Differential high-speed inductivity driver with a bidirectional current limiter output

摘要

An innovative circuit for driving the write head. All of the driving transistors (QN3...8) are NPN, and are prevented from saturation. This is achieved by shifting and scaling down (SSA,SSB) the differential drive current applied to the pull-up transistors (QN3,QN4), to drive the pull-down transistors (QN8,QN7) with levels such that the pull-down transistors cannot reach saturation. This provides a very simple circuit in which all four of the drive transistors are NPN, and all are kept out of saturation. Moreover, the peak write current applied to the head is precisely limited.