Asymmetrical Driver Circuit for HDD Motor Power Dissipation
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Solution Overview
Problem
Existing hard disk drive (HDD) motor driver circuits face inefficiencies in power dissipation due to symmetrical transistor sizing, leading to increased switching losses and power dissipation, especially during spin-up and steady-state operations.
Innovation Solution
Implementing an asymmetrical driver circuit with differently sized high-side and low-side MOSFET transistors, where the low-side transistors are larger and have a smaller RDSon, to optimize the duty cycle and reduce power losses by extending their ON time, thereby reducing the effective diagonal RDSon and overall power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If symmetrical transistor sizing is used in the driver circuit, then the circuit design is simple and balanced, but switching losses and power dissipation increase
Solution Approach 1:
The patent applies asymmetry by sizing the high-side and low-side MOSFET transistors differently in the driver circuit. Specifically, the low-side transistors are made larger than the high-side transistors to optimize their respective operating conditions. This asymmetric sizing reduces switching losses and power dissipation by matching each transistor's size to its specific electrical and thermal environment, directly resolving the contradiction between energy loss and design simplicity.
2Loss of energy
If the low-side transistors are made larger with smaller RDSon, then switching losses are reduced, but the device occupies more area
Solution Approach 1:
The patent applies local quality by making the low-side transistors larger only in the regions where they are most needed for reducing switching losses, while keeping the high-side transistors smaller. This localized optimization allows the driver circuit to reduce overall power dissipation without proportionally increasing the total circuit area, as the area increase is concentrated only where it provides the greatest energy efficiency benefit.
3Loss of energy
If asymmetrical transistor sizing is implemented, then power dissipation decreases, but the design and manufacturing complexity increases
Solution Approach 1:
The patent applies parameter changes by systematically varying the size parameters of the MOSFET transistors based on their position (high-side vs. low-side) and electrical characteristics. This parameter optimization reduces power dissipation while maintaining manufacturability, as the size differences are implemented through standard semiconductor design processes rather than requiring complex manufacturing steps.
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 approach results in a 3.9% decrease in power dissipation during spin-up and 4.7% during steady-state operation, leading to reduced heat generation and increased reliability, with potential for further power savings in larger disk drives.
Implementation Method 1
the low-side transistors are larger and have a smaller RDSon, to optimize the duty cycle and reduce power losses
Data Source
AI summary
A drive circuit having asymmetrical drivers. In an embodiment, a brushless DC motor may be driven by a drive circuit having three high-side MOSFETs and three low-side MOSFETs. A driver controller turns the MOSFETs on and off according to a drive algorithm such that phase currents are injected into motor coils to be driven. The high-side MOSFETs may be sized differently than the low-side MOSFETs. As such, when a MacDonald waveform (or similar drive algorithm) is used to drive the phases of the motor, less power may be required during disk spin-up because the MOSFETs that are on more (e.g., the low-side MOSFETs with a MacDonald waveform) may be sized larger than the MOSFETs that are on less (e.g., the high-side MOSFETs). In this manner, less power is dissipated in the larger size MOSFETs that are on more than the others.