Stepper Motor PWM Timing to Reduce Charge Pump Current
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Solution Overview
Problem
The existing technologies for controlling stepper motors in voltage-controlled or voltage-regulated operating modes face challenges due to the high space requirement and power consumption of charge pumps needed for high-side MOSFET switches, particularly when multiple switches need to be activated simultaneously, leading to large capacitors and increased costs.
Innovation Solution
The method involves delaying the rising and falling edges of PWM voltage pulses within a chopper cycle to prevent simultaneous switching of MOSFET switches, thereby reducing the maximum current required by the charge pump, allowing for smaller capacitors and a more compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple high-side MOSFET switches are activated simultaneously in a bridge circuit, then the motor control performance is improved, but the charge pump current requirement and capacitor size increase significantly
Solution Approach 1:
The patent applies periodic action by introducing a dead time between switching operations of MOSFET switches in the bridge circuit. The switching is performed in alternating phases where one high-side switch is activated, followed by a dead time period, then the other high-side switch is activated. This periodic switching pattern prevents simultaneous activation of multiple switches, thereby reducing the peak current requirement of the charge pump while maintaining effective motor control through sequential PWM voltage application.
2Productivity
If multiple high-side MOSFET switches are activated simultaneously, then the motor control performance is improved, but the capacitor size and space requirement increase
Solution Approach 1:
The patent applies periodic action by introducing a dead time between switching operations of MOSFET switches in the bridge circuit. The switching is performed in alternating phases where one high-side switch is activated, followed by a dead time period, then the other high-side switch is activated. This periodic switching pattern prevents simultaneous activation of multiple switches, thereby reducing the peak current requirement of the charge pump while maintaining effective motor control through sequential PWM voltage application.
3Volume of stationary object
If a dead time is introduced to prevent simultaneous switching, then the charge pump size is reduced, but the switching speed decreases
Solution Approach 1:
The patent applies parameter changes by carefully optimizing the dead time duration and PWM frequency to achieve an optimal balance between charge pump size reduction and switching speed maintenance. By adjusting these parameters, the system minimizes the impact of dead time on overall switching performance while still preventing simultaneous MOSFET activation. The PWM voltage generation and switching sequences are tuned to ensure motor control effectiveness is preserved despite the sequential switching approach.
Data Source
AI summary
Described is a method and a circuit arrangement for controlling a stepper motor in a voltage-controlled or voltage-regulated operating mode, having a bridge circuit provided for a motor coil (A) with semiconductor switches (HS1, HS2, LS1, LS2) for applying a first and a second PWM voltage (U(LA1), U(LA2)) having opposite polarity to the motor coil (A) and having a charge pump for switching at least the high-side semiconductor switch (HS1, HS2) of the bridge circuit. Because the charge pump must wait for a blocking or dead time before a further semiconductor switch can be switched after switching a first semiconductor switch, the time interval between a rising edge of one of the two PWM voltages and a subsequent rising edge of the respective other PWM voltage is increased at least until the blocking or dead time of the charge pump has elapsed.