Magnetic head circuit having a write current changeover circuit with a

Abstract

A magnetic head circuit for a plurality of magnetic heads includes two emitter follower transistors for receiving magnetic head writing data, two differential transistors connected to the two emitter follower transistors for performing differential operation control thereover, and two resistors connected to collectors of the two differential transistors for supplying a base current to the two emitter follower transistors, and wherein the emitter follower transistors are connected in series with each other to perform differential switch operations over a magnetic head writing current. A magnetic head fly-back voltage has a clamp voltage which varies according to a writing current flowing through a pair of signal terminals. A pair of differential transistors, whose bases are connected to the pair of signal terminals and whose emitters are connected directly to each other, are operated according to a voltage appearing between the pair of signal terminals. Connected to the collectors of the pair of differential transistors are amplification transistors respectively. Connected to outputs of the amplification transistors are post-amplifiers. Such a connection configuration provides a small mirror capacitance as viewed from the bases of the amplification transistors. A high writing and reading accessing speed to the magnetic heads can be realized.