DC Motor H-Bridge Current Sensing Without Shunt Resistors
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Solution Overview
Problem
The use of shunt resistors for current measurement in motor control is costly and poses layout challenges, necessitating alternative methods to monitor motor current efficiently.
Innovation Solution
Utilizing a bridge circuit of power switches, such as an H-bridge, to measure current through an electric motor by leveraging known relationships between power switch junction temperatures, resistances, and current, eliminating the need for a shunt resistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shunt resistor is used for current measurement, then current monitoring is achieved, but component cost increases and layout complexity increases
Solution Approach 1:
The patent extracts the current measurement function from the traditional shunt resistor approach and integrates it into the existing power switch structure. By utilizing the body diode of the low-side power switch and measuring voltage during dead-time intervals, the system eliminates the need for separate shunt resistors while maintaining current monitoring capability.
Solution Approach 2:
The patent merges the current measurement function with the power switch structure. The low-side power switch's body diode serves dual purposes: its normal switching function and as a measurement element for current sensing. This consolidation eliminates separate measurement components and simplifies the overall circuit layout.
2Measurement precision
If a shunt resistor is used for current measurement, then current monitoring is achieved, but power dissipation increases
Solution Approach 1:
The system uses the power switch's own body diode for measurement purposes, making the existing component serve dual functions. The body diode naturally conducts during dead-time intervals, and this conduction is utilized for voltage measurement without requiring additional active elements or increasing overall power dissipation.
Solution Approach 2:
The patent recovers useful measurement information from the dead-time intervals that would otherwise be non-productive periods in the switching cycle. By measuring voltage across the body diode during these intervals, the system extracts current information without interfering with the main power transmission function.
3Measurement precision
If a shunt resistor is used for current measurement, then current monitoring is achieved, but the number of functional pins is reduced
Solution Approach 1:
The low-side power switch is designed to perform multiple functions: primary power switching and secondary current measurement. The body diode of the power switch serves both its normal rectification function and as a measurement element, eliminating the need for separate dedicated measurement pins or components.
Solution Approach 2:
The measurement function is extracted from the pin structure and integrated into the power switch device itself. By using the body diode and measuring voltage during dead-time, the system eliminates the need for separate shunt resistor connection pins, freeing up pin resources for other functional purposes.
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 accurate current measurement without shunt resistors, reducing component costs, layout constraints, and power dissipation, while allowing for more functional pins and improved ground connections.
Implementation Method 1
measured parameters through the power switches (e.g., a measured voltage drop over a power switch) may be used to determine a level of current through the electric motor
Implementation Method 2
the techniques may also use known or knowable relationships between power switch junction temperatures, power switch resistance, and current through a given power switch
Data Source
AI summary
In some examples, a method comprises controlling power switches to deliver a current to an electric motor, wherein the power switches are arranged in a bridge (e.g., an H-bridge or an h-bridge) comprising a first high-side power switch, a first low-side power switch, and a second low-side power switch. Controlling the power switches to deliver the current to the electric motor may include controlling the first high-side power switch ON and controlling the second low-side power switch ON, wherein the current to the electric motor flows through the high-side power switch and through the second low-side power switch. The method may comprise determining the current to the electric motor based on a voltage drop over one of the power switches arranged in the bridge. One or more aspects of the method may be performed during dead time.