JP2007221981A - Power supply and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply for saving power by maintaining voltage conversion efficiency to be high in a DC voltage conversion circuit even if a load current changes. <P>SOLUTION: The power supply has the DC voltage conversion circuit 1. In the DC voltage conversion circuit, a variable inductor 10 having a changeable inductance value is connected to a prescribed DC power supply 43, a back electromotive voltage is generated in the variable inductor 10, and the voltage of the DC power supply 43 is converted to a prescribed DC conversion voltage and supplied to a loading device 7. The power supply comprises: an inductor control section 39 for changing an inductance value of the variable inductor 10 corresponding to operation information supplied from the loading device 7; a load current storage section 8b for storing a load current value changing according to the operation of the loading device 7; and a conversion efficiency storage section 8a for storing the inductance value of the variable inductor 10 where the power conversion efficiency in the DC voltage conversion circuit 1 corresponding to the load current value is maximized. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power supply apparatus having a DC voltage conversion circuit that converts a DC power supply into a DC load voltage corresponding to the load apparatus and supplies the DC load voltage to the load apparatus, and a control method thereof.

  In a portable electronic device, a voltage of a battery provided in the electronic device is increased or decreased to be converted into a desired voltage value and supplied to each part of the electronic device (DC: Direct Current). ) Is commonly used. The DC / DC converter is a power supply circuit that converts a DC voltage, and has a characteristic that the power conversion efficiency changes when the current flowing through the load device connected to the circuit changes.

  Patent Document 1 describes a power supply circuit that increases the voltage conversion efficiency by detecting the current of a load device and switching an inductor provided in the DC / DC converter according to the detected current value. .

  In Patent Document 2, the operation of a digital camera is divided into two modes, a high power mode and a power saving mode, and the voltage conversion efficiency of the DC / DC converter is further increased by switching the voltage conversion circuit according to the mode. A power supply circuit for switching to a mode is described.

JP 2005-137172 A JP 2004-343909 A

  However, in the power supply circuit described in Patent Document 1, since the inductor is switched in accordance with the detected current value, the operation with the optimum conversion efficiency is limited after the switching of the inductor. That is, high conversion efficiency cannot be realized in a transient state from when a change in current value is detected until inductor switching. In the power supply circuit described in Patent Document 2, only two types of conversion efficiencies can be selected because it depends on the operation of the synchronous rectifier circuit in the power supply circuit.

  The present invention has been proposed in view of such circumstances, and a power supply device that realizes power saving by maintaining a high voltage conversion efficiency of a DC voltage conversion circuit even when a load current changes. And it aims at providing the control method.

  In order to solve the above-described problems, a power supply device according to the present invention is configured such that a variable inductor whose inductance value can be changed is connected to a predetermined DC power source, and a back electromotive force is generated in the variable inductor, A DC voltage conversion circuit that converts a voltage into a predetermined DC conversion voltage and supplies the voltage to a predetermined load device is provided. The power supply device stores an inductor control unit that changes an inductance value of the variable inductor according to operation information supplied from the load device, and a load current value that changes according to the operation of the load device. A load current storage unit, and a conversion efficiency storage unit in which an inductance value of the variable inductor that maximizes the power conversion efficiency of the DC voltage conversion circuit according to the load current value is stored, and the inductor control The unit reads the load current value from the load current storage unit according to the operation information supplied from the load device, and sets the power conversion efficiency according to the load current value read from the load current storage unit. The highest inductance value is read from the conversion efficiency storage unit, and the variable inductor is read from the conversion efficiency storage unit. Set to the chest of drawers value.

  In the power supply device control method according to the present invention, a variable inductor whose inductance value can be changed is connected to a predetermined DC power supply, a back electromotive force is generated in the variable inductor, and the voltage of the DC power supply is set to a predetermined value. This is a control method for a power supply device having a DC voltage conversion circuit that converts the voltage into a DC conversion voltage and supplies the voltage to a predetermined load device. Further, the power supply device reads the load current value according to the operation of the load device from a storage medium storing a load current value that changes according to the operation of the load device according to the control method, From the storage medium storing the inductance value of the variable inductor that maximizes the power conversion efficiency of the DC voltage conversion circuit according to the load current value, the power conversion efficiency is changed according to the read load current value. The highest inductance value is read, and the variable inductor is set to the read inductance value.

  The present invention prestores a storage medium in which a load current value that changes according to the operation of the load device is stored in advance, and an inductance value that maximizes the power conversion efficiency of the DC voltage conversion circuit in accordance with the load current value. In accordance with the information stored in the storage medium, the inductance value of the variable inductor is set so as to maximize the conversion efficiency.

  Thus, according to the present invention, even when the load current changes, the power conversion efficiency of the DC voltage conversion circuit can be made to an optimum value faster. Therefore, according to the present invention, since the time during which the DC voltage conversion circuit operates with high conversion efficiency increases, the DC voltage conversion circuit can be operated with power saving.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings.

  First, the configuration of the digital camera 100 that is the load device of the present embodiment will be described in detail with reference to FIG.

  The digital camera 100 includes an optical unit 30 including an optical lens that generates a captured image from a subject, and a charge coupled device (hereinafter referred to as “CCD”) 31 that converts the captured image generated by the optical unit 30 into an analog signal. And an analog signal processing unit 32 that performs predetermined signal processing on the analog signal converted by the CCD 31.

  In addition, the digital camera 100 includes an analog / digital converter (hereinafter referred to as “ADC”) 33 that converts an analog signal subjected to signal processing by the analog signal processing unit 32 into digital data, and a digital signal converted by the ADC 33. And a digital signal processing unit 34 that performs predetermined data processing on the data. The digital signal processing unit 34 includes a buffer having a predetermined storage capacity, and also performs control for directly storing digital data in a storage area of a memory 48 described later.

  The digital camera 100 also generates an LCD interface 49 that generates a display signal for displaying an object, a setting operation screen, and the like on the LCD 15 and supplies the display signal to the LCD 15, and a CPU (central processing unit) 39 that controls operations performed by each processing unit. The memory 48 stores a captured image converted into digital data and the like, and a memory interface 47 that controls writing processing and reading processing of stored data in the memory 48.

  The digital camera 100 also includes an external memory interface 45 that performs writing and reading processing with reference to the storage area of the portable memory card 44, and compression processing and decompression processing on the digital data generated by the digital signal processing unit 34. And a compression / decompression processing circuit 46 for performing the above.

  Here, the digital signal processing unit 34, the LCD interface 49, the memory interface 47, the external memory interface 45, and the compression / decompression processing circuit 46 are connected to each other via a BUS 39a provided in the CPU 39. Therefore, the CPU 39 supplies a control command to each unit described above via the BUS 39a to perform a predetermined process.

  In addition, the digital camera 100 includes a timing generator 36 that mainly generates a timing signal for driving the CCD 31 and supplies the timing signal to the CCD 31. The timing generator 36 is connected to the CPU 39 via the BUS 39a, and drives the CCD 31 in accordance with a control command supplied from the CPU 39.

  The digital camera 100 also includes a focus adjustment motor (not shown) provided in the optical unit 20, a zoom motor that enlarges and reduces the subject, and a motor drive unit 35 that drives a diaphragm drive motor that adjusts the amount of light. ing. The motor driving unit 35 is connected to the CPU 39 via the BUS 39a, and drives each of the motors provided in the optical unit 20 in accordance with a control command supplied from the CPU 39.

  In addition, the digital camera 100 includes an operation unit 40 including a plurality of operation buttons for operating the camera. The operation unit 40 is connected to the CPU 39, and supplies operation information to the CPU 39 when a user operates an operation button constituting the operation unit 40. Specifically, the user uses a plurality of operation buttons constituting the operation unit 40 to start the digital camera 100, to switch between the shooting mode and the image reproduction mode, and to enlarge / reduce / focus the subject in the imaging mode. Adjustment / imaging and image data writing to the external memory interface 45 are performed.

  In addition, the digital camera 100 includes a charging unit 38 that is connected to the strobe 37 and the CPU 39 and temporarily charges the power for causing the strobe 37 to emit light according to a control command supplied from the CPU 39. The strobe 37 is connected to the CPU 39 and emits light according to a control command supplied from the CPU 39.

  The digital camera 100 can be loaded with a battery 43 and includes a power supply circuit 41 that supplies power from the battery 43 loaded in the camera to each of the above-described units. The power supply circuit 41 can also be connected to an AC adapter 42 and converts the AC adapter 42 into a DC voltage. Further, the power supply circuit 41 is connected to the CPU 39 and includes a charging circuit that charges the battery 43 with the power supplied from the AC adapter 42 in accordance with a control command supplied from the CPU 39.

  Here, the power supply circuit 41 includes a DC / DC converter 1 that converts a voltage value of a DC voltage of a DC power supply supplied from the battery 43. As described above, the power supply circuit 41 is composed of various electronic circuits such as a charging circuit. The power supply circuit 41 will be described in detail with a focus on the configuration and operation of the DC / DC converter 1 that is the DC voltage conversion circuit of the present embodiment. .

  As shown in FIG. 2, the DC / DC converter 1 is an electric circuit that converts a DC power supply voltage into a DC load voltage that is an operating voltage of each part of the digital camera 100 (hereinafter referred to as a load 7). The DC / DC converter 1 includes a variable inductor unit 10 composed of a plurality of inductor elements, an FET 5 that changes a current flowing through the variable inductance unit 10 by a switching operation, and a switching control unit 4 that controls the switching operation of the FET 5. And a diode 6 for rectifying a load current supplied to the load 7 and a capacitor 9 for smoothing the DC load voltage. The DC / DC converter 1 is controlled by the CPU 39.

  One terminal of the battery 43 is grounded, and the other terminal is connected to the variable inductor section 10 and the switching control section 4 via the branch A.

  The variable inductor unit 10 has one terminal connected to the battery 43 and the other terminal connected to the FET 5 and the diode 6 via the branch B, respectively.

  The variable inductor unit 10 is connected in parallel with a plurality of inductor elements 10a, 10b, and 10c having different inductance values. In addition, selector switches 2a, 2b, and 2c and selector switches 3a, 3b, and 3c are provided at both ends of the inductor elements 10a, 10b, and 10c, respectively. The changeover switches 2 and 3 are formed of switching elements having a relatively low switching resistance, such as MOS-FETs. Furthermore, the change-over switches 2 and 3 are connected to the CPU 39, respectively, and perform a switching operation in accordance with a control signal from the CPU 39. As described above, in the variable inductor unit 10, any one of the inductors 10 a, 10 b, and 10 c is switched according to the control command supplied from the CPU 39, thereby operating as an inductor whose inductance value can be changed in the entire DC / DC converter 1. To do. Note that the variable inductor unit 10 is not limited to three inductor elements, but may be switched between a plurality of other inductor elements.

  For example, a MOS-FET is used as the FET 5, and the variable inductor unit 10 is connected to the drain. The source of the FET 5 is grounded. Further, the switching control unit 4 is connected to the gate of the FET 5.

  The switching control unit 4 generates a switching control voltage signal from the DC voltage supplied from the battery 43 and supplies the switching control voltage signal to the FET 5 to perform ON / OFF control of the FET 5. Specifically, for the switching control voltage signal, a pulse signal, a PWM signal, or the like is used for switching ON / OFF of the FET at predetermined time intervals.

  The diode 6 has an anode side connected to the variable inductor unit 10 and a cathode side connected to the load 7 and the capacitor 9 via the branch C.

  The capacitor 9 has one terminal connected to the cathode side of the diode and the other terminal grounded. That is, the capacitor 9 is connected in parallel with the load 7.

  Next, the voltage conversion operation in the DC / DC converter 1 will be described. First, when the switching control voltage signal is supplied from the switching control unit 4 and the switch of the FET 5 is turned on, the DC / DC converter 1 is switched to (battery 43) → (variable inductor unit 10) → (FET 5) → (ground). A current flows in the loop (No current flows to the diode 6 here). Subsequently, when the switching control voltage signal is supplied from the switching control unit 4 and the switch of the FET 5 is turned off, in the DC / DC converter 1, the current flowing through the variable inductor unit 10 changes to generate a back electromotive force and branch. As the voltage A increases, current flows to the cathode side of the diode 6 and is smoothed by the capacitor 9. Thereafter, the DC / DC converter 1 supplies the load 7 with the DC load voltage converted to a voltage value higher than the DC power supply voltage by repeating the ON / OFF operation by the FET 5.

  The DC / DC converter 1 may be further controlled with a constant voltage for stabilizing the voltage value of the DC load voltage by adding a plurality of operational amplifiers to the above-described configuration.

  Here, the portion of the load 7 that operates in the digital camera 100 differs according to a user operation supplied from the operation unit 40. Therefore, the load current flowing through the load 7 changes depending on the operation of the digital camera 100. For example, when the release button is pressed halfway to perform automatic focusing, a current of 30 mA flows, and the zoom operation for enlarging / reducing the subject is performed. Is changed by an operation input from the operation unit 40, for example, a current of 200 mA flows. Furthermore, when the load current changes, the DC / DC converter 1 changes the conversion efficiency for converting the DC power supply voltage to the DC load voltage.

  Therefore, the CPU 39 performs switching control to change the inductance value by switching the inductor 3 in the variable inductor section 10 in order to perform control to maintain the voltage conversion efficiency in the DC / DC converter 1 in a higher state. Therefore, the CPU 39 is provided with a control information storage unit 8 in which information for performing switching control of the variable inductor unit 10 is stored. The CPU 39 is connected to the battery 43 and detects a voltage value supplied from the battery 43 to the DC / DC converter 1.

  A predetermined arithmetic processor may be provided in the power supply circuit 41 so that the arithmetic processor performs switching control of the changeover switches 2 and 3 of the variable inductor unit 10 in place of the CPU 39. In particular, when a processor having a power saving characteristic better than that of the CPU 39 is used, power saving can be achieved in a standby state where no operation command is supplied from the operation unit 40.

  The control information storage unit 8 is a writable and readable storage medium provided in the CPU 39, and includes a conversion efficiency storage unit 8a and a load current storage unit 8b. The control information stored in these two storage units is stored in the control information storage unit 8. It supplies to CPU39.

  The conversion efficiency storage unit 8 a stores a value of the voltage conversion efficiency of the DC / DC converter 1 that changes in accordance with the load current value and the inductance value of the variable inductor unit 10. Here, a method for measuring the voltage conversion efficiency will be described. First, instead of the battery 43, a DC power supply device whose voltage value can be changed is connected to the DC / DC converter 1 to change the supply voltage. Furthermore, instead of the load 7, a predetermined variable resistance element is connected to the DC / DC converter 1, and the value of the load current is changed by changing the resistance value. Thus, in the DC / DC converter 1, the power conversion efficiency is measured by changing the direct-current power supply voltage and the load current, respectively. This measurement process is performed by switching the inductor elements 10a to 10b of the variable inductor unit 10, and the measurement result is stored in the conversion efficiency storage unit 8a.

  The load current storage unit 8b stores a change in the load current value flowing through the load 7 that changes according to the operation mode of the digital camera 100. Here, the change in the load current value is measured by the ammeter by measuring the current value of the load 7 when the operation unit 40 is actually operated to operate the camera, and is stored in the load current storage unit 8b. This ammeter is used only at the time of manufacture, and is assumed to be inserted between the branch C in the DC / DC converter 1 and the load 7 for current measurement.

  It should be noted that the current consumption is measured for each part such as a processing board and a motor constituting the digital camera 100, the load current value for each operation is calculated by combining the current consumption values for each part, and the load current storage part 8b. You may make it memorize.

  Next, the process of generating control information stored in the control information storage unit 8 will be described in detail with reference to FIG.

  In step S1, a voltage of 3.0 V is supplied to the DC / DC converter 1 from the direct current power supply device, and the load current is changed by a variable resistor to measure the power conversion efficiency. Specifically, the conversion efficiency characteristic A is obtained by switching the inductors 10a, 10b, and 10c of the variable inductor section 10 and measuring the voltage conversion efficiency. As shown in FIG. 4A, the conversion efficiency characteristic A indicates the voltage conversion efficiency corresponding to the load current for each of the inductances 10a, 10b, and 10c, and the information is stored in the conversion efficiency storage unit 8a. Remembered.

  In step S2, a voltage of 3.6V is supplied to the DC / DC converter 1 from the direct current power source, and the voltage conversion efficiency is measured in the same manner as in step S1 to obtain the conversion efficiency characteristic B shown in FIG. Each value written in the conversion efficiency characteristic B is stored in the conversion efficiency storage unit 8a.

  In step S3, a voltage of 4.2 V is supplied to the DC / DC converter 1 from the direct current power source, and the voltage conversion efficiency is measured in the same manner as in step S1 to obtain the conversion efficiency characteristic C shown in FIG. Each value written in the conversion efficiency characteristic C is stored in the conversion efficiency storage unit 8a.

  In step S4, a load current value that changes according to various operations of the digital camera 100 is measured, and a load current characteristic D is obtained. As shown in FIG. 5, the load current characteristic D describes the load current of the digital camera 100 corresponding to various operation modes of the digital camera 100, and these pieces of information are stored in the load current storage unit 8b.

  Next, switching control processing of the variable inductor unit 10 according to the operation of the digital camera 100 will be described in detail with reference to FIG.

  First, in the initial stage of this processing step, the operation unit 40 is operated by the user, and one operation is selected from various operation modes. For example, assuming that a zoom operation for enlarging / reducing a subject from the operation unit 40 is supplied to the CPU 39 as an operation command by the user, the following switching control process is started.

  In step S11, the CPU 39 is supplied with an operation command from the operation unit 40, and determines the operation mode to be a zoom operation.

  In step S12, the CPU 39 reads the load current value corresponding to the zoom operation with reference to the load current characteristic D from the control information storage unit 8. Specifically, when referring to FIG. 5, 400 mA, which is a load current value corresponding to the zoom operation, is read out.

  In step S <b> 13, the CPU 39 detects the DC power supply voltage supplied from the battery 43 to the DC / DC converter 1.

  In step S14, the CPU 39 selects one of the three conversion efficiency characteristics A to C as the conversion efficiency characteristic having the closest voltage value to the detected DC power supply voltage of the battery 43, and selects a control information storage unit. Read from 8. For example, when the DC power supply voltage is detected at 4.0 V in step S13, the conversion efficiency characteristic C is read out.

  In step S15, the CPU 39 sets the inductor elements 3a to 3c to be connected in the variable inductor unit 8 so that the conversion efficiency becomes the highest based on the load current value read in step S13 and the conversion efficiency characteristic selected in step S14. decide. For example, when the load current value 400 mA is read in step S12 and the conversion efficiency characteristic C is read in step S14, the inductor element C is determined according to FIG.

  In step S <b> 16, the CPU 39 supplies a control signal to the variable inductor unit 8 and controls the changeover switches 2 and 3 to switch and connect the inductor element having the highest conversion efficiency in the variable inductor unit 8.

  In step S17, the CPU 39 supplies a control command to each part of the digital camera that performs the zoom operation, and the switching processing step ends.

  Thereafter, when a control command is supplied from the CPU 39 to each unit, the digital camera 100 actually starts a zoom operation.

  In this way, the CPU 39 can control the DC / DC converter 1 to operate at the optimum conversion efficiency before the load current changes according to the zoom operation. That is, even if the operation mode of the digital camera 100 is changed one after another by an operation command supplied from the operation unit 40 to the CPU 39, the CPU 39 changes the DC / DC converter 1 before the load current changes according to these operations. The voltage conversion efficiency can be controlled to be high in advance. Therefore, the digital camera 100 including the power supply circuit 41 according to the present embodiment increases the operation time with high power conversion efficiency, so that the operable time of the battery 43 with a finite amount of power supply can be extended.

  Note that the switching control process shown in FIG. 6 is when the user selects the zoom operation, but even when another operation mode described in the load current characteristic D is selected by the user, The DC / DC converter 1 can be changed to an optimum conversion efficiency by the processing.

  By the way, in the digital camera 100, there are cases where operating voltages having two different values are used. In this case, each part in the digital camera 100 is divided into a load 7a and a load 7b for each of two different operating voltages, and the power supply circuit 41 is changed to a configuration as shown in FIG. That is, the power supply circuit 41 includes two DC / DC converters 1 a and 1 b having the same configuration as that of the DC / DC converter 1. In the power supply circuit 41, one end of each of the DC / DC converters 1a and 1b is connected from the battery 43 via the branch D, and the other end of each of the DC / DC converters 1a and 1b is connected to the load. 7a and 7b. And CPU39 controls the inductor value of the variable inductor part in DC / DC converter 1a, 1b, respectively.

  In this way, even when a plurality of operating voltages are used in the digital camera 100, the conversion efficiency of the DC / DC converter 1 can be maintained in a high state according to the operation mode. In FIG. 7, the power supply circuit 41 using the two DC / DC converters 1 a and 1 b according to the two operating voltages is shown. However, the present invention is not limited to this case, and a plurality of DCs are used according to more operating voltages. A DC / DC converter may be used, and the CPU 39 may switch and control the inductor element of the variable inductance portion in these DC / DC converters to improve the voltage conversion efficiency.

  Furthermore, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

It is a block diagram which shows the structure of a digital camera. It is a block diagram which shows the structure of a power supply circuit. It is a flowchart which shows the process process of the production | generation of the control information memorize | stored in a control information storage part. It is a characteristic diagram which shows the voltage conversion efficiency of a DC / DC converter. It is a table which shows the load current value which flows into load according to the operation mode of a digital camera. It is a flowchart which shows the switching control process of the variable inductor part according to an operation mode. It is a block diagram which shows the structure of the power supply circuit in the case of using two load voltages.

Explanation of symbols

  1 DC / DC converter, 2, 3 selector switch, 4 switching control unit, 5 FET, 6 diode, 7 load, 8 control information storage unit, 10 variable inductor unit, 15 LCD, 30 optical unit, 31 CCD, 32 analog signal Processing unit, 33 ADC, 34 Digital signal processing unit, 35 Motor drive unit, 36 Timing generator, 37 Strobe, 38 Charging unit, 39 CPU, 40 Operation unit, 41 Power supply circuit, 42 AC adapter, 43 Battery, 44 Memory card, 45 External memory interface, 46 Compression / decompression processing function unit, 47 Memory interface, 48 memory, 49 LCD interface

Claims (3)

A variable inductor whose inductance value can be changed is connected to a predetermined DC power source, generates a back electromotive force in the variable inductor, converts the voltage of the DC power source into a predetermined DC conversion voltage, and supplies it to a predetermined load device A power supply device having a DC voltage conversion circuit that
An inductor control unit that changes an inductance value of the variable inductor according to operation information supplied from the load device;
A load current storage unit in which a load current value that changes according to the operation of the load device is stored;
A conversion efficiency storage unit that stores the inductance value of the variable inductor that maximizes the power conversion efficiency of the DC voltage conversion circuit that changes according to the load current value;
The inductor control unit reads the load current value from the load current storage unit according to the operation information supplied from the load device, and the power according to the load current value read from the load current storage unit A power supply apparatus, wherein an inductance value at which conversion efficiency is highest is read from the conversion efficiency storage unit, and the variable inductor is set to an inductance value read from the conversion efficiency storage unit. The conversion efficiency storage unit stores the inductance value of the variable inductor that maximizes the power conversion efficiency, which changes according to the load current value and the DC power supply voltage value of the DC power supply,
The inductor control unit detects the DC power supply voltage value, and an inductance value that maximizes the power conversion efficiency according to the load current value read from the load current storage unit and the detected DC power supply voltage. 2. The power supply apparatus according to claim 1, wherein the conversion efficiency storage unit is read and the variable inductor is set to the inductance value read from the conversion efficiency storage unit. A variable inductor whose inductance value can be changed is connected to a predetermined DC power source, generates a back electromotive force in the variable inductor, converts the voltage of the DC power source into a predetermined DC conversion voltage, and supplies it to a predetermined load device A method of controlling a power supply device having a DC voltage conversion circuit
Read the load current value according to the operation of the load device from the storage medium storing the load current value that changes according to the operation of the load device,
From the storage medium storing the inductance value of the variable inductor that maximizes the power conversion efficiency of the DC voltage conversion circuit that changes according to the load current value, the power according to the read load current value. Read the inductance value that gives the highest conversion efficiency,
A control method for a power supply apparatus, wherein the variable inductor is set to the read inductance value.

Images