Sigma-delta switching power system to drive voice coil motor in hard disk drives
The paper presents a switching power system as an alternative to linear power systems driving voice coil motors (VCM) in hard disk drives (HDD). The system is made up of a switching power stage and a suitable modulator. The power stage uses the zero voltage transition technique to control the output voltage slope. The modulator uses the sigma-delta technique and controls the VCM current through a single-loop architecture. Although the structure of the system makes it general purpose, the authors of the paper chose a VCM for HDDs as a target application to test the system. This application is particularly challenging because it requires high-precision current regulation and is particularly sensitive to disturbance and noise. All the significant aspects of the system are then described and discussed. Results derived from the application of the proposed system to a real HDD are presented. The results demonstrate that the output-voltage slope is a parameter fundamental to avoiding interference between the output stage and the channel circuitry and for which an upper limit does exist. Nevertheless, it is high enough to make a switching drive worth considering. In particular, the relationship between the output-voltage slope, HDD performance, current-sensing properties and power-stage efficiency was analysed. The system was designed to be fully integrated.
