Abstract:
A discontinuous current regulator circuit is composed of a switched-mode power converter circuit, a sensing circuit and a current mode controller circuit. The current mode controller circuit, based on the signal from the sensing circuit, controls the switched-mode power converter circuit to supply a regulated discontinuous current to a light-emitting diode or light-emitting diode arrangement comprising a plurality of light-emitting diodes. The present invention provides a discontinuous current regulator circuit for driving white light-emitting diodes able to provide higher perceived brightness levels and with longer lifetime than existing light-emitting diode drivers.

Description:
TECHNICAL FIELD 
       [0001]    The technical field of this disclosure is current regulator circuits, particularly, a discontinuous current regulator circuit for supplying a discontinuous current to at least one light-emitting diode. 
       BACKGROUND OF THE INVENTION 
       [0002]    Significant advances have been made in the technology of white light-emitting diodes. White light-emitting diodes are commercially available which generate 60˜100 lumens/watt. This is comparable to the performance of fluorescent lamps; therefore there have been a lot of applications in the field of lighting using white light-emitting diodes. 
         [0003]    Various light-emitting diode driver circuits are known from the prior arts. For example, U.S. Pat. No. 6,304,464: “FLYBACK AS LED DRIVER”; U.S. Pat. No. 6,577,512: “POWER SUPPLY FOR LEDS”; and U.S. Pat. No. 6,747,420: “DRIVER CIRCUIT FOR LIGHT-EMITTING DIODES”. All the light-emitting diode driver circuits mentioned above are constant current regulator circuits that act as const current sources to drive light-emitting diodes. 
         [0004]    In the field of lighting applications, for a white light-emitting diode lamp driven by a constant current source and a fluorescent lamp driven by an alternating current source under the condition that both lamps&#39; remitted illumination have the same average illumination value, the fluorescent lamp provides higher perceived brightness levels than the white light-emitting diode lamp, the reason is: human eyes are responsive to the peak value of illumination; therefore, if a lamp can provide higher peak illumination, it provides higher perceived brightness levels. For a fluorescent lamp driven by an alternating current source, it remits illumination with peak value higher than its average illumination value. But for a white light-emitting diode lamp driven by a constant current source, since light generation of a white light-emitting diode is dependent on the current strength through the white light-emitting diode, it remits illumination with peak value close to its average illumination value. Therefore, a white light-emitting diode lamp driven by a constant current regulator circuit constitutes a drawback of its remitted illumination with low perceived brightness levels. 
         [0005]    In addition, for a constant current regulator circuit with flyback type topology, including boost; buck-boost; nonisolated flyback or isolated flyback converter topology, a large enough capacitance is needed in its output filter circuit to supply a constant current continuously during the period when its semiconductor switching element is closed. Thus generally at least one aluminum electrolytic capacitor is used to fulfill the requirement of a large enough capacitance. However, since lifetime of a white light-emitting diode is usually more than 20,000 average life hours, but lifetime of an aluminum electrolytic capacitor is usually from 1,000 to 5,000 average life hours only. Thus this constitutes a drawback of limited lifetime in the field of lighting applications due to the usage of aluminum electrolytic capacitors. 
         [0006]    It would be desirable to have a light-emitting diode driving circuit that would overcome the above disadvantages. 
       SUMMARY OF THE INVENTION 
       [0007]    One aspect of the present invention provides a discontinuous current regulator circuit for driving white light-emitting diodes able to provide higher perceived brightness levels than existing light-emitting diode driving circuit based on a constant current regulator circuit. 
         [0008]    Accordingly, a white light-emitting diode can be driven by a discontinuous current with peak current value higher than its maximum constant current rating or driven by a constant current equal to its maximum constant current rating. Since light generation of a white light-emitting diode is dependent on the current strength through the white light-emitting diode, to drive a white light-emitting diode with a discontinuous current with peak current value higher than its maximum constant current rating can remit illumination with higher peak illumination value to provide higher perceived brightness levels than to drive it with a constant current equal to its maximum constant current rating. 
         [0009]    Another aspect of the present invention provides a discontinuous current regulator circuit for driving light-emitting diodes having longer lifetime than existing light-emitting diode drivers: since the present invention provides a discontinuous current regulator circuit with flyback type topology that don&#39;t have to keep on supplying current to its output during the period when its semiconductor switching element is closed, therefore the usage of aluminum electrolytic capacitors to keep on supplying current to its output is not needed. 
         [0010]    The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention, rather than limiting the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows a block and circuit diagram of a circuit which constitutes a first exemplary embodiment of a discontinuous current regulator circuit with buck converter topology according to the invention. 
           [0012]      FIG. 2  shows a block and circuit diagram of a circuit which constitutes a second exemplary embodiment of a discontinuous current regulator circuit with boost converter topology according to the invention. 
           [0013]      FIG. 3  shows a block and circuit diagram of a circuit which constitutes a third exemplary embodiment of a discontinuous current regulator circuit with buck-boost converter topology according to the invention. 
           [0014]      FIG. 4  shows a block and circuit diagram of a circuit which constitutes a fourth exemplary embodiment of a discontinuous current regulator circuit with nonisolated flyback converter topology according to the invention. 
           [0015]      FIG. 5  shows a block and circuit diagram of a circuit which constitutes a fifth exemplary embodiment of a discontinuous current regulator circuit with isolated flyback converter topology according to the invention. 
           [0016]      FIG. 6  shows a block and circuit diagram of a circuit which constitutes a sixth exemplary embodiment of a discontinuous current regulator circuit with forward converter topology according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]      FIG. 1  shows a block and circuit diagram of a circuit which constitutes a first exemplary embodiment of a discontinuous current regulator circuit with buck converter topology according to the invention. 
         [0018]    The circuit shown in  FIG. 1  essentially comprises a switched-mode power converter circuit with buck converter topology  110 , a sensing circuit  140 , a current mode controller circuit  150 , and a light-emitting diode or light-emitting diode arrangement comprising a plurality of light-emitting diodes  130 . 
         [0019]    The switched-mode power converter circuit  110  comprises a power inductor  111 , a semiconductor switching element  112 , and a diode  113 , wherein the switched-mode power converter circuit  110  has input means for receiving a direct voltage Vin  120  and output means coupled to the light-emitting diodes  130 . 
         [0020]    In the case of the first exemplary embodiment shown in  FIG. 1 , the sensing circuit  140  in the form of an ohmic resistor is connected in series with the semiconductor switching element  112 . To regulate a discontinuous current supplied to the light-emitting diodes  130 , the voltage drop across the sensing circuit  140  is determined and fed to the current mode controller circuit  150  as a measured signal representing the current through the power inductor  111  while the semiconductor switching element  112  is closed. The current mode controller circuit  150  controls the switching of the semiconductor switching element  112  dependent on the current through the power inductor  111 . Wherein the semiconductor switching element  112  is switched on and off continuously: during the period when the semiconductor switching element  112  is closed, energy from the direct voltage Vin  120  is received for storing energy into the power inductor  111  and supplying current to the light-emitting diodes  130 ; during the period when the semiconductor switching element  112  is opened, the previously stored energy in the power inductor  111  is released for supplying current to the light-emitting diodes  130 . To operate the switched-mode power converter circuit  110  under discontinuous conduction mode, then during the period when the semiconductor switching element  112  is opened the current through the power inductor  111  decreases to a value of zero. During the period when the current through the power inductor  111  is zero, there is no current fed to the light-emitting diodes  130 . The current mode controller circuit  150  controls the switching of the semiconductor switching element  112  dependent on the current through the power inductor  111 , the discontinuous current supplied from the power inductor  111  to the light-emitting diodes  130  is regulated accordingly. 
         [0021]      FIG. 2  shows a block and circuit diagram of a circuit which constitutes a second exemplary embodiment of a discontinuous current regulator circuit with boost converter topology according to the invention. 
         [0022]    The circuit shown in  FIG. 2  essentially comprises a switched-mode power converter circuit with boost converter topology  210 , a sensing circuit  240 , a current mode controller circuit  250 , and a light-emitting diode or light-emitting diode arrangement comprising a plurality of light-emitting diodes  130 . 
         [0023]    The switched-mode power converter circuit  210  comprises a power inductor  211 , a semiconductor switching element  212 , and a diode  213 , wherein the switched-mode power converter circuit  210  has input means for receiving a direct voltage Vin  120  and output means coupled to the light-emitting diodes  130 . 
         [0024]    In the case of the second exemplary embodiment shown in  FIG. 2 , the sensing circuit  240  in the form of an ohmic resistor is connected in series with the semiconductor switching element  212 . To regulate a discontinuous current supplied to the light-emitting diodes  130 , the voltage drop across the sensing circuit  240  is determined and fed to the current mode controller circuit  250  as a measured signal representing the current through the power inductor  211  while the semiconductor switching element  212  is closed. The current mode controller circuit  250  controls the switching of the semiconductor switching element  212  dependent on the current through the power inductor  211 . Wherein the semiconductor switching element  212  is switched on and off continuously: during the period when the semiconductor switching element  212  is closed, energy from the direct voltage Vin  120  is stored into the power inductor  211  and since the diode  213  is reverse biased, there is no current fed to the light-emitting diodes  130 ; during the period when the semiconductor switching element  212  is opened, previously stored energy in the power inductor  211  is released and combined with energy supplied from the direct voltage Vin  120  to supply current to the light-emitting diodes  130 . The current mode controller circuit  250  controls the switching of the semiconductor switching element  212  dependent on the current through the power inductor  211 , thus the discontinuous current supplied from the power inductor  211  to the light-emitting diodes  130  is regulated accordingly. 
         [0025]      FIG. 3  shows a block and circuit diagram of a circuit which constitutes a third exemplary embodiment of a discontinuous current regulator circuit with buck-boost converter topology according to the invention. 
         [0026]    The circuit shown in  FIG. 3  essentially comprises a switched-mode power converter circuit with buck-boost converter topology  310 , a sensing circuit  340 , a current mode controller circuit  350 , and a light-emitting diode or light-emitting diode arrangement comprising a plurality of light-emitting diodes  130 . 
         [0027]    The switched-mode power converter  310  comprises a power inductor  311 , two semiconductor switching elements  312  and  313 , and two diodes  314  and  315 , wherein the switched-mode power converter circuit  310  has input means for receiving a direct voltage Vin  120  and output means coupled to the light-emitting diodes  130 . 
         [0028]    In the case of the third exemplary embodiment shown in  FIG. 3 , the sensing circuit  340  in the form of an ohmic resistor is connected in series with the semiconductor switching element  313 . To regulate a discontinuous current supplied to the light-emitting diodes  130 , the voltage drop across the sensing circuit  340  is determined and fed to the current mode controller circuit  350  as a measured signal representing current through the power inductor  311  while the semiconductor switching elements  312  and  313  are closed. The current mode controller circuit  350  controls the switching of the semiconductor switching elements  312  and  313  dependent on the current through the power inductor  311 . Wherein the semiconductor switching elements  312  and  313  are simultaneously switched on and off continuously: during the period when the semiconductor switching elements  312  and  313  are closed, energy from the direct voltage Vin  120  is stored into the power inductor  311  and there is no current fed to the light-emitting diodes  130  since the diode  315  is reverse biased; during the period when the semiconductor switching element  312  and  313  are opened, previously stored energy in the power inductor  311  is released for supplying current to the light-emitting diodes  130 . The current mode controller circuit  350  controls the switching of the semiconductor switching elements  312  and  313  dependent on the current through the power inductor  311 , thus the discontinuous current supplied from the power inductor  311  to the light-emitting diodes  130  is regulated accordingly. 
         [0029]      FIG. 4  shows a block and circuit diagram of a circuit which constitutes a fourth exemplary embodiment of a discontinuous current regulator circuit with nonisolated flyback converter topology according to the invention. 
         [0030]    The circuit shown in  FIG. 4  essentially comprises a switched-mode power converter circuit with nonisolated flyback converter topology  410 , a sensing circuit  440 , a current mode controller circuit  450 , and a light-emitting diode or light-emitting diode arrangement comprising a plurality of light-emitting diodes  130 . 
         [0031]    The switched-mode power converter  410  comprises a power inductor  411 , a semiconductor switching element  412 , and a diode  413 , wherein the switched-mode power converter circuit  410  has input means for receiving a direct voltage Vin  120  and output means coupled to the light-emitting diodes  130 . 
         [0032]    In the case of the fourth exemplary embodiment shown in  FIG. 4 , the sensing circuit  440  in the form of an ohmic resistor is connected in series with the semiconductor switching element  412 . To regulate a discontinuous current supplied to the light-emitting diodes  130 , the voltage drop across the sensing circuit  440  is determined and fed to the current mode controller circuit  450  as a measured signal representing current through the power inductor  411  while the semiconductor switching element  412  is closed. The current mode controller circuit  450  controls the switching of the semiconductor switching element  412  dependent on the current through the power inductor  411 . Wherein the semiconductor switching element  412  is switched on and off continuously: during the period when the semiconductor switching elements  412  is closed, energy from the direct voltage Vin  120  is stored into the power inductor  411  and there is no current fed to the light-emitting diodes  130  since the diode  413  is reverse biased; during the period when the semiconductor switching element  412  is opened, previously stored energy in the power inductor  411  is released for supplying current to the light-emitting diodes  130 . The current mode controller circuit  450  controls the switching of the semiconductor switching elements  412  dependent on the current through the power inductor  411 , thus the discontinuous current supplied from the power inductor  411  to the light-emitting diodes  130  is regulated accordingly. 
         [0033]      FIG. 5  shows a block and circuit diagram of a circuit which constitutes a fifth exemplary embodiment of a discontinuous current regulator circuit with isolated flyback converter topology according to the invention. 
         [0034]    The circuit shown in  FIG. 5  essentially comprises a switched-mode power converter circuit with isolated flyback converter topology  510 , a sensing circuit  540 , a current mode controller circuit  550 , and a light-emitting diode or light-emitting diode arrangement comprising a plurality of light-emitting diodes  130 . 
         [0035]    The switched-mode power converter  510  comprises a transformer  511  provided with a primary winding L 51  and a secondary winding L 52 , a semiconductor switching element  512 , and a diode  513 , wherein the switched-mode power converter circuit  510  has input means for receiving a direct voltage Vin  120  and output means coupled to the light-emitting diodes  130 . 
         [0036]    In the case of the fifth exemplary embodiment shown in  FIG. 5 , the sensing circuit  540  in the form of an ohmic resistor is connected in series with the semiconductor switching element  512 . To regulate a discontinuous current supplied to the light-emitting diodes  130 , the voltage drop across the sensing circuit  540  is determined and fed to the current mode controller circuit  550  as a measured signal representing current through the primary winding L 51  of the transformer  511  while the semiconductor switching element  512  is closed. The current mode controller circuit  550  controls the switching of the semiconductor switching element  512  dependent on the current through the primary winding L 51  of the transformer  511 . Wherein the semiconductor switching element  512  is switched on and off continuously: during the period when the semiconductor switching elements  512  is closed, energy from the direct voltage Vin  120  is stored into the transformer  511  and there is no current fed to the light-emitting diodes  130  since the diode  513  is reverse biased; during the period when the semiconductor switching element  512  is opened, previously stored energy in the transformer  511  is released for supplying current to the light-emitting diodes  130 . The current mode controller circuit  550  controls the switching of the semiconductor switching elements  512  dependent on the current through the primary winding L 51  of the transformer  511 , thus the discontinuous current supplied from the transformer  511  to the light-emitting diodes  130  is regulated accordingly. 
         [0037]      FIG. 6  shows a block and circuit diagram of a circuit which constitutes a sixth exemplary embodiment of a discontinuous current regulator circuit with forward converter topology according to the invention. 
         [0038]    The circuit shown in  FIG. 6  essentially comprises a switched-mode power converter circuit with forward converter topology  610 , a sensing circuit  640 , a current mode controller circuit  650 , and a light-emitting diode or light-emitting diode arrangement comprising a plurality of light-emitting diodes  130 . 
         [0039]    The switched-mode power converter  610  comprises a transformer  611  provided with a primary winding L 61 , a secondary winding L 62  and a clamp winding L 63 , a semiconductor switching element  612 , and two diodes  613  and  614 , wherein the switched-mode power converter circuit  610  has input means for receiving a direct voltage Vin  120  and output means coupled to the light-emitting diodes  130 . 
         [0040]    In the case of the sixth exemplary embodiment shown in  FIG. 6 , the sensing circuit  640  in the form of an ohmic resistor is connected in series with the semiconductor switching element  612 . To regulate a discontinuous current supplied to the light-emitting diodes  130 , the voltage drop across the sensing circuit  640  is determined and fed to the current mode controller circuit  650  as a measured signal representing current through the primary winding L 61  of the transformer  611  while the semiconductor switching element  612  is closed. The current mode controller circuit  650  controls the switching of the semiconductor switching element  612  dependent on the current through the primary winding L 61  of the transformer  611 . Wherein the semiconductor switching element  612  is switched on and off continuously: during the period when the semiconductor switching elements  612  is closed, energy from the direct voltage Vin  120  is transferred from the primary winding L 61  to the secondary winding L 62  for supplying current to the light-emitting diodes  130 ; during the period when the semiconductor switching element  612  is opened, there is no current fed to the light-emitting diodes  130 . The current mode controller circuit  650  controls the switching of the semiconductor switching elements  612  dependent on the current through the primary winding L 61  of the transformer  611 , thus the discontinuous current supplied from the transformer  611  to the light-emitting diodes  130  is regulated accordingly. 
         [0041]    It is to be understood that the above described embodiments are merely illustrative of the principles of the invention and that other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.