Circuit for improving back emf detection in pulse width modulati

Details Circuit for improving back emf detection in pulse width modulati Circuit for improving back emf detection in pulse width modulati

1997-10-24

1999-02-02

Sircus, Brian

Electricity: motive power systems

Switched reluctance motor commutation control

318439, 318811, H02K 2300

Patent

active

058669981

ABSTRACT:
A power-switched driver circuit for a disc drive that provides accurate back emf detection in PWM mode. In one embodiment, a power transistor is coupled between the low side drivers and ground. During the off time of a PWM cycle, all of the high side drivers are off and the current recirculates through two of the low side drivers. The power transistor is off. This disconnects the motor from ground and allows the voltage on the center tap of the motor to be about half of V.sub.cc, which allows the back emf of the motor to be detected during the off time using a conventional comparator as the back emf approaches a zero crossing. During the on time of a PWM cycle, the power transistor is on.
In an alternative embodiment, a power transistor is coupled between the high side drivers and V.sub.cc. During the off time of a PWM cycle, all of the low side drivers are turned off and the current recirculates through two of the high side drivers. The power transistor is off, disconnecting the motor from V.sub.cc and allowing the voltage on the center tap of the motor to be about half of V.sub.cc. This enables the back emf of the motor to be detected during the off time using a conventional comparator as the back emf approaches a zero crossing.

REFERENCES:
patent: 5448149 (1995-09-01), Ehsani et al.
patent: 5517095 (1996-05-01), Carobolante et al.
patent: 5691856 (1997-11-01), Kardash
patent: 5767654 (1998-06-01), Menegoli et al.

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