1338 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 51, NO. 6, DECEMBER 2004 Quasi-Resonant-Converters-Based High-Efficiency Spindle Motor Drives for Magnetic Data Storage M. A. Jabbar, Senior Member, IEEE, Ashwin M. Khambadkone, Member, IEEE, and Guo Chun Abstract—Disk drive spindle motors require accurate speed control and highly efficient drive controllers. Small-volume and high-efficiency converters are of particular interest for portable data storage applications. Quasi-resonant voltage controllers are described in this paper and the experimental results are presented. In contrast to the conventional pulsewidth-modulated voltage controller, this technique reduces the switching loss and enables the controller to operate at very high frequencies. Three types of resonant converters are built and tested for the applica- tion. A comparison of performance in terms of losses and voltage regulation is given. Index Terms—Disk drives, reverse rotation, spindle motor, starting scheme, voltage controller. I. INTRODUCTION S PINDLE motor drives form an important part of hard disk drives (HDDs) used in computers and other data storage equipment. The size of the magnetic disk has been decreasing with the increase in the magnetic storage density. Drives with ca- pacities of 1 Gbit/in [1] are being used. The disk diameter has dropped from 5 1/4 in to 1 in while the capacities have increased from 20 Mb to several hundred gigabytes. The magnetic disks are mounted on a spindle motor. The spindle motor speeds have also increased from 3600 to 10 000 r/min. The spindle motor is supplied by a dc voltage. It is started from zero speed and is run up to a rated speed within a short time. Once the rated speed is reached it has to be maintained. Accurate speed control is nec- essary to ensure proper recording and reproduction of informa- tion with great reliability. A speed error of no more than 0 and 0.02% of the rated speed is permitted. To this end a voltage controller has to be used. Such a controlled voltage source has to have very low voltage ripple and have very high efficiency. The power budget in many computing machines is very tight, especially in portable devices that operate on batteries. A sleep mode has been used in HDDs to reduce the drain on the power supply. However every startup consumes a major portion of the drive power and the power consumed during the operating mode of a drive is considerably less. Hence, sleep mode may not be an optimal solution for all applications. Due to all the constraints the spindle motor drive has to be carefully designed. Since a Manuscript received October 18, 2002; revised January 2, 2004. Abstract published on the Internet September 10, 2004. M. A. Jabbar and A. M Khambadkone are with the Department of Elec- trical and Computer Engineering, National University of Singapore, Singapore 117576 (e-mail: eleamk@nus.edu.sg). G. Chun was with Fujitsu Microelectronics Asia, Singapore. He is now with with Fujitsu Microelectronics (Shanghai) Company Ltd., Shanghai 200002, China. Digital Object Identifier 10.1109/TIE.2004.837895 Fig. 1. Spindle motor voltage profile during startup and run mode. fixed dc voltage is supplied to the HDD a voltage high enough to ensure a fast startup time is selected (Fig. 1). The fast startup time determines the latency and data transfer rate of the HDD. However, the voltage value during startup phase would be higher than the one required to run the motor at rated speed. Hence, a voltage control is mandatory. In this paper we will discuss high efficiency dc–dc converter topologies suitable for spindle motor drives. Before we go into the proposed topologies we would like to describe the conventional method of voltage control used in spindle motor drives. II. CONVENTIONAL SPINDLE MOTOR DRIVES The spindle motor drive requires a high starting voltage. Since the HDD is supplied by a constant voltage, the supply voltage should be high enough to start up the spindle motor within a stip- ulated startup time. Once the drive has reached the rated speed the motor voltage has to be reduced and maintained such that an accurate speed equal to the rated speed is achieved. The desired voltage profile is shown in Fig. 1, where is the startup time and is the back electromotive force (EMF) of the spindle motor In conventional spindle motor drives the controller shown in Fig. 2 is used. The dc supply is connected to a dc–ac con- verter consisting of six MOSFETs. During the starting phase the MOSFETs are switched sequentially such that two phases of the brushless dc spindle motor see the full dc voltage. After the motor speed has reached the rated value, the motor voltage has to be reduced. The reduction in voltage is achieved by op- erating the lower MOSFETs of the converter in the active re- gion. The gate voltage of the MOSFETs is modulated using a pulsewidth-modulated (PWM) signal. By changing the gate voltage the of the MOSFET the drain-to-source voltage can be adjusted for a particular drain current. Thus, the lower tran- sistors act like voltage-controlled resistance. Such an opera- tion increases the conduction losses in the lower MOSFETs. Since the spindle motor is operated at a lower voltage during 0278-0046/04$20.00 © 2004 IEEE