Asymmetrical driver
View Patent ↗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.
1. A controller, comprising:
a disk-drive controller operable to control operation of a disk drive; and
a drive circuit coupled to the disk-drive controller and operable under control of the disk-drive controller to control operation of a motor in the disk drive, the drive circuit comprising a first drive component having a first value of a drive characteristic and a second drive component having a second value of the drive characteristic, the second value being different than the first value, and the first drive component comprising a first transistor and the second drive component comprising a second transistor and the first and second drive characteristics corresponding to respective RDSon values for the first and second transistors; and
wherein the disk-drive controller is operable to asymmetrically activate the first and second drive components and the first and second values of the first and second drive characteristics have values that are a function of characteristics of the asymmetrical activation to thereby reduce a power loss in the first and second drive components relative to a power loss in the first and second drive components when the first and second drive characteristics have the same value, the disk-drive controller operable to pulse width modulate the first and second transistors in an asymmetric manner to thereby activate the one the first and second transistors having the lower RDSon value for a longer duration than the other one of the first and second transistors during a cycle of the pulse width modulation.
2. The controller of claim 1 wherein:
the first transistor of the first drive component comprises one of a high side and a low side driver; and
the second transistor of the second drive component comprises the other of the high side and low side driver.
3. The controller of claim 1 , further comprising a first integrated circuit die comprising the disk-drive controller coupled to a second integrated circuit die comprising the drive circuit.
4. The controller of claim 1 , further comprising a single integrated circuit die.
5. The controller of claim 2 , wherein the first and second transistors comprise MOSFET transistors and width-to-length ratios of these MOSFET transistors is such that the first MOSFET transistor comprises a size that is 50% larger than the second MOSFET transistor.
6. A disk drive system, comprising:
a motor;
a disk coupled to the motor and operable to be rotated by the motor; and
a motor controller having a drive circuit operable to drive the motor, the drive circuit including:
a first drive circuit including a first transistor and having a first value of a drive characteristic corresponding to the RDSon of the first transistor;
a second drive circuit including a second transistor and having a second value of the drive characteristic corresponding to the RDSon of the second transistor, the second value being different than the first value; wherein the motor controller is operable to turn on the first drive circuit for a first portion of a drive period and to turn on the second drive circuit for a second portion of the drive period that is greater than the first portion, the motor controller turning on the one of the first and second transistors having the lower RDSon value for the second portion and the other one of the first and second transistors for the first portion.
7. The disk drive system of claim 6 wherein the motor comprises a three-phase, brushless direct-current motor.
8. The disk drive system of claim 6 , further comprising:
a memory coupled to the drive circuit and operable to store a drive algorithm; and
a driver controller coupled to the memory and operable to control the drive circuit according to the stored drive algorithm.
9. The disk drive system of claim 6 wherein the first and second drive circuits comprise MOSFET transistors and width-to-length ratios of these MOSFET transistors is such that the first MOSFET transistor comprises a size that is 50% larger than the second MOSFET transistor.