Motor Drive Brake Control With Periodic Low-Side Switching
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Solution Overview
Problem
Existing motor drive control devices face challenges in arranging components for controlling motors in limited space on control boards while efficiently stopping motors during power shutdowns, and they suffer from high brake currents and transistor overheating due to insufficient brake control.
Innovation Solution
A motor drive control device with a control circuit that generates drive control signals for multiphase coils, an inverter circuit with switching legs, and pull-up resistors, allowing for efficient brake control by periodically switching low-side transistors and high-side transistors, even when power supply voltage drops below a threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a booster circuit is used to generate a booster voltage different from the power supply voltage to control the low-side transistor, then the transistor can be controlled effectively, but the device complexity increases and it becomes difficult to arrange components in limited space
Solution Approach 1:
The patent extracts the voltage level conversion function from a separate booster circuit and integrates it into the pre-drive circuit using a level shift circuit. This eliminates the need for a complex booster circuit with multiple capacitors and ICs, while still achieving effective control of the low-side transistor through proper gate voltage generation.
Solution Approach 2:
The patent merges the voltage level conversion function with the pre-drive circuit by implementing a level shift circuit that converts the control signal voltage level to match the power supply voltage. This integration reduces component count and simplifies the overall circuit architecture while maintaining transistor control capability.
2Speed
If the low-side transistor is forcibly turned on during power shutdown to quickly stop the motor, then the motor stopping speed increases, but the brake current becomes excessively large causing transistor overheating
Solution Approach 1:
The patent implements periodic switching of the low-side transistor during power shutdown instead of continuous conduction. The control circuit periodically turns the low-side transistor on and off, which maintains effective motor braking while allowing the transistor to dissipate heat during off periods, thereby preventing excessive temperature rise and overheating.
Solution Approach 2:
The patent dynamically adjusts the switching behavior of the low-side transistor based on operating conditions. During normal operation, the transistor switches continuously to maintain motor control, while during power shutdown, it employs periodic switching to achieve rapid stopping without sustained high current that would cause overheating.
3Reliability
If a pull-up resistor is used to turn on the low-side transistor during power shutdown, then the motor can be braked effectively, but the brake current is too large causing the transistor to overheat
Solution Approach 1:
The patent replaces continuous conduction through the pull-up resistor with periodic switching action. The low-side transistor is switched on and off periodically during power shutdown, which maintains reliable brake control while reducing average current and preventing overheating.
Data Source
AI summary
A motor drive control device includes a control circuit generating a drive control signal, and a drive circuit driving a motor. The drive circuit includes a plurality of switching legs each including a high-side transistor and a low-side transistor connected in series between a power line and a ground potential, and pull-up resistors each connected between the power line and a control electrode of the low-side transistor. The control circuit performs brake control to generate a drive control signal for turning off the high-side transistor and periodically switching the low-side transistor, when detecting a power supply voltage to be lower than a threshold voltage.