Abstract:
A surge protection device detects whether a surge voltage occurs at a power input port by using a first Zener diode and a second Zener diode. When the power input port receives a normal voltage, the surge protection device turns on a first transistor to transmit the normal voltage to a load. Otherwise, when the power input port receives the surge voltage, the surge protection device prohibits the first transistor from conducting so as to protect the load from being damaged by the surge voltage. The surge protection device protects the load by controlling conducting or not of the first transistor and is manufactured without a surge protection unit. Therefore, manufacturing cost of the surge protection can be decreased.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a surge protection device, and particularly to a surge protection device to avoid a surge voltage into a load. 
         [0003]    2. Description of the Related Art 
         [0004]    With reference to  FIG. 3 , a conventional surge protection device  30  comprises a power port Vin, a ground port GND, a rectifying diode D, a Zener diode ZD, a resistor R, a transistor Q, a positive port  31 , a negative port  32 , and a surge protection unit  33 . 
         [0005]    The rectifying diode D has an anode electrically connected to the power port Vin, and has a cathode electrically connected to the positive port  31 . The surge protection unit  33  has a positive terminal electrically connected to the cathode of the rectifying diode D, and has a negative terminal electrically connected to the ground port GND. The Zener diode ZD has a cathode electrically connected to the positive terminal of the surge protection unit  33  and the cathode of the rectifying diode D, and has an anode electrically connected to the ground port GND through the resistor R. 
         [0006]    When a surge voltage between the positive terminal and the negative terminal is greater than a threshold voltage of the surge protection unit  33 , the surge protection unit  33  is conducting to transform electric power of the surge voltage to heat power for releasing the surge voltage. 
         [0007]    The transistor Q has a gate electrically connected to the anode of the Zener diode ZD, has a source electrically connected to the ground port GND, and has a drain electrically connected to the negative port  32 . 
         [0008]    The positive port  31  and the negative port  32  are electrically connected to a load such as an LED device  40 . 
         [0009]    A normal voltage for the conventional surge protection device  30  is greater than a breakdown voltage of the Zener diode ZD and is smaller than the threshold voltage of the surge protection unit  33 . When the power port Vin receives the normal voltage, the Zener diode ZD is conducting and the surge protection unit  33  is not conducting. After the Zener diode ZD is conducting, a current flows through the resistor R to generate a voltage across the resistor R. Since the voltage across the resistor can make the transistor Q conducting, the normal voltage can be provided to the LED device  40  through the transistor Q. The LED device  40  receives the normal voltage to emit light normally. 
         [0010]    With reference to  FIG. 4 , the surge voltage is greater than the breakdown voltage of the Zener diode ZD and greater than the threshold voltage of the surge protection unit  33 . When the surge voltage occurs, the surge protection unit  33  is conducting to release the surge voltage to protect the LED device  40  from being damaged. 
         [0011]    When the surge protection unit  33  is conducting to protect the LED device  40 , the surge protection unit  33  withstands the surge voltage. A capability of withstanding the surge voltage of the surge protection unit  33  is directly proportional to manufacturing cost of the surge protection unit  33 . When the surge protection device  30  is designed for withstanding a great surge voltage, the manufacturing cost of the surge protection unit  33  and the surge protection device  30  is also raised. 
       SUMMARY OF THE INVENTION 
       [0012]    An objective of the present invention is to provide a surge protection device that has decreased manufacturing cost. 
         [0013]    To achieve the foregoing objective, the surge protection device comprises a rectifying diode, a first Zener diode, a second Zener diode, a first transistor, a second transistor, a third transistor, a first resistor, a first voltage division unit, and a second voltage division unit. 
         [0014]    The rectifying diode has an anode electrically connected to a power input port, and has a cathode electrically connected to a cathode of the first Zener diode. The second Zener diode has a cathode electrically connected to the cathode of the rectifying diode. 
         [0015]    The first transistor has a drain electrically connected to a power output port, has a source electrically connected to the cathode of the rectifying diode, and has a gate. The first resistor is electrically connected between the gate and the source of the first transistor. 
         [0016]    The second transistor has a collector electrically connected to the gate of the first transistor, has an emitter electrically connected to a ground, and has a base. 
         [0017]    The third transistor has a collector electrically connected to the base of the second transistor, has an emitter electrically connected to the ground, and has a base. 
         [0018]    The first voltage division unit is electrically connected between the anode of the first Zener diode and the ground to divide a first voltage of the first Zener diode, and the first voltage division unit outputs the divided first voltage of the first Zener diode to the base of the second transistor. 
         [0019]    The second voltage division unit is electrically connected between the anode of the second Zener diode and the ground to divide a second voltage of the second Zener diode, and the second voltage division unit outputs the divided second voltage of the second Zener diode to the base of the third transistor. 
         [0020]    A first breakdown voltage of the first Zener diode is smaller than a second breakdown voltage of the second Zener diode. 
         [0021]    A normal voltage is greater than the first breakdown voltage of the first Zener diode and smaller than the second breakdown voltage of the second Zener diode. When the power input port receives the normal voltage, the first Zener diode is conducting, and the first voltage of the first Zener diode is not zero. 
         [0022]    Then, the first voltage division unit divides the first voltage of the first Zener diode, and outputs the divided first voltage of the first Zener diode to the base of the second transistor. The base of the second transistor receives the divided first voltage of the first Zener diode, and the emitter of the second transistor is grounded. Therefore, the collector and the emitter of the second transistor are conducting, and the normal voltage can be provided to the first resistor and the second transistor. 
         [0023]    At the same time, a voltage between two terminals of the first resistor is not zero to make the drain and the source of the first transistor conducting. Therefore, the normal voltage can be output to a load electrically connected to the power output port. 
         [0024]    A surge voltage is greater than the first breakdown voltage of the first Zener diode and the second breakdown voltage of the second Zener diode. When the power input port receives the surge voltage, the first Zener diode and the second Zener diode are conducting. The second voltage of the second Zener diode is not zero. 
         [0025]    Then, the second voltage division unit divides the second voltage of the second Zener diode, and outputs the divided second voltage of the second Zener diode to the base of the third transistor. The base of the third transistor receives the divided second voltage of the second Zener diode, and the emitter of the third transistor is grounded. Therefore, the collector and the emitter of the third transistor are conducting. 
         [0026]    The base of the second transistor is electrically connected to the collector of the third transistor. The base of the second transistor is grounded, because the collector and the emitter of the third transistor are conducting. The base and the emitter of the second transistor, and the collector and the emitter of the second transistor are not conducting. 
         [0027]    The surge voltage cannot be provided to the first resistor and the second transistor. Further, the voltage between the two terminals of the first resistor is zero, and the drain and the source of the first transistor cannot be conducting. The load electrically connected to the power output port would not receive the surge voltage, thereby preventing the load from being damaged by the surge voltage. 
         [0028]    The present invention is manufactured without a surge protection unit, and only comprises a few simple electronic units. Therefore, manufacturing cost of the surge protection device can be decreased. 
         [0029]    Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a circuit diagram of a surge protection device of the present invention when receiving a normal voltage; 
           [0031]      FIG. 2  is a circuit diagram of the surge protection device of the present invention when receiving a surge voltage; 
           [0032]      FIG. 3  is a circuit diagram of a conventional surge protection device when receiving a normal voltage; and 
           [0033]      FIG. 4  is a circuit diagram of the conventional surge protection device when receiving a surge voltage. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    With reference to  FIG. 1 , a surge protection device  10  of the present invention comprises a rectifying diode D 1 , a first Zener diode ZD 1 , a second Zener diode ZD 2 , a first transistor Q 1 , a second transistor Q 2 , a third transistor Q 3 , a first resistor R 1 , a first voltage division unit  11 , a second voltage division unit  12 , a power input port Vin, a power output port Vout, and a ground GND. 
         [0035]    A first breakdown voltage of the first Zener diode ZD 1  is smaller than a second breakdown voltage of the second Zener diode ZD 2 . 
         [0036]    The rectifying diode D 1  has an anode electrically connected to the power input port Vin and has a cathode. 
         [0037]    The first Zener diode ZD 1  has a cathode electrically connected to the cathode of the rectifying diode D 1 , and has an anode. 
         [0038]    The second Zener diode ZD 2  has a cathode electrically connected to the cathode of the rectifying diode D 1 , and has an anode. 
         [0039]    The first transistor Q 1  has a drain electrically connected to the power output port Vout, has a source electrically connected to the cathode of the rectifying diode D 1 , and has a gate. 
         [0040]    The first resistor R 1  is electrically connected between the gate and the source of the first transistor Q 1 . 
         [0041]    The second transistor Q 2  has a collector electrically connected to the gate of the first transistor Q 1 , has an emitter electrically connected to the ground GND, and has a base. 
         [0042]    The third transistor Q 3  has a collector electrically connected to the base of the second transistor Q 2 , has an emitter electrically connected to the ground GND, and has a base. 
         [0043]    The first voltage division unit  11  is electrically connected between the anode of the first Zener diode ZD 1  and the ground GND to divide a first voltage of the first Zener diode ZD 1 , and the first voltage division unit  11  outputs the divided first voltage of the first Zener diode ZD 1  to the base of the second transistor Q 2 . 
         [0044]    The second voltage division unit  12  is electrically connected between the anode of the second Zener diode ZD 2  and the ground GND to divide a second voltage of the second Zener diode ZD 2 , and the second voltage division unit  12  outputs the divided second voltage of the second Zener diode ZD 2  to the base of the second transistor Q 2 . 
         [0045]    A normal voltage is greater than the first breakdown voltage of the first Zener diode ZD 1  and smaller than the second breakdown voltage of the second Zener diode ZD 2 . When the power input port Vin receives the normal voltage, the first Zener diode ZD 1  is conducting, and the second Zener diode ZD 2  is not conducting. The first voltage of the first Zener diode ZD 1  is not zero. 
         [0046]    Therefore, the first voltage division unit  11  divides the first voltage of the first Zener diode ZD 1 , and outputs the divided first voltage of the first Zener diode ZD 1  to the base of the second transistor Q 2 . The emitter of the second transistor Q 2  is grounded, and the base of the second transistor Q 2  receives the divided first voltage of the first Zener diode ZD 1 . The collector and the emitter of the second transistor Q 2  are conducting, and then the normal voltage can be provided to the first resistor R 1  and the second transistor Q 2 . 
         [0047]    When the normal voltage is provided to the first resistor R 1 , a voltage between two terminals of the first resistor R 1  is not zero, making the drain and the source of the first transistor Q 1  conducting. Therefore, the normal voltage can be output to a load electrically connected to the power output port Vout. 
         [0048]    With reference to  FIG. 2 , a surge voltage is greater than the first breakdown voltage of the first Zener diode ZD 1  and the second breakdown voltage of the second Zener diode ZD 2 . When the power input port Vin receives the surge voltage, the first Zener diode ZD 1  and the second Zener diode ZD 2  are conducting. The first voltage of the first Zener diode ZD 1  and the second voltage of the second Zener diode ZD 2  are not zero. 
         [0049]    Therefore, the second voltage division unit  12  divides the second voltage of the second Zener diode ZD 2 , and outputs the divided second voltage of the second Zener diode ZD 2  to the base of the third transistor Q 3 . The emitter of the third transistor Q 3  is grounded, and the base of the third transistor Q 3  receives the divided second voltage of the second Zener diode ZD 2 . 
         [0050]    The collector and the emitter of the third transistor Q 3  are conducting, and the base of the second transistor Q 2  is grounded according to the conducting third transistor Q 3 . The emitter and the base of the second transistor Q 2  are grounded, and the second transistor Q 2  is not conducting. The surge voltage cannot be provided to the first resistor R 1  and the second transistor Q 2 . Therefore, the voltage between the two terminals of the first resistor R 1  is zero, and the drain and the source of the first transistor Q 1  cannot be conducting. The load electrically connected to the power output port Vout would not receive the surge voltage, thereby preventing the load from being damaged by the surge voltage. 
         [0051]    The present invention can protect the load electrically connected to the power output port Vout from being damaged by the surge voltage. When the power input port Vin receives the surge voltage, the second Zener diode ZD 2  is conducting to further make the first transistor Q 1  not conducting. Then, the surge voltage received from the power input port Vin is not output to the load, thereby preventing the load from being damaged by the surge voltage. 
         [0052]    The present invention is manufactured without a surge protection unit, and only comprises a few simple electronic units to prevent the load from being damaged by the surge voltage. Therefore, manufacturing cost of the surge protection device can be decreased. 
         [0053]    The first voltage division unit  11  comprises a second resistor R 2  and a third resistor R 3 . The second resistor R 2  is electrically connected between the anode of the first Zener diode ZD 1  and the base of the second transistor Q 2 . The third resistor R 3  is electrically connected between the ground GND and the base of the second transistor Q 2 . The first voltage of the first Zener diode ZD 1  can be divided by the second resistor R 2  and the third resistor R 3  electrically connected in series, and the divided first voltage of the first Zener diode ZD 1  is output to the base of the second transistor Q 2 . 
         [0054]    The second voltage division unit  12  comprises a fourth resistor R 4  and a fifth resistor R 5 . The fourth resistor R 4  is electrically connected between the anode of the second Zener diode ZD 2  and the base of the third transistor Q 3 . The fifth resistor R 5  is electrically connected between the ground GND and the base of the third transistor Q 3 . The second voltage of the second Zener diode ZD 2  can be divided by the fourth resistor R 4  and the fifth resistor R 5  electrically connected in series, and the divided second voltage of the second Zener diode ZD 2  is output to the base of the third transistor Q 3 . 
         [0055]    Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only. Changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.