Abstract:
An exemplary voltage variance tester includes a first to a third testing circuits each comprising an adjustable power source and an electrical switch; a first to a third signal generators providing a first to a third signals respectively; a connector having a first to a third terminals connected to the first to the third testing circuits respectively for receiving the adjustable power sources, a fourth to a sixth terminals connected to the first to the third signal generators for receiving the first to the third signals, and a seventh terminal; and a control circuit connected to the seventh terminal of the connector for receiving a power on signal to turn on the first to third electrical switch, wherein, voltage variances of the motherboard are tested by adjusting the first to the third adjustable power sources.

Description:
BACKGROUND  
   1. Field of the Invention 
   The present invention relates to testers, and particularly to a voltage variance tester. 
   2. Description of Related Art 
   A typical microprocessor-cored computer system, such as a personal computer or a workstation computer, is turned on and off by a switch device that mechanically connects/disconnects a power supply of the computer system to/from an external voltage source, such as AC 110V. The power supply is connected to the external voltage source and transforms the external voltage into a predetermined DC level, such as +3.3V, ±5V and ±12V, and the computer system is turned on to perform various programs and functions. 
   As known by a person skilled with computers, power supplies are typically either ATX power supply or BTX power supply. A motherboard of a computer can be coupled to the BTX power supply via a 24-pin BTX power connector. The BTX power supply provides +3.3V, ±5V, ±12V, +5V_STBY (stand by), PS-ON (power supply on) signal and PWROK (power ok/power good) signal to a motherboard of the computer. However, each type of power supply has a unique voltage variance/range centered about its rated output; therefore operators need to test a voltage variance of the motherboard corresponding to the power supply output to make sure the motherboard is compatible with that type of power supply. 
   What is needed, therefore, is a voltage variance tester which can test voltage variance of a motherboard. 
   SUMMARY 
   An exemplary voltage variance tester includes a first testing circuit comprising a first adjustable power source and a first electrical switch; a second testing circuit comprising a second adjustable power source and a second electrical switch; a third testing circuit comprising a third adjustable power source and a third electrical switch; a first signal generator connected to the third adjustable power source and providing a first signal; a second signal generator connected to the second testing circuit and the first signal generator to receive the second adjustable power source and the first signal and providing a second signal according to the second adjustable power source and the first signal; a third signal generator connected to the third testing circuit and providing a third signal; a connector arranged to connect to a power connector of a motherboard, the connector having a first to a third terminals connected to the first to third testing circuits respectively for receiving the adjustable power sources via the electrical switches, a fourth to a sixth terminals connected to the first to the third signal generators respectively for receiving the first to the third signals, and a seventh terminal; and a control circuit connected to the seventh terminal of the connector for receiving a power on signal to turn on the first to third electrical switch, wherein, voltage variances of the motherboard are tested by adjusting the first to the third adjustable power sources. 
   Other advantages and novel features of the present invention will become more apparent from the following detailed description of preferred embodiment when taken in conjunction with the accompanying drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a circuit diagram of a voltage variance tester in accordance with an embodiment of the present invention comprising three testing circuits, a 5V_STBY generator, a PWROK generator, a −12V generator, and a connector; 
       FIG. 2  is a circuit diagram of the 5V_STBY generator of  FIG. 1 ; 
       FIG. 3  is a circuit diagram of the testing circuits of  FIG. 1 ; 
       FIG. 4  is a circuit diagram of the PWROK generator of  FIG. 1 ; 
       FIG. 5  is a circuit diagram of the −12V generator of  FIG. 1 ; and 
       FIG. 6  is a circuit diagram of the connector of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , a voltage variance tester in accordance with an embodiment of the present invention includes a 3.3V testing circuit  10 , a 5V testing circuit  20 , a 12V testing circuit  30 , a control circuit  40 , a 5V_STBY generator  50  arranged to generate a 5V standby voltage, a PWROK generator  60  arranged to generate a power ok signal, a −12V generator  70  arranged to generate a −12V voltage, a connector  80 , and an indicator circuit  90 . In this embodiment of the invention, the connector  80  is a 24-pin BTX power connector. 
   Referring to  FIG. 2  and  FIG. 6 , the 5V_STBY generator  50  includes a voltage regulator U 1  and two capacitors C 1  and C 2 . The voltage regulator U 1  is a 7805 voltage regulator with an input terminal VIN connected to an adjustable power source C and grounded via the capacitor C 1 , a ground terminal GND grounded, and an output terminal VOUT grounded via the capacitor C 2  and connected to a +5V_AUX terminal of the connector  80  for providing a 5V voltage. 
   Referring to  FIG. 3  and  FIG. 6 , the 3.3V testing circuit  10  includes an adjustable power source A, an NMOS transistor Q 1  functioning as an electrical switch, and two capacitors C 3  and C 4 . The drain of the NMOS transistor Q 1  is connected to the adjustable power source A and grounded via the capacitor C 3 , and the source of the NMOS transistor Q 2  is connected to a 3.3V terminal of the connector  80  and grounded via the capacitor C 4 . 
   The 5V testing circuit  20  includes an adjustable power source B, an NMOS transistor Q 2  functioning as an electrical switch, and two capacitors C 5  and C 6 . The drain of the NMOS transistor Q 2  is connected to the adjustable power source B and grounded via the capacitor C 5 , and the source of the NMOS transistor Q 2  is connected to a +5V terminal of the connector  80  and grounded via the capacitor C 6 . 
   The 12V testing circuit  30  includes a PMOS transistor Q 3  functioning as an electrical switch, two capacitors C 7  and C 8 , and a resistor R 5 . The drain of the PMOS transistor Q 3  is connected to a +12V terminal of the connector  80  and grounded via the capacitor C 8 , the source of the PMOS transistor Q 3  is connected to the adjustable power source C and grounded via the capacitor C 7 , and the gate of the PMOS transistor Q 3  is connected to the adjustable power source C via the resistor R 5 . 
   The control circuit  40  includes four transistors T 1 ˜T 4  and four resistors R 1 ˜R 4 . The base of the transistor T 1  is connected to a PS_ON terminal of the connector  80  via the resistor R 1 , and the collector of the transistor T 1  is connected to the base of the transistor T 2 . The base of the transistor T 2  is connected to the output terminal VOUT of the voltage regulator U 1  of the 5V_STBY generator  50  via the resistor R 2 , and the collector of the transistor T 2  is connected to the base of the transistor T 3 . The base of the transistor T 3  is connected to the adjustable power source C via the resistor R 3 , and the collector of the transistor T 3  is connected to the gates of the NMOS transistors Q 1  and Q 2 . The gate of the transistor T 4  is connected to the collector of the transistor T 3  and to the adjustable power source C via the resistor R 4 , and the collector of the transistor T 4  is connected to the gate of the PMOS transistor Q 3 . The source of the transistors T 1 ˜T 4  are grounded. 
   Referring to  FIG. 4  and  FIG. 6 , the PWROK generator  60  includes two comparators U 2  and U 3 , four resistors R 6 ˜R 9 , a capacitor C 9 , and a diode D 1 . The non-inverting input terminal of the comparator U 2  is connected to the source of the NMOS transistor Q 2  of the 5V testing circuit  20  via the resistor R 6  and grounded via the capacitor C 9 . The inverting input terminal of the comparator U 2  is connected to the output terminal VOUT of the voltage regulator U 1  of the 5V_STBY generator  50  via the resistor R 7  and grounded via the resistor R 8 . The output terminal of the comparator U 2  is connected to a PWROK terminal of the connector  80  and connected to the source of the NMOS transistor Q 2  of the 5V testing circuit  20  via the resistor R 9 . The non-inverting input terminal of the comparator U 3  is connected to the inverting input terminal of the comparator U 2 , the inverting input terminal of the comparator U 3  is connected to the PS_ON terminal of the connector  80 , and the output terminal of the comparator U 3  is connected to the cathode of the diode D 1 . The anode of the diode D 1  is connected to the non-inverting input terminal of the comparator U 2 . 
   Referring to  FIG. 5  and  FIG. 6 , the −12V generator  70  includes a timer U 4 , three resistors R 10 ˜R 12 , four capacitors C 10 ˜C 13 , and two diodes D 2  and D 3 . The timer U 4  includes a power terminal VCC, a ground terminal GND, a reset terminal /R, a trigger terminal /TR, a control terminal CO, a threshold voltage terminal TH, a discharging terminal D, and an output terminal OUT. The power terminal VCC and the reset terminal /R of the timer U 4  are connected to the drain of the PMOS transistor Q 3  and grounded via the resistors R 10 ˜R 11  and the capacitor C 10  in turn, the ground terminal GND is grounded, the trigger terminal /TR and threshold voltage terminal TH are grounded via the capacitor C 10 , the discharging terminal D is connected to a node between the resistors R 10  and R 11 , the control terminal CO is grounded via the capacitor C 11 , and the output terminal is connected to the anode of the diode D 3  via the capacitor C 12  and to the cathode of the diode D 2  via the capacitor C 12 . The cathode of the diode D 3  is grounded, and the anode of the diode D 2  is connected to a −12V terminal of the connector  80  and grounded via the capacitor  13  and resistor R 12  connected in parallel. 
   In this embodiment of the invention, the connector  80  is coupled to a corresponding connector of a motherboard, the adjustable power sources A˜C provide 3.3V, 5V, and 12V voltages to the motherboard respectively, and the 5V_STBY generator  50  provides the 5V voltage as a 5V_STBY power source. When the motherboard is turned on, the PS_ON terminal of the connector  80  is at a low level, therefore the transistor T 1  is turned off, the transistor T 2  is turned on, the transistor T 3  is turned off, and the transistor T 4  is turn. The NMOS transistors Q 1 ˜Q 2  and the PMOS transistor Q 3  are turned on. 
   In the PWROK generator  60 , the capacitor C 9  is charged by the 5V_STBY generator  50  to make the output terminal of the comparator U 2  at a high level when a voltage on the capacitor C 9  is higher than a voltage on the resistor R 8 , therefore the PWROK terminal of the connector  80  is at a high level. 
   In the −12V generator  70 , the capacitor C 10  is charged by the 12V testing circuit  30 . When voltage across the capacitor C 10  rises to 4V, the timer U 4  is triggered to output a 12V voltage charging the capacitor C 12 . When the voltage across the capacitor C 10  rises to 8V, the timer U 4  is reset to stop outputting and the capacitor C 10  is discharged. At this time, the voltage across the capacitor C 12  is 12V providing a −12V to the motherboard. 
   Therefore, when the motherboard is turned on, the voltage variance tester is turned on to provide 3.3V, 5V, 12V, and −12V voltages to the motherboard and functions as a computer power supply. Then, operators can adjust the adjustable power sources A˜C to test voltage variances of the motherboard. For example, if the motherboard turns off when the adjustable power source A is set lower than 2.67V or higher than 3.63V, then voltage variance is 2.67-3.63V for the 3.3V input. The indicator circuit  90  is provided to show whether the voltage variance tester is turned on or off. 
   The foregoing description of the exemplary embodiments of the invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to enable others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.