Motor Shutdown Circuit Managing Back Current via Threshold Control
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Solution Overview
Problem
Traditional motor shutdown methods fail to protect the higher gate switch, lower gate switch, and power supply from damage due to back current generated by Back Electromotive Force (BEMF), as they cannot simultaneously manage the voltage of the motor coil and BEMF effectively.
Innovation Solution
A shutdown method that involves controlling the higher and lower gate switches based on threshold voltages, where the storage capacitor is charged during shutdown and discharged when the voltage exceeds a first threshold, and the lower gate switch is turned on when the voltage drops below a shutdown threshold, allowing the back current to flow safely to the lower gate switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the lower gate switch is turned on to divert back current away from the power supply and higher gate switch, then the power supply and higher gate switch are protected from damage, but the back current becomes so large as to damage the lower gate switch
Solution Approach 1:
The patent applies preliminary action by detecting the voltage of the storage capacitor before the shutdown process and comparing it with a predetermined threshold voltage. Based on this advance detection, the control unit determines the appropriate shutdown strategy - either turning off both gate switches or turning on the lower gate switch - thereby preventing damage before it occurs rather than reacting after damage has happened.
Solution Approach 2:
The patent utilizes parameter changes by monitoring the voltage level of the storage capacitor as a key parameter. The control unit changes the shutdown approach based on whether the detected voltage is higher or lower than the threshold voltage, dynamically adjusting the gate switch states to optimize protection while avoiding excessive back current that could damage the lower gate switch.
2Reliability
If a protection diode is configured between the power supply and motor driver to prevent back current, then the power supply is protected, but the back current increases the BEMF which can damage the motor driver
Solution Approach 1:
The patent uses the lower gate switch as an intermediary element to manage back current flow. Instead of relying solely on a protection diode that causes BEMF accumulation, the control unit strategically turns on the lower gate switch to provide an alternative path for back current, thereby protecting the power supply while preventing excessive BEMF buildup that could damage the motor driver.
Solution Approach 2:
The patent implements feedback control by continuously detecting the storage capacitor voltage and using this information to control the gate switch states. The control unit adjusts the shutdown strategy based on real-time voltage feedback, ensuring that back current is managed appropriately without causing harmful BEMF accumulation that would damage the motor driver.
3Reliability
If the higher gate switch is turned off and lower gate switch is turned on during shutdown, then the power supply and higher gate switch are protected, but the back current is so large as to damage the lower gate switch
Solution Approach 1:
The patent applies parameter changes by using the storage capacitor voltage as a decision parameter. The control unit compares the detected voltage with a predetermined threshold and changes the gate switch configuration accordingly - turning on the lower gate switch only when the voltage is below the threshold, thereby limiting back current magnitude and protecting the lower gate switch from damage while still protecting the power supply and higher gate switch.
Solution Approach 2:
The patent uses preliminary action by detecting and comparing the storage capacitor voltage before executing the shutdown sequence. This advance detection allows the control unit to determine the safe shutdown approach, turning on the lower gate switch only when conditions are favorable (voltage below threshold), thus preventing excessive back current that would damage the lower gate switch while still providing protection to other components.
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 method effectively reduces the risk of damage to motor components by managing back current flow, ensuring the motor stops quickly and safely, preventing damage from excessive back current.
Implementation Method 1
When the supply voltage is lower than the BEMF, the back current would be generated inside the motor because of the BEMF
Implementation Method 2
driving the motor when the voltage of the storage capacitor is again larger than the first threshold voltage, such that the storage capacitor starts to discharge
Data Source
AI summary
Disclosed are a shutdown method for motor and a motor driving circuit using the same. The method comprises: shutting down a higher gate switch and a lower gate switch when a supply voltage decreases, such that the storage capacitor is charged via a back electromotive force, wherein the back electromotive force decreases as the motor gradually stops; driving the motor when the voltage of the storage capacitor is again larger than the first threshold voltage; determining whether the voltage of the storage capacitor is lower than a shutdown threshold voltage when the voltage of the storage capacitor is lower than the first threshold voltage, wherein the shutdown threshold voltage is lower than the first threshold voltage; and turning on the lower gate switch when the voltage of the first threshold voltage is lower than the shutdown threshold voltage, wherein the back current is related to the back electromotive force.