Abstract:
A dual light source voltage-modulated reciprocal control circuit for a scanner. The circuit includes a voltage modulation circuit, a first lamp driving circuit, a second lamp driving circuit and a reciprocal control circuit. The voltage-modulating circuit generates a modulated voltage whose magnitude can be adjusted through pulse width modulation of a square wave. The first lamp driving circuit receives the modulated voltage to drive a first lamp. Similarly, the second lamp driving circuit receives the modulated voltage to drive a second lamp. The reciprocal control circuit redirects the modulated voltage to the first lamp driving circuit or the second lamp driving circuit according to the dictate of a reciprocal logic signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 09/997,647, filed Nov. 27, 2001, now U.S. Pat. No. 7,070,102 titled “Dual Light Source Voltage-Modulated Reciprocal Control Circuit for Scanner”, inventor Chin-Lin Chang. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a dual light source voltage modulated reciprocal control circuit. More particularly, the present invention relates to a dual light source voltage-modulated reciprocal control circuit for a scanner. 
     2. Description of Related Art 
     A scanner requires a light source to conduct a document scanning. In general, a scanner has two sets of lights for document scanning, namely, a set of back lights for scanning of ordinary opaque documents and a set of cover lights for scanning transparent documents. 
       FIG. 1  is a block diagram showing a dual light source circuit in a conventional scanner. As shown in  FIG. 1 , square wave signals SV 1  and SV 2  are transmitted from an application specific integrated circuit  102  to a first voltage-modulated circuit  104  and a second voltage-modulated circuit  106  respectively. Pulse width of the square wave signals SV 1  and SV 2  can be modulated (for example, within the range 15%˜80%). The larger the pulse width of the square wave signals SV 1  and SV 2 , the greater will be the magnitude of the modulated voltages MV 1  and MV 2  each having a direct current (dc) square wave profile submitted from the first voltage-modulated circuit  104  and the second voltage-modulated circuit  106 . 
     The first voltage-modulated circuit  104  and the second voltage-modulated circuit  106  submit the modulated voltages MV 1  and MV 2  to a back light driving circuit  108  and a cover light driving circuit  110  respectively. The back light driving circuit  108  and the cover light driving circuit  110  are dc-to-ac inverters capable of converting a direct current (dc) voltage into an alternating (ac) voltage. The back light driving circuit  108  issues an alternating voltage INV 1  to a back light  112  and the cover light driving circuit  110  issue an alternating voltage source INV 2  to a cover light  114 . Hence, either the back light  112  or the cover light  114  is triggered to conduct a document scanning but not both. 
     However, most conventional scanners having a dual light source circuit employ two sets of voltage-modulating circuits. With the deployment of two voltage-modulating circuits, more area on a printed circuit board is required to house component devices. Ultimately, a greater hardware cost is incurred. 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the present invention is to provide a dual light source voltage-modulated reciprocal control circuit for a scanner that uses just one set of voltage-modulating circuit. With less component devices, area occupation of the control circuit on a printed circuit board is reduced and some hardware cost is saved. 
     To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a dual light source voltage-modulated reciprocal control circuit for a scanner. The circuit includes a voltage-modulating circuit, a first lamp driving circuit, a second lamp driving circuit and a reciprocal control circuit. The voltage-modulating circuit generates a modulated voltage whose magnitude can be adjusted through pulse width modulation of a square wave. The first lamp driving circuit receives the modulated voltage to drive a first lamp. Similarly, the second lamp driving circuit receives the modulated voltage to drive a second lamp. The reciprocal control circuit redirects the modulated voltage to the first lamp driving circuit or the second lamp driving circuit according to the dictate of a reciprocal logic signal. With such a circuit design, hardware cost for the circuit is reduced. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
         FIG. 1  is a block diagram showing a dual light source circuit in a conventional scanner; 
         FIG. 2  is a block diagram showing a dual light source voltage-modulated reciprocal control circuit for a scanner according to this invention; 
         FIG. 3  is a diagram showing a voltage-modulated circuit according to one embodiment of this invention; 
         FIG. 4  is a diagram showing a reciprocal control circuit according to one preferred embodiment of this invention; 
         FIG. 5  is a diagram of a Darlington circuit; and 
       Table  1  shows the logic behind the switching of the light sources according to this invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
       FIG. 2  is a block diagram showing a dual light source voltage-modulated reciprocal control circuit for a scanner according to this invention. As shown in  FIG. 2 , an application specific integrated circuit  202  outputs a square wave signal SV to a voltage-modulating circuit  204 . Pulse width of the square wave signal SV is adjustable. The higher the pulse width of the square wave signal SV, the greater will be the modulated voltage MV having a direct current (dc) profile output from the voltage-modulating circuit  204 . Furthermore, the application specific integrated circuit  202  also outputs a reciprocal logic signal F/U LAMP to a reciprocal control circuit  206 . The reciprocal logic signal F/U LAMP determines if the modulated voltage MV is sent to a back light driving circuit  208  or a cover light driving circuit  210 . 
     The voltage-modulating circuit  204  outputs the modulated-voltage MV to the reciprocal control circuit  206 . The reciprocal control circuit  206  picks up the reciprocal logic signal F/U LAMP from the application specific integrated circuit  202  and sends the modulated voltage MV to the back light driving circuit  208  or the cover light driving circuit  210  respectively. The back light driving circuit  208  and the cover light driving circuit  210  are dc-to-ac inverters capable of converting a direct current (dc) voltage into an alternating (ac) voltage. The back light driving circuit  208  issues an alternating voltage INV 1  to a back light  212  and the cover light driving circuit  210  issues an alternating voltage source INV 2  to a cover light  214 . Hence, either the back light  212  or the cover light  214  is triggered to conduct a document scanning but not both. 
       FIG. 3  is a diagram showing a voltage-modulated circuit according to one embodiment of this invention. As shown in  FIG. 3 , a first terminal of a resistor R  302  receives the square wave SV from the application specific integrated circuit  202  (shown in  FIG. 2 ). A first terminal of a resistor R  304  is connected to a second terminal of the resistor R  302  and a second terminal of the resistor R  304  is connected to ground. A first terminal of a resistor R  308  is connected to a voltage source at 12V. A first terminal of a resistor R  312  is connected to a second terminal of the resistor R  308 . A voltage source terminal of a transistor  306  is connected to a second terminal of the resistor R  312 . A control terminal of the transistor  306  is connected to the second terminal of the resistor R  302 . A load terminal of the transistor  306  is connected to ground. A voltage terminal of a transistor  310  is connected to a voltage source at 12V. A control terminal of the transistor  310  is connected to a second terminal of the resistor R  308 . The anode of a diode D  314  is connected to ground. A first terminal of an inductor L  316  is connected to the loading terminal of the transistor  310 . The second terminal of the inductor L  316  is an output terminal for outputting the modulated voltage MV. A first terminal of a capacitor C  318  is connected to the first terminal of the inductor L  316  and the second terminal of the capacitor C  318  is connected to ground. 
     In  FIG. 3 , the resistors R  302 ,  304 ,  308 ,  312  and the transistors  310 ,  306  together constitute a circuit for boosting voltage. Each of the resistors R  302 ,  304 ,  308  and  312  has a different resistance value. The inductor L  316  and the capacitor C  318  serve as energy storage devices and the diode D  314  serves as a circuit bypass. 
     The reciprocal control circuit  206  (shown in  FIG. 2 ) comprises a common emitter circuit and a Darlington circuit.  FIG. 4  is a diagram showing a reciprocal control circuit according to one preferred embodiment of this invention. As shown in  FIG. 4 , the common emitter circuit  402  includes resistors R  404 , R  406  and transistors  408 ,  410 . A first terminal of the resistor R  404  receives the reciprocal logic signal F/U LAMP from the application specific integrated circuit  202 . A first terminal of the resistor R  406  is connected to a voltage source at 5V. A source terminal of the transistor  408  is coupled to a second terminal of the resistor R  406 . A control terminal of the transistor  408  is coupled to a second terminal of the resistor R  404 . A loading terminal of the transistor  408  is connected to ground. A source terminal of the transistor  410  is coupled to a ground terminal ULAMP_GND of the cover lamp driving circuit  210 . A control terminal of the transistor  410  is coupled to the second terminal of the resistor R  406 . A loading terminal of the transistor  410  is connected to ground. The transistor  410  of the common emitter circuit  402  is designed as a current sink. Hence, current specification of the transistor  410  is especially important. 
     Input terminals  1 B,  2 B of the integrated circuit IC ULN2003  414  are connected in parallel to the application specific integrated circuit  202  for receiving the reciprocal logic signal F/U LAMP. Output terminals  1 C,  2 C are connected in parallel to the earth terminal FLAMP_GND of the back light driving circuit  208 . The E terminal of the integrated circuit IC ULN2004  414  is connected to ground. The COM terminal of the integrated circuit IC ULN2004  414  is connected to a voltage source at 12V. After receiving the modulated voltage MV submitted from the application specific integrated circuit  202 , the reciprocal control circuit  206  outputs the modulated voltage MV to the source terminal ULAMP_POWER of the cover light driving circuit  210  and the source terminal FLAMP_POWER of the back light driving circuit  208 . The resistor R  404  and the resistor R  406  have different resistance values. The integrated circuit IC ULN2003  414  comprises of seven groups of Darlington circuits. The terminals  1 B,  2 B,  3 B,  4 B,  5 B,  6 B,  7 B on the integrated circuit IC ULN2003  414  are the input terminals and the terminals  1 C,  2 C,  3 C,  4 C,  5 C,  6 C and  7 C on the integrated circuit IC ULN2003  414  are the output terminals of the seven Darlington circuits respectively. 
       FIG. 5  is a diagram of a Darlington circuit. As shown in  FIG. 5 , the Darlington circuit  500  has a resistor R  502  with a first terminal connected to the application specific integrated circuit  202  for receiving the reciprocal logic signal F/U LAMP. A first terminal of a resistor R  504  is coupled to a second terminal of the resistor R  502 . A first terminal of a resistor R  506  is coupled to a second terminal of the resistor R  504 . A second terminal of the resistor R  506  is connected to ground. A source terminal of a transistor  508  is connected to the ground terminal FLAMP_GND of the back light driving circuit  208  (refer to  FIG. 4 ). A control terminal of the transistor  508  is coupled to the second terminal of the resistor R  502 . A loading terminal of the resistor  508  is coupled to the second terminal of the resistor R  504 . A source terminal of a transistor  510  is also coupled to the ground terminal FLAMP_GND of the back light driving circuit  208   20  (refer to  FIG. 4 ). A control terminal of the transistor  510  is coupled to the second terminal of the resistor R  504 . A loading terminal of the transistor  510  is connected to ground. Each of the resistors R  502 ,  504  and  506  has a different resistance value. 
     Table  1  shows the logic behind the switching of the light sources according to this invention. Refer also to the circuit diagrams shown in  FIGS. 4 and 5 . When the reciprocal logic signal F/U LAMP output from the application specific integrated circuit  202  (refer to  FIG. 2 ) is HIGH and the pulse width modulated square wave SV is PULSE/HIGH, the transistor  408  is “ON” and hence the transistor  410  is “OFF”. An open circuit is formed between the source terminal ULAMP_POWER of the cover light driving circuit  210  and the ground terminal ULAMP_GND. Thus, the cover lamp  214  (refer to  FIG. 2 ) is “OFF”. Similarly, when the reciprocal logic signal F/U LAMP output from the application specific integrated circuit  202  (refer to  FIG. 2 ) is HIGH and the pulse width modulated square wave SV is PULSE/HIGH, the transistor  508  and the transistor  510  are “ON”. The source terminal FLAMP_POWER of the back o light driving circuit  208  and the ground terminal FLAMP_GND form a conductive path so that the back light driving circuit  208  receives the modulated voltage MV. Thus, the back light lamp  212  (refer to  FIG. 2 ) is “ON”. 
     In like manner, when the reciprocal logic signal F/U LAMP output from the application specific integrated circuit  202  (refer to  FIG. 2 ) is LOW and the pulse width modulated square wave SV is PULSE/HIGH, the transistor  408  is “OFF”. The transistor  410  is “ON” so that a conductive path is formed between the source terminal ULAMP_POWER of the cover light driving circuit  210  and the ground terminal ULAMP_GND. The cover lamp driving circuit  210  receives the modulated voltage MV and hence the cover lamp  214  (refer to  FIG. 2 ) is “ON”. Similarly, when the reciprocal logic signal F/U LAMP output from the application specific integrated circuit  202  (refer to  FIG. 2 ) is LOW and the pulse width modulated square wave SV is PULSE/HIGH, the transistor  508  and the transistor  510  are both “OFF”. An open circuit is formed between the source terminal FLAMP_POWER of the back light driving circuit  208  and the ground terminal FLAMP_GND. Thus, the back light lamp  212  (refer to  FIG. 2 ) is “OFF”. 
     In Table  1 , the dual light source voltage-modulated reciprocal control circuit may operate in an energy-saving mode. This occurs when the pulse width modulated square wave SV output from the application specific integrated circuit  202  (refer to  FIG. 2 ) is LOW. Under such voltage setting, the reciprocal logic signal F/U LAMP from the application specific integrated circuit  202  (refer to  FIG. 2 ) is incapable of triggering the back light  212  or the cover light  214 . 
     In summary, when the reciprocal control circuit picks up reciprocal logic signal from the application specific integrated circuit, the reciprocal control circuit will output a reciprocal logic signal that switches on either the back light or the cover light. Hence, one set of voltage-modulating circuit can provide necessary power for driving the back light and the cover light. In addition, the integrated circuit IC ULN2003  414  used in  FIG. 4  is one of the components inside the scanner and hence no additional IC is required. Furthermore, comparing the common emitter circuit  402  and the voltage-modulating circuit shown in  FIG. 3 , the common emitter circuit  402  has a simpler configuration, requires fewer electronic devices and occupies less printed circuit board area. 
     Since only one set of voltage modulation circuit is required, the circuit demands fewer electronic devices and occupies a smaller printed circuit board area. Hence some hardware cost is saved. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.