Abstract:
A device for monitoring a voltage of a motherboard includes a first monitoring circuit, a second monitoring circuit, and an indicating circuit. The first and monitoring circuits are connected to output a control voltage. A value of the control voltage is determined according to a value of the voltage of the motherboard. The control voltage is reduced to control the indicating circuit. The indicating circuit indicates whether the voltage of the motherboard is normal.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to monitoring devices, and particularly to a monitoring device for monitoring voltages of a computer motherboard. 
         [0003]    2. Description of Related Art 
         [0004]    In a computer system, a power supply provides power to the motherboard. The motherboard then provides the power at certain voltages such as +5 volts (V), −5V, +3.3V, +12V, −12V, and so on, to chipsets or circuits on the motherboard. However, if any of the voltages provided by the motherboard becomes too high, the chipsets or circuits may be damaged, or if the voltage provided by the motherboard is too low, the chipsets or circuits may be unable to operate properly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0005]    The drawing is a circuit diagram of an embodiment of a device for monitoring a voltage of a computer motherboard. 
       
    
    
     DETAILED DESCRIPTION 
       [0006]    Referring to the drawing, an embodiment of a device is used to monitor a voltage V_meas of a motherboard  100 . The device includes two monitoring circuits  1  and  2 , a voltage reduction circuit  3 , and an indicating circuit  4 . 
         [0007]    The monitoring circuit  1  includes resistors R 1 -R 6 , a comparator U 1 , a variable resistor R 30 , an electric switch Q 1 , and a light-emitting diode (LED) D 1 . A first end of the resistor R 1  receives the voltage V_meas. A second end of the resistor R 1  is connected to a first end of the resistor R 2 . A second end of the resistor R 2  is grounded. A first end of the resistor R 3  receives an external voltage V 1 . A second end of the resistor R 3  is connected to a first end of the variable resistor R 30 . A second end of the variable resistor R 30  is grounded. In this embodiment, the external voltage V 1  is provided by a power supply, such as an advanced technology expanding (ATX) power supply of the motherboard. The comparator U 1  includes a power terminal, a ground terminal, a non-inverting input terminal, an inverting input terminal, and an output terminal. The power terminal of the comparator U 1  receives the voltage V_meas. The non-inverting input terminal of the comparator U 1  is connected to a node between the resistors R 1  and R 2 . The inverting input terminal of the comparator U 1  is connected to a node between the resistor R 3  and the variable resistor R 30 . A first terminal of the electric switch Q 1  is connected to the output terminal of the comparator U 1  via the resistor R 4 . A second terminal of the electric switch Q 1  is grounded. A third terminal of the electric switch Q 1  receives a working voltage V 2  via the resistor R 5 . A cathode of the LED D 1  is connected to the third terminal of the electric switch Q 1 . An anode of the LED D 1  receives the working voltage V 2  via the resistor R 6 . The anode of the LED D 1  functions as an output of the monitoring circuit  1 . 
         [0008]    The monitoring circuit  2  includes resistors R 7 -R 9 , a comparator U 2 , a variable resistor R 40 , an electric switch Q 2 , and an LED D 2 . A first end of the resistor R 7  receives the external voltage V 1 . A second end of the resistor R 7  is connected to a first end of the variable resistor R 40 . A second end of the variable resistor R 40  is grounded. The comparator U 2  includes a power terminal, a ground terminal, a non-inverting input terminal, an inverting input terminal, and an output terminal. The power terminal of the comparator U 2  receives the voltage V_meas. The inverting input terminal of the comparator U 2  is connected to a node between the resistors R 1  and R 2 . The non-inverting input terminal of the comparator U 2  is connected to a node between the resistor R 7  and the variable resistor R 40 . A first terminal of the electric switch Q 2  is connected to the output terminal of the comparator U 2  via the resistor R 8 . A second terminal of the electric switch Q 2  is grounded. A third terminal of the electric switch Q 2  receives the working voltage V 2  via the resistor R 9 . A cathode of the LED D 2  is connected to the third terminal of the electric switch Q 2 . An anode of the LED D 2  is connected to the anode of the LED D 1 . The anode of the LED D 2  functions as an output of the monitoring circuit  2 . 
         [0009]    The voltage reduction circuit  3  includes three electric switches Q 3 , Q 4 , and Q 5 . A first terminal of the electric switch Q 3  is connected to the anodes of the LEDs D 1  and D 2 , and functions as an input of the voltage reduction circuit  3 . A second terminal of the electric switch Q 3  is connected to a first terminal of the electric switch Q 4 . A first terminal of the electric switch Q 5  is connected to a second terminal of the electric switch Q 4 . A third terminal of each of the switches Q 3 , Q 4 , and Q 5  is not connected. The second terminal of the electric switch Q 5  functions as an output of the voltage reduction circuit  3 . 
         [0010]    The indicating circuit  4  includes an LED D 3 , a buzzer B 1 , two electric switches Q 6  and Q 7 , and two resistors R 10  and R 11 . A first terminal of the electric switch Q 6  is connected to the second terminal of the electric switch Q 5 . A second terminal of the electric switch Q 6  is grounded. A third terminal of the electric switch Q 6  is connected to a cathode of the LED D 3 . An anode of the LED D 3  receives the working voltage V 2  via the resistor R 10 . A first terminal of the electric switch Q 7  is connected to the third terminal of the electric switch Q 6 . A second terminal of the electric switch Q 7  is grounded. A third terminal of the electric switch Q 7  is connected to a cathode of the buzzer B 1 . An anode of the buzzer B 1  receives the working voltage V 2  via the resistor R 11 . 
         [0011]    The non-inverting input terminal of the comparator U 1  and the inverting terminal of the comparator U 2  receive a voltage at the node between the resistors R 1  and R 2 . A first reference voltage at the inverting terminal of the comparator U 1  is obtained by adjusting the variable resistor R 30 . The first reference voltage is calculated by dividing the external voltage V 1  by the resistor R 3  and the variable resistor R 30 . The first reference voltage is designated as an upper limit of a variation of the voltage at the node between the resistors R 1  and R 2 . A second reference voltage at the non-inverting terminal of the comparator U 2  is obtained by adjusting the variable resistor R 40 . The second reference voltage is calculated by dividing the external voltage V 1  by the resistor R 7  and the variable resistor R 40 . The second reference voltage is designated as a lower limit of the variation of the voltage at the node between the resistors R 1  and R 2 . 
         [0012]    When the voltage at the node between the resistors R 1  and R 2  is higher than the first reference voltage, the comparator U 1  outputs a transistor-transistor logic (TTL) high level voltage signal. The electric switch Q 1  is turned on. The LED D 1  is turned on to emit light, indicating that the voltage V_meas is higher than an upper limit of variation of the voltage V_meas. When the voltage at the node between the resistors R 1  and R 2  is lower than the second reference voltage, the comparator U 2  outputs a TTL high level voltage signal. The electric switch Q 2  is turned on. The LED D 2  is turned on to emit light, indicating that the voltage V_meas is lower than a lower limit of variation of the voltage V_meas. 
         [0013]    It is determined from characteristics of an LED that when the LED is on, a constant voltage difference between two ends of the LED exists. In this embodiment, the constant voltage difference of each of the LEDs D 1  and D 2  is 2 volts (V). Therefore, when the voltage at the node between the resistors R 1  and R 2  is higher than the first reference voltage or lower than the second reference voltage, a voltage at the node between the anodes of the LEDs D 1  and D 2  is about 2V. The voltage at the node between the anodes of the LEDs D 1  and D 2  is reduced by the electric switches Q 3 , Q 4 , and Q 5 . The voltage reduction circuit  3  then outputs a voltage that is low enough to turn off the electric switch Q 6 . The electric switch Q 7  is turned on. The LED D 3  is turned off. The buzzer B 1  generates sound to indicate that the voltage V_meas is abnormal. 
         [0014]    When the voltage at the node between the resistors R 1  and R 2  is lower than the first reference voltage and higher than the second reference voltage, both of the comparators U 1  and U 2  output TTL low level voltage signals. The electric switches Q 1  and Q 2  are turned off. The LEDs D 1  and D 2  will not emit light. The working voltage V 2  is reduced by the voltage reduction circuit  3 . The voltage reduction circuit  3  then output a voltage that is high enough to turn on the electric switch Q 6 . The electric switch Q 7  is turned off. The buzzer B 1  will not generate sound. The LED D 3  is turned on to emit light. 
         [0015]    Therefore, the LED D 1  emits light when the voltage V_meas is too high. The LED D 2  emits light when the voltage V_meas is too low. The buzzer B 1  generates sound when the voltage V_meas is too high or too low. The LED D 3  emits light when the voltage V_meas is normal. 
         [0016]    In this embodiment, each of the electric switches Q 1 -Q 6  is an npn bipolar junction transistor having a base, an emitter, and a collector functioning as the first, second, and third terminals correspondingly. The electric switch Q 7  is an n-type metal oxide semiconductor field effect transistor having a gate, a source, and a drain functioning as the first, second, and third terminals respectively. 
         [0017]    The foregoing description of the exemplary embodiments of the disclosure has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Many modifications and variations are possible in light of the above everything. The embodiments were chosen and described in order to explain the principles of the disclosure and their practical application so as to enable others of ordinary skill in the art to utilize the disclosure and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those of ordinary skills in the art to which the present disclosure pertains without departing from its spirit and scope. Accordingly, the scope of the present disclosure is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.