Bidirectional motor stall protection circuit

• US 20060232896A1
• Filed: 04/14/2005
• Published: 10/19/2006
• Est. Priority Date: 04/14/2005
• Status: Active Grant

• Current Assignee: Lear Corporation
• Original Assignee: Lear Corporation
• Inventors: Nathan, John F., Maue, H. Winston, Pajor, Michael, Anderson, Jerremy, Ballard, John R., Kucher, Paul, Noorman, Michael
• Granted Patent: US 7,633,252 B2
• Time in Patent Office: Days
• US Class Current: 361/23
• CPC Class Codes: H02H 7/0851 for motors actuating a movable member between two end positions, e.g. detecting an end position or obstruction by overload signal

Abstract

A stall protection circuit is provided for bidirectional motor operation that is controlled by a half bridge switch that has forward, reverse and off positions. A method of protecting a motor is also disclosed. A Hall effect current sensor may be provided in a stall current protection circuit that engages a latching circuit. The latching circuit is operative to interrupt current flowing to the motor by disabling MOSFETs on opposite sides of the motor. Alternatively, FET voltage from drain to source may be used to measure the current supplied to the motor that is used to engage the latching circuit.

Claims

1. A stall protection circuit comprising:

a manual switch having an off position, a forward position and a reverse position;

an electric motor controlled by the switch;

a current sensor that senses the flow of current through the motor and produces a first signal representative of the level of current flowing through the motor;

a stall current detection circuit that receives the first signal and compares the first signal to a threshold value, and if the first signal is above the threshold value a second signal is generated; and

a latching circuit that receives the second signal and shuts off the motor.

2. The stall protection circuit of claim 1 wherein the manual switch is a half bridge circuit.

3. The stall protection circuit of claim 1 wherein the stall current detection circuit is a Hall effect current sensor that provides a voltage output that is proportional to the current supplied to the motor.

4. The stall protection circuit of claim 1 wherein the latching circuit shuts off the motor until the manual switch is in the off position.

5. The stall protection circuit of claim 1 wherein stall current detection circuit is a pair of field effect transistors each of which are operatively connected to one of two opposite sides of the motor wherein the field effect transistor drain to source voltage on each side of the motor are compared to detect stalling of the motor.

6. The stall protection circuit of claim 1 wherein the latch circuit is powered by a power supply that is interrupted when current flow to the motor is interrupted.

7. The stall protection circuit of claim 1 wherein the latch circuit is connected to a pair of field effect transistors on opposite sides of the motor.

8. A stall protection circuit comprising:

a manually actuated switch;

a electric motor controlled by the switch;

a switch controller that senses the level of current flowing through the motor and provides a current signal representative of the sensed level of current;

a stall current detection circuit that receives the current signal and compares the current signal to a threshold value and provides a fault signal if the current value exceeds the threshold value; and

a latch circuit that receives the fault signal and opens at least one motor protection switch that is operatively connected to the motor.

9. The stall protection circuit of claim 8 wherein the manual switch is a half bridge circuit.

10. The stall protection circuit of claim 8 wherein the stall current detection circuit is a Hall effect current sensor that provides a voltage output that is proportional to the current supplied to the motor.

11. The stall protection circuit of claim 8 wherein the latching circuit shuts off the motor until the manual switch is in the off position.

12. The stall protection circuit of claim 8 wherein stall current detection circuit is a pair of field effect transistors each of which are operatively connected to one of two opposite sides of the motor wherein the field effect transistor drain to source voltage on each side of the motor are compared to detect stalling of the motor.

13. The stall protection circuit of claim 8 wherein the latch circuit is powered by a power supply that is interrupted when current flow to the motor is interrupted.

14. The stall protection circuit of claim 8 wherein the latch circuit is connected to a pair of field effect transistors on opposite sides of the motor.

15. A method of protecting an electric motor against damage caused by stalling comprising:

sensing the level of current supplied to the motor;

comparing the sensed level of current to a threshold value;

sending an interrupt signal to a latch circuit if the sensed level of current exceeds the threshold value; and

interrupting the flow of current to the motor when the interrupt signal is received from the latch circuit to protect the motor from damage.

16. The method of claim 15 further comprising providing a manual switch actuator that is held in to cause the motor to turn in either a forward or a reverse direction;

wherein the motor may be caused to stall if the switch actuator is held in until the motor exceeds a maximum limit, and wherein the latch circuit remains latched until the switch is released.

17. The method of claim 16 wherein the latch circuit is powered by a power supply that is interrupted when current flow to the motor is interrupted.

18. The method of claim 15 wherein the sensing step is performed by a Hall effect sensor that produces a voltage signal that is proportionate to the level of current supplied to the motor.

19. The method of claim 15 wherein the sensing step is performed by field effect transistors each of which are operatively connected to one of two opposite sides of the motor wherein the field effect transistor drain to source voltage on each side of the motor are compared.

20. The method of claim 15 wherein a half bridge is provided in the motor power circuit.