DC Motor Current Limit Control Using Virtual Ground
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Solution Overview
Problem
Existing DC motor current limit control methods are hindered by the need for high-power precision resistors, which are costly and inefficient, and are prone to measurement inaccuracies due to interference from bypass capacitors and parasitic inductors, limiting the precision and range of current measurement.
Innovation Solution
A current limit control method that generates a reference voltage based on a preset current limit value, compares it with the voltage drop across a power control switch, and controls the power delivery to the DC motor, using a reference voltage generating unit, a comparing unit, and a control unit to accurately limit the motor current without requiring high-power precision resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-power precision resistor is used to detect motor current, then measurement precision is improved, but manufacturing cost increases and energy consumption increases
Solution Approach 1:
The patent uses an operational amplifier to create a virtual copy of the motor current signal through virtual ground technology. Instead of directly measuring the current through a physical resistor, the circuit creates an equivalent voltage signal that represents the motor current, eliminating the need for expensive high-power precision resistors while maintaining measurement accuracy.
Solution Approach 2:
The patent replaces the physical resistor-based current detection method with an electronic signal processing approach using operational amplifiers and virtual ground technology. This substitution transforms the measurement from a direct physical interaction (current through resistor) to an electronic signal equivalent, reducing both cost and power consumption.
2Measurement precision
If a high-power precision resistor is used to detect motor current, then measurement precision is improved, but energy consumption increases
Solution Approach 1:
The operational amplifier creates a virtual representation of the motor current without requiring actual high-power current flow through a detection resistor. The virtual ground technique allows the circuit to sense current information with minimal power dissipation, as the equivalent resistance in the signal path is extremely low.
3Stability of the object's composition
If bypass capacitors are added to stabilize power voltage, then power stability is improved, but measurement accuracy deteriorates due to capacitor current interference
Solution Approach 1:
The patent extracts the capacitor current from the motor current measurement path by using separate circuit paths. The detection circuit is designed to sense only the motor current through the lower MOSFET, while the bypass capacitor operates on a separate path, preventing its charging/discharging currents from interfering with the measurement.
Solution Approach 2:
The patent implements different circuit characteristics in different parts of the circuit. The lower MOSFET path is designed with low on-resistance for accurate current sensing, while the bypass capacitor path is designed with high impedance to prevent interference. This local differentiation allows both functions to coexist without mutual interference.
4Device complexity
If detecting resistor is placed between power supply and motor, then current detection is simplified, but measurement accuracy deteriorates due to parasitic inductor interference
Solution Approach 1:
The patent introduces the lower MOSFET as an intermediary element between the motor and ground. By placing the current detection function in the MOSFET's source terminal, the circuit eliminates the need for a separate detecting resistor and avoids parasitic inductor interference. The MOSFET's low on-resistance serves as the detection element without introducing significant inductance.
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
This approach allows for precise and efficient current limit control of DC motors, reducing energy wastage and manufacturing costs by eliminating the need for high-power precision resistors and minimizing interference from external sources, thereby enhancing measurement accuracy and operational efficiency.
Implementation Method 1
an operational amplifier to generate a voltage signal of an output end of the DC motor through use of a virtual ground
Implementation Method 2
comparing the reference voltage with the voltage drop of a power control switch which drives the DC motor
Data Source
AI summary
A control method of a current limit of a DC motor includes generating a reference voltage according to a preset current limit value of a DC motor; comparing the reference voltage with the voltage drop of a power control switch which drives the DC motor to generate a compare result; and controlling the power delivered to the DC motor according to the compare result in order to limit the current of the DC motor.