Power down brake latch circuit for a brushless DC motor
First Claim
1. A circuit for braking a spindle motor in a disk drive system, the spindle motor having a plurality of stator coils receiving power from a voltage supply through a plurality of bridge circuits, each stator coil being connected between a high side driving transistor having a flyback diode and a low side driving transistor in a respective one of the bridge circuits, the circuit comprising:
- a smoothing capacitor coupled to the high side driving transistors to receive a back EMF voltage from the stator coils through the flyback diodes after the voltage supply to the spindle motor is terminated, wherein a voltage across the smoothing capacitor is provided in part by the back EMF voltage;
a braking circuit having a first input coupled to the smoothing capacitor and a second input receiving a voltage supply signal indicative of a voltage level of the voltage supply, the braking circuit being structured to generate a braking signal after the voltage supply signal indicates that the voltage supply is below a first threshold and the voltage on the smoothing capacitor falls below a second threshold, wherein the voltage on the smoothing capacitor falls as the back EMF voltage decreases; and
a second circuit having an input receiving the braking signal and an output coupled to the bridge circuits, the second circuit being structured to cause the bridge circuits to couple the stator coils to a reference voltage to brake the spindle motor in response to the braking signal, wherein the EMF voltage received by the smoothing capacitor through the flyback diodes of the high side driving transistors provide a delay to braking the spindle motor.
2 Assignments
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Accused Products
Abstract
A power down brake latch circuit for dynamically braking a spindle motor in a disk drive system is disclosed. The power down brake latch circuit includes a reservoir capacitor, a smoothing capacitor, a timing circuit, and a logic circuit. The timing circuit includes a voltage divider and a bandgap comparator. The smoothing capacitor absorbs a BEMF voltage from the spindle motor as it rotates after losing power. The timing circuit generates a first signal when a voltage on the smoothing capacitor falls below a threshold. The logic circuit brakes the spindle motor in response to the loss of power and the generation of the first signal.
35 Citations
19 Claims
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1. A circuit for braking a spindle motor in a disk drive system, the spindle motor having a plurality of stator coils receiving power from a voltage supply through a plurality of bridge circuits, each stator coil being connected between a high side driving transistor having a flyback diode and a low side driving transistor in a respective one of the bridge circuits, the circuit comprising:
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a smoothing capacitor coupled to the high side driving transistors to receive a back EMF voltage from the stator coils through the flyback diodes after the voltage supply to the spindle motor is terminated, wherein a voltage across the smoothing capacitor is provided in part by the back EMF voltage; a braking circuit having a first input coupled to the smoothing capacitor and a second input receiving a voltage supply signal indicative of a voltage level of the voltage supply, the braking circuit being structured to generate a braking signal after the voltage supply signal indicates that the voltage supply is below a first threshold and the voltage on the smoothing capacitor falls below a second threshold, wherein the voltage on the smoothing capacitor falls as the back EMF voltage decreases; and a second circuit having an input receiving the braking signal and an output coupled to the bridge circuits, the second circuit being structured to cause the bridge circuits to couple the stator coils to a reference voltage to brake the spindle motor in response to the braking signal, wherein the EMF voltage received by the smoothing capacitor through the flyback diodes of the high side driving transistors provide a delay to braking the spindle motor. - View Dependent Claims (2, 3, 4)
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5. A disk drive system, comprising:
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a spindle motor including a plurality of stator coils; a plurality of bridge circuits, each bridge circuit including a high side driving transistor with a flyback diode and a low side driving transistor, the high side and low side driving transistors being connected together at a node which is connected to an end of a respective one of the stator coils; a voltage supply coupled to each of the high side driving transistors; a reference voltage connected to each of the low side driving transistors; a smoothing capacitor coupled to the high side driving transistors to receive a back EMF voltage from the stator coils through each flyback diode when the voltage supply is reduced below a first threshold wherein a voltage on the smoothing capacitor is provided in part by the back EMF voltage; and a braking circuit having a first input coupled to the smoothing capacitor, a second input receiving a voltage supply signal, and an output coupled to the low side driving transistors, the braking circuit being structured to generate a braking signal after the voltage supply signal indicates that the voltage supply is below the first threshold and the voltage on the smoothing capacitor falls below a second threshold wherein the voltage on the smoothing capacitor falls as the back EMF voltage decreases, the braking circuit being structured to apply the braking signal to the low side driving transistors to brake the spindle motor based on a delay provided by the smoothing capacitor receiving the back EMF voltage through the flyback diodes of the high side driving transistors. - View Dependent Claims (6, 7)
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8. A braking circuit for a spindle motor having a plurality of stator coils, each of the stator coils being connected between a high side driving transistor and a low side driving transistor, each low side driving transistor having a control terminal and being connected between a reference voltage and a respective one of the stator coils, each high side driving transistor having a flyback diode and being coupled between a voltage supply and a respective one of the stator coils, the braking circuit comprising:
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a smoothing capacitor having a first plate connected to the reference voltage and a second plate coupled to each high side driving transistor, the second plate having a voltage; a timing circuit having an input coupled to the second plate of the smoothing capacitor and an output, the timing circuit being structured to generate a first signal at its output when the voltage on the second plate of the smoothing capacitor falls below a first threshold; and a logic circuit having a first input connected to the output of the timing circuit, a second input receiving a voltage supply signal, and an output coupled to the control terminals of the low side driving transistors, the logic circuit being structured to generate a braking signal at its output in response to the first signal after the voltage supply signal indicates that the voltage supply is insufficient to drive the spindle motor, the braking signal causing the low side driving transistors to couple the stator coils to the reference voltage to brake the spindle motor, wherein the second plate of the smoothing capacitor receives a back EMF voltage from the stator coils through the flyback diodes of the high side driving transistors when the voltage supply is insufficient to drive the spindle motor, the back EMF voltage initially maintaining the voltage on the second plate, the voltage of the second plate decreasing as the EMF voltage decreases, the back EMF received by the second plate of the smoothing capacitor providing a delay in generating the first signal. - View Dependent Claims (9, 10, 11, 12, 13)
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14. A method for braking a spindle motor having a plurality of stator coils, each of the stator coils being connected between a high side driving transistor and a low side driving transistor and being coupled to a voltage supply through the high side driving transistor, each low side driving transistor being coupled between a reference voltage and a respective one of the stator coils, the method comprising:
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generating a first signal when the voltage supply is insufficient to drive the spindle motor; storing in a smoothing capacitor energy received from the stator coils through the high side driving transistors when the voltage supply is insufficient to drive the spindle motor; sensing a voltage on the smoothing capacitor, wherein the voltage on the smoothing capacitor decreases as the energy received from the stator coils decreases; generating a second signal when the voltage on the smoothing capacitor is less than a first threshold wherein the energy received from the stator coils provide a delay in which the voltage on the smoothing capacitor falls below the first threshold; generating a braking signal in response to the generation of the first and second signals; and coupling the stator coils to the reference voltage in response to the braking signal, thereby braking the spindle motor. - View Dependent Claims (15, 16)
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17. A circuit for braking a spindle motor in a disk drive system, the spindle motor having a plurality of stator coils receiving power from a voltage supply through a plurality of bridge circuits, each stator coil being connected between a high side driving transistor having a flyback diode and a low side driving transistor in a respective one of the bridge circuits, the circuit comprising:
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a smoothing capacitor coupled to the high side driving transistors to receive a back EMF voltage from the stator coils after the voltage supply is terminated; a braking circuit having a first input coupled to the smoothing capacitor and a second input receiving a voltage supply signal indicative of a voltage level of the voltage supply, the braking circuit being structured to generate a braking signal after the voltage supply signal indicates that the voltage supply is below a first threshold and a voltage on the smoothing capacitor is below a second threshold, the braking circuit further comprising a timing circuit having an output coupled to the smoothing capacitor and an output, the timing circuit being structured to generate a first signal at its output when the voltage on the smoothing capacitor is below the second threshold, and a logic circuit having a first input coupled to the output of the timing circuit to receive the first signal and a second input coupled to the voltage supply signal, the logic circuit being structured to generate the braking signal at an output; and a second circuit having an input receiving the braking signal and an output coupled to the bridge circuits, the second circuit being structured to cause the bridge circuits to couple the stator coils to a reference voltage to brake the spindle motor in response to the braking signal. - View Dependent Claims (18, 19)
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Specification