Motor Coil Current Sensing with Voltage Shifted Differential Inputs
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Solution Overview
Problem
Existing current sensing methods for brushless DC electric motors fail to accurately measure bi-directional currents due to clipping by electrostatic discharge protection circuits and parasitic inductances, leading to inaccurate voltage measurements.
Innovation Solution
Implementing current sources and resistors to shift differential voltage within the operating range of programmable gain amplifiers and electrostatic discharge protection circuits, ensuring accurate bi-directional current measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ESD protection circuits are used to protect microcontroller input pins, then the microcontroller is protected from voltage spikes, but negative voltages are clipped by diodes resulting in inaccurate current measurements
Solution Approach 1:
The patent applies preliminary action by shifting the differential voltage from the shunt resistor to a positive voltage range before it reaches the ESD protection circuits. This is achieved by adding a positive voltage (e.g., 2.5V or 3.3V) to the differential signal, ensuring that the voltage never goes negative and thus never triggers the ESD diodes. The ESD protection remains effective for positive voltage spikes while the voltage shifting prevents negative voltage clipping that would cause measurement errors.
Solution Approach 2:
The patent uses an intermediary approach by introducing a voltage shifting mechanism (such as a level shifter circuit or adding a positive bias voltage) between the shunt resistor and the microcontroller input pins. This intermediary shifts the entire differential voltage range to be positive, allowing the signal to pass through the ESD protection circuits without being clipped, thus maintaining both protection and measurement accuracy.
2Measurement precision
If shunt resistors are used to sense current, then current flow can be detected, but the voltage developed is very small requiring conditioning and amplification
Solution Approach 1:
The patent combines multiple functions into a single integrated solution. The voltage shifting mechanism is integrated with the differential amplifier circuit, allowing the signal conditioning to be performed in a unified stage. This merging reduces the overall complexity by eliminating separate conditioning stages and simplifying the signal path from the shunt resistor to the microcontroller.
Solution Approach 2:
The patent applies parameter changes by transforming the voltage range parameters of the differential signal. By adding a positive voltage offset, the signal parameters are changed from a bipolar range (including negative voltages) to a unipolar positive range, making the signal compatible with standard ESD protection circuits and simplifying subsequent amplification and ADC conversion stages.
3Reliability
If voltage is shifted to maintain positive range, then ESD protection circuits function correctly, but additional circuitry is required
Solution Approach 1:
The patent achieves universality by designing the voltage shifting mechanism to serve multiple purposes simultaneously. The same circuit that shifts the voltage to maintain the positive range also provides signal buffering and impedance matching, reducing the need for additional dedicated components. This multi-functionality approach minimizes the increase in device complexity while ensuring ESD protection effectiveness.
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
Ensures accurate measurement of bi-directional currents in electric motor coils, enhancing the microcontroller's ability to monitor and control the motor effectively.
Implementation Method 1
a shunt resistor (105) having a first terminal adaptable for coupling to a switching element configured to provide power to the coil of the electric motor and a second terminal adaptable for coupling to a ground potential
Implementation Method 2
first and second current sources configured to shift a differential voltage to maintain the differential voltage within an operating range of the programmable gain amplifier
Data Source
Figure 1
Figure 2~3
AI summary
Integrated circuitry, such as a microcontroller, for controlling an electric motor includes circuitry for measuring a bi-directional current flowing within a coil of the electric motor. The current is sensed by an externally implemented current sensing element, such as a shunt resistor, to produce a differential voltage that is delivered to input pins of the microcontroller, which are protected by electrostatic discharge protection circuits. Current sources implemented within the microcontroller are coupled to the input pins, and work in concert with external resistors to shift the differential voltage so that it is maintained within an appropriate voltage operating range so that an accurate measurement of the bi-directional current can be made by the microcontroller.