed to handle multiple working modes (buck, boost, and buck-boost) by sensing currents through different low-side switches depending on the operating mode. The circuit universally detects both output current during buck mode and input current during boost mode using the same sensing architecture, eliminating the need for separate sensing circuits for each mode.
Solution Approach 2:
The current sensing circuit dynamically adapts its sensing target based on the working mode. During buck mode, it senses current through the first low-side switch; during boost mode, it senses current through the second low-side switch. This dynamic switching of sensing targets allows a single circuit to fulfill multiple sensing requirements without increasing complexity.
3Measurement precision
If multiple current sensing circuits are implemented for different power switches, then accurate current detection is achieved, but the system size and cost increase
Solution Approach 1:
The patent merges multiple current sensing functions into a single unified sensing circuit. Instead of implementing separate sensing circuits for each power switch and operating mode, the design combines all sensing requirements into one circuit that selectively senses current through appropriate low-side switches based on the working mode, thereby reducing component quantity while maintaining measurement accuracy.
Data Source
AI summary
A current sensing circuit used in a buck-boost converter having a pair of buck switches and a pair of boost switches, including: a first sensing circuit providing a detection current though a first normally-ON transistor and a second normally-ON transistor, and a second sensing circuit detecting an average of the detection current and providing a current sensing signal in accordance with the average. During a turn ON time of a first low side switch of the pair of buck switches, the detection current represents a current flowing through the first low side switch, the current sensing signal represents an output current. During a turn ON time of the second low side switch of the pair of boost switches, the detection current represents a current flowing through the second low side switch, and the current sensing signal represents an input current.