Abstract:
A system and a method for detecting an operational fault condition in a power supply are provided. The power supply has a controller operably coupled to first and second switches. The first and second switches are connected in series between a voltage source and a ground node, wherein a first electrical node is electrically coupled between the first and second switches. The first electrical node is further coupled to a first end of an inductor. The controller is configured to induce the first and second switches to apply voltage pulses to the first electrical node. The method includes monitoring a voltage at the first electrical node to determine a number of voltage pulses being applied to the first electrical node over a predetermined time interval. The method further includes determining when a first operational fault condition has occurred when the number of voltage pulses being applied to the first electrical node over the predetermined time interval is less than or equal to a predetermined number of voltage pulses.

Description:
BACKGROUND OF INVENTION 
   In a redundant power supply system, electrical power is supplied by a plurality of power supplies electrically connected in parallel to one another. Generally, a desired system power requirement can be obtained by utilizing the combined output of N power supplies. By adding one additional backup power supply, resulting in N+1 power supplies in the power supply system, the system can electrically remove a failed power supply to avoid a power disruption and still meet the desired system power requirement of N power supplies. 
   Monitoring circuits have been developed that monitor the operation of a power supply by measuring a DC voltage at an output terminal on the power supply. However, a drawback with the other monitoring circuits is that the power supply may be malfunctioning for a relatively large amount of time before the fault condition causes a voltage or current variance at a power supply output terminal that is detected by the monitoring circuit. 
   Thus, there is a need for a monitoring system that can detect operational fault conditions in a power supply utilizing internal signals generated by the power supply, instead of merely monitoring a voltage at a power supply output terminal. Internal signals of a power supply are defined as any signal, such as a pulse width modulation signal for example, generated within a power supply to subsequently generate an output voltage at an output terminal of the power supply. 
   SUMMARY OF INVENTION 
   A method for detecting an operational fault condition in a power supply in accordance with an exemplary embodiment. The power supply has a controller operably coupled to first and second switches. The first and second switches are connected in series between a voltage source and a ground node, wherein a first electrical node is electrically coupled between the first and second switches. The first electrical node is further electrically coupled to a first end of an inductor. The controller is configured to induce the first and second switches to apply voltage pulses to the first electrical node. The method includes monitoring a voltage at the first electrical node to determine a number of voltage pulses being applied to the first electrical node over a predetermined time interval. The method further includes determining when a first operational fault condition has occurred when the number of voltage pulses being applied to the first electrical node over the predetermined time interval is less than or equal to a predetermined number of voltage pulses. 
   A system for detecting an operational fault condition in a power supply in accordance with another exemplary embodiment is provided. The power supply has a controller operably coupled to first and second switches. The first and second switches are connected in series between a voltage source and a ground node, wherein a first electrical node is electrically coupled between the first and second switches. The first electrical node is further electrically coupled to a first end of an inductor. The controller is configured to induce the first and second switches to apply voltage pulses to the first electrical node. The system includes a voltage pulse detection circuit operably coupled to the first electrical node that determines the number of voltage pulses being applied to the first electrical node over a predetermined time interval, the voltage pulse detection circuit generating a first signal indicating that a first operational fault condition has occurred when the number of voltage pulses being applied to the first electrical node over the predetermined time interval is less than or equal to a predetermined number of voltage pulses. 
   A system for detecting an operational fault condition in a power supply in accordance with another exemplary embodiment is provided. The power supply has a controller operably coupled to first and second switches. The first and second switches are connected in series between a voltage source and a ground node, wherein a first electrical node is electrically coupled between the first and second switches. The first electrical node is further electrically coupled to a first end of an inductor. The controller is configured to induce the first and second switches to apply voltage pulses to the first electrical node. The method includes a means for monitoring a voltage at the first electrical node to determine a number of voltage pulses being applied to the first electrical node over a predetermined time interval. The method further includes a means for determining when a first operational fault condition has occurred when the number of voltage pulses being applied to the first electrical node over the predetermined time interval is less than or equal to a predetermined number of voltage pulses. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a schematic of a power supply system; 
       FIG. 2  is a more detailed schematic of a power supply in the power supply system of  FIG. 1  having a diagnostic system in accordance with an exemplary embodiment; 
       FIG. 3  is a detailed schematic of a voltage pulse detection circuit utilized in the power supply of  FIG. 2 ; 
       FIG. 4  is a voltage level detection circuit utilized in the power supply of  FIG. 2 ; 
       FIG. 5  is a schematic of a signal generated by a pulse width modulation controller at a node  64  of  FIG. 2 ; 
       FIG. 6  is a schematic of a signal generated at a node  82  of the voltage pulse detection circuit of  FIG. 3 ; 
       FIG. 7  is a schematic of a first operational fault signal generated by the voltage pulse detection circuit of  FIG. 2 ; 
       FIG. 8  is a schematic of a signal generated at a node  66  of the power supply of  FIG. 2 ; 
       FIG. 9  is a schematic of a second fault signal generated by a voltage level detection circuit of  FIG. 2 ; 
       FIG. 10  is a schematic of a signal generated by a logic gate of the low-voltage detection circuit of  FIG. 2 . 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , a power supply system  10  for generating electrical power is illustrated. The power supply system  10  includes power supplies  12 ,  14 ,  16 , a load  18 , electrical lines  20 ,  22 . As shown, each of the power supplies  12 ,  14 ,  16  and the load  18  are electrically coupled in parallel via electrical lines  20 ,  22 . Because power supplies  12 ,  14 ,  16  have substantially similar circuitry, only power supply  12  will be explained in greater detail below. It should be noted, that the system for detecting fault conditions in the power supply system  10 , which will be explained below, can be utilized with circuitry used in any switch mode power supplies. 
   Referring to  FIG. 2 , a detailed schematic of the power supply  12  is illustrated. The power supply system  12  comprises a buck topology switching power supply system. The power supply  12  includes a voltage source  30 , a pulse-width modulation (PWM) controller  32 , switches  34 ,  36 , an inductor  38 , a capacitor  40 , a switch  42 , a bias power supply  44 , a voltage pulse detection circuit  46 , a voltage level detection circuit  48 , and a logic gate  50 . The voltage source  30  supplies a DC voltage between nodes  60 ,  62 . 
   The switches  34 ,  36  provide voltage pulses using a voltage from the voltage source  30  that are applied to the inductor  38 . The switch  34  is electrically coupled between a node  60  and a node  64 . The switch  36  is electrically coupled between the node  62  and the node  64 . The switches  34 ,  36  are also operably coupled to the PWM controller  32 . The PWM controller  32  generates control signals that induce the switches  34 ,  36  to open and close to generate voltage pulses for the inductor  38 . Further, the plurality of voltage pulses are applied at a predetermined frequency at the node  64 . The PWM controller  32  can vary the duty cycle of the voltage pulses to adjust a DC output voltage at the node  66  to a predetermined level. 
   The inductor  38  is operably coupled between a node  64  and the node  66  coupled to the capacitor  40 . The capacitor  40  is electrically coupled between the node  66  and the node  62 . The combination of the inductor  38  and the capacitor  40  converts the voltage pulses applied to the node  64  to a DC voltage at a predetermined voltage level at the node  66 . 
   The switch  42  is operably coupled between the node  66  and the electrical line  20 . The switch  42  further is operably coupled to the logic gate  50 . When either the voltage pulse detection circuit  46  or a voltage level detection circuit  48  detects an operational fault condition, the logic gate  50  transmits a signal (F 3 ) to the switch  42  having a high logic level. In response, the switch  42  moves to an open operational position to prevent current from flowing from the inductor  38  and/or capacitor  40  to the load  18 . Alternately, when neither the voltage pulse detection circuit  46  nor the low-voltage detection circuit  48  detects an operational fault condition, the logic gate  50  transmits a signal (F 3 ) to the switch  42  having a low logic level. In response, the switch  42  moves to a closed operational position to supply current from the inductor  38  and/or capacitor  40  to the load  18 . 
   The bias power supply  44  is operably coupled between the node  60  and the node  62  to supply a voltage to the voltage pulse detection circuit  46  and the voltage level detection circuit  48 . The bias power supply  44  is electrically coupled to both the circuit  46  and the circuit  48  at a node  68 . The bias power supply  44  is further electrically coupled to the circuit  46  and the circuit  48  at a node  70 . 
   Referring to  FIG. 3 , the voltage pulse detection circuit  46  is provided to detect when either of switches  34 ,  36  are stuck in an open or closed operational position, that is indicative of a first fault condition of the power supply  12 . When such a condition occurs, one or more voltage pulses that should be detected at the node  64  are not detected. The voltage pulse detection circuit  46  includes a comparator  80 , a resistor  84 , a capacitor  86 , and a diode  88 . A non-inverting terminal (+) of the comparator  80  is electrically coupled to a node  82  and an inverting terminal (−) of the comparator  80  receives a reference voltage (VREF 1 ). The resistor  84  is electrically coupled between the node  68  and the node  82 . Further, a diode  88  is electrically coupled between the node  82  and the node  64 . Finally, a capacitor  86  is electrically coupled between the node  82  and the node  70 . 
   When a voltage pulse at the node  64  has a high logic value, electrical current flows through the resistor  84  to the capacitor  86  to charge the capacitor  86 . As the capacitor  86  charges, a voltage increases at the node  82 . When the voltage at node  82  becomes greater than the voltage (VREF 1 ), the comparator  80  generates a fault signal (F 1 ) having a high logic level that is transmitted to the logic gate  50 . The time constant of the resistor  84  and the capacitor  86  is greater than one or more periods of the voltage pulses being applied to node  82  at a predetermined frequency. This time constant ensures that noise and other perturbations will not cause false triggering of a fault condition. In the exemplary embodiment, the time constant of the resistor  84  and the capacitor  86  is equal to the time duration of a time period from a time (T 3 ) to a time (T 7 ) representing three time periods of the voltage pulses. Thus, in the exemplary embodiment, when the three voltage pulses are not detected at the node  64 , the comparator  80  generates the fault signal (F 1 ) having the high logic level. Alternately, when the voltage at node  82  is less than the voltage (VREF 1 ), the comparator maintains the fault signal (F 1 ) at a low logic level indicating that the first fault condition has not been detected. 
   Referring to  FIG. 4 , the voltage level detection circuit  48  is provided to detect when an output voltage at the node  66  is below a predetermined threshold voltage that is indicative of a second fault condition of the power supply  12 . The second fault condition can occur when the switch  36  is electrically shorted, which induces the voltage at the node  66  to fall below the threshold voltage (VREF 2 ). The voltage level detection circuit  48  includes a comparator  90  having a non-inverting terminal (+) and an inverting terminal (−). The inverting terminal (−) is electrically coupled to the node  66 . The non-inverting terminal (+) receives the reference voltage (VREF 2 ). When a voltage applied to the node  66  falls below the reference voltage (VREF 2 ), the comparator  90  outputs a second fault signal (F 2 ) having a high logic level that is indicative of a second fault condition of the power supply  12 . 
   The logical OR gate  50  is operably coupled to the voltage pulse detection circuit  46  and to the voltage level detection circuit  48  and receives the first and second fault signals (F 1 ), (F 2 ) from the circuits  46 ,  48 , respectively. When either of the signals (F 1 ), (F 2 ) have a high logic level, the gate  50  generates a fault signal (F 3 ) having a high logic level which is transmitted to the switch  42 . In response, the switch  42  moves to an open operational position to stop the flow of current from the power supply  12  through the electrical line  20 . When both of the signals (F 1 ), (F 2 ) have a low logic level, the gate  50  generates a fault signal (F 3 ) having a low logic level that is transmitted to the switch  42 . In response, the switch  42  moves to a closed operational position to allow current to flow through the electrical line  20  from the power supply  12 . 
   Referring to  FIGS. 3 ,  5 – 7 , the detection of fault conditions within the power supply  12  will now be explained. The PWM controller  64  induces the switches  34 ,  36  to generate the voltage pulses  110 ,  112 ,  114 , and  116 . As shown, each of the pulses  110 ,  112 ,  114  comprise a high logic level with a time duration of (ΔT 1 ) indicative of normal operation of the power supply  12 . The voltage pulse  116  has a high logic level with the time duration equal to that of two voltage pulse periods. In other words, one additional voltage pulse that should be present was not detected. However, since the voltage at the node  82  of the comparator  90  never exceeds the reference voltage (VREF 1 ), the voltage pulse detection circuit  70  does not generate a fault signal having high logic value. Thereafter, the switches  34 ,  36  generate the voltage pulse  117  having a high logic level having a time duration equal to that of three voltage pulse periods. Because the voltage at the node  82  exceeds the reference voltage (VREF 1 ) between time (T 6 ) and time (T 7 ), the comparator  90  generates a first fault signal (F 1 ) having a high logic value during this time interval. In response to the signal (F 1 ), the logic gate  50  generates a fault signal (F 3 ) having a high logic value that induces the switch  42  to move to an open operational position. Thus, when at least three missing pulses are detected at the node  64 , the switch  42  is moved to an open operational position to prevent current flow from the power supply  12  to the electrical line  20 . 
   Referring to  FIGS. 4 , and  8 – 10 , between times (T 4 ) and (T 5 ), the voltage at node  66  is less than the reference voltage (VREF 2 ). In response, the comparator  90  of the voltage level detection circuit  48  generates a second fault signal (F 2 ) having a high logic value during the time interval from (T 4 ) to (T 5 ). In response to the signal (F 2 ), the logic gate  50  generates the third fault signal (F 3 ) having a high logic level that induces the switch  42  to move to an open operational position. When a voltage greater than a reference voltage (VREF 2 ) is detected at the node  66 , the switch  42  is moved to an open operational position to prevent current flow from the power supply  12  to the electrical line  20 . 
   The system and method for detecting operational fault conditions in a power supply provides a substantial advantage over other systems and methods. In particular, the system and method provide a technical effect of detecting operational fault conditions in a power supply utilizing internal signals generated by the power supply, instead of merely monitoring an output voltage of the power supply. Thus, the inventive system allows fault conditions to be detected more quickly than other systems, to prevent a disruption of electrical power to the load  18 . 
   While the invention is described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalence may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to the teachings of the invention to adapt to a particular situation without departing from the scope thereof. Therefore, it is intended that the invention not be limited to the embodiment disclosed for carrying out this invention, but that the invention includes all embodiments falling within the scope of the intended claims. Moreover, the use of the term&#39;s first, second, etc. does not denote any order of importance, but rather the term&#39;s first, second, etc. are used to distinguish one element from another.