Motor Drive Circuit Power Loss Brake Control
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Solution Overview
Problem
Existing motor drive circuits fail to effectively retard the rotation of electric motors, such as those coupled to fans, when they are disconnected or malfunctioning, leading to potential safety hazards and disruptions in airflow environments.
Innovation Solution
A motor drive circuit with a half-bridge arrangement of high side and low side transistors, coupled with a capacitor and a power loss brake control circuit, which senses a threshold voltage drop to generate pulse signals that control the low side transistors, enabling a braking mode that reduces motor rotation by boosting the capacitor voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the motor drive circuit is powered off or malfunctioning, then power consumption is reduced, but the motor rotation speed cannot be controlled and may continue to spin freely
Solution Approach 1:
The circuit captures energy from the collapsing magnetic field in the motor winding before complete power loss occurs. The flyback diode and capacitor are pre-positioned to immediately capture and store this residual energy, enabling the control circuit to maintain operation and activate braking transistors to control motor deceleration even after main power is disconnected.
Solution Approach 2:
A flyback diode is introduced as an intermediary component between the motor winding and the capacitor. This diode enables unidirectional current flow, allowing the circuit to capture reverse polarity voltage from the collapsing magnetic field and transfer it to the capacitor, which then powers the control circuitry needed for braking operation.
2Strength
If the unpowered fan is allowed to spin freely, then mechanical stress on the motor is reduced, but safety hazards increase and airflow environment is disrupted
Solution Approach 1:
The circuit converts the potentially harmful residual energy in the motor winding into a beneficial resource. When power is lost, the collapsing magnetic field generates reverse voltage that is captured by the flyback diode and stored in the capacitor. This previously wasted or harmful energy becomes the power source that enables active braking control, turning the motor's own residual energy into the mechanism that stops it safely.
Solution Approach 2:
The circuit changes the electrical parameters (voltage and current) applied to the motor winding after power loss. By switching from normal driving voltage to a controlled negative voltage generated through the flyback diode and capacitor, the motor's rotation speed parameter is actively changed from free spinning to controlled deceleration, eliminating safety hazards while the motor is in the unpowered state.
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 solution effectively reduces the rotation speed of electric motors during power disconnection or malfunction, enhancing safety and airflow management by maintaining controlled motor operation.
Implementation Method 1
a capacitor coupled to the first current passing node of each one of the high side transistors, the capacitor operable to hold a capacitor voltage
Implementation Method 2
the on condition of the at least one of the low side transistors results in the braking mode of operation during the on condition, and wherein the at least two state transitions results in a voltage boosting operation
Data Source
AI summary
A motor drive circuit for driving an electric motor includes a plurality of driver circuits, each one of the plurality of driver circuit comprising a high side transistor coupled to a low side transistor in a half bridge arrangement, wherein each one of the high side transistors and each one of the low side transistors has a respective control node and respective first and second current passing nodes, wherein the second current passing node of each of the high side transistors is coupled to the first current passing node of a respective one of the low side transistors at a respective junction node, wherein each one of the plurality of driver circuits is operable to drive a respective current out of a respective junction node into a respective winding of the electric motor. The motor drive circuit further includes a capacitor coupled to the first current passing node of each one of the high side transistors, the capacitor operable to hold a capacitor voltage. The motor drive circuit further includes a power loss brake control circuit coupled to receive the capacitor voltage from the capacitor and operable to sense when a power supply voltage to the motor drive circuit is below a threshold voltage and, in a braking mode of operation, the high side transistors are off, and also in the braking mode of operation, when the power supply voltage is below the threshold voltage, the power loss brake control circuit is operable to generate at least one pulse signal having at least two state transitions and operable to communicate the at least one pulse signal to a respective at least one of the control nodes of a respective at least one of the low side transistors, resulting in on and off conditions of the at least one of the low side transistors, wherein the on condition of the at least one of the low side transistors results in the braking mode of operation during the on condition, and wherein the at least two state transitions results in a voltage boosting operation such that the capacitor voltage is a boosted voltage, the boosted voltage higher than a voltage that would be achieved without the at least two state transitions.