Abstract:
A method of switching a plurality of switches for supplying a pulsed current to one or more than one light-emitting diodes involves: switching a current from a direct current (DC) voltage to an inductance component, for example an inductor or a flyback transformer, for charging the inductance component; switching a current from the inductance component to the light-emitting diodes for transferring energy from the inductance component to the light-emitting diodes; switching a current from the inductance component to the direct current (DC) voltage for transferring energy from the inductance means back to the direct current (DC) voltage; controlling the switchings to regulate the current in the inductance component for supplying the pulsed current to the light-emitting diodes is disclosed.

Description:
TECHNICAL FIELD 
     The technical field of this disclosure is switching mode pulsed current regulator circuits, particularly, a pulsed current regulator circuit for supplying a pulsed current to one or more than one light-emitting diodes. 
     BACKGROUND OF THE INVENTION 
     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. 
     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 constant current sources to drive light-emitting diodes. 
     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 main 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 (AC) 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. 
     It would be desirable to have a light-emitting diode driving circuit that would overcome the above disadvantages. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention provides a method of supplying a pulsed current to one or more than one light-emitting diodes from a direct current (DC) voltage comprising the steps of: charging an inductance means via switching on a current from the direct current (DC) voltage to the inductance means; discharging the inductance means via switching off the current from the direct current (DC) voltage to the inductance means, and switching on a current from the inductance means either to said light-emitting diodes for transferring energy from the inductance means to said light-emitting diodes or to the direct current (DC) voltage for transferring energy back to the direct current (DC) voltage; controlling said charging and discharging to regulate the current in the inductance means for supplying a pulsed current to said light-emitting diodes. 
     Accordingly, 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 pulsed current can remit illumination with higher peak illumination value to provide higher perceived brightness levels than to drive it with a constant current, the switching mode pulsed current supply disclosed by this application provide a better solution for driving light emitting diodes. 
     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 
       The above and other features and advantages of the present general inventive concept will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a block and circuit diagram illustrating an exemplary embodiment of a switching mode pulsed current supply according to the invention, wherein the inductance means is a flyback transformer. 
         FIG. 2  are exemplary waveform diagrams illustrating the various waveforms at different points of circuits in  FIG. 1  and  FIG. 3  in accordance with the present invention. 
         FIG. 3  is a block and circuit diagram illustrating an exemplary embodiment of a switching mode pulsed current supply according to the invention, wherein the inductance means is an inductor. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The detailed description set forth below in connection with the appended drawings is intended as a description of presently preferred embodiments of the invention and is not intended to represent the only forms in which the present invention may be constructed and or utilized. 
       FIG. 1  is a block and circuit diagram illustrating an exemplary embodiment of a switching mode pulsed current supply according to the invention, wherein the inductance means is a flyback transformer. 
     As illustrated in  FIG. 1 , a switching mode pulsed current supply  100  for supplying a pulsed current to one or more than one light-emitting diodes  101  is disclosed, said circuit comprising: an inductance means  102 ; a first switching unit  103  coupled to the inductance means  102  for switching a current from a direct current (DC) voltage  104  to the inductance means  102 ; a second switching unit  105  coupled between the inductance means and said light-emitting diodes  101  for switching a current from the inductance means  102  to said light-emitting diodes  101 ; a third switching unit  106  coupled between the inductor inductance  102  and the direct current (DC) voltage  104  for switching a current from the inductance means  102  to the direct current (DC) voltage  104 ; an switching control unit  107  coupled to said switching units  103 ,  105 ,  106  to control their switching for supplying a regulated pulsed current to said light-emitting diodes  101 . 
     As further illustrated in  FIG. 1 , the inductance means  102  is a flyback transformer comprising a primary winding  102 A, a first secondary winding  102 B coupled to said light-emitting diodes  101  and a second secondary winding  102 C coupled to the direct current (DC) voltage  104 . The switching control unit  107  coupled to the second switching unit  105  through a photo coupler  105 A and coupled to the third switching unit  106  through a photo coupler  106 A to control their switching 
       FIG. 2  are exemplary waveform diagrams illustrating the various waveforms at different points of circuits in  FIG. 1  and  FIG. 3  in accordance with the present invention. 
     As illustrated in  FIG. 1  and  FIG. 2 , a non-limiting exemplary waveform of switching control signals from the switching control unit  107  to the first switching unit  103  for controlling their switching are illustrated in  FIG. 2(A) ; a non-limiting exemplary waveform of switching control signal from the switching control unit  107  to second switching unit  105  for controlling its switching is illustrated in  FIG. 2(B) ; and a non-limiting exemplary waveform of switching control signal from the switching control unit  107  to third switching unit  106  for controlling its switching are illustrated in  FIG. 2(C) . According to the switching control signals from the switching control unit  107  to the switching units  103 ,  105  and  106  illustrated in  FIGS. 2(A) ,  2 (B) and  2 (C), a non-limiting exemplary waveform of a current from the direct current (DC) voltage  104  to the primary winding  102 A is illustrated in  FIG. 2(D) ; a non-limiting exemplary waveform of a current from the first secondary winding  102 B to said light-emitting diodes  101  is illustrated in  FIG. 2(E) ; a non-limiting exemplary waveform of a current from the second secondary winding  102 C to the direct current (DC) voltage  104  is illustrated in  FIG. 2(F) . 
     Accordingly, as further illustrated in  FIG. 1  and  FIG. 2 , the switching units  103 ,  105  and  106  switch to charge and discharge the inductance means  102  for providing a pulsed current: when the first switching unit  103  switches on and the switching units  105  and  106  switch off, the inductance means  102  is charging energy from the direct current (DC) voltage  104 ; further when the second switching unit  105  switches on and the switching units  103  and  106  both switch off, the energy stored in inductance means  102  is discharged to said light-emitting diodes  101 ; further when the third switching unit  106  switches on and the switching units  103  and  105  both switch off, the energy stored in inductance means  102  is discharged back to the direct current (DC) voltage  104 . Therefore, at steady state, the energy flow in and out of the inductance means  102  are determined according to the duty ratio between the switching units  103 ,  105  and  106  during each switching periods, therefore, the switching of the switching units  103 ,  105  and  106  regulates the current in the inductance means  102  for supplying a pulsed current illustrated in  FIG. 2(E)  to said light-emitting diodes  101 . Accordingly, the pulse width of the pulsed current is controllable, since the duty ratio between the switching units  105  and  106  is adjustable. 
     As further illustrated in  FIG. 1 , the switching mode pulsed current supply  100  further comprises a negative feedback current signal generator  108  to generate a negative feedback current signal  109  corresponding to the current in the inductance means  102 , wherein the switching control unit  107  integrates the negative feedback current signal  109  to process a negative feedback control. 
     As further illustrated in  FIG. 1 , the switching mode pulsed current supply  100  further comprises a negative feedback signal generator  110  to generate a negative feedback signal  111  corresponding to the current of said light-emitting diodes  101 , wherein the switching control unit  107  integrates the negative feedback signal  111  to process a negative feedback control. 
     As further illustrated in  FIG. 1 , the switching mode pulsed current supply  100  further comprises a photo coupler  112  coupled between the negative feedback signal generator  110  and the switching control unit  107  to provide electric isolation between the negative feedback signal generator  110  and the switching control unit  107 . 
     As further illustrated in  FIG. 1 , the switching mode pulsed current supply  100  further comprises a rectifying unit  113  and a smoothing unit  114  to rectify and smooth an alternating current (AC) voltage  115  and to provide the direct current (DC) voltage  104 , wherein the rectifying unit  113  is a full bridge rectifier and the smoothing unit  114  is a capacitor. 
       FIG. 3  is a block and circuit diagram illustrating an exemplary embodiment of a switching mode pulsed current supply according to the invention, wherein the inductance means is an inductor. 
     As illustrated in  FIG. 3 , a switching mode pulsed current supply  300  for supplying a pulsed current to one or more than one light-emitting diodes  301  is disclosed, said circuit comprising: an inductance means  302 ; a first switching unit  303  comprising switches  303 A and  303 B coupled to the inductance means  302  for switching a current from a direct current (DC) voltage  304  to the inductance means  302 ; a second switching unit  305  coupled to said light-emitting diodes  301  for switching a current from the inductance means  302  to said light-emitting diodes  301 ; a third switching unit  306  coupled between the inductance means  302  and the direct current (DC) voltage  304  for switching a current from the inductance means  302  to the direct current (DC) voltage  304 ; an switching control unit  307  coupled to said switching units  303 ,  305 ,  306  to control their switching for supplying a regulated pulsed current to said light-emitting diodes  301 . 
     As further illustrated in  FIG. 3 , the inductance means  302  is an inductor. 
       FIG. 2  shows exemplary waveform diagrams illustrating the various waveforms at different points of circuits in  FIG. 3  in accordance with the present invention. 
     As illustrated in  FIG. 3  and  FIG. 2 , a non-limiting exemplary waveform of switching control signals from the switching control unit  307  to the first switching unit  303  comprising switches  303 A,  303 B for controlling their switching is illustrated in  FIG. 2(A) ; a non-limiting exemplary waveform of switching control signal from the switching control unit  307  to second switching unit  305  for controlling its switching is illustrated in  FIG. 2(B) ; and a non-limiting exemplary waveform of switching control signal from the switching control unit  307  to third switching unit  306  for controlling its switching is illustrated in  FIG. 2(C) . According to the switching control signals from the switching control unit  307  to the switching units  303 ,  305  and  306  illustrated in  FIGS. 2(A) ,  2 (B) and  2 (C), a non-limiting exemplary waveform of a current from the direct current (DC) voltage  304  to the inductor  302  is illustrated in  FIG. 2(D) ; a non-limiting exemplary waveform of a current from the inductor  302  to said light-emitting diodes  301  is illustrated in  FIG. 2(E) ; a non-limiting exemplary waveform of a current from the inductor  302  back to the direct current (DC) voltage  304  is illustrated in  FIG. 2(F) ; a non-limiting exemplary waveform of a current in the inductor  302  is illustrated in  FIG. 2(G) . 
     Accordingly, as further illustrated in  FIG. 3  and  FIG. 2 , the switching units  303 ,  305  and  306  switch to charge and discharge the inductor  302  for providing a pulsed current to said light-emitting diodes  301 : when the first switching unit  303  switches on and the switching units  305  and  306  switch off, the inductor  302  is charging energy from the direct current (DC) voltage  304 ; further when the second switching unit  305  switches on and the switching units  303  and  306  both switch off, the energy stored in the inductor  302  is discharged to said light-emitting diodes  301 ; furthermore when the third switching unit  306  switches on and the switching units  303  and  305  both switch off, the energy stored in the inductor  302  is discharged back to the direct current (DC) voltage  304 . Therefore, at steady state, the energy flow in and out of the inductor  302  are determined according to the duty ratio between the switching units  303 ,  305  and  306  during each switching periods, therefore, this switching regulates the current in the inductor  302  for supplying a pulsed current illustrated in  FIG. 2(E)  to said light-emitting diodes  301 . Accordingly, the pulse width of the pulsed current is controlled according to the duty ratio between the switching units  305  and  306 . 
     As further illustrated in  FIG. 3 , the switching mode pulsed current supply  300  further comprises a negative feedback current signal generator  308  to generate a negative feedback current signal  309  corresponding to the current in the inductance means  302 , wherein the switching control unit  307  integrates the negative feedback current signal  309  to process a negative feedback control. 
     As further illustrated in  FIG. 3 , the switching mode pulsed current supply  300  further comprises a negative feedback signal generator  310  to generate a negative feedback signal  311  corresponding to the current of said light-emitting diodes  301 , wherein the switching control unit  307  integrates the negative feedback signal  311  to process a negative feedback control. 
     Accordingly, 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 pulsed current can remit illumination with higher peak illumination value to provide higher perceived brightness levels than to drive it with a constant current, the switching mode pulsed current supplies  100 ,  300  provide a better solution for driving light emitting diodes. 
     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.