Abstract:
An apparatus is provided for powering at least one electric motor. The apparatus includes at least one driving device for driving the electric motor, a supply path positioned between a supply voltage generator and the at least one driving device, a first circuit, a control device, and a protection device for protecting against over-voltages. The first circuit is inserted in the supply path to enable and prevent the powering of the at least one driving device, and the control device controls at least the first circuit. The protection device includes a second circuit for detecting a current that flows in the supply path from the at least one driving device to the supply voltage generator, and a third circuit for selectively absorbing the current that is detected.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims priority from prior European Patent Application No. 04 425 282.3, filed Apr. 23, 2004, the entire disclosure of which is herein incorporated by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to an apparatus for powering electric motors, and in particular to an apparatus for powering spindle motors and voice coil motors (VCMs).  
       BACKGROUND OF THE INVENTION  
       [0003]     Conventional apparatuses for powering electric motors are known, for example, power combos or other powering devices used for hard disks in computers. A device for powering an electric motor basically comprises a device for driving the electric motor, and a control device suitable for regulating the supply voltage, which comes from a voltage generator outside the powering device, that is input to the driving device, and preferably suitable for controlling the electronic components belonging to the driving device. The regulation of the input supply voltage of the driving device is obtained by suitably controlling a device, preferably constituted by a MOSFET transistor and an intrinsic diode, that is inserted into the supply line that connects the voltage generator to the device for driving the electric motor.  
         [0004]     A conventional power combo  1  is shown in  FIG. 1 . A supply voltage VCV coming from a voltage generator  2  is in input to the power combo  1 . The power combo comprises a first device  3  for driving a spindle motor  4  that is outside the power combo  1 , and a second device  5  for driving a voice coil motor  6 , which is also outside the power combo  1 . Still inside the power combo  1 , a supply line  7  is provided between the voltage generator  2  and the driving devices  3  and  5 . A MOSFET device  8  is inserted in this supply line  7 , preferably an ISO-FET device comprising a MOS transistor M 1  and an intrinsic diode D 1 . The driving devices  3  and  5  and the transistor M 1  are controlled by a single control device  10  inside the power combo  1  and powered by the supply voltage VCV. A serial interface  20  having external input signals, such as clock and data signals, and being suitable for sending command signals to the control device  10 , and a block  30  comprising further voltage regulators suitable for sending out regulated voltage signals are typically also provided inside the power combo  1 .  
         [0005]     During the operation of an electric motor, such as a voice coil or a spindle motor, operating conditions can occur such as to produce an increasing of the voltage between a circuit node VM, located downstream from the MOSFET device  8  and upstream from the driving devices  3  and  5 , and ground. This is due to the current, which instead of flowing from the voltage generator  2  to the devices  3  and  5 , flows in the opposite direction through the MOSFET device  8 .  
         [0006]     Such a situation is encountered, for example, when a voltage lower than the voltage of BEMF (Back Electromotive Force) generated by the motor itself is applied to the electric motor, in the case in which it is in rotation.  
         [0007]     Another similar situation occurs when the driving devices  3  and  5 , which are formed by MOS transistors, are driven in high impedance. The current that flows in the electric motor recirculates towards the voltage generator  2  through the intrinsic diodes of the MOS transistors of the driving devices  3  and  5 .  
         [0008]     In both of these situations, if the voltage generator  2  presents a component of high impedance towards ground it cannot absorb the current that flows from the driving devices  3  and  5  towards it. The current generates an over-voltage that can reach more or less high values according to the filter capacitances, that is the capacitance C 1  connected between the supply voltage and ground and the capacitance C 2  connected between the node VM and ground, which are used to filter the supply voltage VCV. The capacitances C 1  and C 2  are outside the circuit block in which the elements belonging to the apparatus  1  are integrated, that is the circuit elements  3 ,  5 ,  8 ,  10 ,  20  and  30 . The over-voltage can reach high values such that it exceeds the voltage needed for the operating of the driving devices  3  and  5 .  
         [0009]     Methods for limiting the over-voltage are known that are based on the use of high value capacitance, for example increasing the value of the capacitances C 1  and C 2  by a few microfarads to 50 or 100 microfarads, or on the use of, also in combination with the high value capacitance, voltage suppressors, such as the Transil diode Dz of  FIG. 1  positioned between the node VM and ground, that are suitable for limiting the supply voltage.  
         [0010]     However, the known solutions are very expensive and bulky and are not in line with the current technological trends in the research of devices that are less and less bulky and not expensive.  
       SUMMARY OF THE INVENTION  
       [0011]     In view of these drawbacks, it is an object of the present invention to provide an apparatus for powering electric motors that overcomes the above-mentioned drawbacks.  
         [0012]     In accordance with one embodiment of the present invention, an apparatus for powering at least one electric motor is provided. The apparatus includes at least one driving device for the electric motor, a supply path, a first circuit, a control device, and a protection device for protection against over-voltages. The supply path is positioned between a supply voltage generator and the at least one driving device, and the first circuit is inserted in the supply path to enable and to prevent the powering of the at least one driving device. The control device is powered by the supply voltage and is suitable for controlling at least the first circuit. The protection device for protection against over-voltages includes a second circuit suitable for detecting a current that flows in the supply path from the at least one driving device to the supply voltage generator, and a third circuit suitable for selectively absorbing the current that is detected.  
         [0013]     Accordingly, there is provided an apparatus for powering electric motors that is provided with a protection circuit for protecting against the over-voltages.  
         [0014]     Other objects, features, and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only and various modifications may naturally be performed without deviating from the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is a block diagram of a conventional apparatus for powering electric motors;  
         [0016]      FIG. 2  is a block diagram of an apparatus for powering electric motors in accordance with a first embodiment of the present invention;  
         [0017]      FIG. 3  is a circuit diagram of a preferred embodiment of the protection device for protecting against the over-voltages of the apparatus of  FIG. 2 ;  
         [0018]      FIG. 4  is a block diagram of an apparatus for powering electric motors in accordance with a second embodiment of the present invention;  
         [0019]      FIG. 5  is a circuit diagram of a preferred embodiment of the protection device for protecting against the over-voltages of the apparatus of  FIG. 4 ; and  
         [0020]      FIG. 6  shows another embodiment of the device for enabling and preventing powering of the driving device. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0021]     Preferred embodiments of the present invention will be described in detail hereinbelow with reference to the attached drawings.  
         [0022]      FIG. 2  shows an apparatus  100  for powering electric motors according to a first embodiment of the present invention. The elements that are the same as in the apparatus of  FIG. 1  are indicated with the same numerical references. A supply voltage VCV coming from a voltage generator  2  is in input to the apparatus  100 . The apparatus  100  comprises at least one driving device  3  and  5  for driving an electric motor, a supply line  7  between the voltage generator  2  and the driving device, a first device  8 , and a control device  10 . The first device  8  is inserted in the supply line  7  and is suitable for preventing or enabling the powering of the driving device. The control device  10  is suitable for controlling at least the first device  8  and is powered by the supply voltage VCV. Preferably, the control device  10  is also suitable for controlling the circuit elements belonging to the at least one driving device  3  and  5 .  
         [0023]     Preferably, the apparatus  100  is a power combo suitable for powering two electric motors, such as a spindle motor  4  and a voice coil motor  6 , through two different driving devices, a first driving device  5  for driving the voice coil motor  6  and a second driving device  3  for driving the spindle motor  4 . Preferably, the first device  8  is a MOSFET device, and even more preferably it is an ISO-FET device comprising a MOS transistor M 1  and an intrinsic diode D 1 . The driving devices  3  and and the transistor M 1  are controlled by the control device  10  inside the power combo  100 .  
         [0024]     Still inside the apparatus  100 , a protection device  50  is present that is suitable for the protection of the whole apparatus against the over-voltages; the protection device  50  is connected to a circuit node VM of the supply line  7  that is downstream from the first device  8  and upstream from the driving devices  3  and  5 . The protection device  50  comprises a first circuit suitable for detecting the current flow inversion, that is when the current is directed towards the supply voltage generator  2 , and a second circuit suitable for absorbing the current flow.  
         [0025]      FIG. 3  shows a preferred embodiment of the protection device  50  of  FIG. 2 . The second circuit is made up of a MOS transistor Q 2  that has its non-drivable terminals connected respectively to the node VM and to ground and that is driven by the first circuit, which comprises an operational amplifier OPAMP 1  whose output is connected with the drivable terminal of the transistor Q 2 . The transistor Q 2  is preferably an NMOS transistor having its source terminal connected to ground and its drain terminal connected to the node VM. The amplifier OPAMP 1  has its non-inverting input terminal connected to the node VM while on its inverting terminal there is a voltage CLAMP_ref that represents the voltage value at which the protection is required to be carried out. In fact, if the voltage on the node VM is greater than the voltage CLAMP_ref, the transistor Q 2  is turned on and there is the passage of the current Iclamp, that is the current coming from the motors  4  and  6 , through the driving devices  3  and  5 , from the node VM to ground. The value of voltage CLAMP_ref is greater than the supply voltage VCV; for example in one embodiment VCV=13.2V and is fixed, and CLAMP_ref=14.5V.  
         [0026]     The first circuit also comprises a hysteresis comparator COMP 1  that has its input terminals connected to the ends of the first device  8 , that is connected with the non-drivable terminals of the transistor M 1  and with the terminals of the intrinsic diode D 1 . Therefore the inverting terminal is connected to the node VM while on the non-inverting terminal there is a voltage given by VCV+Vth, where the voltage Vth represents the intervention threshold of the comparator COMP 1  with reference to the voltage VCV. The value of the voltage Vth is given by the firing resistance in saturation Rdson (normally some tens of milliohms) of the transistor M 1  for the current that flows in it; that is the value Vth indicates the value of the current that flows in the transistor M 1  at the moment the device  50  intervenes. For example in one embodiment with Rdson=50 mΩ, there can be Vth=10 mV with a current of 200 mA. The output terminal of the comparator COMP 1  is connected to the drivable terminal of another MOS transistor Q 1 , which has one non-drivable terminal connected to the drivable terminal of the transistor Q 2  and the other non-drivable terminal connected to ground. Preferably the transistor Q 1  is an NMOS transistor having the source terminal connected to ground and the drain terminal connected to the gate terminal of the transistor Q 2 . The transistor Q 1  is normally on in order to keep the transistor Q 2  off, but is turned off by the comparator COMP 1  when the voltage on the node VM exceeds the voltage VCV+Vth (for example, VCV+10 mV).  
         [0027]     In this case the difference that the comparator COMP 1  should see is given by the value of the resistance Rdson for the current that flows in the MOS transistor M 1  towards the supply voltage generator  2 . The current generated by the motor cannot pass entirely through the first device  8  but a part of it can flow towards ground through other paths, for example through the capacitance C 2 , of low value, that is positioned between the node VM and ground.  
         [0028]      FIG. 4  shows an apparatus  101  for powering electric motors in accordance with a second embodiment of the present invention. The same elements in common with the first embodiment are indicated with the same numerical references. The apparatus  101  differs from the apparatus  100  of  FIG. 2  in the presence of a different protection device  60  for the protection against the over-voltages that has an output GateDis suitable for driving the first device  8 . The protection device  60 , in turn, differs from the protection device  50  of  FIG. 2 , in the presence of a further circuit suitable for turning off the first device  8 . In this manner, between the supply voltage VCV and the circuit node VM there is only the intrinsic diode D 1  which, in the case in which current flows from the electric motor, that is from the motors  4  and  6 , blocks the passage of the current towards the supply voltage generator  2  while the value of the voltage between the node VM and ground rises and the current can circulate only through the capacitance C 2 .  
         [0029]      FIG. 5  shows a preferred embodiment of the protection device  60  of  FIG. 4 . The further circuit  61  for turning off the first device  8  comprises a further comparator COMP 2  with hysteresis suitable for comparing the voltage on the node VM with a voltage Ref 61  that has an intermediate value between the value of the supply voltage VCV and the voltage CLAMP_ref. More precisely the voltage Ref 61  is supplied to the non-inverting terminal of the further comparator COMP 2  while the voltage VM is supplied to the inverting terminal. When the voltage VM exceeds the voltage Ref 61  the further comparator COMP 2  sends an output signal suitable for turning on a transistor Q 3  whose non-drivable terminals are connected respectively to the drivable terminal of the first device  8  and to ground. Preferably the transistor Q 3  is an NMOS transistor having its source terminal connected to ground and its drain terminal connected to the drivable terminal of the transistor M 1 . The transistor Q 3 , once activated, turns off the transistor M 1  by bringing the signal GateDis to a voltage value that is substantially equal to ground. The rest of the circuitry of the protection device  60  is identical to the circuitry of the protection device  50  of  FIG. 3  and has the same operation.  
         [0030]     The first device  8  used in the above-mentioned embodiments of the present invention can comprise only one transistor M 1  with its own intrinsic diode, or more than one transistor with a relative intrinsic diode, as shown in  FIG. 6 . In the embodiment of  FIG. 6 , the first device  8  comprises two transistors M 2  and M 3  with respective intrinsic diodes Dm 2  and Dm 3 . In this case a resistance R 2  of low value can be inserted, for example 5Ω, at the ends of the diode Dm 2  to limit the value of the current above all at the initial moment of powering the apparatus.  
         [0031]     The apparatus  101  of  FIG. 4  is particularly suited for use in applications in which the first device  8  and the driving device  3  are not integrated in the same chip as the other elements of the apparatus  101 , for example in the case of problems due to high dissipation of power. For the devices  3  and  8  discrete elements are used, for example MOS transistors that have lower firing resistance Rdson characteristics than MOS transistors of the integrated type, that is between 50 and 60 milliohms. The detection of the inversion of the current actuated by the comparator COMP 1  becomes critical given that the voltage at the ends of the firing resistance Rdson is lower (on the order of 5 mV) and is similar to the offset voltage of the comparator.  
         [0032]     With the apparatus  101  of  FIG. 4  , the value of the capacitances C 1  and C 2  has no importance given that with the turning off of transistor M 1  there is no passage of current towards the supply voltage generator  2 .  
         [0033]     While there has been illustrated and described what are presently considered to be the preferred embodiments of the present invention, it will be understood by those skilled in the art that various other modifications may be made, and equivalents may be substituted, without departing from the true scope of the present invention. Additionally, many modifications may be made to adapt a particular situation to the teachings of the present invention without departing from the central inventive concept described herein. Furthermore, an embodiment of the present invention may not include all of the features described above. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed, but that the invention include all embodiments falling within the scope of the appended claims.