Abstract:
An overvoltage protection circuit and a portable electronic device having the same are introduced. The overvoltage protection circuit provides overvoltage protection when an input voltage exceeds a rated voltage tolerable by an internal circuit unit in the portable electronic device. A reference voltage and a partial voltage are generated from the input voltage through a voltage limiting unit and voltage dividing module, respectively, and conveyed to a comparing module for comparison. Comparison of the reference voltage and the partial voltage is followed by generation of a switch signal whereby a switch unit determines whether to apply the input voltage to the internal circuit unit. The voltage dividing module sets the maximum rated voltage tolerable by the internal circuit unit and enables the overvoltage protection circuit to give overvoltage protection to the portable electronic device regardless of temperature.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 100132753 filed in Taiwan, R.O.C. on Sep. 9, 2011, the entire contents of which are hereby incorporated by reference. 
       FIELD OF TECHNOLOGY 
       [0002]    The present invention relates to an overvoltage protection circuit, in particular to the overvoltage protection circuit that provides a protection to an internal circuit unit of a portable electronic device if the voltage of the internal circuit unit exceeds a rated voltage tolerable. 
       BACKGROUND 
       [0003]    In general, a conventional portable electronic device receives an external input voltage through an adapter, and the adaptor is used for supplying an input voltage to the portable electronic device. 
         [0004]    As the number of a user&#39;s portable electronic devices increases, the number of various types of adapters also increases. These adapters generally come with different electric properties including different rated input/output voltages, and a misuse of an adapter by accident may damage the portable electronic device directly. For example, a portable electronic device includes an internal circuit unit such as a battery, an electronic component and an electronic circuit, and the internal circuit unit has a maximum rated voltage equal to 12 volts. If the user uses an adapter with a voltage higher than 12 volts to supply electric power to the portable electronic device, then the battery, electronic component and electronic circuit of the portable electronic device may be damaged by the high voltage and may fail to operate. 
         [0005]    Therefore, the present invention provides an overvoltage protection circuit to overcome the aforementioned drawbacks of the prior art. 
       SUMMARY 
       [0006]    It is a primary objective of the present invention to provide an overvoltage protection circuit to protect an internal circuit unit of a portable electronic device, and prevent the internal circuit unit from receiving an input voltage exceeding a rated voltage tolerable of the internal circuit unit. 
         [0007]    Another objective of the present invention is to provide an overvoltage protection circuit for isolating the input voltage exceeding the rated voltage to be inputted to the internal circuit units, while the protection is not affected by a change of temperature. 
         [0008]    A further objective of the present invention is to provide an overvoltage protection circuit for setting the rated voltage tolerable of the portable electronic device through a program by the voltage dividing module. 
         [0009]    To achieve the aforementioned and other objectives, the present invention provides an overvoltage protection circuit for providing an overvoltage protection when an input voltage exceeds a rated voltage tolerable of an internal circuit unit in a portable electronic device. The overvoltage protection circuit comprises an input unit, an output unit, a voltage limiting unit, a voltage dividing module, a comparing module and a switch unit. The input unit is provided for receiving the input voltage; the output unit is provided for coupling the portable electronic device; the voltage limiting unit is coupled to the input unit for receiving the input voltage and restrictively outputting a reference voltage; the voltage dividing module is coupled to the input unit for receiving the input voltage and dividing the input voltage to produce a partial voltage; the comparing module is coupled to the voltage limiting unit and the voltage dividing module for comparing the reference voltage with the partial voltage and generating a switch signal according to a comparison result; and the switch unit is coupled to the input unit, the output unit and the comparing module, for receiving the switch signal and the input voltage, wherein the switch signal is used for controlling the input voltage to be sent to the output unit through the voltage dividing module. 
         [0010]    Compared with the prior art, the overvoltage protection circuit of the present invention can set the rated voltage tolerable for the internal circuit unit of the portable electronic device simply and easily through the voltage dividing module and operates together with the voltage limiting unit, while the operation is not affected by a change of temperature easily, so as to achieve the effects of supplying an input voltage lower than the rated voltage to the portable electronic device successfully, as well as precisely controlling and isolating the input voltage to be inputted to the portable electronic device before an input voltage exceeding the rated voltage (or known as an over voltage) is inputted, so as to prevent the internal circuit units of the portable electronic device from being damaged by the input voltage exceeding the rated voltage, and protect the internal circuit units of the portable electronic device from being damaged by a misuse of the input voltage. 
     
    
     
       BRIEF DESCRIPTION 
         [0011]      FIG. 1  is a schematic block diagram of an overvoltage protection circuit in accordance with a first preferred embodiment of the present invention; 
           [0012]      FIG. 2  is a schematic diagram of the voltage limiting unit as depicted in  FIG. 1 ; 
           [0013]      FIG. 3  is a schematic diagram of the voltage dividing module as depicted in  FIG. 1 ; 
           [0014]      FIG. 4  is a schematic diagram of the comparing module as depicted in  FIG. 1 ; 
           [0015]      FIG. 5  is a schematic diagram of the switch unit as depicted in  FIG. 1 ; 
           [0016]      FIG. 6  is a schematic block diagram of an overvoltage protection circuit in accordance with a second preferred embodiment of the present invention; 
           [0017]      FIG. 7  is a schematic diagram of connecting the comparing module, the control interface module and the switch unit as depicted in  FIG. 6 ; and 
           [0018]      FIG. 8  is a schematic block diagram of a portable electronic device having an overvoltage protection circuit in accordance with a preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The objects, characteristics and effects of the present invention will become apparent with the detailed description of the preferred embodiments and the illustration of related drawings as follows. 
         [0020]    With reference to  FIG. 1  for a schematic block diagram of an overvoltage protection circuit in accordance with the first preferred embodiment of the present invention, the overvoltage protection circuit  10  is installed between an input voltage V in  and a portable electronic device  2 , for performing an overvoltage protection (OVP). The internal circuit unit  4  of the portable electronic device  2  is configured with a maximum input voltage tolerable which is also called a rated voltage. Therefore, the overvoltage protection circuit can be used for preventing the input voltage V in  exceeding the rated voltage from being inputted to the portable electronic device  2  directly or resulting in damages to the internal circuit unit  4 . 
         [0021]    In addition, the rated voltage is further defined as the maximum operating voltage tolerable of the internal circuit unit  4  of the portable electronic device  2 . In other words, if the input voltage V in  received by the portable electronic device  2  does not exceed the rated voltage, the internal circuit unit such as a rectifier circuit, a charge/discharge circuit or a display circuit of the portable electronic device  2  can be operated normally. On the other hand, if the input voltage V in  received by the portable electronic device  2  exceeds the rated voltage, the portable electronic device  2  will damage the internal circuit unit, and the portable electronic device  2  may perform wrong operations or may even fail. In addition, the input voltage V in  can be an AC voltage obtained from utility power or a rectified DC voltage. 
         [0022]    The overvoltage protection circuit  10  comprises an input unit  12 , a voltage limiting unit  14 , a voltage dividing module  16 , a comparing module  18 , a switch unit  20  and an output unit  22 . Wherein, the input unit  12  is provided for receiving the input voltage V in , and the input voltage V in  can be a DC voltage or an AC voltage. 
         [0023]    The voltage limiting unit  14  has two terminals, wherein one terminal is coupled to the input unit  12 , and the other terminal is coupled to a ground terminal GND. The input voltage V in  produces a corresponding reference voltage V ref  through the voltage limiting unit  14 . Wherein, the voltage limiting unit  14  is a two-terminal device with a temperature change resisting effect, so that the electric properties of the voltage limiting unit  14  such as a Zener diode will not be affected by a change of temperature. In addition, the voltage limiting unit  14  has a default clamping voltage PV provided for the voltage limiting unit  14  to determine whether or not to be conducted according to the received input voltage V in . 
         [0024]    In other words, if the input voltage V in  is applied to the voltage limiting unit  14 , and the input voltage V in  is smaller than or equal to the clamping voltage PV, then the voltage limiting unit  14  will output the reference voltage V ref  equal to zero voltage (which represents an OFF state); on the other hand, if the input voltage V in  is greater than the clamping voltage PV, the voltage limiting unit  14  will output the reference voltage V ref  equal to the clamping voltage PV (which represents an ON state). 
         [0025]    The aforementioned OFF state is defined as a state of disconnecting the voltage limiting unit  14 , and the reference voltage V ref  is equal to a zero potential; and the aforementioned ON state is defined as a state of the voltage limiting unit  14  constantly outputting the clamping voltage PV, or the reference voltage V ref  is equal to the clamping voltage PV. In addition, the selection of the clamping voltage PV of the voltage limiting unit  14  is not related to the rated voltage of the portable electronic device  2 . 
         [0026]    With reference to  FIG. 2 , the Zener diode is used as an example of the voltage limiting unit  14  to illustrate the invention. If the default clamping voltage PV of the Zener diode is designed to be equal to 4 volts, and the input voltage V in  applied to the two terminals of the Zener diode is smaller than 4 volts, the reference voltage V ref  will be a zero potential; and if the input voltage V in  applied to the two terminals of the Zener diode is greater than 4 volts, the reference voltage V ref  is equal to the clamping voltage PV. In other words, the output of the reference voltage V ref  is equal to 4 volts. Compared with a general diode, the Zener diode is connected in a reverse direction, wherein an n-terminal of the Zener diode is coupled to the input unit  12 , and a p-terminal of the Zener diode is coupled to the ground terminal GND. 
         [0027]    The voltage dividing module  16  is coupled to the input unit  12 , and the input voltage V in  of the input unit  12  produces a partial voltage V vd  through the voltage dividing module  12 . In a preferred embodiment, the voltage dividing module  16  includes a first resistor  122  and a second resistor  124  connected in series with each other, and the input voltage V in  produces the partial voltage V vd  at the second resistor  124  as shown in  FIG. 3 . In addition, the ratio of the resistance of the first resistor  122  to the resistance of the second resistor  124  can be adjusted to obtain a partial voltage V vd  with a corresponding resistance ratio, and the relation between the partial voltage and the resistance ratio is given below: 
         [0000]    
       
         
           
             
               V 
               vd 
             
             = 
             
               
                 
                   R 
                   124 
                 
                 
                   
                     R 
                     124 
                   
                   + 
                   
                     R 
                     122 
                   
                 
               
               × 
               
                 V 
                 in 
               
             
           
         
       
     
         [0028]    Wherein, R 122  is the resistance of the first resistor  122 , and R 124  is the resistance of the second resistor  124 . 
         [0029]    In addition, the voltage dividing module  16  is used for setting the rated voltage by the resistance ratio of the first resistor  122  and the second resistor  124  to meet the voltage requirement of the portable electronic device. In other words, if the partial voltage V vd  of the second resistor  124  is greater than or equal to (which is not smaller than) the reference voltage V ref , the following switch unit  20  is open circuited (or the OFF state). In other words, the input voltage V in  cannot be transmitted to the internal circuit unit  4 , and details are described as follows. 
         [0030]    The comparing module  18  is coupled to the voltage limiting unit  14  and the voltage dividing module  16 , and the comparing module  18  compares the reference voltage V ref  with the partial voltage V vd  and uses a comparison result to output the corresponding switch signal SS. 
         [0031]    With reference to  FIG. 4  for a schematic view of the comparing module  18 , the comparing module  18  further comprises a first input terminal  182 , a second input terminal  184 , a first control unit  186  and a second control unit  188 . The first input terminal  182  is coupled to the voltage limiting unit  14  for receiving the reference voltage V ref ; and the second input terminal  184  is coupled to the voltage dividing module  16  for receiving the partial voltage V vd . The first control unit  186  is provided for receiving the reference voltage V ref  and the partial voltage V vd . After the reference voltage V ref  is compared with the partial voltage V vd , the control signal CS is generated and transmitted to the second control unit  184 , such that the control signal CS can control open-circuit and short-circuit conditions of the second control terminal  188 . 
         [0032]    For example, if the rated voltage of the internal circuit unit  4  is equal to 4 volts, the clamping voltage PV is also equal to 4 volts, and the first resistor  122  has a resistance of 90KΩ and the second resistor  124  has a resistance of 10KΩ. If the input voltage V in  (such as 3 volts) is lower than the rated voltage, the voltage limiting unit  14  has the reference voltage V ref  equal to an output voltage of 0, and the partial voltage V vd  is equal to 0.3 volts. The comparing module  18  compares the reference voltage V ref  with the partial voltage V vd  to obtain a comparison result that the partial voltage V vd  is higher than the reference voltage V ref . Since the input voltage V in  is not higher than the rated voltage, therefore the comparing module  18  can control the switch unit  20  to output the input voltage Vin to the output unit  22 . 
         [0033]    In another preferred embodiment, if the input voltage V in  is equal to the rated voltage such as 4 volts, the voltage limiting unit  14  has the reference voltage V ref  equal to the output voltage of 0, and the partial voltage V vd  is equal to 0.4 volts. The comparing module  18  compares the reference voltage V ref  with the partial voltage V vd  to obtain the same comparison result that the partial voltage V vd  is higher than the reference voltage V ref . Since the input voltage V in  is equal to the rated voltage which still falls within the tolerable range of the internal circuit unit  4 , therefore the comparing module  18  can control the switch unit  20  to output the input voltage V in  to the output unit  22  and supply the input voltage V in  to the internal circuit unit  4 . 
         [0034]    In another preferred embodiment, if the input voltage Vin exceeds the rated voltage such as 5 volts, the voltage limiting unit  14  outputs a constant voltage which is the clamping voltage PV equal to 4 volts as the reference voltage V ref , and the partial voltage V vd  is equal to 0.5 volts. The comparing module  18  compares the reference voltage V ref  with the partial voltage V vd  to obtain a comparison result that the partial voltage V vd  is lower than the reference voltage V ref . Since the input voltage V in  exceeds the tolerable range of the rated voltage of the internal circuit unit  4 , therefore the comparing module  18  controls the switch unit  20  according to the aforementioned comparison result, such that the input voltage Vin cannot be supplied to the internal circuit unit  4 . 
         [0035]    In a preferred embodiment, the second control unit  188  is a three-terminal device, wherein one terminal is coupled to the first control unit  186  for receiving the control signal CS, the other terminal is coupled to the switch unit  20 , and the remaining terminal is coupled to a voltage V or a ground GND. In other words, the control signal CS received by one terminal of the second control unit  188  can be used to form an open-circuit state or a short-circuit state of the other two terminals according to the control signal CS used in the two terminals. Wherein, the second control unit  188  is a metal oxide semiconductor field effect transistor (MOSFET). 
         [0036]    In  FIG. 1 , the switch unit  20  is coupled to the input unit  12 , the comparing module  18  and the output unit  22 , and the switch unit  20  drives the input unit  12  to be coupled to the portable electronic device  4  according to the switch signal SS. In a preferred embodiment as shown in  FIG. 5 , the switch unit  20  is a three-terminal device having an input terminal  202 , an output terminal  204  and a controlled terminal  206 , wherein the input terminal  202  is coupled to the input unit  12 , and the controlled terminal  206  is coupled to the second control unit  188 , and the controlled terminal  206  is selectively coupled to the input terminal  202  and the output terminal  204  according to the received switch signal SS, so that the input unit  12  can be coupled to the output unit  22 , and the input voltage Vin can be supplied to the portable electronic device  4  through the output unit  22 . In a preferred embodiment, if the second control unit  188  is situated at a short-circuit state, the voltage V forms the switch signal SS directly by the switch terminal  188  and the switch signal SS is transmitted to the controlled terminal  206  to control the switch unit  20 , or the second control unit  188  makes use of the ground GND and controls the switch unit  20  by using the switch signal SS through the controlled terminal  206 . Wherein, the switch unit  20  is a metal oxide semiconductor field effect transistor (MOSFET). 
         [0037]    With reference to  FIG. 6  for a schematic block diagram of an overvoltage protection circuit in accordance with the second preferred embodiment of the present invention, the overvoltage protection circuit  10 ′ further comprises a control interface module  24 , in addition to the input unit  12 , the voltage limiting unit  14 , the voltage dividing module  16 , the comparing module  18 , the switch unit  20  and the output unit  22  of the foregoing preferred embodiment. Wherein, the control interface module  24  is coupled to the input unit  12 , the comparing module  14  and the switch unit  20 , and the comparing module  14  generates the corresponding switch signal SS through the control interface module  24 . 
         [0038]    With reference to  FIG. 7  for a schematic diagram of connecting the comparing module  18 , the control interface module  24  and the switch unit  20  as depicted in  FIG. 6 , the control interface module  24  is comprised of serial resistors R 1 , R 2 , and the input voltage V in  of the input unit  12  generates the switch signal SS at a portion of the serial resistors R 1 , R 2 . The second control unit  188  of the comparing module  18  is a three-terminal device, wherein one terminal is coupled to the first control unit  186  for receiving the control signal CS, the other terminal is coupled to the control interface module  24 , and the remaining terminal is coupled to the ground terminal GND. 
         [0039]    If the control signal CS drives the second control unit  188  to a short-circuit state, the input voltage V in  generates the switch signal SS through the serial resistors R 1 , R 2  of the control interface module  24 , the second control unit  188  coupled to the ground terminal GND, the voltage drops voltage V R1 , V R2  of the serial resistors R 1 , R 2 , and the use of the voltage drop V R2  of the serial resistors R 2 , and transmits the switch signal SS to the controlled terminal  206  to control the short circuit of the input terminal  202  and the output terminal  204 , such that the input voltage V in  can be supplied to the output unit  22 . On the other hand, if the control signal CS drives the switch terminal  188  to an open-circuit state, the serial resistors R 1 , R 2  do not form an electric circuit, so that the input voltage V in  cannot form a voltage drops V R1 , V R2  at the serial resistors R 1 , R 2 . In other words, the control interface module  24  cannot generate the switch signal SS for controlling the input terminal  202  and the output terminal  204  to be in the short-circuit state, and the input voltage V in  cannot be supplied to the internal circuit unit  4  through the output unit  2 . 
         [0040]    With reference to  FIG. 8  for a schematic block diagram of an overvoltage protection circuit of a portable electronic device in accordance with a preferred embodiment of the present invention, the portable electronic device  2 ′ is provided for receiving an input voltage V in , and the portable electronic device  2 ′ comprises the input unit  12 , the voltage limiting unit  14 , the voltage dividing module  16 , the comparing module  18 , the switch unit  20  and the output unit  22  of the foregoing preferred embodiment. Wherein, the internal circuit unit  4  is installed in the portable electronic device  2 . For example, the internal circuit unit  4  is a circuit of a rectification unit, a micro processing unit, a communication unit or a memory unit. The input unit  12  is provided for receiving the input voltage V in . The output unit  22  is coupled to the internal circuit unit  4  for outputting the input voltage V in  to the internal circuit unit  4 . 
         [0041]    The voltage limiting unit  14  is coupled to the input unit  12  for receiving the input voltage V in  and restrictively outputting a reference voltage V ref . The voltage dividing module  16  is coupled to the input unit  12  for receiving the input voltage V in  and dividing the input voltage V in  to produce a partial voltage V vd . The comparing module  16  is coupled to the voltage limiting unit  14  and the voltage dividing module  16  for comparing the reference voltage Vref with the partial voltage V vd  and generating a switch signal SS according to a comparison result. The switch unit  20  is coupled to the input unit  12 , the output unit  22  and the comparing module  18  for receiving the switch signal SS and the input voltage V in , and the switch signal SS is used for controlling the input voltage V in  to be outputted to the output unit  22  through the switch unit  20 . 
         [0042]    Therefore, the overvoltage protection circuit of the present invention can set the rated voltage tolerable for the internal circuit unit of the portable electronic device simply and easily through the voltage dividing module and operates together with voltage limiting unit while the operation is not affected by a change of temperature, so as to supply an input voltage lower than the rated voltage to the portable electronic device successfully, as well as precisely controlling and isolating the input voltage to be inputted to the portable electronic device before an input voltage exceeding the rated voltage (or known as an over voltage) is inputted, so as to prevent the internal circuit units of the portable electronic device from being damaged by the input voltage exceeding the rated voltage, and protect the internal circuit units of the portable electronic device from being damaged by a misuse of the input voltage. 
         [0043]    While the invention has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims.