Abstract:
This invention discloses a light-emitting semiconductor device with open-bypass function, which comprises two terminals providing a current, at least one LED unit and a bypass switch. Electrodes of the LED unit and the bypass switch are properly connected to the terminals, so that the bypass switch will provide an alternative path for current flowing through if the circuit of the LEDs unit between two terminals is open.

Description:
[0001]     This application claims priority to Taiwan Patent Application 094144011 filed Dec. 13, 2005.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to a light-emitting semiconductor device with open-bypass function.  
         [0004]     2. Related Prior Art  
         [0005]     For serial or parallel LEDs, an open or short circuit may make the LED inoperable so that it cannot be lit to be lit. The open circuit results in failure all LEDs serially connected to this circuit; and the short circuit causes one or more LEDs to be “omitted”.  
         [0006]     Therefore, this invention provides a bypass switch in the LED circuit.  
       SUMMARY OF THE INVENTION  
       [0007]     The light-emitting semiconductor device with an open-bypass function comprises a first terminal, a second terminal, at least one LED unit and a bypass switch. Each LED unit composed of one or more LED die has a first electrode and a second electrode respectively connected to the first terminal and the second terminal. The bypass switch also has a first electrode and a second electrode (referred to as the third and fourth electrodes in the claims) respectively connected to the first terminal and the second terminal of the light-emitting semiconductor device.  
         [0008]     In a normal condition, a current applied to the first and the second terminals can be conducted through the LED unit for lighting it, and the switch is in an “Off” state without current flowing through. If the circuit of the LED unit between two terminals is open and the current cannot be conducted through, the bypass switch will be in an “On” state for conducting the current.  
         [0009]     Accordingly, the first and the second terminals of the light-emitting semiconductor device can be always electrically conductive.  
         [0010]     This invention also comprises a series or parallel circuit comprising several devices and a current source. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  shows the light-emitting semiconductor device of this invention.  
         [0012]      FIGS. 2 and 3  respectively show the LED unit and the bypass switch.  
         [0013]      FIGS. 4 and 5  respectively show the current flow when the switch is in the “On” and “Off” states.  
         [0014]      FIG. 6  shows the electrical connection of this invention  
         [0015]      FIGS. 7 and 8  respectively show the series and the parallel circuits. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]      FIG. 1 ( a ) shows a light-emitting semiconductor device  1  comprising two terminals defined as a first terminal  2  and a second terminal  3 , an LED unit  4  and a switch  7  for bypassing. The LED unit  4  includes several LED dice  10  as shown in  FIG. 2 , and has a first electrode  5  and a second electrode  6  respectively connected to the first terminal  2  and the second terminal  3 . In a normal condition, the circuit involving the LED unit  4  is electrically connected and the LED dice can be lit by applying a current to the terminals  2  and  3 . However, if the circuit is open, the LED unit  4  cannot be lit.  
         [0017]     The switch  7  is made with an integrated circuit and also has a first electrode  8  and a second electrode  9  respectively connected to the terminals  2  and  3 . The switch  7  includes a voltage detection circuit  11  and a switch circuit  12 , as shown in  FIG. 3 . The switch  7  is electrically open and in an “Off” state, but closed and in an “On” state when triggered by a first signal received from the electrodes  8  and  9 . This first signal is a voltage equal to or higher than a predetermined value and generated when the circuit involving the LED unit  4  is open.  
         [0018]      FIG. 1 ( b ) shows the LED unit  4  connected to the switch  7  through a common contact and thus controlled by the switch  7 .  
         [0019]     The voltage detection circuit  11  has an anode, a cathode and a gate, wherein the anode and the cathode are respectively connected to the electrodes  8  and  9 . The switch circuit  12  also has an anode, a cathode and a gate, wherein the anode and the cathode are also respectively connected to the electrodes  8  and  9 . The gates of the circuits  11  and  12  are connected to each other. By detecting voltage of the circuit, the circuit  11  can generate a second signal to drive the gate of the switch circuit  12  through the gate of the voltage detection circuit  11 . Then the switch circuit  12  enters into the “On” state.  
         [0020]     In this invention, the switch circuit can be designed as follows: 
    (1) One PNPN thyristor having a P anode and an N cathode respectively connected to the anode and cathode of the switch circuit.     (2) Two bipolar junction transistors    
 
         [0023]     The first bipolar junction transistor has a first emitter, a first base and a first collector; the second bipolar junction transistor has a second emitter, a second base and a second collector. The first emitter and the second emitter are respectively connected to the anode and the cathode of the switch circuit. The first base is connected to the second collector. The first collector is connected to the second base. 
    (3) Two MOSFETs    
 
         [0025]     The first MOSFET has a first source, a first gate and a first drain; the second MOSFET has a second source, a second gate and a second drain. The first source and the second source are respectively connected to the anode and the cathode of the switch circuit. The first gate is connected to the second drain. The first drain is connected to the second gate. 
    (4) One bipolar junction transistor and one MOSFET    
 
         [0027]     The bipolar junction transistor has an emitter, a base and a collector; the MOSFET has a source, a gate and a drain. The emitter and the source are respectively connected to the anode (or the cathode) and the cathode (or the anode) of the switch circuit. The base is connected to the drain. The collector is connected to the gate.  
         [0028]     The light-emitting semiconductor device  1  is operated as follows: 
    (1) If electrical connection of the LED unit  4  is abnormally open, the current can not be conducted through the LED unit  4 ; and the switch  7  will be in the “On” state and enable the current to flow through, as shown in  FIG. 4 .     (2) If electrical connection of the LED unit  4  is normal, a current can be conducted through the LED unit  4  for lighting it; and the switch  7  is in the “Off” state without current flowing through, as shown in  FIG. 5 .    
 
         [0031]      FIG. 6  shows the electrical connection of the device. The electrode  5  of the LED unit  4  and the electrode  8  of the switch  7  are commonly connected to the first terminal  2  of the device  1 . The electrode  6  of the LED unit  4  and the electrode  9  of the switch  7  are commonly connected to the second terminal  3  of the device  1 .  
         [0032]     The terminals of the light-emitting semiconductor device can be attached to a substrate by wire bonding and surface mount technology.  
         [0033]      FIG. 7  shows a series circuit. The terminal  3  of the device  1  is connected to the terminal  2 ′ of the device  1 ′; and the terminal  2  of the device  1  and the terminal  3 ′ of the device  1 ′ are individually connected to a current source  13 .  FIG. 8  shows a parallel circuit. The terminal  2  of the device  1  and the terminal  2 ′ of the device  1 ′ are commonly connected to a current source; and the terminal  3  of the device  1  and the terminal  3 ′ of the device  1 ′ are commonly connected to the current source. That is, the devices and the current source can form a series or parallel circuit always conductive by providing the bypass switch.