Abstract:
For protecting a power system, two or three of over current, thermal and under voltage protection circuits are integrated as one protection circuit but operate independently, and one or more protection points thereof are adjusted dynamically in response to detected condition of the power system. Specifically, using voltage and current conditions in the power system to modify the over current protection and the thermal protection maximizes the performance of the power system and covers the process bias in the circuits.

Description:
FIELD OF THE INVENTION 
   The present invention is related generally to electric and thermal protections for power systems and, more particularly, to an arrangement and method for an integrated protection for a power system. 
   BACKGROUND OF THE INVENTION 
   In a power system, there is generally provided some limits or protections to prevent the power system circuit from electric or thermal damages. However, a power system usually suffers the protection point trade off issue as the power system works. If the protection point is choused higher limit in consideration of the process bias, the power system would be put in danger. But if a lower limit is choused, it would limit the system performance. 
   For more clear illustration,  FIG. 1  shows a functional block diagram of a conventional protection scheme for a power system. A protection arrangement  10  is connected to an external power control circuit  12  and a power system  14 , and the power control circuit  12  provides an input voltage VIN as the power source for the protection arrangement  10 . The power system  14  comprises a main circuit  142 , including for example reference voltage generator and amplifier, and a power stage  144  driven by the main circuit  142  to produce a regulated output voltage and an output current. Three protection circuits are provided in the protection arrangement  10 , in which the current limit circuit  102  and the temperature sensor  104  are arranged parallel to control the main circuit  142  and limit over current condition and over thermal condition, and the under voltage circuit  106  will generate an error flag  146  to warren the power system  14  for under voltage condition. As shown in this example, the protection circuits  102 ,  104 , and  106  in the protection arrangement  10  may use reference voltage REF provided by the main circuit  142  as bias control signals. The current limit circuit  102  monitors the output current of the power system  14  and provides a current limit signal VTRI 1  for signaling the main circuit  142  once the output current is detected to hit a predetermined threshold, by which the main circuit  142  may adjust the current level and thus prevents the power system  14  from over current damage. The temperature sensor  104  monitors the working temperature of the power system  14  and provides a thermal protection signal VTRI 2  for signaling the main circuit  142  once the temperature is detected to hit a predetermined threshold, in order to prevent the power system  14  from over thermal damage. The under voltage circuit  106  monitors the output voltage of the power system  14  and provides an under voltage signal VTRI 3  to produce the error flag  146  once the output voltage is detected to hit a predetermined threshold, so as to adjust the output voltage level. 
   However, predetermined settings for the over current protection for the current limit circuit  102  and for the thermal protection for the temperature sensor  104  would be affected because of the process bias in the hardware of the protection arrangement  10 . For example, a thermal protection condition is typically set between 150° C. to 170° C., but it could be down to 130° C. due to the process bias, and thus results in the power system  14  operating abnormally as in higher temperature. If a higher thermal protection condition is set for solving the process bias problem, the power system  14  may be burned-out in over thermal condition; but if a lower thermal protection condition is set, the performance of the power system  14  will decrease. The over current protection has the same problem. 
   Unfortunately, conventional protection circuits are all focusing on passive protections and therefore, they can only protect the power system but not improve the performance of the power system. It is thus desired an integrated protection for a power system with maximum system performance and reduced process bias. 
   SUMMARY OF THE INVENTION 
   Accordingly, an object of the present invention is to provide an arrangement and method for an integrated protection for a power system to maximize the system performance and cover the process bias. 
   According to the present invention, up to three of over current, thermal and under voltage protection circuits could be integrated as one protection circuit but operate independently. However, one or more protection points thereof could be adjusted dynamically in response to detected condition of a power system. In a common case, an arrangement for an integrated protection for a power system comprises a current limit circuit and a temperature sensor to prevent the power system from over current condition and over thermal condition, and an under voltage circuit to generate an error flag to warren the power system, by which if an under voltage issue occurs, the current limit will change to lower level, if an over current issue also occurs, the thermal protection will change to lower level, and if a thermal issue occurs, the power system will shutdown. Using voltage and current conditions in the power system to modify the over current protection and the thermal protection will maximize the performance of the power system and cover the process bias in the arrangement. 
   In a first embodiment of the present invention, an arrangement for an integrated protection for a power system comprises an under voltage circuit to monitor an output voltage of the power system, and to provide an under voltage signal and a first adjustment signal when the output voltage hits a first threshold, a current limit circuit to monitor an output current of the power system and to provide a current limit signal and a second adjustment signal when the output current hits a second threshold, and a temperature sensor to monitor a temperature of the power system and to provide a thermal protection signal when the temperature hits a third threshold, in which the first adjustment signal may adjust the second threshold, and the second adjustment signal may adjust the third threshold. 
   In a second embodiment of the present invention, an arrangement for an integrated protection for a power system comprises an under voltage circuit to monitor an output voltage of the power system and to provide an under voltage signal, a first adjustment signal, and a second adjustment signal when the output voltage hits a first threshold, a current limit circuit to monitor an output current of the power system and to provide a current limit signal and a third adjustment signal when the output current hits a second threshold, and a temperature sensor to monitor a temperature of the power system and to provide a thermal protection signal when the temperature hits a third threshold, in which the first adjustment signal may adjust the second threshold, and the second and third adjustment signals may adjust the third threshold. 
   In a third embodiment of the present invention, an arrangement for an integrated protection for a power system comprises an under voltage circuit to monitor an output voltage of the power system and to provide an under voltage signal and an adjustment signal when the output voltage hits a first threshold, a temperature sensor to monitor a temperature of the power system and to provide a thermal protection signal when the temperature hits a second threshold, in which the adjustment signal may adjust the second threshold. 
   In a fourth embodiment of the present invention, an arrangement for an integrated protection for a power system comprises an under voltage circuit to monitor an output voltage of the power system and to provide an under voltage signal and an adjustment signal when the output voltage hits a first threshold, and a current limit circuit to monitor an output current of the power system and to provide a current limit signal when the output current hits a second threshold, in which the adjustment signal may adjust the second threshold. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  shows a functional block diagram of a conventional protection scheme for a power system; 
       FIG. 2  shows a functional block diagram of a first embodiment according to the present invention; 
       FIG. 3  is a diagram of illustrating the relationship among the under voltage protection, the over current protection, and the thermal protection; 
       FIG. 4  shows a functional block diagram of a second embodiment according to the present invention; 
       FIG. 5  shows a functional block diagram of a third embodiment according to the present invention; 
       FIG. 6  shows a functional block diagram of a fourth embodiment according to the present invention; and 
       FIG. 7  shows a circuit diagram of an embodiment for the protection arrangement shown in  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2  shows a functional block diagram of a first embodiment according to the present invention, in which a protection arrangement  20  is connected with an input voltage VIN from an external power control circuit  22  for getting power, a power system  24  comprises a main circuit  242  and a power stage  244  driven by the main circuit  242  to produce a regulated output voltage and an output current, and the main circuit  242  provides a reference signal REF for the protection arrangement  20  as control signals. In the protection arrangement  20 , a current limit circuit  202  monitors the output current of the power system  24  and provides a current limit signal VTRI 1  to signal the main circuit  242  when the output current hits a predetermined current limit threshold, so as to lower the output current, a temperature sensor  204  monitors the temperature of the power system  24  and provides a thermal protection signal VTRI 2  for signaling the main circuit  242  when the temperature hits a predetermined temperature threshold, so as to avoid over thermal condition, and an under voltage circuit  206  monitors the output voltage of the power system  24  and provides an under voltage signal VTRI 3  for generating an error flag  246  when the output voltage hits a predetermined under voltage threshold, so as to warrant the power system  24  an under voltage condition. In addition, when the system triggers an under voltage protection, the under voltage signal VTRI 3  also signals the current limit circuit  202  to adjust the current limit for over current protection, and if the system further triggers an over current protection, the current limit circuit  202  will also signal the temperature sensor  204  by an adjustment signal Sn to change the thermal protection to a lower level. In this embodiment, the under voltage signal VTRI 3  is also used as the adjustment signal Sn′ to signal the current limit circuit  202  to change the current limit threshold; however, in other embodiments, an alternative one may be used. 
     FIG. 3  is a diagram of illustrating the relationship among the under voltage protection, the over current protection, and the thermal protection, in which dashed lines  30  and  32  are referred to the thresholds for under voltage protection, solid lines  34  and  36  are referred to the thresholds for over current protection, and dashed lines  38  and  39  are referred to the thresholds for thermal protection. Usually, the protection arrangement  20  could be set with higher thresholds to cover the process bias, thereby enhancing the performance of the power system  24 . However, for example by the way illustrated in  FIG. 2 , once the output voltage of the power system  24  reaches an under voltage threshold, for example the dashed line  32 , the protection arrangement  20  will lower the current limit threshold, for example from the solid line  34  to the solid line  36 , and if the output current of the power system  24  also reaches the current limit threshold, the protection arrangement  20  further lowers the temperature limit, for example from the dashed line 38  to the dashed line  39 , in order to prevent the power system  24  from over thermal condition. 
   For example, in a case that the power system  24  of  FIG. 2  is set with a thermal protection temperature 170° C. with a hysteresis 30° C., and a current limit protection at 700 mA, it is referred that in normal circumstances, (1) if the power system  24  suffers high temperature environment as the temperature hitting 170° C., then the power system  24  will shutdown until the temperature lowers down to 140° C., and (2) if the power system  24  suffers heavy loading, then the current limit circuit  202  will clamp the output current at 700 mA, which is the general power system thermal and current limit protections work. However, when the system triggers the under voltage protection, then the under voltage signal VTRI 3  will signal the current limit circuit  202  to change the current threshold to a lower level, for example 500 mA. If the system not only triggers the under voltage protection but also triggers the current limit mechanism, the current limit circuit  202  will signal the temperature sensor  204  to change the thermal protection to a lower level, for example 100° C. By this way, it will adjust the thermal protection as the under voltage and current limit triggered. 
     FIG. 4  shows a functional block diagram of a second embodiment according to the present invention, in which a protection arrangement  40  is connected with an input voltage VIN from an external power control circuit  42  for getting power, a power system  44  comprises a main circuit  442  and a power stage  444  driven by the main circuit  442  to produce a regulated output voltage and an output current, and the main circuit  442  provides a reference signal REF for the protection arrangement  40  as control signals. In the protection arrangement  40 , a current limit circuit  402  monitors the output current of the power system  44  and provides a current limit signal VTRI 1  to signal the main circuit  442  when the output current hits a predetermined current limit, so as to lower the output current, a temperature sensor  404  monitors the temperature of the power system  44  and provides a thermal protection signal VTRI 2  for signaling the main circuit  442  when the temperature hits a predetermined temperature threshold, so as to avoid over thermal condition, and an under voltage circuit  406  monitors the output voltage of the power system  44  and provides an under voltage signal VTRI 3  for generating an error flag  446  when the output voltage hits a predetermined under voltage threshold, so as to warrant the power system  44  an under voltage condition. The under voltage circuit  406  also provides an adjustment signal Sn 0  for the current limit circuit  402  and an adjustment signal Sn 1  for the temperature sensor  404  when an under voltage is triggered, and in this embodiment, the adjustment signal Sn 0  is the same as the under voltage signal VTRI 3 . By this way, if the power system  44  suffers an under voltage condition, it may also adjust the current limit threshold and the thermal protection temperature. Similarly, the current limit circuit  402  also provides an adjustment signal Sn 2  for the temperature sensor  404  when a current limit is triggered, and by this way, if the power system  44  suffers a heavy loading to a current limit case, it may also adjust the thermal protection temperature. As such, the adjustment signals Sn 0  and Sn 1  are used to adjust the temperature threshold of the temperature sensor  404 . 
     FIG. 5  shows a functional block diagram of a third embodiment according to the present invention, in which a protection arrangement  50  is connected with an input voltage VIN from an external power control circuit  52  for getting power, a power system  54  comprises a main circuit  542  and a power stage  544  driven by the main circuit  542  to produce a regulated output voltage and an output current, and the main circuit  542  provides a reference signal REF for the protection arrangement  50  as control signals. In the protection arrangement  50 , a temperature sensor  502  monitors the temperature of the power system  54  and provides a thermal protection signal VTRI 2  to shutdown the power system  54  if the temperature hits a predetermined temperature threshold, and an under voltage circuit  504  monitors the output voltage of the power system  54  and provides an under voltage signal VTRI 3  for generating an error flag  546  if the output voltage hits a predetermined under voltage threshold, so as to warrant the power system  54  an under voltage condition. The under voltage circuit  504  further provides an adjustment signal Sn for the temperature sensor  502  to adjust the thermal protection temperature when it is detected an under voltage occurred. 
     FIG. 6  shows a functional block diagram of a fourth embodiment according to the present invention, in which a protection arrangement  60  is connected with an input voltage VIN from an external power control circuit  62  for getting power, a power system  64  comprises a main circuit  642  and a power stage  644  driven by the main circuit  642  to produce a regulated output voltage and an output current, and the main circuit  642  provides a reference signal REF for the protection arrangement  60  as control signals. In the protection arrangement  60 , a current limit circuit  602  monitors the output current of the power system  64  and provides a current limit signal VTRI 1  to signal the main circuit  642  if a current limit triggered, so as to clamp the output current of the power system  64 , and an under voltage circuit  604  monitors the output voltage of the power system  64  and provides an under voltage signal VTRI 3  for generating an error flag  646  to warren the system if an under voltage occurs. The under voltage circuit  604  also uses the under voltage signal VTRI 3  as an adjustment signal Sn to change the current limit threshold of the current limit circuit  602  when an under voltage is detected. In other embodiments, an alternative signal may be used as the adjustment signal Sn. 
     FIG. 7  shows a circuit diagram of an embodiment for the protection arrangement  40  of  FIG. 4 , and in this embodiment, the under voltage signal VTRI 3  is used as the adjustment signal Sn 1 , and the current limit signal VTRI 1  is used as the adjustment signal Sn 2 . In the under voltage circuit  406 , the output voltage Vout of the power system  44  is divided by a voltage divider of resistors R 1  and R 2  to generate a feedback voltage VFB, and a compactor  4062  compares the feedback voltage VFB with a reference voltage Vref to determine the under voltage signal VTRI 3 . In the current limit circuit  402 , resistors R 3  and R 4  are connected in series between a power source Vcc and a node A, a PMOS M 1  is parallel connected to the resistor R 3  with its control gate connected with the under voltage signal VTRI 3 , a bipolar junction transistor (BJT) B 1  and a current source I 1  are connected in series between the power source Vcc and ground GND with its base of the BJT B 1  connected to the node A, and the output current I L  of the power system  44  or a current proportional thereto is drawn from the node A. When the feedback voltage VFB is greater than the reference voltage Vref, the output VTRI 3  of the comparator  4062  keeps the PMOS M 1  on, and thereby bypasses the resistor R 3 . Accordingly, the output current I L  flows through the PMOS M 1  and the resistor R 4 , and in this case, the voltage on the node A increases as the output current I L  increases. However, once the voltage on the node A is high enough to turn on the BJT B 1 , which indicates the output current I L  hits a current limit threshold and the current limit signal VTRI 1  is produced to signal the main circuit  442  to clamp the output current I L . On the other hand, if the feedback voltage VFB hits the reference voltage Vref, the output VTRI 3  of the comparator  4062  will turn off the PMOS M 1 , and thus the output current I L  flows through the resistors R 3  and R 4 . According to the Ohm&#39;s law, a current decreases with an increase in resistance when a constant voltage is supplied for a closed loop. Hence, the BJT B 1  could be turned on by a lower output current I L , which indicates a lower current limit threshold for triggering the current limit signal VTRI 1 . In the temperature sensor  404 , a current source  12  is connected between the power source Vcc and a node B, a BJT B 2  is connected between a current source  13  and ground GND with its base connected to the node B, two thermal resistors R 5  and R 6  are connected in series between the node B and ground GND, a NMOS M 2  is parallel connected to the resistor R 6  with its control gate connected to the output of a XOR gate  4042  which is controlled by the adjustment signals Sn 1  (or VTRI 3 ) and Sn 2  (or VTRI 1 ). When the output voltage Vout and the output current I L  both do not reach the thresholds for protection, the current limit signal VTRI 1  and the under voltage signal VRTI 3  are low level, and the NMOS M 2  turns on accordingly, so that the current I 2  flows through the resistor R 5  and the NMOS M 2 . If the temperature increases, the resistance of the resistor R 5  increases too, and the voltage on the node B increases accordingly. Once the voltage on the node B is high enough to turn on the BJT B 2 , which indicates the temperature hits the thermal protection temperature, the thermal protection signal VTRI 2  is triggered to signal the main circuit  442  to shutdown the system. On the other hand, the NMOS M 2  is turned off by the adjustment signals Sn 1  and Sn 2  if the output voltage Vout and the output current I L  trigger the under voltage and current limit protections, which results in the current I 2  flowing through the resistors R 5  and R 6 . According to the Ohm&#39;s law, in a closed loop, a voltage increases with an increase in resistance when a constant current is supplied thereto. Hence, the BJT B 2  could be turned on at a lower temperature, which indicates a lower thermal protection temperature. 
   Although the circuit of  FIG. 7  is illustrated for the protection arrangement  40  of  FIG. 4 , the circuits for the others shown in  FIGS. 2 ,  5 , and  6  could be conducted therefrom. For example, by replacing the XOR  4042  with the adjustment signal Sn (e.g., using the current limit signal VTRI 1 ) through an inverter to control the NMOS M 2  in the temperature sensor  404  of  FIG. 7 , it will be an embodiment for the protection arrangement  20  of  FIG. 2 ; or, for the protection arrangement  50  of  FIG. 5 , the current limit circuit  402  and the XOR gate  4042  in the temperature sensor  404  of  FIG. 7  are removed, and the under voltage signal VTRI 3  is connected through an inverter to the gate of the NMOS M 2  instead; or, removing the temperature sensor  404  of  FIG. 7  will obtain an embodiment for the protection arrangement  60  of  FIG. 6 . 
   While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as set forth in the appended claims.