Bridge motor driver with short-circuit protection and motor-current limiting feature

• US 5,457,364 A
• Filed: 01/18/1994
• Issued: 10/10/1995
• Est. Priority Date: 01/18/1994
• Status: Expired due to Term

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Tallarico, Jose L., Bilotti, Alberto
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): Masih, Karen
• Application Number:
  US08/182,327
• Time in Patent Office: 630 Days
• Field of Search: 323/365, 318/434, 318/254, 318/138, 318/439, 318/811, 318/801, 363/41, 363/55, 363/56
• US Class Current: 318/434
• CPC Class Codes: H02H 1/043 to inrush currents H02H1/046 takes precedence; differential protection of transformers H02H7/045
• CPC Class Codes: H02H 3/05 with means for increasing reliability, e.g. redundancy arrangements for logic circuits H03K19/003
• CPC Class Codes: H02H 3/087 for dc applications
• CPC Class Codes: H02H 7/0853 specially adapted for motors rotating in both directions H02H7/0851 takes precedence
• CPC Class Codes: H02H 7/0855 avoiding response to transient overloads, e.g. during starting
• CPC Class Codes: H02H 9/002 limiting inrush current on switching on of inductive loads subjected to remanence, e.g. transformers
• CPC Class Codes: H02P 29/027 the fault being an over-current
• CPC Class Codes: H02P 7/04 by means of a H-bridge circuit

Abstract

A full-wave bridge driver has four driver transistors. A motor is connected to the output terminals of the bridge. A fault detector latches off the four driver transistors when the bridge current jumps essentially instantaneously to exceed a predetermined safe-peak value due to a fault occurring in the bridge. A comparator has a predetermined current threshold, that is less than the predetermined safe-peak value of the fault detector, and is connected to a bridge-current sensing resistor for, when the bridge current exceeds the current threshold, producing a signal proportional to the difference between the bridge current and the current threshold. A pulse-width-modulator is connected to the comparator means output, and during periods such as at motor starting when the bridge current gradually exceeds the comparator threshold value, chops the signal at the bases of the four driver transistors, varying the chopped pulse widths to hold the motor current at essentially the threshold current value. For faults that occur across the motor or between the motor and either of the DC-supply terminals, the fault current paths in the bridge do not flow through the inductance of the motor and produce a sharp rising bridge fault current that is essentially transparent to the pulse width modulator which clamps high motor start currents at a level below that at which the fault detector trips the latch and shuts off the driver transistors.

Claims

1. A full-wave bridge driver of the kind having two DC-supply-voltage terminals, four driver transistors connected in a circuit configured as a transistor bridge having two motor load terminals to which a motor may be connected, said bridge being connected between said two DC-supply-voltage terminals, and a fault detector means connected to said bridge for latching off said four driver transistors when the bridge current drawn by said bridge from said DC-supply terminals jumps essentially instantaneously to exceed a predetermined safe-peak value due to a fault occurring in said bridge;

wherein the improvement comprises;

a) a bridge-current sensing means for producing a bridge-current signal that is proportional to the bridge current;

b) a comparator means having a predetermined current threshold that is less than said predetermined safe-peak value, connected to said bridge-current sensing means for when the bridge current exceeds said current threshold producing a signal proportional to the difference between the bridge current and said current threshold; and

c) a pulse-width-modulator means connected to said comparator eans and to said four driver transistors for only during periods when the bridge current exceeds the comparator threshold value, chopping the signal at said control elements of said four driver transistors and varying the chopped pulse widths to hold the bridge current at said threshold current value.

2. A full-wave bridge driver of the kind having two DC-supply-voltage terminals, four driver transistors connected in an H-bridge configured circuit that is connected between said two DC-supply-voltage terminals, a pair of motor terminals to which a motor may be connected located respectively at the junctions between each of the two of said driver transistors forming the two series branches of said bridge circuit, and a fault detector means connected to said bridge circuit for latching off said four driver transistors when the bridge-circuit current drawn from said DC-supply terminals jumps essentially instantaneously to exceed a predetermined safe-peak value;

wherein the improvement comprises;

a) a bridge-current sensing means for producing a bridge-current signal that is proportional to the current drawn by said bridge from said DC-supply-voltage terminals;

b) a comparator means, having a predetermined current threshold that is less than said predetermined safe-peak value, connected to said bridge-current sensing means for when the bridge current exceeds the current threshold producing a signal proportional to the difference between the bridge current and said current threshold; and

c) a pulse-width-modulator means connected to said comparator means and to said four driver transistors for when the bridge current during motor starting exceeds the comparator threshold value, chopping the signal at said control elements of said four driver transistors and varying the chopped pulse widths to hold the bridge current at said threshold value.