Abstract:
A lamp circuit is disclosed, comprising a direct current (DC) power supplier adapted to provide a supply voltage, a driving unit coupled to the DC power supplier so as to receive the supply voltage, and a light-radiating module coupled to the driving unit and having a DC output side. The driving unit generates a constant DC current that passes through the light-radiating module such that a DC voltage to be supplied to a DC load is built at the DC output side.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a lamp circuit and, more particularly, to a lamp circuit that supplies a voltage to a load based on a received voltage from a light-radiating module thereof. 
     2. Description of the Related Art 
     Conventional lamps generally comprise a light-radiating module which radiates light through light-radiating devices such as light-emitting diodes (LEDs), bulbs or light tubes. Since the light-radiating module generates a significant amount of heat during operations, cooling equipments such as fans or heat sinks are required for cooling the light-radiating module in order to prolong the service life of the lamp. 
     Apart from a load of the light-radiating module, the conventional lamps also comprise a direct current (DC) load. Generally, the DC load requires different supply voltage from the light-radiating module. Therefore, multiple supply voltages are irreversibly required in the lamps. 
     Referring to  FIG. 1 , a conventional lamp circuit is disclosed. The lamp circuit comprises a DC power supply  91 , a driving unit  92  and a light-radiating module  93 . The DC power supply  91  is electrically connected to the driving unit  92  which, in turn, is electrically connected to the light-radiating module  93 . The DC power supply  91  generates a first voltage V 91  that is provided to the driving unit  92 . The driving unit  92  generates a constant DC current Ic that passes through the light-radiating module  93 . With the constant DC current Ic, the light luminance of the light-radiating module  93  is kept in a constant level. The light-radiating module  93  comprises a feedback end  931  electrically connected to the driving unit  92 . The light-radiating module  93  sends a feedback signal back to the driving unit  92  via the feedback end  931  such that the driving unit  92  may keep the constant DC current Ic passing through the light-radiating module  93  from varying based on the variation of the feedback signal. 
     A cooling fan  95  is required to be equipped in the lamp for cooling purpose as the light-radiating module  93  generates a significant amount of heat due to the constant DC current Ic passing therethrough. Since the cooling fan  95  requires different supply voltage from the light-radiating module  93 , an additional supply voltage has to be provided therefor. 
     Referring to  FIG. 1 , the lamp circuit further comprises a voltage regulation unit  94  electrically connected to the driving unit  92  to receive a DC voltage therefrom. Alternatively, the voltage regulation unit  94  may also be electrically connected to the output ends of the DC power supply  91  to receive a first voltage V 91 . The voltage regulation unit  94  converts the first voltage V 91  into a second voltage V 92  that is provided to the cooling fan  95 . 
     The conventional lamp circuit has some drawbacks. For instance, the conventional lamp circuit requires the voltage regulation unit  94  for providing the second voltage V 92  to the cooling fan  95 . In this regard, circuitry complexity and costs are increased. 
     Therefore, it is desired to improve the conventional lamp circuit. 
     SUMMARY OF THE INVENTION 
     It is therefore the primary objective of this invention to provide a lamp circuit which simplifies the circuitry complexity and reduces the costs by avoiding extra components used. 
     It is another objective of this invention to provide a lamp circuit which has more functions and simplifies the circuit complexity of the feedback circuit. 
     It is another objective of this invention to provide a lamp circuit which requires smaller volume of a transformer by using a micro-controller unit. 
     The invention discloses a lamp circuit, comprising a direct current (DC) power supplier adapted to provide a supply voltage, a driving unit coupled to the DC power supplier so as to receive the supply voltage, and a light-radiating module coupled to the driving unit and having a DC output side. The driving unit generates a constant DC current that passes through the light-radiating module such that a DC voltage to be supplied to a DC load is built at the DC output side. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  shows a conventional lamp circuit. 
         FIG. 2  shows a lamp circuit according to a first embodiment of the invention. 
         FIG. 3  shows a lamp circuit according to a second embodiment of the invention. 
     
    
    
     In the various figures of the drawings, the same numerals designate the same or similar parts. Furthermore, when the term “first”, “second”, “third”, “fourth”, “inner”, “outer” “top”, “bottom” and similar terms are used hereinafter, it should be understood that these terms are reference only to the structure shown in the drawings as it would appear to a person viewing the drawings and are utilized only to facilitate describing the invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 2 , a lamp circuit is disclosed according to a first embodiment of the invention. The lamp circuit comprises a DC power supply  1 , a driving unit  2  and a light-radiating module  3 . The DC power supply  1  is electrically connected to the driving unit  2  which, in turn, is electrically connected to the light-radiating module  3 . The DC power supply  1  receives an external supply voltage (not shown) and processes the received supply voltage with a series of procedures to generates a supply voltage V 1  at an output side thereof, such as voltage dropping, rectifying and voltage regulation and so on. The supply voltage V 1  is provided to the driving unit  2 . The driving unit  2  generates a constant DC current Ic that passes through the light-radiating module  3 . The constant DC current Ic is kept from varying such that the light luminance of the light-radiating module  3  is kept in a constant level. 
     The driving unit  2  is an independent unit which ensures the operation of the lamp circuit by separating the control loop and power loop. The driving unit  2  comprises a switching unit  21 , a transformer  22 , a rectifying and filtering element  23  and a feedback unit  24 . The switching unit  21  is connected to the DC power supply  1 . A primary side of the transformer  22  is electrically connected to the switching unit  21  and a secondary side of the transformer  22  is electrically connected to the rectifying and filtering element  23 . The rectifying and filtering element  23  has an output end electrically connected to the light-radiating module  3 . 
     The switching unit  21  receives the supply voltage V 1  and generates a first pulse to be received at the primary side of the transformer  22 . The transformer  22  converts the first pulse into a second pulse at the secondary side thereof. The second pulse is sent to the rectifying and filtering element  23  which, in turn, converts the second pulse into the constant DC current Ic. Note that by adjusting the turn ratio between the primary side and the secondary side, the voltage ratio and current ratio between the first pulse and the second pulse may be designed based on power consumption and power characteristic of a load (not shown). 
     To prevent the constant DC current Ic from varying, the light-radiating module  3  comprises a feedback end  31  electrically connected to the feedback unit  24  of the driving unit  2 . The feedback end  31  sends a feedback signal to the feedback unit  24  of the driving unit  2 . Based on the feedback signal, the driving unit  2  keeps the constant DC current Ic from varying so as to keep the light luminance of the light-radiating module  3  in a constant level. 
     Referring to  FIG. 2  again, the light-radiating module  3  in the first embodiment of the invention comprises a plurality of light-radiating elements  32  and a DC output side  33 . The light-radiating elements  32  are connected in series, with a connection node  321  being formed between two series-connected light-radiating elements  32 . In  FIG. 2 , at least one connection node  321  is formed. 
     The DC output side  33  of the light-radiating module  3  is electrically connected to a DC load  4  so that the DC output side  33  may provide a DC voltage V 2  to the DC load  4 . The DC load  4  may be a cooling fan or DC motor. The DC output side  33  has a first connection end  331  and a second connection end  332 . The first connection end  331  is electrically connected to ground and the second connection end  332  is electrically connected to one of the connection nodes  321 . 
     Specifically, since each light-radiating element  32  has an internal resistance, the DC voltage V 2  is established at a connection node  321  when the constant DC the current Ic passes through the light-radiating module  3 . Each connection node  321  has different voltage with respect to ground. The second connection end  332  of the DC output side  33  may be connected to a proper connection node  321  according to the voltage requirement of the DC load  4 . In this way, a proper voltage (i.e. DC voltage V 2  shown in  FIG. 2 ) may be provided to the DC load  4  by the light-radiating module  3  through the DC output side  33 . 
     Referring to  FIG. 3 , a lamp circuit is disclosed according to a second embodiment of the invention. In comparison with the first embodiment, a digital driving unit  5  is provided in the second embodiment. The digital driving unit  5  comprises a micro-controller unit (MCU)  51 , an electronic switch  52 , a transformer  53  and a rectifying and filtering element  54 . The MCU  51  is electrically connected to the DC power supply  1  so as to receive the supply voltage V 1  therefrom. The electronic switch  52  is electrically connected to a control end  511  of the MCU  51  such that a control signal, that is used to control the ON/OFF operation of the electronic switch  52 , may be sent to the electronic switch  52  via the control end  511 . A primary side of the transformer  53  is electrically connected to the electronic switch  52  and a secondary side of the transformer  53  is electrically connected to the rectifying and filtering element  54 . The rectifying and filtering element  54  is electrically connected to the light-radiating module  3 . A first pulse is generated at the primary side of the transformer  53  during switching operation of the electronic switch  52 . A second pulse is generated at the secondary side of the transformer  53 . The rectifying and filtering element  54  generates and outputs the constant DC current Ic to the light-radiating module  3 . The electronic switch  52  may be a transistor switch. 
     The MCU  51  in the second embodiment further comprises a feedback signal receiving end  512  electrically connected to the feedback end  31  of the light-radiating module  3 . Upon receipt of the feedback signal from the feedback end  31 , the MCU  51  may control the digital driving unit  5  to output the constant DC current Ic. 
     Specifically, the light-radiating module  3  in the second embodiment may also output the DC voltage V 2  to the DC load  4  via the DC output side  33  thereof. Since the DC load  4  and the DC output side  33  are connected in parallel, a portion of the constant DC current Ic will be shared by the DC load  4 , resulting in a variation of the feedback signal. In response thereto, the feedback signal receiving end  512  increases or reduces the magnitude of the outputted DC current thereof based on the variation of the feedback signal in order to prevent the constant DC current Ic from varying. 
     In comparison with the independent driving unit  2  in the first embodiment, the digital driving unit  5  has advantages such as reducing the costs as well as circuit complexity of feedback circuit. Furthermore, since the digital driving unit  5  is not operated under large currents, a small-volume transformer  53  may be used. In another embodiment, the MCU  51  in the second embodiment may comprise an additional control end electrically connected to an input end of the DC load  4 . For example, assume that the DC load  4  is a cooling fan; the MCU  51  may send a rotation speed control signal to the cooling fan via the input end of the cooling fan. In this way, the rotational speed of the cooling fan may be controlled. Based on this, by using the MCU  51 , more functions may be implemented in the lamp circuit without using complex rotation speed control circuit. 
     To achieve high circuit integrity, the digital driving unit  5  (or some components of the digital driving unit  5  such as the MCU  51 ) may be mounted on a circuit board in the cooling fan. 
     In conclusion, the invention provides the DC voltage V 2  to the DC load  4  through the light-radiating module  3  without using an extra voltage regulation unit  94 . Thus, costs are reduced and circuit complexity is simplified. 
     Although the invention has been described in detail with reference to its presently preferable embodiment, it will be understood by one of ordinary skill in the art that various modifications can be made without departing from the spirit and the scope of the invention, as set forth in the appended claims.