Abstract:
Disclosed are methods and lighting system with LEDs. An exemplified system comprises series-coupled light-emitting diodes, an integrated circuit, and an energy storage apparatus. The series-coupled light-emitting diodes are divided into several LED groups coupled in series. The integrated circuit comprises nodes respectively coupled to the LED groups, for providing a driving current to selectively flow through at least one of the LED groups. The energy storage apparatus has two ends coupled to a predetermined LED in a predetermined LED group. When the driving current flows through the predetermined LED group the energy storage apparatus energizes; and when the driving current does not flow through the predetermined LED group the energy storage apparatus de-energizes to illuminate the predetermined LED.

Description:
BACKGROUND 
       [0001]    The present disclosure relates generally to Light-Emitting Diode (LED) lighting systems and controls; and more particularly to Alternating Current (AC) driven LED lighting systems and controls. 
         [0002]    Light-Emitting Diodes or LEDs are increasingly being used for general lighting purposes. In one example, a group of so-called white LEDs is powered from an AC power source and the term “AC LED” is sometimes used to refer to such circuit. Concerns for AC LED include manufacture cost, power efficiency, power factor, flicker, lifespan, etc. 
         [0003]      FIG. 1  demonstrates AC LED circuit  10  in the art, which simply has LED module  12  and current-limiting resistor  14 . LED module consists of two LED strings connected in anti-parallel. AC LED circuit  10  requires neither an AC-DC converter nor a rectifier. Even though a DC voltage can be supplied, an AC voltage is typically supplied to input port  8  and directly powers AC LED circuit  10 . Simplicity in structure and low-price in manufacture are two advantages AC LED circuit  10  has. Nevertheless, AC LED circuit  10  can only shine in a very narrow time period for each AC cycle time, suffering either low average luminance or high-current stress to LEDs. 
         [0004]      FIG. 2A  demonstrates AC LED circuit  15  in the art. Examples of AC LED circuit  15  can be found in U.S. Pat. No. 7,708,172. AC LED circuit  15  employs full-wave rectifier  18 . A DC or AC voltage signal is received on input port  16 . A string of LEDs are grouped into LED groups  20   1 ,  20   2 ,  20   3 , and  20   4 . Integrated circuit  22  has nodes PIN 1 , PIN 2 , PIN 3 , and PIN 4 , connected to the cathodes of LED groups  20   1 ,  20   2 ,  20   3 , and  20   4  respectively. Inside integrated circuit  22  are ground switches SG 1 , SG 2 , SG 3 , and SG 4 , together with controller  24 . When the voltage on input port  16  increases, controller  24  can switch ground switches SG 1 , SG 2 , SG 3 , and SG 4 , to possibly light on more LEDs. Operations of integrated circuit  22  have been exemplified in U.S. Pat. No. 7,708,172 and are omitted here for brevity. 
         [0005]      FIG. 2B  demonstrates AC LED circuit  30  in the art, whose example can be found in U.S. Pat. No. 8,299,724. Different from integrated circuit  22  in  FIG. 2A , integrated circuit  34  in  FIG. 2B  has an addition node PIN 0 . Integrated circuit  34  further employs bypass switches SP 1 , SP 2 , SP 3 , and SP 4 , each selectively providing a bypass current path for driving current to detour a corresponding LED group. For example, when controller  32  turns on bypass switches SP 1 , nodes PIN 0  and PIN 1  are shorted together and LED group  20   1  darkens because no driving current flows through LED group  20   1 . 
         [0006]      FIG. 3  illustrates the waveforms of signals when input port  16  in  FIG. 2A  or  2 B is supplied with an AC voltage signal. The upmost waveform shows rectified voltage V REC , which, as indicated in  FIGS. 2A and 2B , refers to the voltage after full-wave rectifier  18  and upon LED group  20   1 . The second waveform shows active LED count, meaning the number of LEDs of the LED groups that are made to light on. The four following waveforms regard with currents I G4 , I G3 , I G2  and I G1 , respectively flowing through LED groups  20   4 ,  20   3 ,  20   2  and  20   1 . Active LED count rises or descends stepwise, following the increase or decrease of rectified voltage V REC . When rectified voltage V REC  increases, LED groups  20   1 ,  20   2 ,  20   3 , and  20   4 , according to a forward sequence, join to light on. When rectified voltage V REC  decreases, LED groups  20   1 ,  20   2 ,  20   3 , and  20   4 , according to a backward sequence, darken. AC LED circuits  15  and  30  both enjoy simple circuit architecture and, as can be derived, good power efficiency. 
         [0007]    There in  FIG. 3  however has dark zone T DARK  when no LED activates or shines. If rectified voltage V REC  is a 120 Hertz signal, voltage valley, where rectified voltage V REC  is about zero Volt, appears as a 120 Hertz signal, causing dark zone T DARK  to appear in the same frequency of 120 Hertz. Even though dark zone T DARK  of 120 Hertz might not be perceivable by human eyes, it is reported that human may feel dizzy or nauseated when looking, for a long period of time, objects exposed under the lighting with the non-perceivable dark zone T DARK  of 120 Hertz. 
       SUMMARY 
       [0008]    Embodiments of the present invention comprise a system with series-coupled light-emitting diodes, an integrated circuit, and an energy storage apparatus. The series-coupled light-emitting diodes are divided into several LED groups coupled in series. The integrated circuit comprises nodes respectively coupled to the LED groups, for providing a driving current to selectively flow through at least one of the LED groups. The energy storage apparatus has two ends coupled to a predetermined LED in a predetermined LED group. When the driving current flows through the predetermined LED group the energy storage apparatus energizes; and when the driving current does not flow through the predetermined LED group the energy storage apparatus de-energizes to illuminate the predetermined LED. 
         [0009]    Embodiments of the present invention comprise a method for a system with series-coupled light-emitting diodes. The LEDs are divided into several LED groups coupled in series. A driving current is provided. One of the LED groups is selected, such that the driving current flows through a selected LED group. Electrical energy is stored when the driving current flows through a predetermined LED group. Stored electrical energy is released to light on a predetermined LED in the predetermined LED group when the driving current does not flow through the predetermined LED group. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The invention can be more fully understood by the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0011]      FIGS. 1 ,  2 A and  2 B demonstrate three AC LED circuits in the art; 
           [0012]      FIG. 3  illustrates the waveforms of signals when the input port in  FIG. 2A  or  2 B is supplied with an AC voltage signal; 
           [0013]      FIG. 4  shows a system with an AC LED circuit in accordance with an embodiment of the invention; 
           [0014]      FIG. 5A  shows that ground switches SG 1 , SG 2 , SG 3  and SG 4  operate in the Open, CC, Short, and Short modes, respectively; 
           [0015]      FIG. 5B  shows the operation modes of ground switches SG 1 , SG 2 , SG 3  and SG 4  when rectified voltage V REC  in  FIG. 5A  declines to a certain level; 
           [0016]      FIG. 6  illustrates the waveforms of signals when the input port in  FIG. 4  is supplied with an AC voltage signal; 
           [0017]      FIG. 7  employs some additional regular diodes to sustain reverse-bias voltages, preventing LEDs from being damaged; 
           [0018]      FIG. 8  shows only one ground switch operating in the CC mode and all other ground switches operating in the Open mode; 
           [0019]      FIG. 9A  shows another system with an AC LED circuit; 
           [0020]      FIG. 9B  demonstrates an embodiment of the charge/discharge controller in  FIG. 9A ; and 
           [0021]      FIG. 10  shows a system with another AC LED circuit  100  in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 4  shows a system with AC LED circuit  40  in accordance with an embodiment of the invention. A DC or AC voltage signal is received on input port  50 . The AC voltage signal may be, for example, a 60 Hertz AC sinusoidal signal having a 110-volt amplitude. Full-wave rectifier  48  rectifies the voltage signal on input port  50  to provide a rectified voltage V REC  and a ground voltage GND as two power supply lines to power the LEDs and integrated circuit  44  in  FIG. 4 . The LEDs are, but not limited to be, grouped into LED groups  46   1 ,  46   2 ,  46   3 , and  46   4 . As an illustrative example, each LED group in  FIG. 4  has 3 LEDs coupled in series, and all LED groups are coupled in series to form a LED string. 
         [0023]      FIG. 4  includes several capacitors  52 ,  54 ,  56 ,  58 , and  60  to shunt with some LEDs respectively. The invention is not limited to  FIG. 4 , however. Other embodiments of the invention might have more or less capacitors, shunted to different LEDs. Capacitor  52  shunts with LED L 1 , capacitor  54  the LED group  46   1 , capacitor  56  the LED string consisting of LEDs L 4  and L 5 , capacitor  58  the LED string consisting of LEDs L 8  and L 9 , and capacitor  60  LED L 11 . These capacitors act as energy storage apparatuses. They can charge or energize in some periods of time and later on discharge or de-energize to light on some LEDs. 
         [0024]    Integrated circuit  44  has 4 nodes PIN 1 , PIN 2 , PIN 3 , and PIN 4 . Integrated circuit  44  further has ground switches SG 1 , SG 2 , SG 3  and SG 4 , each coupled between a corresponding node and the ground voltage GND. Controller  42  in integrated circuit  44  controls the control terminals of ground switches SG 1 , SG 2 , SG 3  and SG 4 . In one embodiment, controller  42  can sense the currents flowing through nodes PIN 1 , PIN 2 , PIN 3 , and PIN 4 , to determine the operation mode of each ground switch. For example, each ground switch can be individually switched to operate in one of three modes: including Open mode, Short mode, and constant current (CC) mode. Ground switch SG 1 , for instance, shorts node PIN 1  to the ground voltage GND if operating in the Short mode; performs an open circuit if operating in the Open mode; and provides a constant driving current I DRV  flowing through node PIN 1  to the ground voltage if operating in the CC mode. 
         [0025]    For terminology, if devices A and B have similar circuit configurations but A has a work voltage higher than device B does, then device A is an upstream one in respect with device B. For example, ground switch SG 1  is an upstream one to ground switch SG 2  because the voltage at node PIN 1  is not less than that at node PIN 2 . In the opposite, ground switch SG 2  is a downstream one to ground switch SG 1 . The same terminology could be applied to other objects. For instance, LED group  46   1  is the most upstream LED group and LED group  46   4  the most downstream LED group in  FIG. 4 . 
         [0026]    In one embodiment, controller  42  is configured to select and have only one ground switch operating in the CC mode. Any ground switches upstream to the ground switch in the CC mode operate in the Open mode, and any ground switches downstream to the ground switch in the CC mode operate in the Short mode.  FIG. 5A  shows that ground switches SG 1 , SG 2 , SG 3  and SG 4  operate in the Open, CC, Short, and Short modes, respectively, in an occasion when rectified voltage V REC  is high enough to conquer the forward threshold voltage of the LED string consisting of LED groups  46   1  and  46   2 , but fails to further conquer the forward threshold voltage of LED group  46   3 . It can be derived in  FIG. 5A  that driving current I DRV  provided by ground switch SG 2  flows, in an steady state, through the LEDs in LED groups  46   1  and  46   2 , and lights on the LEDs therein, while LED groups  46   3  and  46   4 , through which no current flows, darken. In that steady state, capacitor  56  is charged to have a voltage drop of about the driving voltage for LEDs L 4  and L 5 . Analogously, driving current I DRV  charges capacitors  52  and  54  in the meantime to have their voltage drops about the driving voltages of LED L 1  and LED group  46   1 , respectively. 
         [0027]    Controller  42  of  FIG. 4  might shift the CC mode to an adjacent ground switch if rectified voltage V REC  varies.  FIG. 5B  shows the operation modes of ground switches SG 1 , SG 2 , SG 3  and SG 4  when rectified voltage V REC  in  FIG. 5A  declines to a certain level and can no longer light on both LED groups  46   1  and  46   2 . In comparison with the operation modes in  FIG. 5A , controller  42  apparently shifts the CC mode from ground switch SG 2  to ground switch SG 1 , such that all but ground switch SG 1  operate in the Short mode. After the shifting, driving current I DRV  flows through the LEDs in LED group  46   1 , but not those in LED groups  46   2 ,  46   3 , and  46   4 . Please note that, right after the shifting, capacitor  56  initially has the voltage drop capable of driving LEDs L 4  and L 5 , and starts discharging to generate discharge current I DIS  flowing through LEDs L 4  and L 5  as shown in  FIG. 5B . Discharge current I DIS  could have an amplitude significant to keep LEDs L 4  and L 5  illuminating for a while. The larger the capacitance of capacitor  56 , the longer the LEDs L 4  and L 5  lasting to illuminate after the shifting. 
         [0028]      FIG. 6  illustrates the waveforms of signals when input port  50  in  FIG. 4  is supplied with an AC voltage signal. The first waveform shows rectified voltage V REC , and the second waveform shows active LED count. The rests show waveforms of currents I L11 , I L8  I L4 , and I L1 , respectively flowing through LEDs L 11 , L 8 , L 4  and L 1 . In comparison with  FIG. 3 , where the active LED count is zero during the dark zone T DARK , the active LED count of  FIG. 6  never falls to zero, such that dark zone T DARK  disappears in  FIG. 6 . At time point t 1  when LED group L 1  starts to be driven by driving current I DRV , for example, a portion of driving current I DRV , referred to as charging current I c52 , goes to charge capacitor  52 , and the rest of driving current I DRV  flows through LED L 1  to be current I L1 . As time goes by from time point t 1  to t 2 , capacitor  52  reaches or approaches saturation such that charging current I C52  decreases and current I L1  accordingly increases, as shown in  FIG. 6 . At time point t 2 , driving current I DRV , no longer drives LED group L 1 , and capacitor  52  starts to discharge, providing current I L1  to keep LED L 1  illuminating. Current I L1  decreases as capacitor  52  loses the stored electrical energy therein. In  FIG. 6 , the tilted portions in the waveform of the currents I L11 , I L8 , I L4 , and I L1  are all caused by the existence of the shunt capacitors in  FIG. 4 . If the shunt capacitor  52  or  54  has capacitance so large that at least one LED in LED group  46   1  can keep on illuminating over the voltage valleys where rectified voltage is about 0 Volt, there could be at least one LED illuminating all the time. In other words, dark zone T DARK , which is demonstrated in  FIG. 3  and causes human dizzy and nauseated, can be eliminated by embodiments of the invention, as exemplified in  FIG. 6 . For example, if the capacitance of capacitor  52  in  FIG. 4  is very large, LED L 1  might continuously illuminate, driven by either the driving current I DRV  from the ground switches or the discharge current I DIS  from capacitor  52 . In this embodiment, integrated circuit  44  is configured such that LED group  46   1  is the priority one to light on when rectified voltage V REC  increases and also the last one to darken when rectified voltage V REC  decreases. 
         [0029]    LEDs are designed for illuminating or lighting when being forward-bias driven and that is why semiconductor process engineers in LED manufactures devote their efforts in forward-bias operations for LEDs. Nevertheless, LEDs might be vulnerable to reverse-bias operations even though LEDs ought to function as rectifiers. Accordingly, it is better for circuit designers to avoid LEDs from reverse-bias operations. Please refer back to  FIG. 5B . When capacitor  56  discharges or de-energizes to illuminate LEDs L 4  and L 5 , it is possible for LED L 6  to experience reverse-bias voltage and be damaged. 
         [0030]      FIG. 7  employs some additional regular diodes to sustain reverse-bias voltages, preventing LEDs from being damaged. Different from the AC LED circuit  40  in  FIG. 4 ,  FIG. 7  has regular diode D 1 , D 2  and D 3 . D 1  is connected between LED group  46   2  and node PIN 2 , regular diode D 2  is between node PIN 2  and LED group  46   3 , and regular diode D 3  is between LED groups  46   4  and node PIN 4 . Here in this specification, a regular diode means a rectifier which is not an LED, and stands for reverse-bias voltage better than a LED does. For example, a regular diode could be a Schottky barrier diode, which requires a low forward-bias voltage to turn on. When capacitor  56  of  FIG. 7  discharges or de-energizes to illuminate LEDs L 4  and L 5 , the anode of LED L 5  might have a negative voltage and node PIN 2  be grounded. Most of this negative voltage drops across regular diode D 1  since it can sustain a reverse-bias voltage operation. LED L 6  accordingly experiences little or no reverse-bias voltage, and is protected by regular diode D 1 . Analogously, regular diode D 2  can protect LED L 7  from being damaged by a reverse-bias voltage, and regular diode D 3  can protect LEDs L 10  and L 12 . 
         [0031]    Please refer back to  FIG. 5B  again. One reason for the occurrence of the reverse-bias voltage on LED L 6  is node PIN 2  shorted to the ground voltage GND when capacitor  56  de-energizes. Unlike integrated circuit  44  did in  FIG. 5B , integrated circuit  49  in  FIG. 8  has only one ground switch operating in the CC mode and all other ground switches operating in the Open mode. As shown in  FIG. 8 , for a certain magnitude of rectified voltage V REC , only ground switch SG 2  works in the CC mode, providing constant driving current I DRV . All ground switches but ground switch SG 2  perform as an open circuit. Integrated circuit  49  in  FIG. 8  could shift the CC mode to an adjacent ground switch as well, when rectified voltage V REC  varies. For another magnitude of rectified voltage V REC , ground switch SG 1  might operate in the CC mode while others operate in the Open mode. Accordingly, in the time when capacitor  56  de-energizes to illuminate LED L 4  and L 5 , node PIN 2  is floating, and LED L 6  no more experiences a reverse-bias voltage. 
         [0032]    The charging and discharging speeds of a capacitor might be different.  FIG. 9A  shows another system with AC LED circuit  90 . Some devices in  FIG. 9A  have been described in previous paragraphs and will not be redundantly detailed. Charge/discharge controller  54   A  is demonstratively connected between capacitor  54  and node PIN 1  and charge/discharge controller  58   A  is between capacitor  58  and LED L 8 . Taking charge/discharge controller  54   A  as an example, charge/discharge controller  54   A  is connected in series with capacitor and can provide different conductivities for charging and discharging capacitor  54 .  FIG. 9B  demonstrates an embodiment of charge/discharge controller  54   A , comprising a resistor and a diode connected in parallel. If the diode is forward biased, current will flow through path P D , which has relatively-high conductivity. In the opposite, if the diode is reverse biased, current will flow through path P u  with relatively-low conductivity. To shorten or eliminate a dark zone, capacitor  54  connected in series with charge/discharge controller  54   A  is preferably charged quicker but discharged slower.  FIG. 9B  is not intended to limit the scope of the invention, however. A charge/discharge controller in another embodiment of the invention has, for example, a sensor and an active device. The active device is connected in series with capacitor  54 . The sensor detects whether capacitor  54  energizes or de-energizes and accordingly controls a control node of the active device, such that charging and discharging rates are different. The active device could be a BJT or MOS transistor, for example. 
         [0033]    Although the previous embodiments are all implemented with an integrated circuit having ground switches, this invention is not limited to.  FIG. 10  shows a system with AC LED circuit  100  in accordance with an embodiment of the invention.  FIG. 10  is almost the same with  FIG. 4 , but integrated circuit  44  in  FIG. 4  is replaced by integrated circuit  33  in  FIG. 10 . Controller  31  can turn on or off bypass switches SP 1 , SP 2 , SP 3  and SP 4 , individually. In a moment, controller  31  might make bypass switches SP 1  and SP 3  short and bypass switches SP 2  and SP 4  open, so that driving current I DRV  flows through only LED groups  46   2  and  46   4 . In other words, controller  31  could illuminate an LED group by making a corresponding bypass switch an open circuit, or darken the LED group by making the corresponding bypass switch a short circuit. If bypass switches SP 2  acts as an open circuit, LED group  46   2  is selected to illuminate, and capacitor  56  energizes. When bypass switches SP 2  acts as a short circuit, LED group  46   2  is unselected, LED L 6  darkens, and capacitor  56  de-energizes to temporarily illuminate LEDs L 4  and L 5 . Accordingly, capacitor  56  could last the illumination of LEDs L 4  and L 5 . 
         [0034]    According to the embodiment, capacitors shunted with LEDs can last the illumination of the LEDs, and probably shorten or eliminate the dark zone, which could cause dizziness or nausea in the art. 
         [0035]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.