Abstract:
The present application describes a system and method for driving a power supply device in an initial activation stage. In one embodiment, the method comprises providing in the power supply device at least one voltage regulator that is coupled with a voltage output adapted to supply a power voltage to a client device, receiving a signal indicative of an activation of the power supply device, and converting the at least one voltage regulator to an equivalent shunting circuit coupled between the voltage output and a reference voltage. Before power voltages are applied at the outputs of the power supply device, shunting paths are thus provided for releasing undesired currents.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is related to a power supply device, and particularly to a system and method for driving a power supply device. 
       BACKGROUND OF THE INVENTION 
       [0002]    When a power supply device is initially activated to supply power voltages to a client device (e.g., a driver integrated circuit (IC)), excessive transient currents and latch-up effects occurring at the output of the power supply device may be susceptible to cause damage and failure of the client device. An excessive transient current, which may be caused by electrostatic discharge or circuit inner residual charges, may result in an excessive amount of heat and burn the internal circuitry of the power supply device, jeopardizing the system reliability. In addition, the latch-up effect, usually triggered by the input of an overload transient current or voltage to the client device, may disrupt the proper operation and possibly leading to the destruction of circuit components in the client device. 
         [0003]    To remedy the aforementioned problems,  FIG. 1  illustrates a conventional approach for preventing excessive transient currents and latch-up effects when the power supply device is initially activated. For this purpose, a protection circuit is externally coupled with each voltage output of a power supply device  102  where a client device is to be connected (not shown). Each protection circuit typically includes an Schottky diode coupled between one output of the power supply device  102  and a reference voltage. For example, with respect to a negative voltage output V N , a Schottky diode  104  is forward-connected from the output V N  to a ground potential. For a positive voltage output V P , a Schottky diode  106  is forward-connected from another reference voltage V DD  to the positive voltage output V P . While these external protection circuits provide effective shunting paths to release excessive transient currents, extra manufacturing costs are required. 
         [0004]    Excessive transient currents and latch-up effects can also be prevented by providing a latch-up detection circuit, as disclosed in U.S. Pat. No. 7,221,027, the disclosure of which is incorporated herein by reference. However, the approach disclosed in this patent still requires a complex layout and additional semiconductor devices, which increases the manufacturing cost. 
         [0005]    Therefore, there is a need for a system and method that can overcome the aforementioned issues in a more cost-effective manner. 
       SUMMARY OF THE INVENTION 
       [0006]    The present application describes a system and method for driving a power supply device in an initial activation stage. In one embodiment, the method for driving the power supply device comprises providing in the power supply device at least one voltage regulator that is coupled with a voltage output adapted to supply a power voltage to a client device, receiving a signal indicative of an activation of the power supply device, and converting the at least one voltage regulator to an equivalent shunting circuit coupled between the voltage output and a reference voltage. 
         [0007]    In one embodiment, a power supply device is also described. The power supply device comprises a first voltage regulator coupled with a first voltage output, and a second voltage regulator coupled with a second voltage output, wherein the first and second voltage outputs are adapted to supply different power voltages to a client device. In response to a signal indicative of an activation of the power supply device, the first voltage regulator is switchable to form an equivalent shunting circuit coupled between the first voltage output and a first reference voltage. 
         [0008]    At least one advantage of the systems and methods described herein is the ability to conveniently convert voltage regulators provided in the power supply device into equivalent shunting circuits. As a result, before power voltages are applied at the outputs of the power supply device, shunting paths are provided for releasing undesired currents. 
         [0009]    The foregoing is a summary and shall not be construed to limit the scope of the claims. The operations and structures disclosed herein may be implemented in a number of ways, and such changes and modifications may be made without departing from this invention and its broader aspects. Other aspects, inventive features, and advantages of the invention, as defined solely by the claims, are described in the non-limiting detailed description set forth below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a block diagram illustrating a conventional power supply device; 
           [0011]      FIG. 2  is a block diagram illustrating a power supply device according to one embodiment of the present invention; 
           [0012]      FIG. 3A  is a diagram illustrating an equivalent shunting circuit formed by a first voltage regulator of the power supply device shown in  FIG. 2 , according to an embodiment of the present invention; 
           [0013]      FIG. 3B  is a diagram illustrating another equivalent shunting circuit formed by a second voltage regulator of the power supply device shown in  FIG. 2 , according to an embodiment of the present invention; and 
           [0014]      FIG. 4  is a flowchart of method steps applied when a power supply device is initially activated, according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0015]      FIG. 2  is a schematic block diagram of a power supply device  200  according to an embodiment of the present invention. The power supply device  200  comprises a PFM/PWM (pulse frequency modulation and/or pulse width modulation) controller  202  coupled with a positive voltage output (V P ) and a negative voltage output (V N ), a first voltage regulator  204  coupled with the positive voltage output V P , a second voltage regulator  206  coupled with the negative voltage output V N , and an inductor  208  having a first node  1  coupled with the first voltage regulator  204  and a second node  2  coupled with the second voltage regulator  206 . The first and second voltage regulators  204  and  206  are operable to supply desired constant voltages through the positive/negative voltage output V P /V N  to a client device  209 . Examples of the client device  209  may include, without limitation, a driving integrated circuit (IC), a controller IC, or the like. 
         [0016]    As shown in  FIG. 2 , the first voltage regulator  204  is connected between the node  1 , the positive voltage output V P  and a reference voltage V SS . In one embodiment, the reference voltage V SS  may be a negative voltage or ground potential. The first voltage regulator  204  includes a first switch element SW 1  that is operable to selectively connect the first node  1  of the inductor  208  with the reference voltage V SS . In one embodiment, the first switch SW 1  can be an n-type MOSFET (metal-oxide-semiconductor field-effect transistor)  210 . A first non-linear element, such as a Schottky diode  214 , is forward-connected from the first node  1  to the positive voltage output V P . The diode  214  turns on in forward-biasing and turns off in reverse-biasing, hence limiting the direction of the electric current that allows increasing of the positive voltage output V P . A first capacitor  212  is coupled between a ground potential and the positive voltage output V P  for maintaining the voltage level at the positive voltage output V P . A first controller  216  is coupled between the positive voltage output V P  and a gate electrode of the MOSFET  210 . The first controller  216  is operable to switch the state of the MOSFET  210  by applying an adequate voltage to the gate electrode of the MOSFET  210 . In one embodiment, the first controller  216  may be incorporated in the PFM/PWM controller  202 . 
         [0017]    Referring again to  FIG. 2 , the second voltage regulator  206  may have a circuitry very similar to the first voltage regulator  204  for regulating the negative voltage output V N . The second voltage regulator  206 , coupled between the second node  2  and the negative voltage output V N , includes a second switch element SW 2  operable to selectively connect the second node  2  of the inductor  208  with a reference voltage V DD . In one embodiment, the reference voltage V DD  is a positive voltage. Further, the second switch SW 2  can be an p-type MOSFET  218 . A second non-linear element, such as a Schottky diode  222 , is forward-connected from the negative voltage output V N  to the second node  2 . The diode  222  turns on in forward-biasing and turns off in reverse-biasing, hence limiting a direction of the electric current that allows decreasing of the voltage level at the negative voltage output V N . A second capacitor  220  is coupled between a ground potential and the negative voltage output V N  for maintaining the voltage level at the negative voltage output V N . A second controller  224  is also coupled between the negative voltage output V N  and a gate electrode of the MOSFET  218 . The second controller  224  is operable to switch the state of the MOSFET  218  by applying an adequate voltage to the gate electrode of the MOSFET  218 . In one embodiment, the second controller  224  may also be integrated in the PFM/PWM controller  202 . While two separate controllers have been illustrated in connection with the first and second voltage regulators  204  and  206 , alternate embodiments may also integrate the two controllers  216  and  224  into a single controller for controlling the MOSFETs  210  and  218  as switch elements SW 1  and SW 2 . 
         [0018]    The inductor  208  coupled between the first and second voltage regulator  204  and  206  is adapted to store energy when both the first switch element  210  and the second switch element  218  turn on. By operation of the first switch element  210  and the second switch element  218 , the stored energy can be released to modify the voltage level of either the positive voltage output V P  or negative voltage output V N . 
         [0019]    At initial activation of the power supply device  200 , by suitably setting the first and second switch SW 1  and SW 2 , each of the first and second voltage regulator  204  and  206  can be selectively converted into an equivalent shunting circuit coupled with either of the positive or negative voltage output V P  and V N . More specifically, when the first switch element SW 1  is OFF (or non-conducting state) and the second switch element SW 2  is ON (or conducting state), the first voltage regulator  204  can advantageously form an equivalent shunting circuit  300  including a shunting diode  302  forward-connected from the reference voltage V DD  to the positive voltage output V P  ( FIG. 3A ). This equivalent shunting circuit can be used for bypassing and releasing excessive currents that may occur at the positive voltage output V P , and also prevent latch-up issues. 
         [0020]    Conversely, when the first switch element SW 1  is ON and the second switch element SW 2  is OFF, the second voltage regulator  206  is converted into a second equivalent shunting circuit  310  including a shunting diode  312  forward-connected from the negative voltage output V N  to the reference voltage V SS  ( FIG. 3B ). At initial activation of the power supply device  200 , this second shunting circuit can likewise act for releasing excessive currents that may occur at the positive voltage output V P . By adequately operating the MOSFETs  210  and  218  as switch elements SW 1  and SW 2 , the first and second voltage regulators  204  and  206  can thus be converted into equivalent shunting circuits adapted to prevent the occurrence of excessive transient currents and latch-up effects. 
         [0021]    In conjunction with  FIGS. 2 ,  3 A and  3 B,  FIG. 4  is a flowchart of method steps applied when the power supply device  200  is initially activated, according to an embodiment of the present invention. At initial step  402 , the power supply device  200  receives an activation signal. Such activation signal may occur when the client device  209  wakes up or is activated. In response to the activation signal, step  404  is then performed, whereby the first voltage regulator  204  is converted into an equivalent shunting circuit by turning off the first switch element SW 1  (i.e., non-conducting state) and turning on the second switch element SW 2  (i.e., conducting state). In one embodiment, the OFF state of the first switch element SW 1  and the ON state of the second switch element SW 2  may be achieved by applying a same first gate voltage to the n-type MOSFET  210  and p-type MOSFET  218 . This first gate voltage may be equal to about the reference voltage V SS , for example. As a result, the first node  1  of the inductor  208  is disconnected from the reference voltage V SS , whereas the second node  2  of the inductor  208  is connected with the reference voltage V DD . As shown in  FIG. 3A , the first voltage regulator  204  consequently forms a first equivalent shunting circuit  300  where the diode  214  acts as a shunting diode  302  forward-connected from the reference voltage V DD  to the positive voltage output V P . Before a power voltage is applied, a shunting path is thereby provided for bypassing and releasing undesired currents that may occur at the positive voltage output V P . 
         [0022]    In next step  406 , the second voltage regulator  206  is converted into a second equivalent shunting circuit by turning on the first switch element SW 1  and turning off the second switch element SW 2 . In one embodiment, the ON state of the first switch element SW 1  and the OFF state of the second switch element SW 2  may be achieved by applying a same second gate voltage to the n-type MOSFET  210  and p-type MOSFET  218 . This second gate voltage may be equal to about the reference voltage V DD , for example. As a result, the first node  1  of the inductor  208  is connected with the reference voltage V SS , whereas the second node  2  of the inductor  208  is disconnected from the reference voltage V DD . As shown in  FIG. 3B , the second voltage regulator  206  consequently forms a second equivalent shunting circuit  310  in which the diode  222  acts as a shunting diode  312  forward-connected from the negative voltage output V N  to the reference voltage V SS . Before a power voltage is applied, a shunting path is thereby provided for bypassing and releasing undesired currents that may occur at the negative voltage output V N . 
         [0023]    In step  408 , the first and second voltage regulator  204  and  206  may then be switched to a regulation mode of operation, where they act to regulate the power voltages applied by the PFM/PWM controller  202  at the positive and negative voltage output V P  and V N . In one embodiment, the regulation of the positive and negative voltage output V P  and V N  may be achieved by, for example, comparing each of the positive and negative voltage output V P  and V N  with predetermined reference values through the controllers  216  and  224 , and accordingly control the conducting states of the n-type MOSFET  210  and p-type MOSFET  218 . 
         [0024]    It will be readily appreciated that while the illustrated embodiment has described a specific sequence where step  404  is performed before step  406 , other embodiments may also perform step  404  and  406  in a different order, for example step  406  may be conducted before step  404 . 
         [0025]    As described above, the voltage regulators provided in the power supply device can be conveniently converted into equivalent shunting circuits at initial activation of the power supply device. The occurrence of excessive currents and latch-up events can thereby be prevented in a more cost-effective manner, without the need of extra diodes coupled external to the power supply device. 
         [0026]    Realizations in accordance with the present invention have been described in the context of particular embodiments. These embodiments are meant to be illustrative and not limiting. Many variations, modifications, additions, and improvements are possible. Accordingly, plural instances may be provided for components described herein as a single instance. Structures and functionality presented as discrete components in the exemplary configurations may be implemented as a combined structure or component. These and other variations, modifications, additions, and improvements may fall within the scope of the invention as defined in the claims that follow