Abstract:
Driving circuitry having driving means for driving a load using a first DC voltage, regulator means for receiving an input voltage and deriving a regulated output voltage from the input voltage, and power source switch means switchable between a first state in which the first DC voltage is supplied to the regulator means as the input voltage and a second state in which a second DC voltage, lower than the first DC voltage and higher than the regulated output voltage, is supplied to the regulator means as the input voltage, second voltage deriving means for deriving the second DC voltage from the first DC voltage, and switch control means connected to the power source switch means for causing the power source switch means to switch from the first state to the second state when the second DC voltage is suitable for supply to the regulator means as the input voltage.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to driving circuitry and to an integrated circuit usable in such driving circuitry and its control. 
         [0003]    2. Description of the Related Art 
         [0004]    An electronic apparatus such as an inkjet recording apparatus includes a plurality of motors, for example, a scanning motor for a recording head and a conveying motor for a recording paper. Some motor driving circuits for driving a plurality of motors are formed as one integrated circuit (IC). Further, there is a direct current/direct current (DC/DC) converter for supplying electric power to a motor, a recording head, a control circuit or the like. Japanese Patent Application Laid-Open No. 2006-20495 discusses one integrated circuit in which a DC/DC converter circuit and a motor driving circuit are integrated. 
         [0005]    A DC/DC converter circuit provided on an integrated circuit converts an input voltage to a lower output voltage. In some central processing units (CPUs) and application-specific integrated circuits (ASICs) in recent years, a driving voltage is reduced. Thus, a voltage to be output to a low voltage circuit is also reduced. Under such circumstances, a difference between an input voltage and an output voltage is increased. Accordingly, in a DC/DC converter circuit, the amount of heat generated due to conversion loss of a voltage is increased. The heating amount in an integrated circuit including a motor driving circuit causes malfunction of a driving circuit. Further, a control unit of an electronic apparatus uses electric power generated in an integrated circuit. Thus, heat generated in an integrated circuit causes operation of a DC/DC converter circuit to stop and as a result, operation of an electronic apparatus is discontinued. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is directed to driving circuitry, an integrated circuit, and an electronic apparatus. According to an aspect of the present invention, driving circuitry has driving means for driving a load using a first DC voltage, regulator means for receiving an input voltage and for deriving a regulated output voltage from the input voltage, and power source switch means switchable between a first state in which the first DC voltage is supplied to the regulator means as the input voltage and a second state in which a second DC voltage (Vb), lower than the first DC voltage and higher than the regulated output voltage, is supplied to the regulator means as the input voltage. The driving circuitry also has second voltage deriving means for deriving the second DC voltage from the first DC voltage, and switch control means connected to the power source switch means for causing the power source switch means to switch from the first state to the second state when the second DC voltage is suitable for supply to the regulator means as the input voltage. 
         [0007]    Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention. 
           [0009]      FIG. 1  is a block diagram illustrating an electronic apparatus according to a first exemplary embodiment of the present invention. 
           [0010]      FIG. 2  is a flowchart illustrating operation of an electronic apparatus according to the first exemplary embodiment. 
           [0011]      FIG. 3  is a block diagram illustrating an electronic apparatus according to a second exemplary embodiment. 
           [0012]      FIG. 4  is a control flowchart illustrating operation of an electronic apparatus according to the second exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0013]    Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings. 
         [0014]      FIG. 1  is a block diagram illustrating an electronic apparatus according to a first exemplary embodiment of the present invention. The electronic apparatus is a recording apparatus which applies signals (scan signals) to a recording head to execute recording on a recoding medium. An integrated circuit  104  includes a driving circuit for driving a load (for example, motor). 
         [0015]    A power source  101  is an alternating current/direct current (AC/DC) power source. The power source  101  receives input from an AC power source  102 , thereby outputting a DC voltage  103 . A voltage (for example, 32 volts (V))  103  for use in motor driving or the like is output from the power source  101  and input via an input unit (first input unit)  10  of the integrated circuit  104 . The integrated circuit  104  includes an input unit (second input unit)  11  configured to input a voltage (5 volts) from a smoothing circuit  121  which will be described later. The integrated circuit  104  communicates with a CPU  113  using a signal line  122 . The CPU  113  controls operation of a recording apparatus. 
         [0016]    The integrated circuit  104  includes a regulator  106 , a controller  107 , a motor driver  108 , and a switching circuit  109 . The integrated circuit  104  further includes a switch  105 . The regulator (voltage conversion circuit)  106  decreases an input voltage to a predetermined voltage. The switch  105  selects an electric power source supplied to the regulator  106 . With the switch  105 , it is determined whether electric power is supplied from the input unit  10  or the input unit  11 . For example, when the integrated circuit  104  is started, electric power input from the input unit  10  is supplied to the regulator  106 . Then, once a predetermined condition is met, electric power input from the input unit  11  is supplied to the regulator  106 . 
         [0017]    The controller  107  operates at a voltage of 3.3 volts generated by the regulator  106 . The controller  107  controls the motor driver  108  and the switching circuit  109 . The controller  107  controls the motor driver  108  and the switching circuit  109  based on commands and data input from an input and output unit  17 . Further, the controller  107  outputs information concerning a state of an integrated circuit or the like from the input and output unit  17  to a CPU. A capacitor  110  is connected to an output of the regulator  106  via an external terminal for the purpose of stabilizing a voltage. 
         [0018]    The switching circuit  109  executes output of two systems. The switching circuit  109  has two outputs  13  and  14 . A switching element (for example, field effect transistor (FET)) within the switching circuit  109  is associated with each of these outputs. The IC controller  107  includes two control circuits, each of which controls one of the switching elements in the switching circuit  109 . The switching circuit  109  cooperates with the smoothing circuit  121  to generate two different power supply voltages (voltage pulse signals) Va and Vb. One of these power supply voltages Va is used to power the CPU  113  and other components (not shown) connected to a power supply line  114 . The CPU  113  and other components connected to the power supply line  114  can be considered to be a first system. The other of these power supply voltages Vb is used to power logic circuits  116  connected to another power supply line  115  and as the reduced power source voltage for the regulator  106  when the switch  105  is switched over by the CPU. The logic circuits  116  and other elements connected to the power supply line  115  can be considered a second system. 
         [0019]    The smoothing circuit  121 , including inductors ( 111 - a,    111 - b ) and capacitors ( 112 - a,    112 - b ), smoothes an output voltage of each output  13  and  14  to convert the voltage into a DC voltage of a desired voltage value. For example, a voltage (Va) of the power source line  114  is 1.6 volts and is supplied to the CPU  113 . Further, for example, a voltage (Vb) of the power source line  115  is 5 volts and is supplied to a logic circuit  116 . When, for example, an electronic apparatus is a recording apparatus, a voltage from the logic circuit  116  is supplied to an operational amplifier provided on a recording head. Further, a voltage of the power source line  115  is supplied to the switch  105  provided in the integrated circuit  104  via the input unit  11 . 
         [0020]    A voltage divided by resistances  117  and  118  is input as a monitoring signal to a port of the CPU  113  via a power source line  119 . After the CPU  113  is activated, the CPU  113  determines whether output  115  is normal (suitable for use as a power source for the regulator  106 ) based on a voltage level input to the port. In this embodiment the CPU  113  determines that the output  115  is normal or suitable when the input voltage level at the port connected to line  119  reaches a predetermined level but in other embodiments the determination could be based on stability of the output  115  or some other relevant criteria. Also, in this embodiment the suitability of the output  115  is judged by the CPU  113  indirectly, based on the monitoring signal on line  119 , which is possible because the output  119  is dependent on the output  115  as a result of the voltage divider formed by the resistances  117  and  118 . However, in other embodiments the suitability could be judged based on the output  115  directly. When the CPU  113  determines that the output  115  is normal, the CPU  113  outputs a control signal  120  for switching to the switch  105 . The integrated circuit  104  includes an input unit  12  configured to input the control signal  120 . Thus, the switch  105  switches an electric power supply line to the regulator  106  from the DC voltage  103  to the power source line  115 . 
         [0021]    The switch  105  can change an input voltage into the regulator  106  from 32 volts to 5 volts. Subsequently, the regulator  106  decreases a voltage of 5 volts. Control of a motor  122  is executed according to a command from the CPU  113 . 
         [0022]    In another exemplary embodiment, the CPU  113  may confirm a state of a voltage of the power source line  115  by confirming normal activation of the switching element  109 . Thus, the resistances  117  and  118  become unnecessary, and a port do not need to be allocated to the CPU  113 . Thus, a reduction in resistance element and allocation of a port to other applications can be achieved. 
         [0023]      FIG. 2  is a flowchart illustrating operation of an electronic apparatus according to the first exemplary embodiment. In step S 201 , the power source  101  outputs a direct current voltage of 32 volts. In step S 202 , the regulator  106  generates a voltage of 3.3 volts. In step S 203 , the controller  107  and the switching circuit  109  start operating. When the switching circuit  109  starts operation, a voltage is generated in the smoothing circuit  121 . In step S 204 , the CPU  113  receives the power supply voltage Va from the smoothing circuit  121  and is activated. After the CPU  113  is activated, the CPU  113  compares output  119  of the smoothing circuit  121  and a threshold voltage, thereby confirming that the switching circuit  109  and the smoothing circuit  121  are operating normally. After confirmation of the operation, in step S 205 , the CPU  113  outputs the control signal  120  to the integrated circuit  104 . In step S 206 , when the control signal  120  is input, the switch  105  is operated and the regulator  106  generates a voltage of 3.3 volts from a voltage of 5 volts. Subsequently, the regulator  106  continues to generate a voltage of 3.3 volts from a voltage of 5 volts. 
         [0024]    In the example described above, a relation between electric power and heat generation is as follows. Output of the power source  103  is 32 V (volts), a voltage generated in the smoothing circuit  121  and input to the integrated circuit  104  is 5 V (volts), and a voltage generated by the regulator is 3.3 V (volts). A heat resistance is 25° C./W with an integrated circuit mounted on a substrate and a logic current consumed when an integrated circuit is operated is 20 mA. Under the above-described conditions, a difference in loss caused by switching an input voltage from 32 V (volts) to 5 V (volts) is calculated as follows: 
         [0000]      (32 V−3.3 V)×20 mA −(5 V−3.3 V)×20 mA=0.54 W   (1) 
         [0000]      0.54 W×25° C./W=13.5° C.   (2) 
         [0000]    Under the above-described conditions, a reduction of about 13.5° C. in temperature of an integrated circuit can be realized. 
         [0025]      FIG. 3  is a block diagram illustrating an electronic apparatus according to a second exemplary embodiment of the present invention. Only points different from the first exemplary embodiment will be described. In the second exemplary embodiment, with respect to points similar to the first exemplary embodiments, descriptions will be omitted. In the first exemplary embodiment, the operation of a switch  305  has been executed based on a signal from the CPU  113  outside an integrated circuit. However, in the second exemplary embodiment, the operation of the switch  305  is executed by a switch controller  323 . The switch controller  323  receives the power supply it needs for its operation from a regulator  306 . 
         [0026]    In a switching circuit  309 , a DC voltage  303  is subjected to pulse control by a switching element and is output. This pulse is smoothed by a smoothing circuit including an inductor  311  and a capacitor  312 , and is converted into a DC voltage. This DC voltage is supplied to a CPU  313  via a power source line  314 . Further, this DC voltage is input from an input unit  31  to the switch  305  and the switch controller  323  in the integrated circuit  104 . 
         [0027]      FIG. 4  is a flowchart illustrating operation of an electronic apparatus according to the second exemplary embodiment. Since processing from step S 401  to step S 403  is similar to that in  FIG. 2  described in the first exemplary embodiment, their descriptions will be omitted. 
         [0028]    In step S 404 , the switch controller  323  is activated by receiving power supply from the smoothing circuit  321 . In step S 405 , the switch controller  323  outputs a control signal  320 . In step S 406 , the switch is operated by the control signal  320  and the regulator  306  generates a voltage of 3.3 volts from a voltage of 5 volts. 
         [0029]    Note that in the above-described exemplary embodiment, a driving circuit provided in an integrated circuit is not limited to that used for a motor. For example, a driving circuit for driving a recording head, a charge coupled device (CCD), a light emitting diode (LED) or the like as a load may be employed. 
         [0030]    In the above-described second exemplary embodiment, the switch controller  323  may be configured to check a voltage input from the input unit  31  using an upper limit voltage value, a lower limit voltage value, or both. When an input voltage is in an abnormal condition, the switch controller  323  may inform the CPU  313  of the abnormal condition. 
         [0031]    Further, in order to determine in advance whether the input unit  31  of an integrated circuit is connected to a ground, in step S 404 , the switch controller  323  may execute processing whether an electrical potential of the input unit  31  is 0 V. 
         [0032]    Further, in an exemplary embodiment, an integrated circuit includes one motor driver circuit. However, an integrated circuit may include a plurality of motor driver circuits. 
         [0033]    An embodiment of the present invention can provide an integrated circuit  104  including a driving circuit for driving a load with a DC voltage generated by a power source circuit and a voltage conversion circuit  106  for decreasing the DC voltage, the integrated circuit  104  comprising: a switching circuit  109  for generating a voltage pulse using the DC voltage; an output unit configured to output the voltage pulse generated by the switching circuit  109  to a smoothing circuit provided outside the integrated circuit  104 ; a first input unit configured to receive a first DC voltage generated by the power source circuit; a second input unit configured to receive a second DC voltage which is generated by the smoothing circuit and is lower than the first DC voltage; and a control circuit  107  configured to operate based on a voltage decreased by the voltage conversion circuit  106 , and control the switching circuit  109  and the driving circuit. 
         [0034]    The integrated circuit  104  may further comprise: a switch circuit configured to perform switching to supply a voltage input from the first input unit to the voltage conversion circuit  106  and supply a voltage input from the second input unit to the voltage conversion circuit  106  after the second DC voltage reaches a predetermined voltage value. 
         [0035]    In one embodiment the switch circuit executes the switching based on a signal output from a second control circuit  107  that is operated based on electric power supplied from the smoothing circuit. 
         [0036]    In one embodiment the load is a motor. 
         [0037]    In one embodiment the integrated circuit  104  is a semiconductor circuit of one chip. 
         [0038]    Another embodiment of the present invention can provide an electronic apparatus comprising: an integrated circuit  104  as described above. The electronic apparatus may be a recording apparatus. 
         [0039]    While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures, and functions. 
         [0040]    This application claims priority from Japanese Patent Application No. 2008-134320 filed May 22, 2008, which is hereby incorporated by reference herein in its entirety.