Abstract:
The present invention is an apparatus for testing a power supply. A power supply testing apparatus may include a remote load which may sink an adjustable amount of current with an adjustable slew rate and may test the response of the power supply to determine its operability with a dynamic load. Additionally, in an alternative embodiment of the invention, the testing apparatus may source an adjustable amount of current with an adjustable slew rate to the output of a power supply. In yet another embodiment of the invention, the testing apparatus may include an adjustable current sink and adjustable current source with an adjustable slew rate. The power supply testing apparatus of the present invention may be implemented with standard circuit components on a circuit board and thus provide a small form factor. Additionally, due to the small form factor and low weight implementation, the power supply testing apparatus may utilize reduced length test wires which reduce the inductance in the test wires and increases the apparatus&#39; slew rate for more effective testing.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to the field of power supplies, and more particularly to an apparatus and method for testing a power supply. 
   BACKGROUND OF THE INVENTION 
   Many electrical systems require a fixed and stable supply of electrical energy to operate optimally. One type of electrical system is a computing system. Computing systems typically include a motherboard which may refer to a main circuit board of a computing system. Typically, a motherboard may contain one or more modular or embedded power supplies for supplying power to the various components of a motherboard. Components of a motherboard may include a processor, BIOS, memory, interfaces and controllers which require power to operate. 
   In an application such as a computing system, a power supply may be a DC/DC power supply and may receive a twelve (12) volt input supply and provide a one (1) volt, three (3) volt or five (5) volt output supply to a power bus. Many components may receive power from the power bus, including active and passive switching devices which create a dynamic load. A dynamic load may be a device or set of devices coupled to the output of a power supply that draws varying current. A dynamic load may create load transients which may inject a disturbance into the power supply. The injection of a disturbance into the power supply may affect the power supply output which may negatively affect performance of components being supplied power through the power bus. For example, a processor is extremely sensitive to an unstable power supply and thus a disturbance will affect operation of the processor and the overall performance of a computing system employing the processor. 
   In order to ensure optimal performance of a computing system, load dynamics and steady-state performance of a power supply may be tested. However, it is difficult to adequately test the load dynamics and steady-state performance of a motherboard power supply. Conventional power supply testers include large form factor appliances comprising banks of electronic loads. Thus, conventional power supply testers are heavy and cumbersome. Due to their size and form factor, conventional power supply testers require a fixed placement on a work bench. As a result, long supply wires must be utilized to connect the power supply tester to the output terminals of a power supply under test. This reduces performance and quality of the test due to the substantial inductance of the supply wires which limits the external electronic load slew rate (di/dt). A slew rate may refer to a change in output current divided by a rise/fall time. Rise/fall time may refer to an amount of time required to transition between two values of current. Additionally, the load percentage rating and load dynamics (e.g. 0.5 to 50 A/usec) to a power supply module soldered into the motherboard or embedded into the motherboard (the power supply components are soldered into the motherboard) and loaded by circuits on the motherboard at what load currents and at what slew rate is not always known. Thus, a motherboard power supply must be tested while the power supply is soldered to or embedded into the motherboard. Consequently, an improved apparatus and method for testing a power supply is necessary. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is directed to an apparatus and method for testing a power supply. In an embodiment of the invention, a power supply testing apparatus may include a remote load which may sink an adjustable amount of current with an adjustable slew rate and may test the response of the power supply to determine its operability with a dynamic load. Additionally, in an alternative embodiment of the invention, the testing apparatus may source an adjustable amount of current with an adjustable slew rate to the output of a power supply to compensate what the circuits loading the power supply may load to the power supply. In yet another embodiment of the invention, the testing apparatus may include an adjustable current sink and adjustable current source with an adjustable slew rate. The power supply testing apparatus of the present invention may be implemented with transistors, resistors, diodes and capacitors on a circuit board and may be contained within a small form factor. Additionally, due to the small form factor and low weight implementation, the power supply testing apparatus may utilize reduced length supply wires of less than two inches which reduce the inductance in the supply wires to a value which assures the insertion of the load current into the power supply under test on a motherboard with adequately high slew rate for more effective testing. 
   It is to be understood that both the forgoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The numerous advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying figures in which: 
       FIG. 1  depicts an apparatus for testing a power supply in accordance with an embodiment of the present invention; 
       FIG. 2  depicts a block diagram of an apparatus for testing a power supply in accordance with an embodiment of the present invention; 
       FIG. 3  depicts a schematic diagram of an apparatus for testing a power supply in accordance with an embodiment of the present invention; 
       FIG. 4  depicts a method for testing a power supply in accordance with an embodiment of the present invention; and 
       FIG. 5  depicts a testing apparatus board coupled to a circuit board power supply in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
   Referring generally to  FIGS. 1-5 , exemplary embodiments of an apparatus and method for testing a power supply in accordance with the present invention are shown. The power supply testing apparatus of the present invention may be employed with conventional power supplies to determine the load dynamics and steady-state performance of the power supply. Advantageously, the testing apparatus of the present invention may be assembled in a low weight, small form factor implementation. The low weight, small form factor implementation may be placed in proximity with conventional power supplies, such as power supply modules soldered to a motherboard or embedded into the motherboard of a computing system, to allow short supply wires with reduced inductance than the long supply wires of conventional power supply testers. 
   Referring to  FIG. 1 , an apparatus for testing a power supply in accordance with an embodiment of the present invention is shown. Power supply testing apparatus  110  may be coupled to the output terminals  126 ,  128  of a power supply  120 . Power supply  120  may be a DC/DC power supply which receives a DC input voltage at input terminals  122 ,  124 . Power supply testing apparatus  110  may provide a dynamic load of a few one hundred milliamperes to several hundred amperes with an adjustable slew rate. Power supply testing apparatus  110  may be coupled to a test results device  130  for display of the testing results. In one embodiment of the invention, test results device may be an oscilloscope. Other types of test results devices may include a volt meter and current meter. It is contemplated that testing results may include peak voltage, low voltage, peak current, low current, time response, frequency response and the like. 
   Referring now to  FIG. 2 , a block diagram of an apparatus  110  for testing a power supply in accordance with an embodiment of the present invention is shown. Apparatus  110  may include a controller  210 , a current source  220  and current sink  230 . Controller  210  may operate to control testing of a power supply. In an embodiment of the invention, controller  210  may include a function generator. A function generator may refer to a piece of electronic equipment which may generate repetitive waveforms. The repetitive waveforms from the function generator may be converted into source and sink current by current source  220  and current sink  230  which may be injected into the output terminals of the power supply (as shown in  FIG. 1 ). Waveforms may include a duty cycle of 10 to 90% and may be a frequency up to 1 MHz. It is contemplated that current source  220  may supply a current to the output terminals of a power supply where current sink  230  may receive current from the output terminals of a power supply. Current source  220  may supply a current of a few milliamperes to two hundred (200) amperes. Current sink  230  may receive a current from a few milliamperes to two hundred (200) amperes. While apparatus  110  is shown with a current source  220  and current sink  230 , it is contemplated that apparatus  110  may include a controller  210  and current source  220  in one embodiment of the invention. In another embodiment of the invention, apparatus  110  may include a controller  210  and current sink  230  while omitting the current source  220  for testing of power supplies with reduced load dynamics. 
   Referring to  FIG. 3 , a schematic diagram of an apparatus  300  for testing a power supply in accordance with an embodiment of the present invention is shown. Apparatus  300  may be one exemplary implementation of apparatus  110  of  FIG. 2 . In an embodiment of the invention, apparatus  300  may not include a current source  220  of  FIG. 2  providing a less complex implementation of apparatus  300 . 
   Apparatus  300  may include current sink circuitry which may sink a variable amount of current, for example 0.3 to 200 amperes. Apparatus  300  may include a plurality of stages, six stages  310 - 315  according to one embodiment of the invention for sinking a varying amount of current, for example a few hundred milliamperes to two hundred (200) amperes. Each stage  310 - 315  may include a transistor  320 - 325  respectively. In one embodiment of the invention, transistors  320 - 325  may be field effect transistors (FETs). Transistors  320 - 325  may be emitter-follower buffer transistors. Each stage  310 - 315  may include a current setting resistor  330 - 335  of a different resistance value. Current setting resistor may have a resistance value to test a particular amount of current within each stage. The current sink range may be adjusted by switching one of switches  370 - 375  to control one of stages  310 - 315  and by varying the transistor gate drive voltage from an attached function generator  350  and switching emitter-follower buffer transistors  320 - 325  with different current setting resistors  330 - 335  in their sources. A function generator  350  may be coupled through resistor  355  to two emitter follower buffer transistors  360 ,  362 . Function generator  350  may generate repetitive waveforms. The repetitive waveforms from the function generator  350  may be converted into sink current by stages  310 - 315  and injected into the output terminals of the power supply. Waveforms may include a duty cycle of 10 to 90% and may be a frequency up to 1 MHz. Slew rate may be adjusted through resistance variation of potentiometers  340 ,  341 . 
   An output  390  of apparatus  300 , provided through supply wires (not shown), may be provided from the common drains of the transistors  320 - 325  which may be connected to the output of a power supply on a motherboard, for example. The power supply may be connected to a return terminal  391  of apparatus  300 , which may be coupled to a common ground of apparatus  300 . In an embodiment of the invention, a variable sink current of 1.6 to 200 amperes was tested with a variable slew rate. In an embodiment of the invention, supply wires may be coupled to peak voltage and current supplied by the power supply tested with the apparatus  300  could be monitored to determine if the power supply was capable of handling such a dynamic load. 
   Testing of the power supply may be implemented by coupling leads of a test results device with a test point  380 - 385  and ground of the apparatus. It is contemplated that the test results device may be coupled with an associated test point of the stage which is being utilized to sink the selected amount of current. For example, in one embodiment of the invention, switch  370  could be closed to operate stage  310  and sink a small current of a few milliamperes. The leads of a test results device could be coupled to test point  380  and ground to test the load dynamics of a power supply. It is further contemplated that the slew rate may be adjusted through adjustment of a resistance of potentiometers  340 ,  341 . In another example, switch  375  could be closed to operate stage  315  to sink a current of 200 amperes and test the load dynamics of the power supply with a current sink of 200 amperes. The leads of a test results device could be coupled to test point  385  and ground to test the load dynamics of a power supply. It is further contemplated that current of a value between a few milliamperes and 200 amperes could be tested by closing one of switches  371 - 374  to operate one of stages  311 - 314 . It is further contemplated that each stage of apparatus  300  may be employed to test a power supply across a varying amount of current, whereby each stage is individually operated and tested. In alternative embodiments of the present invention, apparatus  300  may be implemented with various circuit components and configurations for sinking and sourcing a variable amount of current without departing from the scope and intent of the present invention. 
   Referring to  FIG. 4 , a method  400  for testing a power supply in accordance with an embodiment of the present invention is shown. It is contemplated that method  300  for testing a power supply may be implemented with apparatus  300  for testing power supplies as described in  FIG. 3 . Method  400  may include receiving a selection for an amount of current sink  410 . It is contemplated that receiving a selection for an amount of current sink may include the closing of a switch associated with a particular stage for sinking a particular amount of current as described in  FIG. 3 . Current may be sunk from a power supply  420  through a particular stage of the apparatus whereby the load dynamics of the power supply may be tested  430 . It is further contemplated that method  400  may include an adjustment of a slew rate. Slew rate may be adjusted through adjustment of resistance of potentiometers  340 ,  341  of apparatus  300  of  FIG. 3 . It is contemplated that testing results may include peak voltage, low voltage, peak current, low current, time response, frequency response and the like whereby a power supply may be determined to be within a particular set of load dynamic specifications  440 . 
   Referring to  FIG. 5 , a testing apparatus board coupled to a soldered power supply module or embedded power supply module in accordance with an embodiment of the present invention is shown. Testing apparatus board  500  may include the components of apparatus  300  of  FIG. 3  in one embodiment of the invention. Testing apparatus board  500  may be assembled in a low weight, small form factor implementation. For example, testing apparatus board may be implemented with a width of two inches, a length of three inches and a height of one inch. It is further contemplated that testing apparatus board may be implemented in a smaller form factor with dimensions less than a length of three inches, a width of two inches and a height of one inch, the overall form factor being limited only by the space required for integration of the circuit components on a board, chip and the like. A function generator may be coupled to the testing apparatus board  500  and since the testing apparatus board  500  may be assembled in a small form factor implementation, supply wires  510 ,  512  for coupling to a power supply under test may be short. Supply wires  510 ,  512  may also be referred as test wires. Supply wires  510 ,  512  may be varies types of low inductance supply wire, including cladded wire, ribbon cable and coaxial cable. It is contemplated that supply wires  510 ,  512  may be less than two inches. In an embodiment of the invention, an inner wire of coaxial cable may supply the load from apparatus board  500  and the return of the power supply  530  may be connected through the ground shield of the coaxial cable to the ground of the apparatus board  500 . Such short length and use of coaxial cable substantially reduces the inductance to a value which allows injection of a high di/dt current pulses into the power supply  530  compared with supply wires of conventional power supply testers which create a substantial amount of inductance. For example, inductance of a typical two foot twisted pair wire employing #10 wire is at least 500 nanohenry (nH) where a two inch coaxial cable may have an inductance of less than 50 nH. The reduced inductance improves the external electronic load slew rate (di/dt) and enhances the quality of the power supply testing. 
   The testing apparatus board  500  with short supply wires  510 ,  512  allows testing of embedded power supplies and power supplies soldered to a main circuit board  520 , such as a motherboard. A main circuit board  520  may include a power supply  530 , memory  540 , a processor such as a central processing unit (CPU)  550 , PCI slots  560 ,  562  and ISA slots  570 ,  572 . Power supply  530  may be a DC/DC power supply. When a power supply  530  is soldered in or embedded to a main circuit board  520 , it is difficult to determine load percentage rating/dynamics of a power supply  530 . Thus, for effective testing, the power supply  530  may be tested while the power supply  530  is coupled to the main circuit board  520  as allowed by the testing apparatus board  500  of the present invention. 
   It is believed that the system and method and system of the present invention and many of its attendant advantages will be understood by the forgoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely an explanatory embodiment thereof. It is the intention of the following claims to encompass and include such changes.