8V ring clamp circuit

Details 8V ring clamp circuit 8V ring clamp circuit

1999-04-05

2001-08-28

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

General recording or reproducing

Specifics of the amplifier

C360S046000, C327S110000, C327S309000

Reexamination Certificate

active

06282044

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to write drivers for an inductive head in a magnetic data storage system and more particularly to write drivers that include a damping circuit connected to an H-bridge circuit to drive the head.
BACKGROUND OF THE INVENTION
Conventional storage systems include an inductive head that uses an inductive element to write information onto a recording surface of the magnetic medium, such as a magnetic disk. The inductive element usually includes an inductive coil that writes information by creating a changing magnetic field near the magnetic medium. A write driver circuit is connected to the magnetic head at two head terminals. During writing operations, the write driver circuit forces a relatively large write current through the inductive coil to create a magnetic field that polarizes adjacent bit positions on the recording surface. Digital information is stored by reversing the polarization of selected bit positions which is done by reversing the direction of the current flow in the inductive coil.
The typical write driver circuit includes an “H-switch” for controlling the direction of current flow through the inductive coil. The H-switch includes upper “pull-up” bi-polar transistors and lower “pull-down” bi-polar transistors. The upper bi-polar transistors are connected between a first supply voltage and the head contacts or terminals. The lower bi-polar transistors are connected between another set of head terminals and a second supply voltage through a write current sink. The write driver circuit controls the direction of flow through the inductive coil by driving selected transistors in the H-switch between ON and OFF states, thereby applying a limited voltage swing across the head contacts or terminals for reversing current flow and polarizing the adjacent bit position on the magnetic medium.
The rate at which information can be stored on a recording surface through an inductive head is directly proportional to the rate at which the direction of current can be reversed in the inductive coil. The rise/fall time of the inductive coil is determined by:
di/dt=V/L
where di/dt is the rate of change of the current over time across the inductive coil, V is the available voltage across the inductive coil, and L is the inductive load. Therefore, the speed of the H-switch is directly proportional to the available voltage across the inductive coil. The available voltage is determined by subtracting the voltage drops across the pull-up transistors, the pull-down transistors, and the write current sink from the supply voltage.
FIG. 3
illustrates a clamp circuit of the prior art.
The write circuit is a portion of a preamplifier system. The preamplifier system also includes a read circuit which, together with the write circuit, reads and writes information to and from the magnetic medium.
A preamplifier system is connected to the magnetic head coil at the head contacts.
SUMMARY OF THE INVENTION
The write circuit of the present invention provides protection for devices that may have 8 volts across the device from the breakdown which results as the voltage approaches 8 volts. The present invention provides a clamping function with overshoot control and ringing control.
The present invention protects the lower transistors of an H-bridge circuit from saturating and reduces the excursions of the output nodes (HX, HY). More particularly, the present invention dampens the negative ringing resulting from transitions. Additionally, the write circuit of the present invention allows Schottky diodes to be removed from the collector of the lower transistors of the bridge circuit. The write driver of the present invention charges the output nodes of the writer during time periods of transitions. The write driver of the present invention compensates for transient voltages which are the result of the head inductance. Furthermore, the present invention protects 5-volt devices in 8-volt supply environments.


REFERENCES:
patent: 5392172 (1995-02-01), Yoshinaga et al.
patent: 5638012 (1997-06-01), Hashimoto et al.
patent: 6166579 (2000-12-01), Hojabri et al.

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