Regenerative Current Detection Circuit Using MOSFET Body Diodes
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Solution Overview
Problem
Existing motor current detection methods face challenges in accurately detecting regenerative current, particularly at high currents, due to the use of external sense resistors and reduced detection accuracy when relying on drain-source voltage of output power MOS transistors.
Innovation Solution
A regenerative current detection circuit utilizing a current mirror configuration with body diodes and feedback amplifiers to accurately detect regenerative current by comparing currents flowing through power MOS transistors, eliminating the need for external resistors and enhancing detection accuracy across a wide current range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an external sense resistor is used to detect motor current, then the motor current can be detected as a voltage between both ends of the sense resistor, but the number of components increases and detection accuracy is reduced at high currents
Solution Approach 1:
The patent extracts the current detection function from the external sense resistor and relocates it to the body diode of the low-side power MOS transistor. This eliminates the need for external sense resistors while maintaining detection capability, directly resolving the contradiction between component count and detection accuracy
Solution Approach 2:
The body diode of the low-side power MOS transistor serves dual functions: as a necessary component for the power circuit operation and as a current detection element. This multi-functionality eliminates the need for separate sense resistors, reducing component count while enabling accurate current detection
2Device complexity
If the drain-source voltage of an output power MOS transistor is used to detect motor current, then the number of components is reduced, but the detection accuracy of regenerative current is reduced
Solution Approach 1:
The patent introduces body diodes as intermediary elements that convert the difficult-to-measure drain-source voltage into an easily measurable voltage across the body diode during regenerative braking. This intermediary approach maintains component simplicity while dramatically improving regenerative current detection accuracy
Solution Approach 2:
The patent changes the detection parameter from drain-source voltage (which has poor linearity and accuracy during regenerative braking) to body diode voltage, which provides excellent linearity and accuracy. This parameter change resolves the contradiction by maintaining simple circuit topology while achieving high detection precision
3Measurement precision
If a sense resistor is inserted between motor and drive circuit to detect current, then current detection is achieved, but external components are required and detection accuracy deteriorates in high current areas
Solution Approach 1:
The patent extracts the current sensing function from external sense resistors and relocates it to the integrated body diode of the power MOS transistor. This eliminates the harmful effects of external resistors at high currents while maintaining accurate detection capability
Solution Approach 2:
The patent utilizes the composite structure of the power MOS transistor, specifically the body diode formed within the transistor structure, to achieve current detection. This integrated approach eliminates the need for separate sense resistors and provides accurate detection across the full current range including high current conditions
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
The proposed solution enables high-accuracy detection of regenerative current, reducing component count and improving detection precision across both low and high current ranges without the limitations of external resistors or reduced accuracy in high current areas.
Implementation Method 1
a first power MOS transistor that is configured as a current mirror to a second power MOS transistor connected to drive a motor winding
Implementation Method 2
a first feedback amplifier that compares a first regenerative current that flows in the first power MOS transistor with a second regenerative current that flows in the second power MOS transistor and outputs a comparison result
Data Source
AI summary
A regenerative current detection circuit includes a first power MOS transistor that is configured as a current mirror to a second power MOS transistor connected to drive a motor winding, a first feedback amplifier that compares a first regenerative current that flows in the first power MOS transistor with a second regenerative current that flows in the second power MOS transistor and outputs a comparison result, the first regenerative current being obtained by multiplying the second regenerative current by a current mirror ratio, and a current detection circuit that outputs a detection current based on the comparison result.