Patent Publication Number: US-9894727-B2

Title: System and device for driving a plurality of high powered LED units

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The instant application is a divisional application and claims priority to co-pending U.S. patent application Ser. No. 14/009,449, filed on Oct. 2, 2013, which is a National Stage Application of, and claims priority to, PCT/SG2012/000415, filed on Nov. 2, 2012, which claims priority to SG 201108173-4, filed on Nov. 4, 2011 and SG 201202701-7, filed on Apr. 13, 2012, the contents of all of the applications incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a system and device for driving a plurality of high-powered light emitting diodes (LED) units. The device is particularly suitable, but not limited for use in high powered LED light units such as down lights, T5, T8, Light Troffer, Hi-Bay lamps and MR16 light bulbs etc. 
     BACKGROUND TO THE INVENTION 
     The following discussion of the background of the invention is intended to facilitate an understanding of the present invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge in any jurisdiction as at the priority date of the application. 
     Conventional lighting systems typically have a configuration where light products used in the systems are individually driven. For example, a light product such as a down light lamp has its own in-built power supply or ballast which converts incoming AC electrical supply to higher AC voltage and desired current that is required to provide electrical power to for example ignite and excite the gases (referring to CFL light) for lighting up of the down light. Examples of such other light products include T5, T8, Light Troffer, High-Bay lamps, street lamps and flood lamps. 
     Similarly, when Light Emitting Diodes (LEDs) were introduced in lighting systems, the configuration adopted for LEDs was based on a similar ‘one-ballast (controller)’ to ‘one-lamp’ arrangement of conventional lighting systems. Therefore, each LED light unit has its own in-built LED driver or controller that converts the incoming AC supply to DC voltage and current to light up the LED down light. This means that each LED light unit that is present in a lighting system has an accompanying controller dedicated to that particular LED light unit for converting the incoming AC supply to DC voltage and current for lighting up that particular LED light unit, i.e. a chain of ten LED down lights in a lighting system will require correspondingly ten LED controller circuits. These LED controllers increase the cost and overall form factor of each lamp unit. 
     A prior art LED light unit and system is illustrated in  FIG. 1  and  FIG. 2  respectively. The LED lamp unit comprises an AC source supply via AC Input Terminal  4 , an AC-DC LED driver  3 , a LED light/lamp module  1  and heat sink  2 . 
     When connected, AC electrical supply current will flow to the input of the AC-DC LED driver  3 . The AC supply current will be rectified via switch mode power supply circuitry in the AC-DC LED driver  3  to supply the desired DC voltage and current to the LED light module  1 . For continuous light-up operation, as heat will be generated by both the AC-DC LED driver  3  and the LEDs on the LED light module  1 , introduction of heat sink  2  is important to ensure the heat generated along the light-up operation is drawn from the heat source and dissipated accordingly. The heat sink  2  has to account for heat dissipation from both the LED light module and AC-DC LED driver. Consequently, if at any time along the light-up operation the heat sink  2  reaches its maximum heat dissipation capability due to the design limitation in size for standard form factor for the particular LED lighting unit fulfillment will lead to the degradation of light performance and product life span. 
     The above-mentioned configuration has several disadvantages including: 
     As each LED light unit requires its own in-built controller circuit  3  for lighting up, when the LED light unit is in continuous operation, considerable heat will be generated by both the LED and controller circuit. To moderate the heat, heat sink(s) must be present in each LED light unit for drawing the heat from the heat source and dissipating the heat to the surroundings so as to provide a thermally cool environment for the LED and controller circuit to operate in. It is important that the LED and controller circuit operate in a thermally cool environment because this will reduce power loss and hence improve efficiency. However, due to standard form factors, there is a limit as to the size of the heat sink in each LED light unit. As there are two heat generating sources in each LED light unit (i.e. the LED lamp unit and the LED controller), the heat sink  2  typically reaches its maximum heat dissipation capability during continuous operation where considerable heat is generated. Consequently, this will lead to the degradation of the LED light unit&#39;s light performance and product life span. 
     It is typically costly to manufacture LED light units which have built-in controller circuits and heat sinks  2  as they increase the number of components that are needed for manufacture. Furthermore, the heat sink must also be designed to cope with the dissipation of heat from two heat sources with the constraints on its size due to standard form factors. This further increases the overall cost of producing the LED light units. 
     As the AC supply will be converted to DC voltage and current in the LED light units by the controller circuits  3 , there will be safety related issues that must be addressed. Hence, the LED light units will have to be designed such that they meet the standard safety requirements and size limitations imposed by standard form factors. 
     Therefore, it is an object of the present invention to overcome, or at least alleviate, at least the aforementioned problems. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system and device to alleviate the above problems and to provide a ‘one driver-too-many high powered LED lamp units’ solution. To achieve the same, the system and device are suited to provide at least a relatively ‘ripple free’ current of less than 5% from the specified rated current. The specified rated current is typically (but not limited to) around 350 mA to 700 mA per lamp unit. 
     In addition, references to ‘current’, ‘connection(s)’ refer to electrical current and connections unless otherwise stated. 
     In accordance with a first aspect of the present invention there is a system for driving a plurality of high powered LED units, the system comprising a single driver for providing ripple free constant direct current to a plurality of high powered LED lamp units, wherein the single driver comprises a digital controller programmable to adjust the ripple free constant direct current at every predetermined time interval based on detection and computation of the duration taken for the energy to be discharged to the LED lamp unit to adjust the ripple free constant direct current. 
     Preferably, the single driver operates in an isolated alternating current fly back configuration having an inductive element as a transformer isolating the plurality of high powered LEDs at the secondary end of the transformer. 
     Preferably the digital controller is an Application Specific Integrated Circuit (ASIC); the ASIC further operable to detect and compute the duration of the energy discharged by the core of transformer to the plurality of high powered LEDs to regulate and provide the ripple free output DC current. The ASIC is preferably programmed to receive feedback at each clock-cycle based on the duration of the energy discharged by the core of the transformer as an input to determine the amount of ripple free constant DC current at the next clock-cycle. More preferably the ASIC is programmed to provide a voltage waveform to turn an electronic switch on and off at each clock-cycle. 
     Preferably each of the plurality of high powered LED lamp units is in series with the other high powered LED lamp units. 
     Preferably the single driver is electrically connected to a dimmer circuitry for adjusting the brightness of the plurality of high powered LED lamp units. The dimmer circuitry preferably comprises a potential meter, infra-red interface, motion sensor or ambient sensor. 
     Preferably the system comprises a filter capacitor operable to vary its capacitance to maintain a power factor of at least 0.9 when the dimmer is adjusted. 
     In the case where the dimmer is a potential meter, the potential meter is operable to work within a voltage of 0 to 10V. 
     Preferably in an isolated fly back mode the secondary end of the transformer is electrically connected to a short circuit protection circuit. 
     Preferably, the ASIC is coupled with an active power factor controller. More preferably the active power factor controller comprises at least one voltage follower. In such a case the ASIC is preferably a 14-pin configuration so as to control both the active power factor controller and the adjustment of the ripple-free constant DC current. 
     Preferably, each high powered LED lamp is provided with a heat sink shaped and configured to dissipate heat away from the high powered LED only. 
     Preferably, the system further comprises an electronic switch, wherein the ripple free constant DC current is achieved by means of voltage control according to the following equation:— 
     
       
         
           
             
               V 
               OUT 
             
             = 
             
               
                 
                   
                     V 
                     IN 
                   
                   * 
                   
                     T 
                     ON 
                   
                 
                 
                   T 
                   OFF 
                 
               
               ⁢ 
               
                 
                   
                     L 
                     2 
                   
                   
                     L 
                     1 
                   
                 
               
             
           
         
       
     
     where V OUT  is the voltage across the output; V IN  is the input voltage; T OFF  is the time of the discharge of the core of the isolating transformer; T ON  is the switch on time of the electronic switch; L 1  is the inductance value of the primary windings of the transformer and L 2  is the inductance value of the secondary windings of the transformer. 
     As an alternative to the isolated configuration mode, the single driver may operate in a non-isolated configuration having an inductive element operating in a continuous mode in according to the following equation: 
               I   OUT     =       (         T   OFF     *     I   1       +         I   MAX     *     T   OFF       2       )     *     1   T             
where T OFF  is fixed as a constant; T ON  is the switch on time of the electronic switch; T is the summation of T ON , T OFF , and T CALC  where T CALC  is the time after the discharge time of the inductive element to compute the formula; I 1  is the desired reference current and I MAX  is the peak current. In a hysteretic controller configuration, the value of I MAX  and I 1  may be fixed, and the T ON  and T OFF  timings determined.
 
     In accordance with a second aspect of the invention there is a LED driver comprising: 
     at least one Integrated Circuit (IC), the IC programmable using a hardware description language; a first electronic switch operable to provide a first switching time period to control power factor voltage, the first switching time period programmable by the at least one IC; and a second electronic switch operable to provide a second switching time period to regulate ripple free constant DC electrical current flowing into the at least one LED, the second switching time period is programmable by the at least one IC. Such an LED driver provides for an additional current control in the form of the power factor controller to achieve a ripple-free DC current. 
     Preferably, the first and second electronic switches are power MOSFETs. 
     Preferably, the at least one IC is an ASIC. 
     In accordance with a third aspect of the invention there is a LED driver comprising: a device having an input port and a plurality of output ports comprising a reverse polarity protector arranged to be electrically connected to the input port and each of the plurality of output ports; and a plurality of open circuit protection circuits, each of the plurality of open circuit protector operable to connect to an output port; wherein the reverse polarity protector is operable to negate the polarity requirement in the event where a load is connected with a wrong polarity to any of the output port; and the open circuit protection circuit is operable to form a closed loop series connection in the event where no load is connected to an output port or when a load breaks down. 
     Preferably the reverse polarity protector is a diode bridge rectifier. 
     Preferably each output port comprises a corresponding open circuit protector. 
     Preferably the input port is suitable for connection with a LED driver and each of the output port is suitable for connection with a load comprising a high powered LED lamp unit. 
     In accordance with a fourth aspect of the invention there is a system according to the first aspect wherein the load is in a series connection, further comprising the device according to the second or third aspect of the invention, wherein the input port of the device of the second or third aspect is operable to be connected to the single driver. 
     In accordance with a fifth aspect of the invention there is a dimmer circuitry for use with a LED driver, the dimmer circuitry comprising at least a dimming interface operable to connect to at least one dimming controller; and a capacitive element adjustable to maintain a power factor of at least 0.9 within the dimmer circuitry. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following invention will be described with reference to the following drawings of which: 
         FIG. 1  is a perspective side view of a prior art LED lamp unit with driver and heat sink; 
         FIG. 2  is a system configuration of the ‘one driver one lamp unit’ configuration of the prior art LED lamp system; 
         FIG. 3  is a system view of a ‘one driver multiple lamp units’ or ‘string driver’ in accordance to an embodiment of the invention; 
         FIG. 4  is a circuit diagram of the LED driver circuit in accordance with an embodiment of the invention for isolated alternating current (AC) application; 
         FIGS. 5 a  and 5 b    are circuit diagrams of the LED driver circuit with a power factor convertor driven by a 14-pin ASIC in accordance with another embodiment of the invention for isolating alternating current (AC) application; 
         FIG. 6  is a table summarizing the advantages of the invention on a plurality of MR 16 LED lamp as compared to the prior art system; 
         FIG. 7  illustrates simulation results of the ripple free constant DC current based on a MR16 load; 
         FIG. 8  illustrates another embodiment with an arrangement of circuit wherein the decoupling transformer operates in a continuous mode; 
         FIG. 9  illustrates electrical current flowing through rectifier circuitry in a continuous mode; 
         FIG. 10  illustrates a structure of hysteretic controller used for continuous operation of the circuit; 
         FIG. 11  is a PCB arrangement of an intermediary connector between the LED drivers and load in accordance with another embodiment of the invention; 
         FIG. 12  is a possible arrangement of a lighting system illustrating the use of an intermediary connector between the driver and load; 
         FIG. 13  is another possible arrangement of a lighting system illustrating the use of two intermediary connectors; 
         FIG. 14  shows the circuit diagram of the intermediary connector; and 
         FIG. 15  shows a general block diagram on the dimmer circuitry. 
     
    
    
     Other arrangements of the invention are possible and, consequently, the accompanying drawings are not to be understood as superseding the generality of the preceding description of the invention. 
     DETAILED DESCRIPTION 
     In the context of the invention, the mention of ‘ripple free’ current and approximations to ripple free current refers to allowable ripple of less than (&lt;) 5% from the specified rated current. 
     In the context of the invention, high powered LED lamp units refer to any LED lamp unit requiring a power of at least 5 watts. 
     In accordance with an embodiment of the invention there is a LED driver  10  for driving a plurality of high powered LED lamps  100  as illustrated in  FIG. 4 . LED driver  10  is particularly suited for an isolated alternating current (AC) application and comprises a primary side and a secondary side. The primary side of the LED driver  10  is decoupled with the secondary side via a decoupling transformer  11 . The primary side comprises an electronic switch  14 , bridge rectifier circuit  16 , and an Integrated Circuit (IC) controller  18 . Although  FIG. 4  shows an isolated configuration, it is appreciated by a skilled person that the circuit may be modified for non-isolated configuration where the decoupling transformer  11  may be replaced by other inductive elements. 
     To satisfy the decoupling function, transformer  11  is an isolation transformer, and may preferably be a planar transformer. Transformer  11  is operable to work in either a continuous or discontinuous mode, although for purpose of illustration  FIGS. 4, 5   a , and  5   b  illustrates the circuitry suited for transformer  11  working in a discontinuous mode. In continuous mode certain output capacitors may be omitted as illustrated in  FIG. 8 or 10 . Where transformer  11  is a planer transformer based on printed circuit board technology, the printed circuit board may be FR4 PCB, Polyimide or other thick copper foil (lead frame). 
     Resistor R P  and capacitor C P  are connected in a parallel configuration with the primary end of the transformer  11 . A diode D P  is connected to the Resistors R P , capacitor C P , and the transformer  11 . The conducting end of the diode D P  is connected in a series configuration to the primary end of the transformer  11 . The non-conducting end of the diode D P  is connected in series configuration to the resistor R P  and capacitor C P . 
     A capacitor C S  is connected in parallel to the secondary end of the transformer  11  for filtering the output electrical voltage. A diode D S  is connected to the secondary end of the transformer  11  and the capacitor C S . The conducting end of the diode D S  is connected to the secondary end of the transformer  11  in a series configuration. The non-conducting end of the diode D S  is connected to the positive end of capacitor C S  (where applicable) in a series configuration. The LED load  100  is connected in a parallel configuration to the capacitor C S . Each LED load  100  may be connected in series with the other LED load  100 . The secondary side may optionally include a short circuit protection circuit  44  as will be elaborated later. 
     Electronic switch  14  is typically a power transistor. In this particular embodiment, electronic switch  14  is more preferably a power MOSFET. In the MOSFET configuration, the drain of the electronic switch  14  is connected to the conducting end of the diode D P  and to the primary end of transformer  11 . The gate of the electronic switch  14  is connected to the output pin of the IC  18 , and the source of the electronic switch  14  is connected to the electrical ground. 
     It is to be appreciated that the electronic switch  14  may be replaced by other functionally equivalent component. 
     The IC controller  18  comprises an internal oscillator which is configured to turn on the gate of the electronic switch  14  with a particular turn-on time period T ON  (switching frequency) for each clock cycle as determined by the internal oscillator. IC controller  18  is preferably an Application Specific Integrated Circuit (ASIC) programmed to sense and calculate the discharge time of the inductive elements L 1  and L 2  as a main input. ASIC  18  is programmed and configured to turn on the gate of the electronic switch  14  having a turn on period of T ON  at each clock cycle based on the following inputs:— 
     (a.) A reference constant K based on the discharge time of the inductive element L 1  and L 2 ; 
     (b.) Desired output DC ripple free current for LED I OUT ; 
     (c.) A digitized voltage value V DD  (V in ) tapped and digitized from potential divider  22 , the potential divider  22  connected in parallel with the bridge rectifier  16 ; 
     (d.) A time value T OFF  of the discharge of the core of transformer  11  measured through voltage potential divider  30  and compared to a reference voltage; and 
     (e.) The switching period T (i.e. the switching period of the electronic switch  14  as determined by the oscillator). 
     Using the received five inputs, the IC  18  computes an output T ON  which is the switch on time of the electronic switch  14  mathematically expressed as equation (1). 
     
       
         
           
             
               
                 
                   
                     T 
                     ON 
                   
                   = 
                   
                     
                       
                         I 
                         out 
                       
                       * 
                       T 
                     
                     
                       K 
                       * 
                       
                         V 
                         in 
                       
                       * 
                       
                         T 
                         off 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     The reference constant K is calculated based on the inductance value of the primary and secondary windings of the transformer  11  as described in formula 2. 
     
       
         
           
             
               
                 
                   K 
                   = 
                   
                     1 
                     
                       2 
                       * 
                       
                         
                           
                             L 
                             1 
                           
                           * 
                           
                             L 
                             2 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     Where L 1  is the inductance value of the primary windings of the transformer  11  and L 2  is the inductance value of the secondary windings of the transformer  11 . The value of reference K may be stored in a memory within the IC  16 . For a non-isolated direct current (DC) fly-back configuration, the reference constant K is calculated according to the following mathematical expression:— 
     
       
         
           
             
               
                 
                   K 
                   = 
                   
                     1 
                     
                       L 
                       3 
                     
                   
                 
               
               
                 
                   ( 
                   
                     2 
                     ⁢ 
                     a 
                   
                   ) 
                 
               
             
           
         
       
     
     Where L 3  is the inductance value of the inductive element in the fly-back configuration. 
     Manipulating equation (1) and (2), I OUT  is derived as follows: 
     
       
         
           
             
               
                 
                   
                     I 
                     OUT 
                   
                   = 
                   
                     
                       
                         V 
                         IN 
                       
                       * 
                       
                         T 
                         ON 
                       
                       * 
                       
                         T 
                         OFF 
                       
                     
                     
                       2 
                       * 
                       
                         
                           
                             L 
                             1 
                           
                           * 
                           
                             L 
                             2 
                           
                         
                       
                       * 
                       T 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     The IC controller  18  may further comprises a dimming pin coupled to a variable resistor  40  for performing dimming on the LED load  100 . The dimming pin facilitates the flexibility to perform dimming via various dimming device such as potential meter, motion sensor or Infra-red sensor. 
     The IC controller  18  described above is typically 8-pin. To fine-tune the level of control of the IC controller  18 , a higher resolution IC controller may be used. In addition to the fine-tune control of a desired ripple free current Iota, active power factor controller (PFC) to improve the performance of the circuit. 
     A higher resolution IC controller having capabilities to fine-tune the control of desired ripple-free current I OUT  and provide active power factor control is described in another embodiment below. 
     Another embodiment of the invention in the form of a LED driver  500  for driving a plurality of high powered LED lamp units  100  is illustrated in  FIG. 5 a    and  FIG. 5 b    (with emphasis on primary side). LED driver  500  comprises a first electronic switch  513 ; a second electronic switch  514 ; a bridge rectifier circuit  516  and an integrated circuit controller  518 . LED driver  500  further comprises an active power factor controller (PFC) circuitry  520 . Comparing with the previous embodiment, the active power factor controller (PFC) is operable to form an additional stage of current controller to achieve an improved ripple free constant DC current. The integrated circuit controller  518  is operable to control the switching frequencies of the first electronic switch  513  and second electric switch  514  to achieve a desired power factor and output ripple free current I OUT . 
     Integrated IC controller  518  is similar to the IC controller  18  comprising internal oscillators, built in Analogue to Digital convertor etc. It additionally comprises more pins for further control of the PFC controller. In this embodiment IC controller  518  comprises 14-pin. The overall resolution is higher (10 bits) thus allowing better adjustment and fine-tuning of the switching frequencies for the electronic switches  513 ,  514  and I OUT . 
     The bridge rectifier  516  is operable to receive an AC input and produces a rectified voltage output. The rectified voltage output is passed through a capacitor C 4 . C 4  is operable to function as an input voltage filter to further filter the rectified voltage from the rectifier circuit  516 . Capacitor C 4  is connected parallel to resistors R 8  and R 9  and in series with an inductor L 4 . 
     Resistors R 8  and R 9  form an input voltage divider. In operation, the voltage between R 8  and R 9  is tapped as an input voltage (denoted as V inP ) to the ASIC. 
     The inductor L 4  is connected in series with resistors R 10  and R 11 . Resistors R 10  and R 11  form a PFC voltage divider, which is used to provide the PFC feedback voltage to the controller  518  via a T 2P  pin input for PFC output voltage measurement. 
     The first electronic switch  513  is connected in series to inductive element L 4  and in parallel to the PFC voltage divider. First electronic switch  513  provides the variable frequency to control the PFC output voltage. Both the first electronic switch  513  and the second electronic switch  514  may be N-channel power MOSFET. The gate of the first electronic switch  513  is activated by the ASIC (MOSOUT pin), its drain is connected in series with L 4  and the source is grounded. 
     In operation, the controller  518  drives the first electronic switch  513  to provide the necessary power factor voltage at the drain of the first electronic switch  513 . 
     It is to be appreciated that the first electronic switch  513  may be replaced by another functionally equivalent component. 
     A power diode D 3  is connected in series with inductive element L 4 . It allows the forward pass of the rectified PFC current; which is moderated by the first electronic switch  513 . 
     C 5  is a capacitive filter for filtering the PFC output voltage. 
     Inductive element L 4  may be a standard inductor as illustrated in  FIG. 5 a    or a transformer as illustrated in  FIG. 5 b   . For the case where L 4  is a transformer, the transformer comprises L 4p  primary inductance and L 4s  secondary inductance. As illustrated in  FIG. 5 b   , L 4p  is connected from pin 1 to pin 6; L 4s  is connected from pin 1 to pin 7 of the IC controller  518 . 
     The following equation (4) is applicable to the transformer variant to control the output voltage of the PFC:— 
     
       
         
           
             
               
                 
                   
                     V 
                     
                       PFC 
                       , 
                       OUT 
                     
                   
                   = 
                   
                     
                       
                         
                           L 
                           
                             4 
                             ⁢ 
                             p 
                           
                         
                         
                           L 
                           
                             4 
                             ⁢ 
                             s 
                           
                         
                       
                     
                     ⁢ 
                     
                       
                         
                           V 
                           IN 
                         
                         * 
                         
                           T 
                           
                             Q 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                             ⁢ 
                             on 
                           
                         
                       
                       
                         T 
                         
                           Q 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                           ⁢ 
                           off 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     V PFC,OUT  is the output voltage of the PFC, L 4p  is the PFC transformer primary inductor value, Las is the PFC transformer secondary inductor value, V in  is the input voltage, T Q2on  is the switch on time of the first electronic switch  513 , and T Q2off  is the discharge time of the PFC transformer. T Q2on  is controlled via the MOS OUT pin of the controller  518  and V in  and T Q2off  are feedback values used for ensuring and verifying that V PFC,OUT  properly tracks a desired output voltage V OUT . 
     Equation (4) is known as a voltage follower, where V PFC,OUT  follows V OUT ; in the sense that after solving the equation, if V PFC,OUT  is less than expected (within allowable deviation) T Q2on  is increased, otherwise T Q2on  is decreased. 
     V OUT  is determined based on the total number of LED units and the desired current I OUT  to be supplied to the LED units. 
     For the second electronic switch  514 , the operation and equations for adjusting and calculation I OUT  is identical to that described in equations (1) to (3). 
     As mentioned above, the secondary side of the LED driver  10 ,  500  may further comprise a voltage protection circuit  44 . Referring to  FIG. 4  for the voltage protection circuit which may be incorporated in the secondary side of the LED driver  500  although not explicitly shown in  FIGS. 5 a  and 5 b   , voltage protection circuit  44  comprises a zener diode  46 , a silicon controlled rectifier (SCR)  48  and a resistor  50 . When a short circuit is detected, the zener diode  46  will conduct electricity thus enabling the SCR  48  and reducing the output voltage to the LEDs  100 . 
     The LED driver  10 ,  500  in the context of operation of driving a string of LED light units, will be described in the following example:— 
     To operate the circuit, the variable resistors are adjusted to produce a voltage value of N for V R  (LED driver  10 ), or V inP  (for LED driver  500 ), where value N is an adjustment of turn on time period T ON  of the electronic switch  14 ,  514  corresponding to the generation of the maximum approximately ripple-free constant current to drive a plurality of LED lamp units  100 . The decrement or increment of adjustment N value will be based on the feedback and cause changes in T ON , T directly, thus varying I OUT  accordingly based on the variable resistor V R  to dim or brighten the LED lamp units  100 . 
     For optimization of the equations (1) to (3); the equations of the circuits may be expressed in an alternative form
 
 A=V   IN   *T   ON   *T   OFF   (5)
 
 B= 1/ K*I   OUT *( T   ON   +T   OFF   +T   CALC )  (6)
 
     Wherein T CALC  is the time after the discharge time of the inductive element to compute the formula and the switching time period of the electronic switch is the summation of T ON , T OFF  and T CALC ; 
     In each adjustment cycle of I OUT , the values of A and B are compared. 
     If A is greater than B, i.e. A&gt;B, then T ON  is adjusted to T ON −N for the next time period T. 
     If A is smaller than B, i.e. A&lt;B, then T ON  is adjusted to T ON +N. 
     In the situation where A is equals to B, there is no updating of T ON  and T ON  remains unchanged. 
     Depending on the number of lamp units  100  and the desired current I OUT , a user performs design optimization by changing a few critical components as follows:— 
     inductance L 1  and L 2  of the transformer  11 ; 
     switching frequency, V DS  Drain-Source Voltage and I D  Drain current of the electronic switches  14 ,  514 ; 
     values of Capacitor C S  and Diode D S . Care must be taken to ensure that voltage across capacitor C S  voltage should be higher than the voltage of the LED load  100 . The diode&#39;s forward current I F  and repetitive peak reverse voltage V RRM  are parameters to consider for the choice of a suitable diode Ds. 
     Once the above components are tuned to the load specification, the IC controllers  18 ,  518  detects and computes the duration of the energy discharged to the load via the core of transformer  11  (or inductive element for a non-isolated fly-back configuration) to the LED loads  100  to regulate the constant output current. Therefore, the controller  18 ,  518  can work on a wide range of load voltage and constant current for high powered LED lights  100 . 
     The described embodiment provides for an approximately ripple free constant DC current to the plurality of high powered LED lamp units  100 . The described configuration of one driver to multiple lamps is termed by the applicant as ‘string configuration’. 
     As an optional feature, the IC controller  18 ,  518  may further comprise a multipoint control unit (MCU) to enable communication with intelligent control means such as power line, Digital Addressable Lighting Interface (DALI), wireless protocol for total lighting control system. 
     The described embodiments are based on the concept of a single LED driver  10 ,  500  to drive many high powered LED lamp units  100 , each high powered LED lamp unit provided with a heat sink shaped and configured to dissipate heat away from the high powered LED only and the single driver configured to provide approximately ripple free constant DC current to the plurality of high powered LED lamp units has been compared with a prior art MR 16 system where one LED driver  3  is required for each LED lamp unit  4 . This standard ASIC driver design solution drive in constant current and offer a wide range of flexibility to drive a series of any numbers of LEDs within the entire lighting system, the advantages of which are summarized in  FIG. 6 . 
       FIG. 7  illustrates an I OUT  measured from a high powered LED load  100  illustrating the extent of ripple free constant DC current. 
     The above embodiments illustrated in  FIGS. 4, 5   a , and  5   b  have described the IC controller implementation as current controllers (i.e. manipulating I OUT ); and the transformer  11 ,  511  working in a discontinuous mode. Due to the flexibility of programming the ASIC based controller  18 ,  518 , four different combination and/or modes may be achievable as follows:— 
     A. Voltage control instead of current control; 
     B. Discontinuous mode with primary inductor current feedback instead of T OFF  based feedback (or monitoring); 
     C. Continuous mode with primary inductor current feedback instead of T OFF  based feedback (or monitoring); and 
     D. Continuous mode for hysteretic controller. 
     A. Voltage Control Instead of Current Control 
     For using voltage control instead of current control, equation (3) may be re-written as:— 
                     V   OUT     =           V   IN     *     T   ON         T   OFF       ⁢         L   2       L   1                   (   5   )               
where V OUT  is the output voltage. Where L 1  is equals to L 2 , the equation is modified as:—
 
                     V   OUT     =         V   IN     *     T   ON         T   OFF               (     5   ⁢   a     )               
B. Discontinuous Mode with Primary Inductor Current Feedback Instead of T OFF  Based Feedback (or Monitoring)
 
     For Discontinuous mode with primary inductor current feedback instead of T OFF  based feedback (or monitoring), the relationship between the peak current I MAX , input voltage V IN , and the inductive element L is expressed mathematically as:— 
     
       
         
           
             
               
                 
                   
                     I 
                     MAX 
                   
                   = 
                   
                     
                       
                         V 
                         IN 
                       
                       * 
                       
                         T 
                         ON 
                       
                     
                     L 
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     Substituting equation (6) into equation (3) results in:— 
                     I   OUT     =         I   MAX     *     T   OFF         2   ⁢   T               (   7   )               
in the case where the inductive element L is a single inductor used in cases for example in an non-isolated configuration; and
 
                     I   OUT     =           I   MAX     *     T   OFF         2   ⁢   T       ⁢         L   1       L   2                   (   8   )               
in the case where the inductive element L is a transformer and L 1  and L 2  denotes the primary and secondary inductances respectively.
 
     For application of equations (7) or (8), the circuit illustrated in  FIGS. 4, 5   a  and  5   b  may be modified such that the primary current may be read by the ASIC controller through a resistor from the source of the electronic switch  14 ,  514  to ground or using a current transformer in series to the electronic switch  14 ,  514  or, in case of forward structure, the filter inductor. 
     C. Continuous Mode with Primary Inductor Current Feedback Instead of T OFF  Based Feedback (or Monitoring) 
     For the case of continuous mode with primary inductor current feedback instead of T OFF  based feedback (or monitoring), it is appreciated that the current flowing through the rectifier diode series to the LED is the same as the current on the LED. 
     The waveform of the electrical current in continuous mode is illustrated in  FIG. 9 . For a given switch on timing T ON , if the T OFF  is fixed, the current across the diodes could be computed as:— 
     
       
         
           
             
               
                 
                   
                     I 
                     D 
                   
                   = 
                   
                     
                       I 
                       OUT 
                     
                     = 
                     
                       
                         ( 
                         
                           
                             
                               T 
                               OFF 
                             
                             * 
                             
                               I 
                               1 
                             
                           
                           + 
                           
                             
                               
                                 I 
                                 MAX 
                               
                               * 
                               
                                 T 
                                 OFF 
                               
                             
                             2 
                           
                         
                         ) 
                       
                       * 
                       
                         1 
                         T 
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     Where T=T ON +T OFF +T CALC ; T CALC  is the discharge timing of the transformer or inductor element. 
     All the above information may be obtained from the primary inductive element L. In particular, the circuit arrangement shown in  FIG. 8  comprises:— 
     i. a resister in series with the electronic switch; 
     ii. a current transformer in series with the electronic switch; and 
     iii. a filter inductor. 
     The circuit arrangement shown in  FIG. 8  comprises a first transformer  811  to isolate the load. A filter inductor  820  is used in the same way as the inductor in the hysteretic controller. 
     The output current I OUT  is controlled via the feedback from the resistor  822  connected to the source of the electronic switch. 
     Resistor  822  is used for protection purpose not for controlling purpose. A reset circuit  812  comprising an inductor  823  and a diode  824  is used in the forward structure to completely discharge the transformer core from the residual energy. This serves to prevent the core from saturation after a certain working time. 
     D. Continuous Mode for Hysteretic Controller 
     The structure of a hysteretic controller is as shown in  FIG. 10 . For implementation, the value of I MAX  and I 1  may be fixed according to Equation (9), and the T ON  and T OFF  timings determined. The current I OUT  will however be the area under the figure. 
     It is to be appreciated that the continuous mode described above is particularly suited for non-isolated fly-back or feed-forward configurations only. However, it reduces the minimum number of components required and is able to provide ripple free current without the need for load capacitors. Cost savings may thus be achieved. 
     In the described embodiments, the dimmer  40  may be used as a means for SSL lighting dimming control for energy saving instead of conventional triac dimmer. The dimmer  40  is arranged and operable to use energy only when light is required; otherwise the light is dimmed automatically to a low intensity or completely switched off (both saving electricity as compared to full switching on of light). 
     As illustrated in  FIGS. 4, 5   a  and  5   b ; the IC controller is connected to the dimmer  40  for better dimming performance and energy saving, such as at a low dimming level, a light output of less than 10% of total light, the power factor is maintained at more than or equals to 0.9 to meet the objective of the energy saving. 
     Although the dimmer  40  is illustrated in  FIGS. 4, 5   a  and  5   b , it is easily appreciated by a skilled person that the dimmer  40  may easily be incorporated in circuits as illustrated in both isolated/non-isolated configurations as well as continuous or discontinuous mode. 
     Further description relating to the operation of the dimmer  40  for purpose of meeting the above objectives of energy saving and maintenance of high power factor is elaborated with reference to  FIG. 15  which forms another embodiment comprising a dimmer circuitry for use with a LED driver, the dimmer circuitry comprising at least an dimming interface operable to connect to at least one dimming controller; and a capacitive element adjustable to maintain a power factor of at least 0.9 within the dimmer circuitry. 
     As illustrated in  FIG. 15 , dimmer  40  may include a variety of devices capable of interfacing with a dimming interface  1670 , the interfacing including the IC controller  18 ,  518  pin for lighting dimming control. 
     When electricity supply is switched on, current flows to rectifier  1516 , which then turns on the switching power supply  1600  comprising ASIC controller  18 ,  518 . An isolated or non-isolated supply of ripple-free constant DC output current  1610  is provided. The switching power supply  1600  may be isolated or non-isolated, and depending on the configuration, inductive element  1511  may be an isolating transformer. The output of inductive element  1511  provides a isolated or non-isolated ripple free constant DC output current  1610  to the LED load  1700  to turn on the light. By default, the LED load  1700  consumes 100% energy to turning on the light, unless electrical power is switched off. 
     The dimmer  40  may be a 0-10V dimmer  1708 . When the dimmer set to 10V, DC output current  1610  will set the light output to 100%, when dimmer set to 5V, DC output current  1610  will set the light output to 50% of total light. At 0V, no light is provided. 
     An infra-red (IR) remote control  1711  may also be used for remote lighting control. Such configuration requires the dimming interface to have a suitable IR receiver such that when the IR transmitter transmits the signal, the IR receiver will decode the signal and generate a PWM duty cycle accordingly from range 0-100% for dimming control. When duty cycle set to 100%, DC output current  1610  will then set the light output 100%, while IR transmitter sends 50% duty cycle, DC output current  1610  will sends 50% of total light output. If IR transmitter sends 0% duty cycle PWM signal, no light will be provided. 
     Another type of dimmer may be embodied as a motion sensor  1712 . When there is no movement detected by motion sensor  1712 , DC output current  1610  will turn the output current from 100% to 20% for dimming purpose, or even switched off the output current. This means that energy is only being used when the motion sensor  1712  detects movement. 
     Another option is to use an ambient sensor  1714  to detect environmental conditions, for example when dawn is approaching; DC output current  1610  will switch off the output current and turn lights  1700  off. When ambient sensor  1714  detects environment turning to dusk, DC output current  1610  will switch on the output current to 100%. 
     It is to be appreciated that any other devices designed with PWM output duty cycle from 0-100% may connect to the dimmer interface for LED lighting dimming control. Dimmer interface is a circuitry comprising one or more micro-controller device for detection of dimming signal from various dimmers (IR remote, motion, ambient, . . . etc), and convert input dimming signal to analog voltage to the ASIC controller for dimming control. It may also be incorporated within the ASIC controller mentioned in other embodiments. In terms of implementation, the ‘Dimmer Interface’ may be a small module board mounted on power supply PCB or integrate into power supply circuitry PCB. 
     Capacitor  1630  is a component that would affect power factor. When dimming circuit is activated, the switching power supply  1600  will automatically charge the capacitance of  1630  to maintain power factor ≧0.9, such that no matter how low the dimming level goes, power factor always stay at ≧0.9. 
     The dimmer design from the various embodiments enable the user to dim their LED lighting unit to as low as 1˜2% of the original driving current without any flickering phenomena. 
     In accordance with another embodiment of the invention there is provided a device  1100  for use with any of the LED driver  10 ,  500  described in the previous embodiment(s). As illustrated in  FIG. 11 , the device  1100  is an intermediary connector between the LED drivers  10 ,  500  and LED load  100 . The intermediary connector is hereinafter referred to as ‘junction box’. 
       FIG. 11  shows a PCBA design of the junction box  1100 . The junction box  1100  comprises an input connector  1120  and a plurality of output connectors  1140  arranged to achieve the following:— 
     a. Ease of installation of the high powered LED lamps load  100 ; 
     b. Advantageous for a plurality of LED lamps  100  connected in series, and alleviates the problem of a system wide open circuit in the event where a high powered LED lamp  100  breaks down; 
     c. Reduce or completely eliminate common errors during installation, in particular errors relating to reversal in electrical polarities. 
     On point (b.) above, series connection of LED lighting units  100  ensures that each lamp unit  100  would be driven with exactly the same driving current hence each LED lighting unit  100  will produce the same brightness. For lighting systems where uniform brightness is important series connection would be advantageous over parallel connection. 
     To achieve the above, the junction box comprises a reverse polarity protector  1160  and an open circuit protector  1180 . Reverse polarity protector is preferably a rectifier  1160 . 
     As illustrated in  FIG. 11 , there are nine output connectors  1140 . The input connector  1120  is arranged to interface with the driver output connector; and the junction box output connector  1140  is arranged to interface with the LED load  100  which comprises the SSL driverless lighting unit strip end cable. 
     The input connector  1120  is typically a header type connector for coupling with LED driver  10 ,  500  output connector which is typically a cable entry plug-in type. The output connector  1140  is typically of a cable entry type so that the electrical connector for LED lamp  100 , for example those of a strip end SSL driverless cable type can be inserted to it to produce a close electrical loop. 
       FIG. 12  illustrates the lamp system comprising the single LED driver  10 ,  500 , a single junction box  1100  and the SSL driverless light unit/load  100 . 
     LED Driver  10 ,  500  with cable plug in type connector  1100  will be connected to the input connector  1120  and the SSL driverless with strip end cable will be inserted into the output connector  1140  in order to create a complete networking lighting system for lighting purposes once electrical power is switched on. 
       FIG. 13  illustrates another possible arrangement with two junction boxes  1100 , wherein the entire system comprises the single string driver  10 ,  500 , dual junction boxes  1100  and SSL driverless light unit  100 . 
     The desired driver output voltage as predetermined by a qualified personnel will determine the total number of SSL driverless lighting units  100  or numbers of junction box  1100  that should be used for the entire lighting network in order for all the SSL driverless lighting units  100  to be driven with expected designed ripple free constant current. 
     As a simplified example, if the designed driver  10 ,  500  has a maximum output voltage rating of 170V DC and only single junction box  1100  exists in the lighting system, then each SSL driverless lighting unit forward voltage is limited to 18.8 VDC/unit (170 VDC divided by 9 units). If two junction boxes  1100  are used, then SSL driverless lighting unit forward voltage is limited to 10 VDC per unit (170 VDC divided by 17 units). 
       FIG. 14  shows the circuitry diagram between the input and output connectors and the arrangement of the rectifier  1160  and the open circuit protection circuit  1180 . Bridge rectifier  1160  acts as a reverse polarity protection so that there will be no polarity concern between driver  10 ,  500  and junction box  1100  during installation. If an installer makes a mistake and connects a lamp unit  100  in reverse polarity, the reverse polarity protector in the form of a bridge rectifier  1160  protects the driver  10 ,  500  and junction box  1100  from damaging. The Open load protection circuit  1180  preferably comprises a Zener Diode  1220 ; Silicon Controller Rectifier (SCR)  1240  and Resistor  1260  at each output port  1140 . 
     Additional rectifiers may also be added to the lighting units  100 . This addresses the following problem:— 
     Although rectifiers  1160  provide reverse polarity protection between driver  10 ,  500  and the junction box  1100 , a particular lighting load  100  must be connected in the correct polarity in order for that particular to work correctly. If lighting  100  is connected in reverse polarity the system wouldn&#39;t not work, so to overcome this the lighting units also must having a rectifier to provide reverse polarity protection. 
     When any open circuit occurs at any of the output connector  1140 , and/or when the voltage exceed the specified reverse breakdown voltage of the Zener Diode  1220 ; hence causing the Zener Diode  1220  to be operated in reverse bias mode, the Silicon Controller Rectifier (SCR)  1240  will be triggered at the gate terminal to enable current to flow through the Silicon Controller Rectifier (SCR)  1240  thereby maintaining a close loop for the entire lighting system so that the other connected lighting  100  within the networking continue to operate regularly. Resistor  1260  is used a current limiter for the Zener Diode  1220  so as to prevent too large a current flowing through Zener Diode  1220 . Another resistor  1280  may be connected in parallel with the open circuit protection circuit and in parallel with the output connector  1140 . 
     As an alternative or addition to the open load protector  1180 , it is appreciated that a resistor  1280  may be deployed to act as a jumper/bypass resistor for deployment to specific output connector(s)  1140  which has (have) no load  100  connected to the same so as to maintain a close loop of the entire lighting system. Where specific output connector(s)  1140  is (are) permanently not supposed to be connected any load, the open circuit protector(s) connected to these output connector(s) may be removed. 
     Thus, junction box  1100  has been designed and will be implemented together with string driver to overcome the above described weaknesses arising from series connection. 
     Examples of Operating Technical Specification 
     The recommended operating technical specification for the LED driver  10 , 8-pin (lower resolution) configuration is listed as follows:—
     Operating Voltage: 100 to 120 VAC for US; 220 to 240 VAC for EU   Operating frequency: 50/60 Hertz (Hz)   AC current: 0.2 Amperes (A) for US; 0.1 A for EU   Inrush current: maximum allowable at 4 A for US; maximum allowable at 12 A for EU   Leakage current: less than (&lt;) 0.7 milli-A   Efficiency (full load): more than (&gt;) 83%   Power factor (full load): more than (&gt;) 0.98   

     The output specification (8-pin configuration) based on 120 VAC (US)/230 VAC (EU) input; rated load and 25 degrees Celsius ambient temperature are listed as follows:
     Output channel: 1   Output voltage range: 12 to 36 VDC   Output current: 600 or 700 mA   Current tolerance: ±5%   Current adjust range: Not adjustable   Rated Power: 21.6 W MAX (at 600 mA) and 25.2 W MAX (at 700 mA)   

     The recommended operating input specification for the LED driver  10 , 500, 14-pin configuration is listed as follows:—
     Operating Voltage: 100 to 120 VAC for US; 220 to 240 VAC for EU   Operating frequency: 50/60 Hertz (Hz)   AC current: 1.3 Amperes (A) for US; 0.6 A for EU   Inrush current: maximum allowable at 7 A for US; maximum allowable at 30 A for EU   Leakage current: less than (&lt;) 0.7 milli-A   Efficiency (full load): more than (&gt;) 86%   Power factor (full load): more than (&gt;) 0.96   

     The output specification for the LED driver  10 ,  500   14 -pin configuration based on 120 VAC (US)/230 VAC (EU) input; rated load and 25 degrees Celsius ambient temperature having two output channels are listed as follows:
     Output channel: 2   Output voltage range: 35 to 85 VDC (single channel) Total of 70 to 170 VDC   Output current: 600 or 700 mA   Current tolerance: ±5%   Current adjust range: Not adjustable   Rated Power: 102 W MAX  (at 600 mA) and 119 W MAX  (at 700 mA)   

     The LED driver  10 ,  500  are especially suitable for LED downlights, Troffer LED lighting and MR 16, particularly at a temperature range of 0 degree Celsius to 40 degrees Celsius. 
     In addition, the following advantages are also apparent:— 
     a. Safer Methodology for LED Lighting Unit 
     As the LED driver  10 ,  500  are isolated DC configuration and only work with DC driven LED lighting Unit, there will be no safety related issue associated with AC currents for the LED lighting units  100  which are at the secondary side and isolated from the mains. As the LED driver  10 ,  500  will be isolated from the LED lighting unit  100  there will also be not size limitation on the design as in build in configuration so the LED driver  10 ,  500  can be designed in accordance to safety requirement. 
     b. High Electrical Efficiency 
     The LED Driver  10 ,  500 ; termed ‘string driver’ operates in thermally cooler environment because it is isolated from the LED load units  100  and not affected by the heat dissipated by the LEDs unit  100  during the continuous operation. This reduces thermal loss on the LED driver  10 ,  500  hence less power is consumed during operation to improve efficiency. Compared to the prior art, where each LED lamp comprises its own driver which is directly connected to the AC mains, power efficiency will be significantly improved compared to AC driver lighting unit in a complete lighting system because total power losses only apply to the particular single driver whereas AC driven lighting unit will having higher total power loss due to losses on each lighting. 
     c. High Efficacy (Lumens/Watt) 
     As an associated advantage, the string configuration offer cooler operating environment which resulted lower optical loss for the LEDs device hence higher luminous flux exhibited by the LED devices eventually improved the efficacy (lumens/watt) for the entire lighting system. 
     d. Longer Lifetimes 
     The LED driver  10 ,  500  using ASIC control, eliminates the use of short lifetimes components such as Aluminum Electrolytic Capacitor where this is extended the lifetimes of the LED driver  10 ,  500 . As for the LEDs lamp units  100 , the thermally cooler and operation with approximately ripple free constant current improves the performance and reliability of LED devices significantly and slow down the entire degradation progress on the LED device  100  eventually prolong the lifespan for the entire LED lighting unit. 
     e. Wide Range Application Options 
     The flexibility design for the single LED driver  10 ,  500  is applicable for any type of DC driven LED lighting unit and theoretically is able to drive unlimited numbers of LEDs in the entire lighting system by minor fine tuning of specific components as described earlier. 
     f. Cost Effective Solution 
     String driver configuration is a cost effective solution since single the LED Driver  10 ,  500  is capable to drive a series of DC driven LED lighting units whereas the prior art configuration require one driver for each LED lighting. Further, the solution also offer more competitive manufacturing cost as well as design part cost especially for heat sink. 
     g. Ease of Maintenance 
     Since the single LED Driver  10 ,  500  is isolated from the LED lighting unit  100 , if any failure occurred within the lighting system that due to a faulty LED driver  10 ,  500 , the user just need to replace the faulty LED driver instead of dismantling the entire LED lighting (Build-in concept). Such maintenance process is simple and may be completed within a relatively short period. 
     h. Miniature in Form Factor 
     The heat sink for the lighting luminaries will be smaller in size where the heat sink just to design to dissipate heat generated by the LED lighting unit  100  where not heat generated from the AC-DC LED driver because of isolating between them. Also the single driver can be design in such an optimized size due to less components count require for the entire system compare to integral concept and thus less material used and the introduction of planar transformer will further enhance the slim look of the driver solution instead of conventional transformer that is in bulky form factor. 
     It is further apparent that the LED Driver  10 ,  500  requires less components count and less repetition of components compared to prior art systems where each LED lamp unit requires its own AC to DC driver. The driver solution form factor is thus reduced. Besides that, manufacturing process will be simplified such that production throughput and yield rate will be improved. 
     It is further apparent that the heat sink form factor for each LED lighting unit  100  will be reduced in the string configuration because the each heat sink will be required to only handle the heat distributed by the LED lighting unit  100 . This is because the LED driver  10 ,  500  is isolated from the LED lighting unit  100 . This will beneficial on part cost due to less material utilization. Furthermore, the entire design cycle will be further shorten since both LED lighting unit  100  and LED driver  10 ,  500  design activity can be carried out simultaneously that leads to improve product time to market. 
     The junction box  1100  further provides additional advantages to the string driver concept as follows:— 
     a. Error Free Installation 
     The Junction Box  1100  is designed with “fool proof” concept so that to provide an error free installation experience to the end user. Polarity is a concern during installation to ensure the entire lighting system work as expected. With the bridge rectifier at each junction box providing an interface with the driver  10 ,  500  and the SSL driverless lighting unit  100 , accidental reverse polarity connection is negated during the installation. The lighting units  100  within the lighting system will operate normally as long as continuity exist between driver  10 ,  500  and SSL driverless lighting unit  100  regardless of polarity consideration. Further, header and plug in connector design exist on the interface between driver output and junction box input where this will totally eliminate the possibility to connect the driver output to any of the junction box output connector. 
     b. Ease of Installation 
     The junction box  1100  comprises connector design for interfacing purposes with driver  10 ,  500  and driverless SSL lighting units  100 . A user will thus find it easy to plug in or inserting the strip end cable to the correct or dedicated connector. In addition, due to the simplification of the installation, shorter time and thus lower cost is expended for installation and system set-up. 
     c. Safer Installation 
     As only DC supply exists on the junction box  1100  a safety environment is created for installation. 
     d. Flexibility of Installation 
     Since the string driver concept do not have a wire length constraint during installation, users have the flexibility to position the SSL driverless lighting units according to their preference design and/or needs. A user may lengthen the electrical wire of the SSL driverless lighting unit  100  easily to their desire length so as to meet the application with the specific wire specification, example American wire gauge (AWG) 16˜24 to have a perfect match to the junction box input/output connectors  1120 ,  1140 . Furthermore, the junction box is also designed to support dual (or possibly larger number of junction boxes linkage) which will provide additional flexibility on the installation. 
     e. Ease of Maintenance 
     The special design feature of the junction box as described in the embodiment enables a user/installer to identify the failure unit easily and to carry out the necessary maintenance as what they experienced in conventional practice even though the string driver is running in series connection 
     f. Reliable Connection 
     The described input/output connectors  1120 ,  1140  used for the connections within the lighting system is either wire entry or latch lock type which gives a good connection compared to conventional screw tightening method widely used on the market. 
     It is to be understood that the above embodiments have been provided only by way of exemplification of this invention, and that further modifications and improvements thereto, as would be apparent to persons skilled in the relevant art, are deemed to fall within the broad scope and ambit of the present invention described. Furthermore although individual embodiments of the invention may have been described it is intended that the invention also covers various combinations of the embodiments discussed.