Abstract:
An electrical circuit for use as a string of lights in one embodiment includes a rectifier for converting AC into DC; and a plurality of lamps connected in series, each lamp having an LED, and wherein at least one of the lamps each has a Zener diode connected in series with the LED, a positive terminal of the lamp proximate the rectifier is connected to a positive terminal of an output of the rectifier, and a negative terminal of the lamp distal the rectifier is connected to a negative terminal of the output of the rectifier. In another embodiment, the Zener diode is replaced with a resistor. Hence, no resistors are provided externally of the lamp.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The invention relates to providing electrical power to a plurality of low voltage electrical loads, and more particularly to a string of LED (light-emitting diode) light having a plurality of lamps wired in series, each lamp having an LED and some or all lamps having an additional one of a Zener diode and a resistor connected in series with the LED, thereby eliminating the provision of any additional resistors externally of the lamp. 
         [0003]    2. Description of Related Art 
         [0004]    LEDs are renowned for their long life and their ability to resist shock. Also, an LED consumes much less electrical power than fluorescent lamps (i.e., energy saving). Therefore, LED lighting devices are gaining popularity worldwide. 
         [0005]    A conventional string of lights including a plurality of LED bulbs arranged electrically in a series circuit is shown in  FIGS. 1 and 2 . AC 120V is rectified by a full-wave rectifier (not shown) to convert into DC (e.g., DC 120V) to be consumed by the plurality of LED bulbs. Each LED bulb is wired in series with a resistor  1 . For example, the LED bulb is a blue LED bulb of 3.2V 0.02 A. The number of the blue LED bulbs is 25. The light string has a nominal operating voltage of DC 80V. The light string will be damaged if DC 120V is directly applied thereto without any voltage reduction. Resistance (R) of additional resistor(s) other than the LED bulbs of the light string is equal to 40V (i.e., 120V-80V) divided by 0.02 A according to Ohm&#39;s Law. Hence, the resistance (R) is 2,000•. Resistor is an electrical component that may generate much heat when energized. 40V power may be applied to a single resistor of 2,000• inserted in series with one of the LED bulbs. Disadvantageously excessive heat generated by the resistor will burn out the LED bulb, thereby killing the circuit. Hence, it is typical to arrange five resistors  1  of 400• each to connect in series to one LED bulb, i.e., five connected LED bulbs in total. Each resistor  1  has a voltage component of 8V and is adapted to generate much less heat. Therefore, the light string is protected. 
         [0006]    Another conventional string of lights including a plurality of LED bulbs arranged electrically in a series circuit is shown in  FIGS. 3 and 4 . AC 120V is rectified by a full-wave rectifier in a plug (not shown) to convert into DC (e.g., DC 120V) which is to be consumed by the plurality of LED bulbs. A resistor  1  is interconnected the rectifier output and the adjacent LED bulb (i.e., the load). For example, the LED bulb is a blue LED bulb of 3.0V 0.02 A. The number of the blue LED bulbs is 30. The light string has a nominal operating voltage of DC 90V. The light string will be damaged if DC 120V is directly applied thereto without any voltage reduction. Resistance (R) of the additional resistor  1  other than the LED bulbs of the light string is equal to 30V (i.e., 120V−90V) divided by 0.02 A according to Ohm&#39;s Law. Hence, the resistance (R) of the resistor  1  is 1,500•. DC 30V is applied to the resistor  1 . Also, the resistor  1  is adapted to generate much less heat. Therefore, the light string is protected. 
         [0007]    However, both the well known light strings suffer from a number of disadvantages. In detail, each resistor is required to dispose in the light string by soldering which may pollute the environment if sufficient care is not taken. LED bulbs may be damaged due to high temperature and electrostatic discharge (ESD) while soldering. Soldering is a manual, laborious task such that these light strings cannot be mass produced easily. Heat generated by the resistor may damage the adjacent LED bulb and even cause a fire hazard. Moreover, the manufacturing cost is very high. 
         [0008]    There have been numerous suggestions in prior patents for light string. For example, U.S. Pat. No. 6,344,716 discloses a Christmas light string. Thus, continuing improvements in the exploitation of light string employing LED bulbs are constantly being sought. 
       SUMMARY OF THE INVENTION 
       [0009]    It is therefore one object of the invention to provide a string of LED light having a plurality of lamps wired in series, each lamp having an LED and some or all lamps having an additional one of a Zener diode and a resistor connected in series with the LED, thereby eliminating the provision of any additional resistors externally of the lamp. 
         [0010]    The above and other objects, features and advantages of the invention will become apparent from the following detailed description taken with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  schematically shows an LED bulb of a conventional LED light string with an additional resistor connected in series to the LED bulb; 
           [0012]      FIG. 2  schematically shows the conventional LED light string of  FIG. 1 ; 
           [0013]      FIG. 3  schematically shows another conventional LED light string with an additional resistor interconnected the rectifier output and the adjacent LED bulb of the light string; 
           [0014]      FIG. 4  is a circuit diagram of the light string of  FIG. 3 ; 
           [0015]      FIG. 5  is a circuit diagram of a first preferred embodiment of rectifier according to the invention to be used in an LED light string of the invention; 
           [0016]      FIG. 6  is a circuit diagram of a second preferred embodiment of rectifier according to the invention to be used in an LED light string of the invention; 
           [0017]      FIG. 7  is a circuit diagram of a third preferred embodiment of rectifier according to the invention to be used in an LED light string of the invention; 
           [0018]      FIG. 8  is a circuit diagram of a first preferred embodiment of LED bulb according to the invention to be used in an LED light string of the invention; 
           [0019]      FIG. 9  is a circuit diagram of a second preferred embodiment of LED bulb according to the invention to be used in an LED light string of the invention; 
           [0020]      FIG. 10  schematically shows an LED light string of the invention; 
           [0021]      FIG. 11  is a circuit diagram of a first preferred embodiment of the LED light string of  FIG. 10 ; 
           [0022]      FIG. 12  is a circuit diagram of a second preferred embodiment of the LED light string of  FIG. 10 ; 
           [0023]      FIG. 13  is a circuit diagram of a third preferred embodiment of the LED light string of  FIG. 10 ; 
           [0024]      FIG. 14  is a perspective view in part section of the LED bulb of  FIG. 10 ; 
           [0025]      FIG. 15  is a circuit diagram of a fourth preferred embodiment of the LED light string of  FIG. 10 ; 
           [0026]      FIG. 16  is a circuit diagram of a fifth preferred embodiment of the LED light string of  FIG. 10 ; 
           [0027]      FIG. 17  is a circuit diagram of a sixth preferred embodiment of the LED light string of  FIG. 10 ; 
           [0028]      FIG. 18  is a circuit diagram of a third preferred embodiment of LED bulb according to the invention to be used in an LED light string of the invention; 
           [0029]      FIG. 19  is a circuit diagram of a seventh preferred embodiment of the LED light string of  FIG. 10 ; 
           [0030]      FIG. 20  is a circuit diagram of an eighth preferred embodiment of the LED light string of  FIG. 10 ; 
           [0031]      FIG. 21  is a circuit diagram of a ninth preferred embodiment of the LED light string of  FIG. 10 ; 
           [0032]      FIG. 22  is a circuit diagram of a tenth preferred embodiment of the LED light string of  FIG. 10 ; 
           [0033]      FIG. 23  is a circuit diagram of an eleventh preferred embodiment of the LED light string of  FIG. 10 ; and 
           [0034]      FIG. 24  is a circuit diagram of a twelfth preferred embodiment of the LED light string of  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    Referring to  FIG. 5 , it shows a circuit diagram of a first preferred embodiment of rectifier  2  according to the invention to be used in an LED light string of the invention. The rectifier  2  is implemented as a full-wave rectifier (e.g., bridge rectifier) and is adapted to convert an AC power source (e.g., AC 120V) into DC current. 
         [0036]    Referring to  FIG. 6 , it shows a second preferred embodiment of rectifier  2  according to the invention to be used in an LED light string of the invention. The rectifier  2  is also a bridge rectifier having a capacitor filter being inserted in parallel with the load (not shown). Hence, the output voltage is smoothed by the action of the capacitor as well known in the art. 
         [0037]    Referring to  FIG. 7 , it shows a third preferred embodiment of rectifier  2  according to the invention to be used in an LED light string of the invention. The rectifier (e.g., a diode)  2  is implemented as a half-wave rectifier having a capacitor filter being inserted in parallel with the load (not shown). Hence, the output voltage is smoothed by the action of the capacitor as well known in the art. 
         [0038]    Referring to  FIG. 8 , it is a circuit diagram of a first preferred embodiment of LED bulb  8  according to the invention to be used in an LED light string of the invention. The LED bulb  8  comprises a Zener diode  9  and an LED (not numbered) having a positive electrode (i.e., anode) connected to a positive electrode (i.e., anode) of the Zener diode  9 . Negative electrode (i.e., cathode) of the Zener diode  9  is positive terminal of the LED bulb  8  and negative electrode (i.e., cathode) of the LED is negative terminal of the LED bulb  8  respectively. 
         [0039]    For example, the Zener diode  9  has a Zener voltage (i.e., reverse breakdown voltage) of 9V, the LED has a forward voltage of 3V, and current flowing through both the LED and the Zener diode  9  is 0.02 A prior to avalanche breakdown of the Zener diode  9 . Hence, the operating voltage of the LED bulb  8  is 12V (i.e., 9V+3V). That is, the resistor  8  may light by applying DC 12V thereto. 
         [0040]    Referring to  FIG. 9 , it is a circuit diagram of a second preferred embodiment of LED bulb  8  according to the invention to be used in an LED light string of the invention. The LED bulb  8  comprises a Zener diode  9  and an LED (not numbered) having a negative electrode (i.e., cathode) connected to a negative electrode (i.e., cathode) of the Zener diode  9 . Positive electrode (i.e., anode) of the Zener diode  9  is negative terminal of the LED bulb  8  and positive electrode (i.e., anode) of the LED is positive terminal of the LED bulb  8  respectively. 
         [0041]    For example, the Zener diode  9  has a Zener voltage of 3V, the LED has a forward voltage of 2.2V, and current flowing through both the LED and the Zener diode  9  is 0.02 A prior to avalanche breakdown of the Zener diode  9 . Hence, the operating voltage of the LED bulb  8  is 5.2V (i.e., 3V+2.2V). That is, the resistor  8  may light by applying DC 5.2V thereto. 
         [0042]    Referring to  FIGS. 10 and 14 , it shows an LED light string in accordance with the invention. The LED light string comprises a plug  1  having positive and negative prongs (not numbered), a rectifier  2  as any one shown above provided in the plug  1 , and a plurality of typical LEDs  7  as one set and a plurality of LED bulbs  8  as the other set both sets being electrically connected together in series between positive terminal of the rectifier output and negative terminal thereof through a cord  3  to construct a complete circuit. 
         [0043]    The LED bulb  8  comprises a first filament wire  6  connected to one end of a section of the cord  3 , a second filament wire  6  connected to one end of another section of the cord  3 , a cylindrical body  4  for storing LED, other electrical components, and the filament wire  6 , and a cap  5  formed of flexible material with the LED projecting therefrom. Also, both the Zener diode  9  and the LED in the LED bulb  8  are electrically connected to the filament wires  6 , or the LED  7  is electrically connected to the filament wires  6 . 
         [0044]    For example, the blue LED  7  is of 3.2V 0.02 A, the blue LED bulb  8  is of 11.2V 0.02 A the number of the blue LEDs  7  is 20, the number of the blue LED bulbs  8  is 5, AC power source is AC 120V and operating voltage of the light string is DC 120V. It is envisaged by the invention that the light string can operate normally by wiring as above. 
         [0045]    Referring to  FIG. 11 , it shows a circuit diagram of a first preferred embodiment of the LED light string of  FIG. 10 . The characteristics of the first preferred embodiment are detailed below. The rectifier  2  is a bridge rectifier as that shown in  FIG. 5 , the LED bulbs  8  are that shown in  FIG. 8 , the blue LED  7  is of 3.0V 0.02 A, the blue LED bulb  8  is of 13.0V 0.02 A, the number of the blue LEDs  7  is 27, the number of the blue LED bulbs  8  is 3, AC power source is AC 120V, and operating voltage of the light string is DC 120V. It is envisaged by the invention that the light string can operate normally by wiring as above. 
         [0046]    Referring to  FIG. 12 , it shows a circuit diagram of a second preferred embodiment of the LED light string of  FIG. 10 . The characteristics of the second preferred embodiment are detailed below. The rectifier  2  is a bridge rectifier having a capacitor parallel connected with the load (i.e., the LED bulbs  8  and the LEDs  7 ) as that shown in  FIG. 6 , the LED bulbs  8  are that shown in  FIG. 8 , the white LED  7  is of 3.0V 0.02 A, the white LED bulb  8  is of 13.0V 0.02 A, the number of the white LEDs  7  is 27, the number of the white LED bulbs  8  is 3, AC power source is AC 120V, and operating voltage of the light string is DC 120V. It is envisaged by the invention that the light string can operate normally by wiring as above. 
         [0047]    Referring to  FIG. 13 , it shows a circuit diagram of a third preferred embodiment of the LED light string of  FIG. 10 . The characteristics of the third preferred embodiment are detailed below. The rectifier  2  is a half-wave rectifier having a capacitor parallel connected with the load (i.e., the LED bulbs  8  and the LEDs  7 ) as that shown in  FIG. 7 , the LED bulbs  8  are that shown in  FIG. 8 , the white LED  7  is of 3.0V 0.02 A, the white LED bulb  8  is of 13.0V 0.02 A, the number of the white LEDs  7  is 27, the number of the white LED bulbs  8  is 3, AC power source is AC 120V, and operating voltage of the light string is DC 120V. It is envisaged by the invention that the light string can operate normally by wiring as above. 
         [0048]    Referring to  FIG. 15 , it shows a circuit diagram of a fourth preferred embodiment of the LED light string of  FIG. 10 . The characteristics of the fourth preferred embodiment are detailed below. The rectifier  2  is a bridge rectifier as that shown in  FIG. 5 , the LED bulbs  8  are that shown in  FIG. 8 , the typical LEDs are eliminated, the blue LED bulb  8  is of 10V 0.02 A, the number of the blue LED bulbs  8  is 12, AC power source is AC 120V, and operating voltage of the light string is DC 120V. It is envisaged by the invention that the light string can operate normally by wiring as above. 
         [0049]    Referring to  FIG. 16 , it shows a circuit diagram of a fifth preferred embodiment of the LED light string of  FIG. 10 . The characteristics of the fifth preferred embodiment are detailed below. The rectifier  2  is a bridge rectifier having a capacitor parallel connected with the load (i.e., the LED bulbs  8 ) as that shown in  FIG. 6 , the LED bulbs  8  are that shown in  FIG. 8 , the typical LEDs are eliminated, the white LED bulb  8  is of 8V 0.02 A, the number of the white LED bulbs  8  is 15, AC power source is AC 120V, and operating voltage of the light string is DC 120V. It is envisaged by the invention that the light string can operate normally by wiring as above. 
         [0050]    Referring to  FIG. 17 , it shows a circuit diagram of a sixth preferred embodiment of the LED light string of  FIG. 10 . The characteristics of the sixth preferred embodiment are detailed below. The rectifier  2  is a half-wave rectifier having a capacitor parallel connected with the load (i.e., the LED bulbs  8 ) as that shown in  FIG. 7 , the LED bulbs  8  are that shown in  FIG. 8 , the typical LEDs are eliminated, the red LED bulb  8  is of 6V 0.02 A, the number of the red LED bulbs  8  is 20, AC power source is AC 120V, and operating voltage of the light string is DC 120V. It is envisaged by the invention that the light string can operate normally by wiring as above. 
         [0051]    Referring to  FIG. 18 , it shows a circuit diagram of a third preferred embodiment of LED bulb according to the invention to be used in an LED light string of the invention. The LED bulb  8  comprises a resistor  10  and an LED (not numbered) connected in series therewith. Negative electrode (i.e., cathode) of the LED is negative terminal of the LED bulb  8 . 
         [0052]    For example, the resistor  10  has a resistance of 400•, the forward voltage of the LED is 3.2V, and current flowing through both the LED and the resistor  10  is 0.02 A. Hence, the voltage component of the resistor  10  is 8.0V (i.e., 400•×0.02 A). The operating voltage of the LED bulb  8  is 11.2V (i.e., 8V+3.2V). That is, the resistor  8  may light by applying DC 11.2V thereto. 
         [0053]    Referring to  FIG. 19 , it shows a circuit diagram of a seventh preferred embodiment of the LED light string of  FIG. 10 . The characteristics of the seventh preferred embodiment are detailed below. The rectifier  2  is a bridge rectifier as that shown in  FIG. 5 , the LED bulbs  8  are that shown in  FIG. 18 , the blue LED  7  is of 3.0V 0.02 A, the blue LED bulb  8  is of 13.0V 0.02 A, the number of the blue LEDs  7  is 27, the number of the blue LED bulbs  8  is 3, AC power source is AC 120V, and operating voltage of the light string is DC 120V. It is envisaged by the invention that the light string can operate normally by wiring as above. 
         [0054]    Referring to  FIG. 20 , it shows a circuit diagram of an eighth preferred embodiment of the LED light string of  FIG. 10 . The characteristics of the eighth preferred embodiment are detailed below. The rectifier  2  is a bridge rectifier having a capacitor parallel connected with the load (i.e., the LED bulbs  8  and the LEDs  7 ) as that shown in  FIG. 6 , the LED bulbs  8  are that shown in  FIG. 18 , the white LED  7  is of 3.0V 0.02 A, the white LED bulb  8  is of 13.0V 0.02 A, the number of the white LEDs  7  is 27, the number of the white LED bulbs  8  is 3, AC power source is AC 120V, and operating voltage of the light string is DC 120V. It is envisaged by the invention that the light string can operate normally by wiring as above. 
         [0055]    Referring to  FIG. 21 , it shows a circuit diagram of a ninth preferred embodiment of the LED light string of  FIG. 10 . The characteristics of the ninth preferred embodiment are detailed below. The rectifier  2  is a half-wave rectifier having a capacitor parallel connected with the load (i.e., the LED bulbs  8  and the LEDs  7 ) as that shown in  FIG. 7 , the LED bulbs  8  are that shown in  FIG. 18 , the white LED  7  is of 3.0V 0.02 A, the white LED bulb  8  is of 13.0V 0.02 A, the number of the white LEDs  7  is 27, the number of the white LED bulbs  8  is 3, AC power source is AC 120V, and operating voltage of the light string is DC 120V. It is envisaged by the invention that the light string can operate normally by wiring as above. 
         [0056]    Referring to  FIG. 22 , it shows a circuit diagram of a tenth preferred embodiment of the LED light string of  FIG. 10 . The characteristics of the tenth preferred embodiment are detailed below. The rectifier  2  is a bridge rectifier as that shown in  FIG. 5 , the LED bulbs  8  are that shown in  FIG. 18 , the typical LEDs are eliminated, the blue LED bulb  8  is of 10V 0.02A, the number of the blue LED bulbs  8  is 12, AC power source is AC 120V, and operating voltage of the light string is DC 120V. It is envisaged by the invention that the light string can operate normally by wiring as above. 
         [0057]    Referring to  FIG. 23 , it shows a circuit diagram of an eleventh preferred embodiment of the LED light string of  FIG. 10 . The characteristics of the eleventh preferred embodiment are detailed below. The rectifier  2  is a bridge rectifier having a capacitor parallel connected with the load (i.e., the LED bulbs  8 ) as that shown in  FIG. 6 , the LED bulbs  8  are that shown in  FIG. 18 , the typical LEDs are eliminated, the white LED bulb  8  is of 8V 0.02 A, the number of the white LED bulbs  8  is 15, AC power source is AC 120V, and operating voltage of the light string is DC 120V. It is envisaged by the invention that the light string can operate normally by wiring as above. 
         [0058]    Referring to  FIG. 24  it shows a circuit diagram of a twelfth preferred embodiment of the LED light string of  FIG. 10 . The characteristics of the twelfth preferred embodiment are detailed below. The rectifier  2  is a half-wave rectifier having a capacitor parallel connected with the load (i.e., the LED bulbs  8 ) as that shown in FIG.  7 , the LED bulbs  8  are that shown in  FIG. 18 , the typical LEDs are eliminated, the red LED bulb  8  is of 6V 0.02 A, the number of the red LED bulbs  8  is 20, AC power source is AC 120V, and operating voltage of the light string is DC 120V. It is envisaged by the invention that the light string can operate normally by wiring as above. 
         [0059]    While the invention herein disclosed 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.