Motor Drive Circuit Voltage Constraint Using Regenerative Diodes
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing motor drive circuits face increased costs due to the need for large Zener diodes and capacitors to constrain voltage increases caused by kickback currents, which can lead to MOSFET breakdown.
Innovation Solution
A motor drive circuit with an H-bridge configuration and a voltage constraint circuit that uses regenerative diodes and a reduced-capacity condenser to manage voltage increases, allowing the gate voltage of MOSFETs to be constrained to a threshold voltage, eliminating the need for large Zener diodes and reducing capacitor size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Zener diode is used to constrain voltage increase during kickback, then MOSFET breakdown is prevented, but the size and cost of the Zener diode and condenser must be enlarged
Solution Approach 1:
The patent combines the voltage constraint function with the gate control circuitry by using the gate-source voltage relationship of the MOSFET itself. The gate is connected to the power line through a resistor, creating an automatic voltage constraint mechanism where the gate voltage naturally follows the power line voltage, eliminating the need for separate Zener diode and large condenser components.
Solution Approach 2:
The MOSFET's own gate-source junction serves as the voltage constraint mechanism. When kickback occurs and the power line voltage increases, the gate voltage automatically increases through the resistive connection, maintaining the voltage difference across the gate-source junction within safe limits. The system uses its own components (resistor and MOSFET gate capacitance) to provide the voltage constraint function.
2Reliability
If the condenser capacity is increased to 100 μF to 1000 μF to handle kickback current, then voltage constraint is improved, but cost and device size increase
Solution Approach 1:
The MOSFET's internal gate capacitance serves as the condenser, eliminating the need for external large-capacity condensers. The gate-source capacitance of the MOSFET itself provides the necessary energy storage and voltage smoothing function during kickback events, reducing component quantity and cost.
Solution Approach 2:
The patent recovers the kickback current energy by allowing it to charge the gate capacitance and the condenser connected to the power line. Instead of dissipating the kickback energy as heat through large Zener diodes, the system recovers it by charging available capacitances, reducing the need for large energy-dissipating 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 configuration effectively constrains voltage increases during kickback events, preventing MOSFET breakdown while reducing the size and cost of components, allowing for a low-cost motor drive circuit.
Implementation Method 1
first to fourth regenerative diodes disposed respectively on the first and second source transistors and the first and second sink transistors
Implementation Method 2
the size of the condenser 121 must be enlarged to about 100 μF to 1000 μF
Implementation Method 3
the voltage of the second power line being a voltage that turns off the second source transistor if a current flows from the first source transistor to the second sink transistor
Data Source
AI summary
A motor drive circuit comprises a first power line; a second power line; an H-bridge circuit that includes a first source transistor and a first sink transistor connected serially, a second source transistor and a second sink transistor connected serially, a motor coil connected at a connection point between the first source transistor and the first sink transistor, and first to fourth regenerative diodes disposed respectively on the first and second source transistors and the first and second sink transistors, the H-bridge circuit being connected between the first power line and the ground, the first source transistor and the second sink transistor being switched complementarily to the second source transistor and the first sink transistor; and a voltage constraint circuit connected between the second power line and control electrodes of the first and second source transistors, the voltage constraint circuit constraining increase in the voltage of the control electrodes of the first and second source transistors to a voltage corresponding to the voltage of the second power line, the first and second source transistors being transistors turned on/off in accordance with a voltage difference between an electrode on the first power line and the control electrode, the voltage of the second power line being a voltage that turns off the second source transistor if a current flows from the first source transistor to the second sink transistor.