Design and development of a new controller for disk-drive spindle motors

Current disk drive motor controllers are simple in design but inefficient. Brushless operation of spindle motors requires an inverter system which normally uses MOSFETs as switches. However, not all of the MOSFETS are operated in the perfect switch-mode. Some of them are operated in the linear mode and hence become lossy. To overcome this problem, the conventional method is to use pulse width modulated (PWM) controllers. However, due to switching losses, which increase as switching frequency increases, PWM controllers are normally operated below 100 kHz. This may limit the scope of really miniaturizing controllers. The controller presented in this paper was developed using a quasi-resonant converter (QRC) and all the MOSFETS are operated as perfect switches. This new controller design was built and tested. Its performance was compared with that of a conventional PWM controller and was found to consume less power from the supply, and also requires less power to keep the motor running at constant speeds. This paper discusses the idea behind this new controller and gives the analysis and design. Some test results are also presented in the paper.