Abstract:
The invention is to provide a projector of external power supply, which comprises: a DC (direct current) power supply port, a step-up circuit, a voltage regulation circuit, a lamp, and an igniter. Wherein, a DC voltage provided from outside is received by the DC power supply port and is converted to a first electric potential by the step-up circuit. The first electric potential may actuate the igniter to light up the lamp and, after the lamp is lighted up, the step-up circuit regulates the working voltage of the lamp to a second potential voltage. Wherein, the first electric potential is higher than the second electric potential.

Description:
1. FIELD OF THE INVENTION  
         [0001]    This invention is related to an projector of external power supply, wherein an external power supply outside the projector is provided to supply a DC power supply, and operates in coordination with a ballast circuit framework with step-up circuit that is set up inside the projector. Consequently, the objectives of moving the power supply to the outside and reducing the volume of projector are achieved.  
         2. BACKGROUND OF THE INVENTION  
         [0002]    In a present day projector, a built-in AC/DC power converter is most prevailing. As shown in FIG. 1, power supply  11  and ballast  12  are set up inside the casing  10  of projector. The power supply  11  is connected to an external power cord  112  of the projector. The grid power of 110 VAC or 220 VAC is introduced to the power supply  11  by an external plug  111  and is converted to different voltages required by the projector through the circuit framework of the power supply  11  and the circuit framework of the ballast  12 . Please refer to FIG. 2, which illustrates the circuit framework of the power supply  11  and the circuit framework of the ballast  12  according to the prior arts. The power supply  11  is a power factor refining circuit (PFC), by which the grid power of 110 VAC or 220 VAC can be transformed into a high voltage of 380 volts and thereafter output to both the ballast  12  and a sub-power circuit  13  which is required by the circuit board. The ballast  12  applies a step-down circuit to transform the 380 volts voltage into the voltage (about 80 volts) needed by the lamp  121 . The sub-power circuit  13  applies a fly-back circuit framework to transform the 380 volts voltage into different voltages (such as: 12 volts, 5 volts, and 3.3 volts, etc.) needed by the circuit board, wherein a transformer T 1  and an opto-coupler IC 1  are needed by the sub-power circuit  13  to isolate the first side and the second side.  
           [0003]    According to the national security test standard and the consideration of safety factor, an exposed voltage can not exceed 60 volts while the voltage generated in the power supply of a projector must reach 380 volts to light up the lamp. Therefore, this is the main reason why the power supply device must be built in a traditional projector. Because of the specific space occupied by power supply that is set up in the projector, the volume of the projector can not be reduced. Hence, to move the power supply out of the projector has become an arduous problem for current manufacturers.  
         SUMMARY OF THE INVENTION  
         [0004]    In view of the shortcomings of the power supply according to the prior arts, the main objective of the present invention is to provide a projector of external power supply which can receive a DC voltage supplied from exterior, and operates in coordination with a ballast circuit framework with step-up circuit that is set up inside the projector. Hence, the objectives of moving the DC/AC converter out of the projector and reducing the volume of the projector can be achieved.  
           [0005]    The secondary objective of the present invention is to provide a projector with external power supply that its refined circuit is also applicable to the other portable electrical apparatuses which a voltage step-up action are required in their interior.  
           [0006]    For your esteemed member of reviewing committee to further recognize and understand the characteristics, objectives, and functions of the present invention, a detailed description together with corresponding drawings are presented thereinafter. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a schematic drawing illustrating a projector with built-in power supply according to the prior arts.  
         [0008]    [0008]FIG. 2 is a circuit framework of a projector with built-in power supply according to the prior arts.  
         [0009]    [0009]FIG. 3 is a schematic drawing illustrating a projector of external power supply according to the present invention.  
         [0010]    [0010]FIG. 4 is a circuit framework of the preferable external power supply embodiment according to the present invention.  
         [0011]    [0011]FIG. 5 is a circuit framework of the preferred ballast embodiment according to the present invention.  
         [0012]    [0012]FIG. 6 is a circuit framework of the fly-back circuit adapted by the ballast according to the invention.  
         [0013]    [0013]FIG. 7 is a circuit framework of ballast with step-up circuit according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    Referring now to FIG. 3, which is an projector with a voltage converter  20  setting up outside the casing  10  of the projector and a ballast circuit  30  setting up inside the casing  10  of the projector. The ballast circuit  30  is connected to a DC power supply port  14 . A power supply cord  23   a  is set up at one side of the voltage converter that has a plug  231   a  connecting to the grid power (110/220 VAC). Moreover, a power supply cord  23   b  is set up at the other side of the voltage converter  20  that has a plug  231   b  connecting to the DC power supply port  14 . Hence, the plug  231   a  and the power supply cord  23   a  introduce the grid power (110/220 VAC) into the voltage converter  20 , by which the grid power (110/220 VAC) is converted to a DC voltage (48 VDC) needed by the projector. Moreover, the power supply cord  23   b  and the plug  231   b  send the DC voltage (48 VDC) into the ballast circuit  30  through the DC power supply port  14 .  
         [0015]    Please refer to FIG. 4, which is a voltage converter  20  used by the projector of external power supply according to the present invention. The voltage converter  20  has a power factor refining circuit  21 , by which the grid power of 110 volts or 220 volts is converted to 380 volts voltage. The high voltage of 380 volts then is converted to a low voltage ranging from 2.5 volts to 60 volts by a set of fly-back circuit  22 . Taking the low voltage of 48 volts as an example with reference to FIG. 4, the fly-back circuit  22  employs transformer T 1  and opto-coupler IC 1  as a isolation of the first side and the second side. Therefore, since the output voltage is lower than 60 volts, the safety requirement can be fulfilled and there is no hazard for both the power supply cord and the connecting plug. However, the designing purpose of the above-mentioned voltage converter  20  is to ensure the voltage converter  20  is able to raise the voltage to 380 volts. When the specification of current and voltage is within the safe working range of the projector, a voltage converter that is commonly available in current market can be used to provide a DC power supply to the projector according to the present invention.  
         [0016]    To cooperate with the projector of external power supply according to the present invention, a ballast circuit  30  with the functions of step-up and step-down circuits is set up inside the projector. As shown in FIG. 5, the ballast circuit  30  is connected to DC power supply port  14  for receiving a DC voltage of 48 volts supplied from exterior. At the beginning stage of lighting-up the lamp, the transistor Q 1  is completely conducted (same as a switch), and the step-up circuit  33  that is constituted by an inductance L 1 , a transistor Q 2 , a diode D 2 , and a capacitance C 1  can raise the voltage to a first voltage which is slightly higher than 200 volts. 250 volts is used in the present invention as an example. Thereafter, an igniter  32  generates a transient high voltage to light up the lamp  31 . After the lamp  31  is lighted up, the transistor Q 2  is closed completely. The voltage is step-down by a step-down circuit  34  formed by the transistor Q 1 , the diode D 1 , the inductance L 1 , the diode D 2 , the capacitance C 1 , and feedback controller  35  to provide a voltage of 20 volts to the lamp  31 . The lamp  31  and the feedback controller  35  control the output wattage of the ballast circuit  30  to be raised gradually. The feedback controller  35  is connected to a detecting resistance R 5 , of which the voltage is based to regulate the output wattage; The detecting resistance R 5  is connected in series to the lamp  31  and its another end is grounded, so that the voltage over this detecting resistance R 5  is proportional to the current passing through the lamp  31 . The feedback controller  35  can regulate the voltage of the lamp according to this voltage until the transistor Q 1  is opened completely. At this time, the step-up circuit  33  constituted by the inductance L 1 , the transistor Q 2 , the diode D 2 , and the capacitance C 1  raises the voltage to a voltage and wattage needed by the lamp  31  to complete the lighting-up procedure; Please refer to FIG. 5, in which three sets of step-down circuit  40   a ,  40   b ,  40   c  are respectively operated in cooperation with the ballast circuit  30  to directly convert the input voltage of 48 volts to three different voltages of 12 volts, 5 volts, and 3.3 volts that are needed by the circuit board. This is a so-called DC-DC converter  40 . Since the step-down circuits  40   a ,  40   b ,  40   c  are all located at second side and are all in low voltages, there is no safety distance precaution and it is easy to miniaturize.  
         [0017]    A fly-back circuit can also replace the ballast circuit  30  of FIG. 5. Please refer to FIG. 6, which is a circuit framework of the fly-back circuit  130 . Similarly, the flying-back circuit  130  is connected to a DC power supply port  14  for receiving a DC voltage of 48 volts supplied from the exterior. The fly-back circuit  130  includes a field effect transistor Q 1 , a transformer T 1 , a capacitance C 1 , and a feedback controller  133 . The transistor Q 1  is a field effect transistor switch that includes: a source, a drain, and a gate, wherein the source is connected to the transformer T 1 , the gate is connected to the feedback controller  133 , and the drain is grounded. When the transistor Q 1  is opened, the energy can be stored in the transformer T 1 . When the transistor Q 1  is closed, the transformer T 1  then releases the energy to the capacitance C 1  through the diode D 1 . At the beginning stage of lighting-up the lamp, the transformer T 1  can raise the voltage of the capacitance C 1  to 250 volts (i.e., the voltage of the lamp is 250 volts). Thereafter, the igniter  132  generates a high voltage to light up the lamp  131 . After the lamp  131  is lighted up, the transformer T 1  lower the voltage of the capacitance C 1  to about 20 volts (i.e., the voltage of the lamp  131  is 20 volts) and then the current of the lamp  131  will decrease gradually through time. The transformer T 1  can gradually increased the voltage of the capacitance C 1  by employing the feedback of the feedback controller  133 . The feedback controller  133  is connected to a detecting resistance R 4 , of which the voltage is based to regulate the output wattage; The detecting resistance R 4  is connected in series to the lamp  131 , and its another end is grounded. Hence, the voltage over the detecting resistance R 4  is proportional to the current passing through the lamp  131 . The feedback controller  35  can regulate the voltage of the lamp according to this voltage, and the output wattage also increases gradually to the normal rated value of the lamp  131 ; The method for the feedback controller  133  to regulate the voltage of the lamp  131  is by controlling the period of open and close of Q 1  to control the charging/discharging time of C 1 , so as to regulate the voltage of the lamp  131 ; Resistances R 2 , R 3  are feedback resistances of the lamp voltage, and resistance R 4  is the sensing resistance of the lamp current. Similarly, the fly-back circuit  130  can operate in cooperation with the DC-DC converter  40  of FIG. 5 to respectively convert the input voltage of 48 volts into three different voltages of 12 volts, 5 volts, 3.3 volts that are needed by the circuit board.  
         [0018]    A step-up/step-down circuit can also replace the ballast circuit  30  of FIG. 5. Please refer to FIG. 7, which is a circuit framework of a step-up/step-down circuit  230 . The circuit can be employed for stepping up voltage and also for stepping down voltage. Similarly, the step-down circuit  230  is connected to the DC power supply port  14  for receiving the DC voltage of 48 volts supplied from the exterior. When the transistor Q 1  is opened, the energy is stored in the inductance L 1 . When the transistor Q 1  is closed, the inductance L 1  releases the energy to the capacitance C 1  through the diode D 1 . To regulate the voltage of the capacitance C 1  can be accomplished simply by control the duty cycle of the transistor Q 1  using the controller  233 . The output voltage range of the capacitance C 1  is about 10 to 150 volts. The voltage of the capacitance C 1  reaches the lamp  231  through the inductance L 2  then, through the transformer T 1 , resistance R 5 , and goes back to capacitance C 1 . The operation of the transformer T 1  is equivalent to the igniters  32 ,  132  of FIG. 5 and FIG. 6. At the beginning stage of lighting up the lamp, the transformer T 1  can supply a high voltage to the lamp  231  to light up the lamp  231 ; The resistance R 5  is a current sensing resistance, which is used to feed back the current of the lamp  231 . The feedback is amplified by the opto-coupler IC 1  and is then sent to the controller  233  to control the current of the lamp  231 . Resistances R 6 , R 7  are the feedbacks of the voltage of the capacitance C 1  which are used to control the voltage of the capacitance C 1 . Since the internal resistances of the inductance L 2 , the transformer T 1 , and resistance R 5  are very low, the voltage of the capacitance C 1  is approximately equal to the voltage of the lamp  231 . And the above-mentioned to control the voltage and current of the lamp  231  are equivalent to control the wattage of the lamp  231 . Equally, the step-down circuit  230  can operate in cooperation with the DC-DC converter  40  of FIG. 5 to respectively convert the input voltage of 48 volts into three different voltages of 12 volts, 5 volts, 3.3 volts that are needed by the circuit board.  
         [0019]    It is noted that the lighting-up voltage needed by the lamp of the traditional projector with built-in power supply is about 380 VAC. After the power supply and the ballast circuit framework are improved according to the present invention, a low input voltage is stepped up to 380 volts to light up the lamp, then the high voltage is stepped down to a low voltage to provide current to the lamp and, after a short period of time, the voltage is again stepped up to the working voltage of the lamp. Yet, there is no serious influence to the brightness effect of the lamp. Namely, Fulfilling the requirement to miniaturize the volume of projector, the present invention indeed has an obvious improvement, as to enhance the portable convenience for carrying a projector. Furthermore, although the circuit framework of the above-mentioned step-up circuit operates in cooperation with the circuit of the adjustable voltage circuit capable of stepping down is a technique of the prior arts, this technique is never employed in ballast circuit._ The present invention applies the step-up/step-down circuits in the ballast to give a new usage to the step-up/step-down circuits. At the same time that the objective for reducing the volume of a projector can be achieved and the arduous problem for traditional manufacturers of projector can be overcome. Moreover, the circuit framework constituted by the cooperation between the external power supply and the ballast not only can be employed in a projector, but also can be applied to other electronic apparatuses driven by high voltage. In other words, this circuit framework may effectively reduce the volumes of such kinds of electronic apparatuses to achieve the objective of portable convenience. Since this kind of technique is an adaptation of the same technique, therefore no repetitious description is presented herein.  
         [0020]    In summary, a projector of external power supply according to the present invention is depicted illustrating by employing a power factor refining circuit and a fly-back circuit to construct a circuit framework of power supply which operates in cooperation with a ballast circuit framework with step-up circuit that is set up inside the projector, so as to achieve the objectives for moving its power supply to the outside and reducing its volume. Consequently, the invention should obviously possess the applicability and the progressiveness for industry. However, the description and the drawings disclosed hereinbefore are only applied as preferred embodiments according to the present invention and can not be used to restrict the range of its actual implementation. Therefore, any variation of the structural characteristics and of functions according to the above description and the writings of the following claims, e.g. the change of value and the replacement of equivalent devices, are all within the field of the present invention.