Abstract:
A driving circuit for a T8 light-emitting diode (LED) lamp mainly includes two bridge rectifiers. According to the electrical characteristics and the circuit designs of the bridge rectifiers, the T8 LED lamp can be driven to illuminate by the driving circuit while a starter needs not be removed from the T8 lamp holder.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a driving circuit for a T8 lamp, and more particularly to a driving circuit for a T8 light-emitting diode (LED) lamp. 
         [0003]    2. Description of Prior Art 
         [0004]    Nowadays, the conventional T8 light-emitting diode (LED) lamp is widely used. Reference is made to  FIG. 3  which is a block diagram of a conventional T8 lamp and a T8 lamp holder  20 . A starter  21  is installed between a first lamp contact  22  and a third lamp contact  26  of a T8 lamp holder  20 . An AC power source  50  is electrically connected to a fourth lamp contact  28  of the T8 lamp holder  20  through a switch  60 . 
         [0005]    The AC power source  50  provides electricity in turn to the fourth lamp contact  28 , to a conventional T8 lamp  40 , the third lamp contact  26 , the starter  21 , the first lamp contact  22 , the conventional T8 lamp  40 , and a second lamp contact  24  of the T8 lamp holder  20  when the switch  60  is closed (turned on). Hence, the conventional T8 lamp illuminates. 
         [0006]    The conventional T8 lamp  40  has the disadvantages of containing mercury and lacking of energy saving. Hence, a T8 light-emitting diode (LED) lamp is presented to solve the above-mentioned disadvantages. 
         [0007]    The starter  21  is needed for operating conventional T8 lamp  40 , whereas the starter  21  is not needed for the T8 LED lamp. It is not convenient that the starter  21  needs to be removed when the T8 LED lamp is installed in the T8 lamp holder. If the starter  21  is not removed, the T8 LED lamp can not illuminate. 
       SUMMARY OF THE INVENTION 
       [0008]    In order to improve the above-mentioned disadvantages, a driving circuit for a T8 light-emitting diode (LED) lamp is disclosed. The driving circuit is provided to drive the T8 LED lamp without removing the starter installed in the T8 lamp holder. 
         [0009]    In order to achieve the above-mentioned objectives, a driving circuit for a T8 LED lamp applied to a T8 lamp holder and at least one light-emitting diode. The T8 lamp holder has a first lamp contact, a second lamp contact, a third lamp contact, and a fourth lamp contact. The driving circuit of the T8 LED lamp includes a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a sixth diode, a seventh diode, an eighth diode, an inductor unit, a first capacitor, and a power factor corrector unit. 
         [0010]    The first diode has an anode and a cathode, and the cathode of the first diode is electrically connected to the first lamp contact. The second diode has an anode and a cathode, and the anode of the second diode is electrically connected to the first lamp contact. The third diode has an anode and a cathode, and the cathode of the third diode is electrically connected to the second lamp contact and the anode of the third diode is electrically connected to the anode of the first diode. The fourth diode has an anode and a cathode, and the anode of the fourth diode is electrically connected to the second lamp contact and the cathode of the fourth diode is electrically connected to the cathode of the second diode. The fifth diode has an anode and a cathode, and the anode of the fifth diode is electrically connected to the third lamp contact and the cathode of the fifth diode is electrically connected to the cathode of the second diode. The sixth diode has an anode and a cathode, and the cathode of the sixth diode is electrically connected to the third lamp contact and the anode of the sixth diode is electrically connected to the anode of the first diode. The seventh diode has an anode and a cathode, and the anode of the seventh diode is electrically connected to the fourth lamp contact and the cathode of the seventh diode is electrically connected to the cathode of the second diode. The eighth diode has an anode and a cathode, and the cathode of the eighth diode is electrically connected to the fourth lamp contact and the anode of the eighth diode is electrically connected to the anode of the first diode. The inductor unit has a first terminal and a second terminal, and the first terminal is electrically connected to the cathode of the second diode. The first capacitor has a first terminal and a second terminal, and the first terminal of the first capacitor is electrically connected to the second terminal of the inductor unit and the second terminal of the first capacitor is electrically connected to the anode of the first diode. The power factor corrector is electrically connected to the cathode of the second diode. 
         [0011]    It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. Other advantages and features of the invention will be apparent from the following description, drawings and claims. 
     
    
     
       BRIEF DESCRIPTION OF DRAWING 
         [0012]    The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, may be best understood by reference to the following detailed description of the invention, which describes an exemplary embodiment of the invention, taken in conjunction with the accompanying drawings, in which: 
           [0013]      FIG. 1  is a block diagram of a driving circuit for a T8 LED lamp according to the present invention; 
           [0014]      FIG. 2  is a block diagram of an equivalent circuit of the driving circuit for the T8 LED lamp; and 
           [0015]      FIG. 3  is a block diagram of a conventional T8 lamp and a T8 lamp holder. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Reference will now be made to the drawing figures to describe the present invention in detail. 
         [0017]    Reference is made to  FIG. 1  which is s a block diagram of a driving circuit for a T8 LED lamp according to the present invention. The driving circuit of the T8 LED lamp  10  is applied to a T8 lamp holder  20  and at least one light-emitting diode  30 . The T8 lamp holder  20  has a first lamp contact  22 , a second lamp contact  24 , a third lamp contact  26 , and a fourth lamp contact  28 . 
         [0018]    The driving circuit of the T8 LED lamp  10  includes a first diode D 1 , a second diode D 2 , a third diode D 3 , a fourth diode D 4 , a fifth diode D 5 , a sixth diode D 6 , a seventh diode D 7 , an eighth diode D 8 , an inductor unit  102 , a first capacitor  104 , a power factor corrector unit  106 , a transformer unit  108 , a transistor unit  110 , a first resistor  112 , a second resistor  114 , a second capacitor  116 , a third resistor  118 , an optical coupler unit  120 , a fourth resistor  122 , a fifth resistor  124 , a third capacitor  126 , a protection unit  128 , a ninth diode  130 , a fourth capacitor  132 , a sixth resistor  134 , a seventh resistor  136 , and an eighth resistor  138 . 
         [0019]    Each of the first diode D 1 , the second diode D 2 , the third diode D 3 , the fourth diode D 4 , the fifth diode D 5 , the sixth diode D 6 , the seventh diode D 7 , the eighth diode D 8 , and the ninth diode  130  has an anode and a cathode, respectively. Each of the first resistor  112 , the second resistor  114 , the third resistor  118 , the fourth resistor  122 , the fifth resistor  124 , the sixth resistor  134 , the seventh resistor  136 , the eighth resistor  138 , the inductor unit  102 , the first capacitor  104 , the second capacitor  116 , the third capacitor  126 , the fourth capacitor  132 , the optical coupler unit  120 , and the light-emitting diode  30  has a first terminal and a second terminal, respectively. The first lamp contact  22  is electrically connected to the cathode of the first diode D 1  and the anode of the second diode D 2 . The second lamp contact  24  is electrically connected to the cathode of the third diode D 3  and the anode of the fourth diode D 4 . The third lamp contact  26  is electrically connected to the anode of the fifth diode D 5  and the cathode of the sixth diode D 6 . The fourth lamp contact  28  is electrically connected to the anode of the seventh diode D 7  and the cathode of the eighth diode D 8 . 
         [0020]    The cathode of the second diode D 2  is electrically connected to the cathode of the fourth diode D 4 , the cathode of the fifth diode D 5 , the cathode of the seventh diode D 7 , the first terminal of the first resistor  112 , and the first terminal of the inductor unit  102 , respectively. The second terminal of the first resistor  112  is electrically connected to the first terminal of the second capacitor  116 , the first terminal of the second resistor  114 , and the power factor corrector unit  106 . The second terminal of the second capacitor  116  and the second terminal of the second resistor  114  are grounded. 
         [0021]    The transformer unit  108  has four terminals, namely, a first terminal, a second terminal, a third terminal, and a fourth terminal. The transistor unit  110  has four terminals, namely, a first terminal, a second terminal, a third terminal, and a fourth terminal. The first terminal of the transformer unit  108  is electrically connected to the second terminal of the inductor unit  102  and the first terminal of the first capacitor  104 . The second terminal of the transformer unit  108  is electrically connected to the first terminal of the transistor unit  110 . The fourth terminal of the transformer unit  108  is electrically connected to the anode of the ninth diode  130 . The cathode of the ninth diode  130  is electrically connected to the first terminal of the fourth capacitor  132  and the first terminal of the light-emitting diode  30 . 
         [0022]    The third terminal of the transformer unit  108  is electrically connected to the first terminal of the third resistor  118 , the second terminal of the fourth capacitor  132 , the first terminal of the sixth resistor  134 , and the first terminal of the seventh resistor  136 , respectively. The second terminal of the light-emitting diode  130  is electrically connected to the second terminal of the sixth resistor  134  and the first terminal of the eighth resistor  138 . The second terminal of the seventh resistor  136  is electrically connected to the protection unit  128 . The second terminal of the eighth resistor  138  is electrically connected to the protection unit  128 . 
         [0023]    The second terminal of the transistor unit  110  is electrically connected to the power factor corrector unit  106 . The first terminal of the optical coupler unit  120  is electrically connected to the second terminal of the third resistor  118 . The second terminal of the optical coupler unit  120  is electrically connected to the power factor corrector unit  106 . The third terminal of the optical coupler unit  120  is grounded. The fourth terminal of the optical coupler unit  120  is electrically connected to the first terminal of the fourth resistor  122 . The second terminal of the fourth resistor  122  is electrically connected to the protection unit  128  and the first terminal of the fifth resistor  124 . 
         [0024]    The anode of the first diode D 1  is electrically connected to the anode of the third diode D 3 , the anode of the sixth diode D 6 , the anode of the eighth diode D 8 , the second terminal of the first capacitor  104 , the power factor corrector unit  106 , the third terminal of the transistor unit  110 , and the first terminal of the third capacitor  126 , respectively. The second terminal of the third capacitor  126  is electrically connected to the second terminal of the fifth resistor  124 . 
         [0025]    The first diode D 1 , the second diode D 2 , the third diode D 3 , and the fourth diode D 4  form a bridge rectifier. The fifth diode D 5 , the sixth diode D 6 , the seventh diode D 7 , and the eighth diode D 8  form a bridge rectifier. 
         [0026]    The inductor unit  102  and the first capacitor  104  are provided to prevent the electromagnetic interference (EMI) from interfering with signal transmission. In the applied circuit design, the rectifying functions, which are provided though the first diode D 1 , the second diode D 2 , the third diode D 3 , the fourth diode D 4 , the fifth diode D 5 , the sixth diode D 6 , the seventh diode D 7 , and the eighth diode D 8 , are designed ahead of the inductor unit  102  and the first capacitor  104 . 
         [0027]    The sampling function, which is provided through the power factor corrector unit  106 , is designed ahead of the inductor unit  102  and the first capacitor  104 . 
         [0028]    Reference is made to  FIG. 2  which is a block diagram of an equivalent circuit of the driving circuit for the T8 LED lamp to demonstrate the principle of the driving circuit with ease. The remaining components are represented though an equivalent circuit  140  except the first diode D 1 , the second diode D 2 , the third diode D 3 , the fourth diode D 4 , the fifth diode D 5 , the sixth diode D 6 , the seventh diode D 7 , and the eighth diode D 8 . 
         [0029]    As the above-mentioned description in the prior art, a starter  21  is installed between the first lamp contact  22  and the third lamp contact  26  to drive a conventional T8 lamp. An AC power source is electrically connected to the fourth lamp contact  28  through a switch  60 . When the switch  60  is closed (turned on), different operations will be described as follows:
   1. During the positive half-cycle of the AC power source  50 , the seventh diode D 7 , the equivalent circuit unit  140 , and the third diode D 3  provide a half-wave rectifying function between the fourth lamp contact  28  and the second lamp contact  24 . The first lamp contact  22  has a contact potential but the third lamp contact  26  does not because the fifth diode D 5  is not conducted. Hence, the starter  21  is not activated.   2. During the negative half-cycle of the AC power source  50 , the fourth diode D 4 , the equivalent circuit unit  140 , and the eighth diode D 8  provide a half-wave rectifying function between the second lamp contact  24  and the fourth lamp contact  28 . The third lamp contact  26  has a contact potential but the first lamp contact  22  does not because the second diode D 2  is not conducted. Hence, the starter  21  is not activated.   
 
         [0032]    Accordingly, the light-emitting diode  30  can be driven to illuminate by the driving circuit for the T8 LED lamp  10 . In fact, the existing lamp contacts of the T8 lamp holder  20  have various combinations in the market. According to the above-mentioned principle of the present invention, the light-emitting diode  30  can be driven by the driving circuit for T8 LED lamp while the starter  21  needs not be removed from the T8 lamp holder  20 . 
         [0033]    Although the present invention has been described with reference to the preferred embodiment thereof, it will be understood that the invention is not limited to the details thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.