Browse Prior Art Database

Motor Protection Circuit

IP.com Disclosure Number: IPCOM000048942D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 54K

Publishing Venue

IBM

Related People

Arnold, RW: AUTHOR

Abstract

A DC motor operable bidirectionally through an H drive is protected from shorts caused by failure of the power transistor devices or logic inputs errors.

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Motor Protection Circuit

A DC motor operable bidirectionally through an H drive is protected from shorts caused by failure of the power transistor devices or logic inputs errors.

Motor 10 is operated in a forward direction by the concurrent application of down signals to terminals 11 and 14 while up signals are present at terminals 12 and 13. Reverse direction is obtained when down signals are applied to terminals 12 and 13 while up signals are applied to 11 and 14. In the event that an erroneous down signal were applied to one of the up terminals, a direct connection of the power transistors would be made across the voltage source, causing burn out to occur. For example, if a down signal were present at terminal 12 at the time down signals were applied to terminals 11 and 14, power transistors 15 and 16 would be directly connected across the voltage source of the power supply. To prevent this from occurring, buffers B1, B2, B3 and B4 are connected between terminals 11 through 14, respectively, and the bases of power transistors 16, 17 and 20, respectively. In the event that a down signal appears at terminal 12 concurrently with the down signals on terminals 11 and 14 which produce forward drive motion, buffer B2 would block the switching of power transistor 15 by holding the base of transistor 19 off independently of the state of the input at terminal 11. In the event that terminals 11 and 12 were brought down concurrently, a short duration current could be obtained if transistors 15 and 16 were sufficiently fast. This type of condition can be corrected as follows.

Diodes 21-24 serve as isolation diodes. With the driver circuit off, motor 10 is floating at the voltage established by resistors 25 and 26. When one of the power transistors fails due to shorting, a very high current short can occur. To prevent this, comparators 27 through 30 are provide...