Motor current detection circuit
First Claim
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1. A motor current detection circuit for detecting an overload of a motor by detecting an increase in motor current, comprising:
- comparing means for comparing said motor current and a current value corresponding to a variable overload detection level; and
detection level changing means for varying said current value corresponding to the variable overload detection level based on variation in a voltage supplied to said motor.
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Abstract
A motor current detection circuit in which a level for detecting an overload state is varied when motor drive voltage varies so as to prevent erroneous detection due to variation in-motor current which occurs when the drive voltage varies.
23 Citations
18 Claims
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1. A motor current detection circuit for detecting an overload of a motor by detecting an increase in motor current, comprising:
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comparing means for comparing said motor current and a current value corresponding to a variable overload detection level; and detection level changing means for varying said current value corresponding to the variable overload detection level based on variation in a voltage supplied to said motor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A motor current detection circuit for detecting an overload of a motor by detecting an increase in motor current, comprising:
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comparing means for comparing said motor current and a current value corresponding to a variable overload detection level; and detection level changing means for varying said current value corresponding to the variable overload detection level based on a variation in a voltage supplied to said motor, and for changing an amount of variation of said current value corresponding to the variable overload detection level depending on whether the motor current increases or decreases. - View Dependent Claims (12, 13)
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14. A motor current detection circuit for detecting an overload of a motor by detecting an increase in motor current, comprising:
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comparing means for comparing said motor current and a current value corresponding to a variable overload detection level; detection level changing means for changing said current value corresponding to the overload detection level based on variation in a voltage supplied to said motor; and restricting means for restricting an amount of variation in the current value corresponding to the variable overload detection level from exceeding a predetermined amount when the current value corresponding to the variable overload detection level is changed by said variable overload detection level changing means based on a decrease in said motor drive voltage. - View Dependent Claims (15, 16, 17)
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18. A motor current detection circuit for detecting an overload of a motor by detecting an increase in motor current, comprising:
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comparing means for comparing said motor current and a current value corresponding to an overload detection level; detection level changing means for changing said current value corresponding to the overload detection level in accordance with variation in motor drive voltage; and restricting means for restricting an amount of variation in the current value corresponding to the detection level, when the current value corresponding to the detection level is changed by said detection level changing means in accordance with a decrease in said motor drive voltage, so that the amount of variation in the current value corresponding to the detection level is prevented from exceeding a predetermined amount, wherein said restricting means comprises a resistor connected to a rectifier element in parallel, said rectifier element provided between one terminal of said motor and said comparing means such that the forward direction of said diode coincides with the direction of flow of current toward said comparing means.
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Specification