JP2005261019A - Apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus which can prevent a rush current by a simple circuit structure. <P>SOLUTION: The apparatus includes a DC/DC converter 12 having a duty control circuit 12_1 for converting an input DC power into an AC power of duty ratio according to controlling, and a load circuit 100 operating in response to the supply of the DC power from the DC/DC converter 12. A conversion to the AC power of the low maximum duty ratio is directed by a controller 14 rather than the maximum duty ratio after the predetermined time progress to the duty control circuit 12_1 after timing to which a switch 13 changes from off to on less than a predetermined time. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a device including a DC / DC converter and a load circuit that operates by receiving DC power supplied from the DC / DC converter.

  A DC / DC converter that converts input DC power into AC power, converts it into predetermined output DC power, and outputs it, and a load circuit that operates by receiving DC power supplied from the DC / DC converter. One is a digital camera. In this digital camera, DC power from a built-in battery is once converted into AC power by a DC / DC converter and converted into predetermined output DC power, and the output DC power is supplied to an internal circuit. It is done.

  Here, in order to extend the life of the built-in battery, a switch such as a transistor switch is provided between the DC / DC converter and the internal circuit, and power is supplied to only necessary circuit parts in advance. Accordingly, the output DC power from the DC / DC converter is supplied to an internal circuit other than the circuit portion by switching the switch from OFF to ON in accordance with a signal from the circuit portion. In general, an internal circuit is provided with a capacitor element having a relatively large capacity in order to stably supply power to the internal circuit. Is charged. Then, an inrush current flows through the DC / DC converter, and the output of the DC / DC converter temporarily decreases. In order to compensate for this, the DC / DC converter operates to increase the duty ratio of a PWM (Pulse Width Modulation) circuit that constitutes the DC / DC converter, and to quickly return the output voltage. At this time, the input voltage of the DC / DC converter temporarily decreases.

  Usually, the voltage on the input side of the DC / DC converter is monitored by the voltage monitoring unit, and the voltage monitoring unit determines that the power supply is abnormal when the voltage on the input side falls below a preset voltage. . Then, the problem that the system is stopped occurs.

  Here, several techniques for preventing inrush current have been proposed. For example, a current-limited first transistor and a second transistor with high driving capability are connected in parallel, and when the power switch is turned on, the first and second transistors are turned on and off to be limited by the first transistor. A technique has been proposed in which the first and second transistors are turned off and on when the difference in voltage between the input side and the output side becomes equal to or less than a predetermined value after a predetermined time has passed. Reference 1).

  In addition, a technology has been proposed in which the current flowing through the control FET is limited by a resistor inserted in series with a smoothing capacitor provided in front of the control FET, and the control FET is prevented from being destroyed by the discharge current of the smoothing capacitor. (See Patent Document 2).

Furthermore, a technique for suppressing a rush current by providing a current limit circuit between the switching transistor and the control circuit has been proposed (see Patent Document 3).
JP-A-10-135806 JP-A-10-117435 JP 2000-166218 A

  However, in the technique proposed in Patent Document 1 described above, it is necessary to provide two transistors for passing a current to the load side, and a circuit for detecting a voltage difference between the input side and the output side is also necessary. . Therefore, there is a problem that the circuit configuration is complicated.

  Although the technique proposed in Patent Document 2 can prevent the control FET from being destroyed by the discharge current of the smoothing capacitor, a switch is provided on the output side to switch from off to on and supply power to the load side. When such a configuration is adopted, there arises a problem that an inrush current flows.

  Further, the technique proposed in Patent Document 3 has a problem that the circuit configuration is complicated because a current limit circuit is provided between the switching transistor and the control circuit.

  An object of this invention is to provide the apparatus which can prevent an inrush current with a simple circuit structure in view of the said situation.

The first device of the present invention that achieves the above object includes a DC / DC converter that once converts input DC power into AC power, converts it into predetermined output DC power, and outputs the DC power, and the DC / DC converter. In a device provided with a load circuit that operates by receiving supply of DC power from
The DC / DC converter includes a DC / AC conversion circuit that converts input DC power into AC power having a duty ratio according to control,
A power switch for turning on and off the supply of DC power output from the DC / DC converter to the load circuit;
A controller that instructs the DC / AC converter circuit to convert the power switch to AC power having a maximum duty ratio lower than the maximum duty ratio after the predetermined time has elapsed within a predetermined time after the timing when the power switch changes from OFF to ON. It is characterized by comprising.

  The first device of the present invention is a DC / DC converter provided in a DC / DC converter, wherein the maximum duty ratio after the elapse of the predetermined time is within a predetermined time after the timing when the power switch changes from OFF to ON. Since the control unit instructs conversion to AC power having a lower maximum duty ratio, the output DC power from the DC / DC converter is small within a predetermined time after the timing when the power switch changes from OFF to ON. It can be suppressed. Therefore, the inrush current flows through the DC / DC converter, the input voltage of the DC / DC converter temporarily decreases, and the problem that the power supply is determined to be abnormal and the system stops is solved. In general, a DC / DC converter is often provided with a DC / AC conversion circuit, and the present invention is configured to instruct the conversion to such a DC / DC converter. As shown in FIG. 3, inrush current can be prevented with a simple circuit configuration.

The second device of the present invention that achieves the above object includes a DC / DC converter that once converts input DC power into AC power, converts the DC power into predetermined output DC power, and outputs the DC / DC converter. In a device including a load circuit that operates by receiving DC power supplied from a DC converter,
The DC / DC converter includes an output current limiting circuit that limits the output current to an output current equal to or less than the maximum output power according to the control,
A power switch for turning on and off the supply of DC power output from the DC / DC converter to the load circuit;
The output current limiting circuit includes a control unit that limits the output current to a maximum output current lower than a maximum output current within a predetermined time after the timing when the power switch changes from OFF to ON. Features.

  According to a second device of the present invention, the maximum output current after a predetermined time has elapsed within a predetermined time after the timing when the power switch changes from OFF to ON with respect to the output current limiting circuit provided in the DC / DC converter. Since the control unit limits the output current to a lower maximum output current, the output DC power from the DC / DC converter can be kept small within a predetermined time after the timing when the power switch changes from OFF to ON. Therefore, the inrush current flows through the DC / DC converter, the input voltage of the DC / DC converter temporarily decreases, and the problem that the power supply is determined to be abnormal and the system stops is solved. In general, the DC / DC converter is often provided with an output current limiting circuit, and the present invention is configured to perform the above limitation on such a DC / DC converter. As shown, an inrush current can be prevented with a simple circuit configuration.

  According to the device of the present invention, with a simple circuit configuration, the DC power output from the DC / DC converter is suppressed to be small and prevent an inrush current within a predetermined time after the timing when the power switch changes from OFF to ON. Can do.

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is an external perspective view of a digital camera, which is an embodiment of the first device of the present invention, seen from diagonally above the front.

  A zoom lens barrel 10_1 having a photographing lens 10_1a, which is an optical zoom lens, is provided at the center of the front surface of the digital camera 10 shown in FIG. In addition, on the front upper portion of the digital camera 10, a flash light emitting device 10_2 that emits flash light in synchronization with photographing and a light amount of the flash light are detected in order to control the light amount of the flash light from the flash light emitting device 10_2. A flash light control sensor 10_3 and an optical viewfinder objective window 10_4 are provided.

  Further, on the left side of the front surface of the digital camera 10, a slide-type power switch 10_5 is turned on when a battery built in the digital camera 10 is charged, when image data is transmitted, or when a self-timer is activated. Illumination lamp 10_6 that blinks is provided.

  Further, on the upper surface of the digital camera 10, a shutter button 10_7 and a microphone 10_8 for picking up sound are provided.

  Further, on the right side surface of the digital camera 10 shown in FIG. 1, a speaker 10_9, a USB terminal 10_10 to which a USB cable used when transmitting photographed image data to a personal computer or the like is connected, and an external power supply terminal 10_11.

  FIG. 2 is an external perspective view of the digital camera shown in FIG.

  An optical viewfinder eyepiece window 10_22, a viewfinder lamp 10_23 that is turned on when shooting preparation is completed or flashes during shooting, a still image mode, a playback mode, and a moving image shooting are provided on the upper back of the digital camera 10 shown in FIG. And a mode switch 10_24 for switching modes. Further, on the right side of the mode switch 10_24, a macro button 10_25, a zoom button 10_26, and a flash button 10_27 are provided.

  The macro button 10_25 is a button for switching whether or not to perform macro shooting. When the macro button 10_25 is pressed once, the macro shooting mode is set, and when pressed again, the macro shooting mode is canceled.

  The zoom button 10_26 is a button that zooms up to the telephoto side (tele side) by pressing down and zooms down to the wide angle side (wide side) by pressing down. The zoom button 10_26 is a button for selecting various menus displayed on the liquid crystal monitor 10_28 described later by simply pressing the zoom button 10_26.

  The flash button 10_27 is a button for repeatedly switching the flash state, such as auto flash → red-eye reduction flash → forced flash → flash prohibition → slow shutter flash → auto flash each time it is pressed.

  In addition, a liquid crystal monitor 10_28, a MENU / OK button 10_29, a BACK button 10_30, a DISP button 10_31, and a photo mode button 10_32 are provided at the center of the back of the digital camera 10.

  The liquid crystal monitor 28 displays an image composed of image data generated by capturing subject light with the digital camera 10, information at various settings, and the like.

  The MENU / OK button 10_29 is a button for displaying various menus at the time of shooting and playback and determining the menu selected by the zoom button 10_26.

  The BACK button 10_30 is a button for returning or canceling the operation state by the MENU / OK button 10_29 or the like.

  The DISP button 10_31 is a button for switching the state of the screen displayed on the liquid crystal monitor 10_28. For example, the display of the liquid crystal monitor 10_28 is turned on / off at the time of shooting, and the character display is turned on / off at the time of reproduction. It is a button.

  The photo mode button 10_32 is a button for setting the number of pixels, sensitivity, color, number of prints, and the like.

Further, a housing lid 10_33 for housing a battery and a memory card is provided at the lower back of the digital camera 10. Further, a strap attaching portion 10_34 is also provided on the side surface portion of the digital camera 10. FIG. 3 is a block diagram showing a circuit configuration of the digital camera shown in FIGS.

  The digital camera 10 includes the above-described photographing lens 10_1a and an image sensor 10_41 that converts a subject image formed through the photographing lens 10_1a into an analog image signal.

  The digital camera 10 also includes an analog signal processing unit 10_42 for analog processing of an analog image signal from the image sensor 10_41, and an analog image signal processed by the analog signal processing unit 10_42 as a digital image signal A. An A / D converter 10_43 that performs / D conversion and a digital signal processing unit 10_44 that digitally processes an image signal from the A / D converter 10_43 are provided.

  Further, the digital camera 10 includes a ROM 10_45 storing program data necessary for digital processing in the digital signal processing unit 10_44, a CPU 10_46 for exchanging with the digital signal processing unit 10_44, and exposure control and focusing control. AE / AF unit 10_47 for outputting the information for use to CPU 10_46, operation unit 10_48 including zoom button 10_26 described above, and shutter button 10_17 described above.

  Further, the digital camera 10 stores the image data from the digital signal processing unit 10_44 and outputs the stored image data to the digital signal processing unit 10_44, and the image from the digital signal processing unit 10_44. A memory card 10_50 for storing data, an I / F unit 10_51 for transmitting image data from the digital signal processing unit 10_44 to a personal computer or the like, and the above-described liquid crystal monitor 10_28 are provided.

  Further, the digital camera 10 includes a battery 11, a DC / DC converter 12, a switch 13 (corresponding to an example of a power switch in the present invention), and a control unit 14. Hereinafter, a description will be given with reference to FIG.

  FIG. 4 is a schematic configuration diagram of the DC / DC converter, the switch, and the control unit shown in FIG.

  The DC / DC converter 12 shown in FIG. 4 once converts input DC power from the battery 11 into AC power, converts it into predetermined output DC power, and outputs it. The DC / DC converter 12 includes a duty control circuit 12_1 for converting input DC power into AC power having a duty ratio according to control.

  The load circuit 100 includes a capacitor element 101 having a relatively large capacity mounted on a circuit board and an electric circuit 102 including a large number of electric components constituting the circuit shown in FIG. The load circuit 100 operates by receiving supply of DC power from the DC / DC converter 12.

  The switch 13 is a transistor switch that turns on / off the supply of the DC power output from the DC / DC converter 12 to the load circuit 100 in accordance with a signal from the control unit 14.

  The control unit 14 instructs the duty control circuit 12_1 to convert to AC power having a maximum duty ratio lower than the maximum duty ratio after the predetermined time has elapsed within a predetermined time after the timing when the switch 13 changes from OFF to ON. To do. Hereinafter, a description will be given with reference to FIG.

  FIG. 5 is a diagram showing a detailed configuration of the DC / DC converter shown in FIG. 4 together with a switch and a control unit.

  The DC / DC converter 12 shown in FIG. 5 includes input terminals 12a and 12b to which DC power from the battery 11 is input, output terminals 12c and 12d for outputting DC power to the load circuit 100, and control. And a control terminal 12e connected to the port terminal PA2 of the unit 14.

  The DC / DC converter 12 includes the above-described duty control circuit 12_1, and an inductor element 12_2 and a diode element 12_3 connected in series between the input terminal 12a and the output terminal 12c.

  Further, the DC / DC converter 12 includes a MOSFET 12_4 and a diode element 12_5 connected in parallel between the connection point of the inductor element 12_2 and the diode element 12_3 and the input terminal 12b, and between the duty control circuit 12_1 and the MOSFET 12_4. A connected resistance element 12_6 is provided.

  Further, the DC / DC converter 12 includes a comparator 12_7 whose positive phase input (+) side is connected to the control terminal 12e, and a first reference voltage connected to the negative phase input (−) side of the comparator 12_7. Is provided with a reference power supply VREF12_8. The output side of the comparator 12_7 is connected to the first input side of the duty control circuit 12_1.

  Further, the DC / DC converter 12 has resistance elements 12_9 and 12_10 connected in series between the output terminal 12c and the output terminal 12d, and a positive-phase input (+) side at the connection point of the resistance elements 12_9 and 12_10. A connected comparator 12_11 and a reference power supply VREF12_12 connected to the negative phase input (−) side of the comparator 12_11 and outputting a second reference voltage are provided. The output side of the comparator 12_11 is connected to the second input side of the duty control circuit 12_1. The duty control circuit 12_1, the inductor element 12_2, the MOSFET 12_4, the diode element 12_5, and the resistance element 12_6 constitute an example of a DC / AC conversion circuit according to the present invention.

  The switch 13 is ON / OFF controlled by a first control signal output from the port terminal PA1 of the control unit 14.

  Next, operations of the DC / DC converter, the switch, and the control unit will be described with reference to FIGS. 5 and 6.

  FIG. 6 is a flowchart of an operation processing routine of the DC / DC converter, the switch, and the control unit shown in FIG.

  In step S1, the DC / DC converter 12 is activated. The first and second control signals output from the port terminals PA1 and PA2 of the control unit 14 are both at the 'L' level. Accordingly, the switch 13 is in an off state. Further, since the positive phase input (+) side of the comparator 12_7 is at the ‘L’ level, the ‘L’ level signal is output from the comparator 12_7. This 'L' level signal is input to the first input side of the duty control circuit 12_1. Here, when an 'L' level signal is input to the first input side of the duty control circuit 12_1, the duty control circuit according to the level input to the second input side of the duty control circuit 12_1. The duty ratio of 12_1 is controlled. On the other hand, when the “H” level signal is input to the first input side of the duty control circuit 12_1, the “H” level signal is output regardless of the level of the second input side of the duty control circuit 12_1. Is prioritized and is controlled to operate at a low duty ratio as will be described later.

  Next, in step S2, current control by duty control is performed. Specifically, the DC / DC converter 12 performs DC / AC conversion by switching the MOSFET 12_4 with a pulse signal having a predetermined duty ratio from the duty control circuit 12_1, and outputs DC power via the diode element 12_3. 12c is output. The comparator 12_11 compares the voltage determined by the resistance values of both the resistance elements 12_9 and 12_10 with the first reference voltage from the reference power supply VREF12_12, and inputs the comparison result to the second input side of the duty control circuit 12_1. To do. The duty control circuit 12_1 controls the duty ratio so that predetermined DC power is output based on the comparison result.

  Next, in step S3, the control unit 14 determines whether or not a predetermined period has elapsed. If it is determined that the predetermined period has not elapsed, the process returns to step S2. On the other hand, if it is determined that the predetermined period has elapsed, the process proceeds to step S4.

  In step S4, since the predetermined period has elapsed, the output voltage from the DC / DC converter 12 is stable.

  Next, in step S5, the control unit 14 turns on the switch 13. Specifically, the control unit 14 switches the first control signal output from the port terminal PA1 from the ‘L’ level to the ‘H’ level. Then, the switch 13 is turned on. Thereby, the DC power output from the DC / DC converter 12 is supplied to the load circuit 100.

  Further, in step S <b> 6, the control unit 14 performs output current control of the DC / DC converter 12. Specifically, the control unit 14 switches the second control signal output from the port terminal PA2 from the ‘L’ level to the ‘H’ level. The second control signal of “H” level is input to the positive phase input (+) side of the comparator 12_7. On the other hand, the first reference voltage having a level lower than the 'H' level is input from the reference power supply VREF12_8 to the negative phase input (−) side of the comparator 12_7. Therefore, the comparator 12_7 outputs an “H” level signal. This 'H' level signal is input to the first input side of the duty control circuit 12_1.

  Then, the duty control circuit 12_1 performs DC / AC conversion by switching the MOSFET 12_4 with a pulse signal having a maximum duty ratio lower than the maximum duty ratio after the predetermined time has elapsed, and outputs DC power via the diode element 12_3. Output from terminal 12c. This DC power is supplied to the load circuit 100 via the switch 13. In this way, the output DC power from the DC / DC converter 12 is kept small. Therefore, inrush current flows through the DC / DC converter 12 to charge the capacitor element 101 constituting the load circuit 100, and the input voltage of the DC / DC converter 12 is temporarily reduced, so that the power supply is determined to be abnormal. The problem of the system being stopped is solved.

  Further, in step S7, it is determined whether or not a predetermined period has elapsed. If it is determined that the predetermined period has not elapsed, the process returns to step S6. On the other hand, if it is determined that the predetermined period has elapsed, the process proceeds to step S8.

  In step S8, the output voltage stabilization operation (normal operation start) of the DC / DC converter 12 is performed. Specifically, the control unit 14 switches the second control signal output from the port terminal PA2 from the “H” level to the “L” level. As a result, an 'L' level signal is output from the comparator 12_7, and this 'L' level signal is input to the first input side of the duty control circuit 12_1. Then, the duty control circuit 12_1 performs duty ratio control by the comparator 12_11 and ends this routine.

  Here, the DC / DC converter 12 only needs to be added with a comparator 12_7 and a reference power supply VREF12_8 in addition to the functions provided in the normal DC / DC converter, and the control unit 14 is also connected to the port terminals PA1 and PA2. The first and second control signals described above may be output, and thus an inrush current can be prevented with a simple circuit configuration.

  Next, a digital camera which is an embodiment of the second device of the present invention will be described. The external perspective view of this digital camera is the same as the external perspective view of the digital camera shown in FIGS. The circuit configuration of this digital camera is different from that of the digital camera shown in FIG. 3 in the DC / DC converter and the control unit.

  FIG. 7 is a schematic configuration diagram of a DC / DC converter, a switch, and a control unit constituting a digital camera which is an embodiment of the second device of the present invention.

  The DC / DC converter 112 illustrated in FIG. 7 includes an output current limiting circuit 112_1 that limits the output current to an output current that is equal to or lower than the maximum output power according to the control.

  The control unit 114 causes the output current limiting circuit 112_1 to limit the output current to a maximum output current lower than the maximum output current after the predetermined time has elapsed within a predetermined time after the timing when the switch 13 changes from OFF to ON.

  FIG. 8 is a diagram showing a detailed configuration of the DC / DC converter shown in FIG. 7 together with a switch and a control unit.

  The DC / DC converter 112 shown in FIG. 8 includes input terminals 12a and 12b to which DC power from the battery 11 is input, output terminals 12c and 12d for outputting DC power to the load circuit 100, and control. And a control terminal 12e to which a second control signal output from the port terminal PA2 of the unit 114 is input.

  The DC / DC converter 112 includes the above-described duty control circuit 12_1, inductor element 12_2, diode element 12_3, MOSFET 12_4, diode element 12_5, and resistance element 12_6.

  Further, the DC / DC converter 112 is provided with an output current limiting circuit 112_1. The output current limiting circuit 112_1 includes a transistor 112_1a disposed between the diode element 12_3 and the output terminal 12c, a resistance element 112_1b having one end connected to the base of the transistor 112_1a, and an output OUT having the other end of the resistance element 112_1b. Output current limiter 112_1c connected to the output terminal 12c, and resistor elements 112_1d and 112_1e connected in series between the output terminals 12c and 12d. The first input IN1 of the output current limiting unit 112_1c is connected to the connection point of the resistance elements 112_1d and 112_1e, and the second input IN2 is connected to the control terminal 12e.

  Next, operations of the DC / DC converter, the switch, and the control unit will be described with reference to FIGS.

  FIG. 9 is a flowchart of an operation processing routine of the DC / DC converter, the switch, and the control unit shown in FIG.

  In step S11, the DC / DC converter 112 is activated. The first and second control signals output from the port terminals PA1 and PA2 of the control unit 114 are both at the 'L' level. Accordingly, the switch 13 is in an off state. Further, the second input IN2 of the output current limiting unit 112_1c is at the 'L' level. Here, when an 'L' level signal signal is input to the second input IN2, the output current of the output current limiting unit 112_1c is limited according to the voltage level input to the first input IN1. The On the other hand, when a 'H' level signal is input to the second input IN2, the output current is limited to a low output current as described later regardless of the voltage level input to the first input IN1.

  Next, in step S12, current control by duty control is performed. Specifically, the DC / DC converter 112 performs DC / AC conversion by switching the MOSFET 12_4 with a pulse signal having a predetermined duty ratio from the duty control circuit 12_1 and outputs DC power via the diode element 12_3. 12c is output.

  The output current limiting unit 112_1c outputs a predetermined DC power by outputting from the output OUT a voltage corresponding to the voltage determined by the resistance values of both the resistance elements 112_1d and 112_1e, which is input to the first input IN1. Thus, the current flowing through the transistor 112_1a is limited.

  Next, in step S13, the control unit 114 determines whether or not a predetermined period has elapsed. If it is determined that the predetermined period has not elapsed, the process returns to step S12. On the other hand, if it is determined that the predetermined period has elapsed, the process proceeds to step S14.

  In step S14, since the predetermined period has elapsed, the output voltage from the DC / DC converter 112 is stable.

  Next, in step S15, the control unit 114 turns on the switch 13. Specifically, the control unit 114 switches the first control signal output from the port terminal PA1 from the ‘L’ level to the ‘H’ level, and turns on the switch 13. As a result, the DC power output from the DC / DC converter 112 is supplied to the load circuit 100.

  Further, in step S <b> 16, control unit 114 performs output current limitation of DC / DC converter 112. Specifically, the control unit 114 switches the second control signal output from the port terminal PA2 from the ‘L’ level to the ‘H’ level. The second control signal is input to the second input IN2 of the output current limiting unit 112_1c. Then, the output current limiting unit 112_1c flows from the output OUT to the transistor 112_1a so that predetermined DC power is output by outputting a voltage according to the second control signal input to the second input IN2. Limit current. As a result, the output DC power from the DC / DC converter 112 is kept small. Therefore, inrush current flows to the DC / DC converter 12 to charge the capacitor element 101 constituting the load circuit 100, and the input voltage of the DC / DC converter 112 is temporarily reduced, and it is determined that the power supply is abnormal. The problem of the system being stopped is solved.

  Further, in step S17, it is determined whether or not a predetermined period has elapsed. If it is determined that the predetermined period has not elapsed, the process returns to step S16. On the other hand, if it is determined that the predetermined period has elapsed, the process proceeds to step S18.

  In step S18, the output voltage stabilization operation (normal operation start) of the DC / DC converter 112 is performed. Specifically, the control unit 114 switches the second control signal output from the port terminal PA2 from the “H” level to the “L” level. The output current limiting unit 112_1c limits the current flowing through the transistor 112_1a according to the voltage input to the first input IN1, and ends this routine.

  As described above, in the DC / DC converter 112, the second input IN for inputting the second control signal from the control unit 114 to the function of the output current limiting circuit provided in the normal DC / DC converter. The controller 114 may also be configured to output the first and second control signals described above from the port terminals PA1 and PA2, so that an inrush current can be prevented with a simple circuit configuration. .

  In the present embodiment, a digital camera has been described as an example of the device of the present invention. However, the device of the present invention is not limited to this. It may be a portable device or the like.

It is the external appearance perspective view which looked at the digital camera which is one Embodiment of the 1st apparatus of this invention from the front diagonally upward. It is the external appearance perspective view which looked at the digital camera shown in FIG. 1 from back diagonally upward. FIG. 3 is a block diagram showing a circuit configuration of the digital camera shown in FIGS. 1 and 2. It is a schematic block diagram of the DC / DC converter, switch, and control part which are shown in FIG. It is the figure which showed the detailed structure of the DC / DC converter shown in FIG. 4 with the switch and the control part. 6 is a flowchart of an operation processing routine of a DC / DC converter, a switch, and a control unit shown in FIG. 5. It is a schematic block diagram of the DC / DC converter, switch, and control part which comprise the digital camera which is one Embodiment of the 2nd apparatus of this invention. It is the figure which showed the detailed structure of the DC / DC converter shown in FIG. 7 with the switch and the control part. It is a flowchart of the operation processing routine of the DC / DC converter, switch, and control part shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Digital camera 10_1a Shooting lens 10_1 Zoom lens barrel 10_2 Flash light emitting device 10_3 Flash dimming sensor 10_4 Optical viewfinder objective window 10_5 Power switch 10_6 Illumination lamp 10_7 Shutter button 10_8 Microphone 10_9 Speaker 10_10 USB terminal 10_11 External power terminal 10_22 Window 10_23 Finder lamp 10_24 Mode switch 10_25 Macro button 10_26 Zoom button 10_27 Flash button 10_28 Liquid crystal monitor 10_29 MENU / OK button 10_30 BACK button 10_31 DISP button 10_32 Photo mode button 10_33 Storage lid 10_34 Strap mount 10_41 _42 analog signal processing section 10_43 A / D converter 10_44 digital signal processor 10_45 ROM
10_46 CPU
10_47 AE / AF section 10_48 operation section 10_49 memory 10_50 memory card 10_51 I / F section 11 battery 12, 112 DC / DC converter 12a, 12b input terminal 12c, 12d output terminal 12e control terminal 12_1 duty control circuit 12_2 inductor element 12_3, 12_5 Diode element 12_4 MOSFET
12_6, 12_9, 12_10, 112_1b, 112_1d, 112_1e Resistance element 12_7, 12_11 Comparator 12_8, 12_12 Reference power supply VREF
13 Switch 14, 114 Control unit 100 Load circuit 101 Capacitor element 102 Electric circuit 112_1 Output current limiting circuit 112_1a Transistor 112_1c Output current limiting unit

Claims (2)

In a device including a DC / DC converter that converts input DC power into AC power, converts the DC power into predetermined output DC power, and outputs the DC power, and a load circuit that operates by receiving DC power supplied from the DC / DC converter ,
The DC / DC converter includes a DC / AC conversion circuit that converts input DC power into AC power having a duty ratio according to control,
A power switch for turning on / off the supply of DC power output from the DC / DC converter to the load circuit;
A control unit that instructs the DC / AC converter circuit to convert to AC power having a maximum duty ratio lower than the maximum duty ratio after the predetermined time has elapsed within a predetermined time after the timing when the power switch changes from OFF to ON. A device characterized by comprising In a device including a DC / DC converter that converts input DC power into AC power, converts the DC power into predetermined output DC power, and outputs the DC power, and a load circuit that operates by receiving DC power supplied from the DC / DC converter ,
The DC / DC converter includes an output current limiting circuit that limits the output current to an output current equal to or lower than the maximum output power according to control,
A power switch for turning on / off the supply of DC power output from the DC / DC converter to the load circuit;
The output current limiting circuit includes a control unit that limits the output current to a maximum output current lower than the maximum output current after the predetermined time has elapsed within a predetermined time after the timing when the power switch changes from OFF to ON. Features equipment.

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