Abstract:
A replacement light tube for replacing a fluorescent light tube includes a bulb portion extending between a first end and a second end, the bulb portion comprising a support structure, a plurality of white light emitting diodes (LEDs) and an elongate light-transmissive cover. The support structure has a first surface extending between the first end and the second end. The plurality of LEDs are supported by the first surface and arranged between the first end and the second end. The elongate light-transmissive cover extends between the first end and the second end and over the first surface of the support structure. A first end cap and a second end cap are disposed on the first end and the second end, respectively, each configured to fit with a socket for a fluorescent light tube. A power supply circuit is configured to provide power to the plurality of LEDs. The plurality of LEDs are arranged to emit light through the elongate light-transmissive cover and at least a portion of the power supply circuit is packaged inside at least one of the end caps.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 15/187,456, filed Jun. 20, 2016, which is a continuation of U.S. patent application Ser. No. 14/865,325, filed Sep. 25, 2015 and issued as U.S. Pat. No. 9,416,923 on Aug. 16, 2016, which is a continuation of U.S. patent application Ser. No. 14/669,963, filed on Mar. 26, 2015 and issued as U.S. Pat. No. 9,222,626 on Dec. 29, 2015, which is a continuation of U.S. patent application Ser. No. 14/299,909, filed on Jun. 9, 2014 and issued as U.S. Pat. No. 9,006,990 on Apr. 14, 2015 and a continuation of U.S. patent application Ser. No. 14/299,915, filed Jun. 9, 2014 and issued as U.S. Pat. No. 9,006,993 on Apr. 14, 2015, which are continuations of U.S. Patent Application No. 13/777,331, filed Feb. 26, 2013 and issued as U.S. Pat. No. 8,866,396 on Oct. 21, 2014, which is a continuation of U.S. patent application Ser. No. 12/965,019, filed Dec. 10, 2010 and issued as U.S. Pat. No. 8,382,327 on Feb. 26, 2013, which is a continuation of U.S. patent application Ser. No. 11/085,744, filed Mar. 21, 2005 and issued as U.S. Pat. No. 8,247,985 on Aug. 21, 2012, which is a continuation of U.S. patent application Ser. No. 09/782,375, filed Feb. 12, 2001 and issued as U.S. Pat. No. 7,049,761 on May 23, 2006, which claims the benefit of U.S. Provisional Application No. 60/181,744 filed Feb. 11, 2000. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a light tube illuminated by LEDs (light emitting diodes) which are packaged inside the light tube and powered by a power supply circuit. 
       BACKGROUND OF THE INVENTION 
       [0003]    Conventional fluorescent lighting systems include fluorescent light tubes and ballasts. Such lighting systems are used in a variety of locations, such as buildings and transit buses, for a variety of lighting purposes, such as area lighting or backlighting. Although conventional fluorescent lighting systems have some advantages over known lighting options, such as incandescent lighting systems, conventional fluorescent light tubes and ballasts have several shortcomings. Conventional fluorescent light tubes have a short life expectancy, are prone to fail when subjected to excessive vibration, consume high amounts of power, require a high operating voltage, and include several electrical connections which reduce reliability. Conventional ballasts are highly prone to fail when subjected to excessive vibration. Accordingly, there is a desire to provide a light tube and power supply circuit which overcome the shortcomings of conventional fluorescent lighting systems. That is, there is a desire to provide a light tube and power supply circuit which have a long life expectancy, are resistant to vibration failure, consume low amounts of power, operate on a low voltage, and are highly reliable. It would also be desirable for such a light tube to mount within a conventional fluorescent light tube socket. 
       SUMMARY OF THE INVENTION 
       [0004]    Embodiments of a replacement light tube for replacing a fluorescent light tube are disclosed herein. In one embodiment, the replacement light tube for replacing a fluorescent light tube includes a bulb portion extending between a first end and a second end, the bulb portion comprising a support structure, a plurality of white light emitting diodes (LEDs) and an elongate light-transmissive cover. The support structure has a first surface extending between the first end and the second end. The plurality of LEDs are supported by the first surface and arranged between the first end and the second end. The elongate light-transmissive cover extends between the first end and the second end and over the first surface of the support structure. A first end cap and a second end cap are disposed on the first end and the second end, respectively, each configured to fit with a socket for a fluorescent light tube. A power supply circuit is configured to provide power to the plurality of LEDs. The plurality of LEDs are arranged to emit light through the elongate light-transmissive cover and at least a portion of the power supply circuit is packaged inside at least one of the end caps. 
         [0005]    In another embodiment, the replacement light tube includes a bulb portion extending between a first end and a second end, the bulb portion comprising a support structure, a plurality of white light emitting diodes (LEDs) and an elongate light-transmissive cover. The support structure has a first surface extending between the first end and the second end. The plurality of LEDs are supported by the first surface and arranged between the first end and the second end, the LEDs being disposed along a base of a channel defined by the support structure. The elongate light-transmissive cover extends between the first end and the second end and over the first surface of the support structure. A first end cap and a second end cap are disposed on the first end and the second end, respectively, each configured to fit with a socket for a fluorescent light tube. A power supply circuit is configured to provide power to the plurality of LEDs, the power supply circuit comprising a rectifier configured to receive alternating current (AC) input from a ballast and to provide direct current (DC) output. The plurality of LEDs are arranged to emit light through the elongate light-transmissive cover and at least a portion of the power supply circuit is packaged inside at least one of the end caps. 
         [0006]    These and other embodiments will be discussed in additional detail hereafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0008]      FIG. 1  is a line drawing showing a light tube, in perspective view, which in accordance with the present invention is illuminated by LEDs packaged inside the light tube; 
           [0009]      FIG. 2  is a perspective view of the LEDs mounted on a circuit board; 
           [0010]      FIG. 3  is a cross-sectional view of  FIG. 2  taken along lines  3 - 3 ; 
           [0011]      FIG. 4  is a fragmentary, perspective view of one embodiment of the present invention showing one end of the light tube disconnected from one end of a light tube socket; 
           [0012]      FIG. 5  is an electrical block diagram of a first power supply circuit for supplying power to the light tube; 
           [0013]      FIG. 6  is an electrical schematic of a switching power supply type current limiter; 
           [0014]      FIG. 7  is an electrical block diagram of a second power supply circuit for supplying power to the light tube; 
           [0015]      FIG. 8  is an electrical block diagram of a third power supply circuit for supplying power to the light tube; 
           [0016]      FIG. 9  is a fragmentary, perspective view of another embodiment of the present invention showing one end of the light tube disconnected from one end of the light tube socket; and 
           [0017]      FIG. 10  is an electrical block diagram of a fourth power supply circuit for supplying power to the light tube. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIG. 1  is a line drawing showing a light tube  20  in perspective view. In accordance with the present invention, the light tube  20  is illuminated by LEDs  22  packaged inside the light tube  20 . The light tube  20  includes a cylindrically shaped bulb portion  24  having a pair of end caps  26  and  28  disposed at opposite ends of the bulb portion. Preferably, the bulb portion  24  is made from a transparent or translucent material such as glass, plastic, or the like. As such, the bulb material may be either clear or frosted. 
         [0019]    In a preferred embodiment of the present invention, the light tube  20  has the same dimensions and end caps  26  and  28  (e.g. electrical male bi-pin connectors, type G13) as a conventional fluorescent light tube. As such, the present invention can be mounted in a conventional fluorescent light tube socket. 
         [0020]    The line drawing of  FIG. 1  also reveals the internal components of the light tube  20 . The light tube  20  further includes a circuit board  30  with the LEDs  22  mounted thereon. The circuit board  30  and LEDs  22  are enclosed inside the bulb portion  24  and the end caps  26  and  28 . 
         [0021]      FIG. 2  is a perspective view of the LEDs  22  mounted on the circuit board  30 . A group of LEDs  22 , as shown in  FIG. 2 , is commonly referred to as a bank or array of LEDs. Within the scope of the present invention, the light tube  20  may include one or more banks or arrays of LEDs  22  mounted on one or more circuit boards  30 . In a preferred embodiment of the present invention, the LEDs  22  emit white light and, thus, are commonly referred to in the art as white LEDs. In  FIGS. 1 and 2 , the LEDs  22  are mounted to one surface  32  of the circuit board  30 . In a preferred embodiment of the present invention, the LEDs  22  are arranged to emit or shine white light through only one side of the bulb portion  24 , thus directing the white light to a predetermined point of use. This arrangement reduces light losses due to imperfect reflection in a conventional lighting fixture. In alternative embodiments of the present invention, LEDs  22  may also be mounted, in any combination, to the other surfaces  34 ,  36 , and/or  38  of the circuit board  30 . 
         [0022]      FIG. 3  is a cross-sectional view of  FIG. 2  taken along lines  3 - 3 . To provide structural strength along the length of the light tube  20 , the circuit board  30  is designed with a H-shaped cross-section. To produce a predetermined radiation pattern or dispersion of light from the light tube  20 , each LED  22  is mounted at an angle relative to adjacent LEDs and/or the mounting surface  32 . The total radiation pattern of light from the light tube  20  is effected by (1) the mounting angle of the LEDs  22  and (2) the radiation pattern of light from each LED. Currently, white LEDs having a viewing range between 6° and 45° are commercially available. 
         [0023]      FIG. 4  is a fragmentary, perspective view of one embodiment of the present invention showing one end of the light tube  20  disconnected from one end of a light tube socket  40 . Similar to conventional fluorescent lighting systems and in this embodiment of the present invention, the light tube socket  40  includes a pair of electrical female connectors  42  and the light tube  20  includes a pair of mating electrical male connectors  44 . 
         [0024]    Within the scope of the present invention, the light tube  20  may be powered by one of four power supply circuits  100 ,  200 ,  300 , and  400 . A first power supply circuit includes a power source and a conventional fluorescent ballast. A second power supply circuit includes a power source and a rectifier/filter circuit. A third power supply circuit includes a DC power source and a PWM (Pulse Width Modulation) circuit. A fourth power supply circuit powers the light tube  20  inductively. 
         [0025]      FIG. 5  is an electrical block diagram of a first power supply circuit  100  for supplying power to the light tube  20 . The first power supply circuit  100  is particularly adapted to operate within an existing, conventional fluorescent lighting system. As such, the first power supply circuit  100  includes a conventional fluorescent light tube socket  40  having two electrical female connectors  42  disposed at opposite ends of the socket. Accordingly, a light tube  20  particularly adapted for use with the first power supply circuit  100  includes two end caps  26  and  28 , each end cap having the form of an electrical male connector  44  which mates with a corresponding electrical female connector  42  in the socket  40 . 
         [0026]    The first power supply circuit  100  also includes a power source  46  and a conventional magnetic or electronic fluorescent ballast  48 . The power source  46  supplies power to the conventional fluorescent ballast  48 . 
         [0027]    The first power supply circuit  100  further includes a rectifier/filter circuit  50 , a PWM circuit  52 , and one or more current-limiting circuits  54 . The rectifier/filter circuit  50 , the PWM circuit  52 , and the one or more current-limiting circuits  54  of the first power supply circuit  100  are packaged inside one of the two end caps  26  or  28  of the light tube  20 . 
         [0028]    The rectifier/filter circuit  50  receives AC power from the ballast  48  and converts the AC power to DC power. The PWM circuit  52  receives the DC power from the rectifier/filter circuit  50  and pulse-width modulates the DC power to the one or more current-limiting circuits  54 . In a preferred embodiment of the present invention, the PWM circuit  52  receives the DC power from the rectifier/filter circuit  50  and cyclically switches the DC power on and off to the one or more current-limiting circuits  54 . The DC power is switched on and off by the PWM circuit  52  at a frequency which causes the white light emitted from the LEDs  22  to appear, when viewed with a “naked” human eye, to shine continuously. The PWM duty cycle can be adjusted or varied by control circuitry (not shown) to maintain the power consumption of the LEDs  22  at safe levels. 
         [0029]    The DC power is modulated for several reasons. First, the DC power is modulated to adjust the brightness or intensity of the white light emitted from the LEDs  22  and, in turn, adjust the brightness or intensity of the white light emitted from the light tube  20 . Optionally, the brightness or intensity of the white light emitted from the light tube  20  may be adjusted by a user. Second, the DC power is modulated to improve the illumination efficiency of the light tube  20  by capitalizing upon a phenomenon in which short pulses of light at high brightness or intensity to appear brighter than a continuous, lower brightness or intensity of light having the same average power. Third, the DC power is modulated to regulate the intensity of light emitted from the light tube  20  to compensate for supply voltage fluctuations, ambient temperature changes, and other such factors that affect the intensity of white light emitted by the LEDs  22 . Fourth, the DC power is modulated to raise the variations of the frequency of light above the nominal variation of 120 to 100 Hz thereby reducing illumination artifacts caused by low frequency light variations, including interactions with video screens. Fifth, the DC power may optionally be modulated to provide an alarm function wherein light from the light tube  20  cyclically flashes on and off 
         [0030]    The one or more current-limiting circuits  54  receive the pulse-width modulated or switched DC power from the PWM circuit  52  and transmit a regulated amount of power to one or more arrays of LEDs  22 . Each current-limiting circuit  54  powers a bank of one or more white LEDs  22 . If a bank of LEDs  22  consists of more than one LED, the LEDs are electrically connected in series in an anode to cathode arrangement. If brightness or intensity variation between the LEDs  22  can be tolerated, the LEDs can be electrically connected in parallel. 
         [0031]    The one or more current-limiting circuits  54  may include (1) a resistor, (2) a current-limiting semiconductor circuit, or (3) a switching power supply type current limiter. 
         [0032]      FIG. 6  is an electrical schematic of a switching power supply type current limiter  56 . The limiter  56  includes an inductor  58 , electrically connected in series between the PWM circuit  52  and the array of LEDs  22 , and a power diode  60 , electrically connected between ground  62  and a PWM circuit/inductor node  64 . The diode  60  is designed to begin conduction after the PWM circuit  52  is switched off. In this case, the value of the inductor  58  is adjusted in conjunction with the PWM duty cycle to provide the benefits described above. The switching power supply type current limiter  56  provides higher power efficiency than the other types of current-limiting circuits listed above. 
         [0033]      FIG. 7  is an electrical block diagram of a second power supply circuit  200  for supplying power to the light tube  20 . Similar to the first power supply circuit  100 , the second power supply circuit  200  includes a conventional fluorescent light tube socket  40  having two electrical female connectors  42  disposed at opposite ends of the socket  40 . Accordingly, a light tube  20  particularly adapted for use with the second power supply circuit  200  includes two end caps  26  and  28 , each end cap having the form of an electrical male connector  44  which mates with a corresponding electrical female connector  42  in the socket  40 . 
         [0034]    In the second power supply circuit  200 , the power source  46  supplies power directly to the rectifier/filter circuit  50 . The rectifier/filter circuit  50 , the PWM circuit  52 , and the one or more current-limiting circuits  54  operate as described above to power the one or more arrays of LEDs  22 . The rectifier/filter circuit  50 , the PWM circuit  52 , and the one or more current-limiting circuits  54  of the second power supply circuit  200  are preferably packaged inside the end caps  26  and  28  or the bulb portion  24  of the light tube  20  or inside the light tube socket  40 . 
         [0035]      FIG. 8  is an electrical block diagram of a third power supply circuit  300  for supplying power to the light tube  20 . Similar to the first and second power supply circuits  100  and  200 , the third power supply circuit  300  includes a conventional fluorescent light tube socket  40  having two electrical female connectors  42  disposed at opposite ends of the socket  40 . Accordingly, a light tube  20  particularly adapted for use with the third power supply circuit  300  includes two end caps  26  and  28 , each end cap having the form of an electrical male connector  44  which mates with a corresponding electrical female connector  42  in the socket  40 . 
         [0036]    The third power supply circuit  300  includes a DC power source  66 , such as a vehicle battery. In the third power supply circuit  300 , the DC power source  66  supplies DC power directly to the PWM circuit  52 . The PWM circuit  52  and the one or more current-limiting circuits  54  operate as described above to power the one or more arrays of LEDs  22 . In the third power supply circuit  300 , the PWM circuit  52  is preferably packaged in physical location typically occupied by the ballast of a conventional fluorescent lighting system while the one or more current-limiting circuits  54  and LEDs  22  are preferably packaged inside the light tube  20 , in either one of the two end caps  26  or  28  or the bulb portion  24 . 
         [0037]      FIG. 9  is a fragmentary, perspective view of another embodiment of the present invention showing one end of the light tube  20  disconnected from one end of the light tube socket  40 . In this embodiment of the present invention, the light tube socket  40  includes a pair of brackets  68  and the light tube  20  includes a pair of end caps  26  and  28  which mate with the brackets  68 . 
         [0038]      FIG. 10  is an electrical block diagram of a fourth power supply circuit  400  for supplying power to the light tube  20 . Unlike the first, second, and third power supply circuits  100 ,  200 , and  300  which are powered through direct electrical male and female connectors  44  and  42 , the fourth power supply circuit  400  is powered inductively. As such, the fourth power supply circuit  400  includes a light tube socket  40  having two brackets  68  disposed at opposite ends of the socket  40 . At least one bracket  68  includes an inductive transmitter  70 . Accordingly, a light tube  20  particularly adapted for use with the fourth power supply circuit  400  has two end caps  26  and  28  with at least one end cap including an inductive receiver or antenna  72 . When the light tube  20  is mounted in the light tube socket  40 , the at least one inductive receiver  72  in the light tube  20  is disposed adjacent to the at least one inductive transmitter  70  in the light tube socket  40 . 
         [0039]    The fourth power supply circuit  400  includes the power source  46  which supplies power to the at least one inductive transmitter  70  in the light tube socket  40 . The at least one transmitter  70  inductively supplies power to the at least one receiver  72  in one of the end caps  26  and/or  28  of the light tube  20 . The at least one inductive receiver  72  supplies power to the rectifier/filter circuit  50 . The rectifier/filter circuit  50 , PWM circuit  52 , and the one or more current-limiting circuits  54  operate as described above to power the one or more arrays of LEDs  22 . In this manner, the light tube  20  is powered without direct electrical connection.