Motor drive system with variable gain

Electricity: motive power systems – Switched reluctance motor commutation control

Reexamination Certificate

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Details

C318S132000, C318S434000, C318S245000, C318S560000

Reexamination Certificate

active

06291950

ABSTRACT:

BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a motor drive system. More particularly, the present invention relates to a motor drive system for a CD-ROM spindle motor, the motor drive system having a variable gain.
(b) Description of the Related Art
A three-phase BLDC (brushless direct current) motor is generally used as the spindle motor in a CD-ROM. An output torque of the BLDC motor is proportional to a current flowing to a motor load. To control rpm, the spindle motor includes a system that frequently detects an output current such that the output current can be controlled to a level proportional to an input control voltage.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a motor drive system for a CD-ROM spindle motor in which a gain of the motor drive system can be easily varied.
To achieve the above object, the present invention provides a motor drive system comprising a control voltage output portion receiving a first control voltage and a second control voltage from an external servo, and outputting a voltage that is proportional to a difference between the first and second control voltages; a driver receiving the voltage output from the control voltage output portion via a non-inversion terminal and receiving feedback signals through an inversion terminal to generate drive signals for a motor; a commutation distributor outputting ON/OFF signals such that the motor is optimally driven, the ON/OFF signals being output according to hole signals of each phase of the motor that are input externally; a power transistor, which is ON/OFF controlled according to an output of the driver to supply the drive signals to the motor; an output current detector detecting the drive signals output from the power transistor and converting the drive signals into a voltage, and outputting an output voltage; and a voltage amplifier, a voltage gain of which is varied by an external pin, the voltage amplifier amplifying the output voltage of the output current detector to supply the voltage as the feedback signals to the driver.
According to a feature of the present invention, the control voltage output portion comprises a transconductance amplifier receiving the first and second control voltages from the external servo, and outputting a current proportional to a difference between the first and second control voltages; an absolute value circuit obtaining an absolute value from the current output from the transconductance amplifier, and outputting a corresponding output current; and a current/voltage converter for converting the output current of the absolute value circuit to a voltage.
According to another feature of the present invention, the current/voltage converter includes a resistor, a first end of the resistor being connected to an output of the absolute value circuit and a second end of the resistor being grounded.
According to yet another feature of the present invention, the voltage gain of the voltage amplifier is varied by a voltage applied to the external pin.
According to still yet another feature of the present invention, the output current detector includes a sensing resistor, the sensing resistor converting the drive signals output from the power transistor into a voltage.
According to still yet another feature of the present invention, a resistance value of the sensing resistor is changed to vary transmission characteristics of the entire system.


REFERENCES:
patent: 4415844 (1983-11-01), Mendenhall et al.
patent: 4639798 (1987-01-01), Harrison et al.
patent: 5010282 (1991-04-01), Moberg
patent: 5838515 (1998-11-01), Mortazavi et al.
patent: 5952798 (1999-09-01), Jones et al.
patent: 6008603 (1999-12-01), Jones et al.
patent: 6020700 (2000-02-01), Tien

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