JP3837000B2 - Power supply circuit device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power supply circuit device including a constant current circuit and a constant voltage circuit, and more particularly to a power supply circuit device including a constant current circuit for lighting an LED of a liquid crystal panel.
[0002]
[Prior art]
At present, attempts are being made to reduce the size and weight of portable devices such as digital cameras and mobile phones. The power supply unit of the battery-driven electronic device is also being reduced in size and weight by making it into an IC, but further power saving and space saving are required. A digital camera has a liquid crystal display (LCD) as an essential component, and a conventional LCD requires a backlight inverter. The power consumption of the backlight inverter accounts for 1/3 of the total, and a large space is required for the backlight inverter.
[0003]
By configuring the backlight using the white LED, the power consumption can be reduced to about 60% of the conventional one. Further, since a transformer for the inverter is not necessary, space saving can be realized. On the other hand, when a white LED is used as a backlight, a constant current control circuit for lighting the white LED is newly required.
[0004]
Japanese Patent Laid-Open No. 7-104876 aims to realize a constant current circuit built-in IC with a small area occupied by a constant current circuit. This object is achieved by reducing the area occupied by the resistance in the transistor circuit. Japanese Patent Laid-Open No. 7-104876 is directed to a reference current source inside an IC, and can only supply a current value of about several hundreds of μA.
[0005]
[Problems to be solved by the invention]
A constant current circuit incorporated in a conventional IC as shown in the above-mentioned document (Japanese Patent Laid-Open No. 7-104876) is a reference current source that supplies a reference current, and supplies a large current that can light an LED. It is not possible. A conventional LED lighting current source is provided outside the IC and occupies a large space. Accordingly, an object of the present invention is to provide a power supply circuit device including a constant current circuit capable of realizing space saving. Another object of the present invention is to provide a power supply circuit device including both a constant current circuit and a constant voltage circuit. This problem is solved by a combination of features described in the independent claims. The dependent claims define further advantageous specific examples of the present invention.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problem, a first aspect of the present invention provides a first transistor that determines a conduction state between a first reference voltage source and an output port based on an input signal, and a duty ratio signal having a desired duty ratio. When a duty ratio signal is input to the first transistor, a predetermined constant voltage is output using the output voltage output from the output port based on the duty ratio of the duty ratio signal. A constant voltage circuit that generates a voltage, a resistor that provides a corresponding voltage corresponding to the current value of the current output from the output port, a corresponding voltage and a predetermined comparison voltage, and an analog signal corresponding to the difference And a switching unit that outputs one of the duty ratio signal or the analog signal as an input signal to the first transistor. Source to provide a supply circuit device.
[0007]
The power supply circuit device may include a second transistor that determines a conduction state between the second reference voltage source and the output port based on the input signal, and the constant voltage circuit has a duty ratio signal of the first transistor and the second transistor. When input to the transistor, a predetermined constant voltage may be generated by using the output voltage output from the output port. The first reference voltage source may supply a predetermined positive voltage, and the second reference voltage source may be ground. During the operation of the power supply circuit device, it is preferable that either the first transistor or the second transistor is in a conductive state.
[0008]
The switching unit includes a first switch that determines whether to supply a duty ratio signal to the first transistor, a second switch that determines whether to supply an analog signal to the first transistor, and the first switch or the second switch. And a circuit switching unit that turns on one of them. The switching unit includes a third switch that determines whether or not the output of the output port is supplied to the constant voltage circuit, and the circuit switching unit turns on the first switch and turns off the second switch. It is preferable to turn on the third switch.
[0009]
According to a second aspect of the present invention, there is provided an integrated circuit device for realizing a constant current circuit that supplies a constant current in cooperation with an externally formed circuit. A first transistor that determines a conduction state between one reference voltage source and an output port; a second transistor that defines a conduction state between the second reference voltage source and the output port based on an input signal; and a duty having a desired duty ratio A control unit that can output a ratio signal, a comparator that compares a corresponding voltage corresponding to the current value of the current output from the output port with a predetermined comparison voltage, and outputs an analog signal corresponding to the difference And a switching unit that outputs one of the duty ratio signal or the analog signal as an input signal to the first transistor, and when the duty ratio signal is output to the first transistor Output signal having a duty ratio is output from the output port, the analog signal when it is output to the first transistor provides an integrated circuit device characterized by a constant current is output from the output port.
[0010]
The switching unit includes a first switch that determines whether to supply a duty ratio signal to the first transistor, a second switch that determines whether to supply an analog signal to the first transistor, and the first switch or the second switch. And a circuit switching unit that turns on one of them.
[0011]
The above summary of the invention does not enumerate all the necessary features of the present invention, and sub-combinations of these feature groups can also be the invention.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the invention according to the claims, and all combinations of features described in the embodiments are included. It is not necessarily essential for the solution of the invention.
[0013]
FIG. 1 shows a configuration of a digital camera 10 according to the embodiment. The digital camera 10 mainly includes an imaging unit 20, an imaging control unit 40, a processing unit 60, a display unit 100, an operation unit 110, and a power supply unit 130.
[0014]
The power supply unit 130 supplies power for driving each component of the digital camera 10. The power supply unit 130 includes a power supply circuit device 134 and a backup power supply device 136. A battery 132 is inserted into the power supply unit 130 from the outside. The power supply circuit device 134 can selectively generate a constant current or a constant voltage supplied to each component of the digital camera 10 as required. The power supply circuit device 134 can generate a constant current to be supplied to the LCD monitor 102 in the display unit 100 and the backlight LED 101 of the LCD panel 104. Further, the power supply circuit device 134 can generate a constant voltage to be supplied to the backup power supply 136. Details of the power supply circuit device 134 will be described with reference to FIG.
[0015]
The imaging unit 20 includes a mechanism member and an electrical member related to shooting and imaging. The imaging unit 20 includes a photographic lens 22 that captures and processes an image, a diaphragm 24, a shutter 26, an optical LPF (low-pass filter) 28, a CCD 30, and an imaging signal processing unit 32. The photographing lens 22 includes a focus lens, a zoom lens, and the like. With this configuration, a subject image is formed on the light receiving surface of the CCD 30. Charges are accumulated in each sensor element (not shown) of the CCD 30 in accordance with the amount of light of the formed subject image (hereinafter, the charges are referred to as “accumulated charges”). The accumulated charge is read to a shift register (not shown) by a read gate pulse, and sequentially read as a voltage signal by a register transfer pulse.
[0016]
Since the digital camera 10 generally has an electronic shutter function, a mechanical shutter such as the shutter 26 is not essential. In order to realize the electronic shutter function, the CCD 30 is provided with a shutter drain via a shutter gate. When the shutter gate is driven, the accumulated charge is swept out to the shutter drain. By controlling the shutter gate, the time for accumulating charges in each sensor element, that is, the shutter speed can be controlled.
[0017]
A voltage signal output from the CCD 30, that is, an analog signal, is color-separated into R, G, and B components by the imaging signal processing unit 32, and first, white balance is adjusted. Subsequently, the imaging signal processing unit 32 performs gamma correction, sequentially A / D-converts the R, G, and B signals at a necessary timing, and the resulting digital image data (hereinafter simply referred to as “digital image data”). ) To the processing unit 60.
[0018]
The imaging unit 20 further includes a finder 34 and a strobe 36. The finder 34 may be equipped with an LCD (not shown). In this case, various information from the main CPU 62 and the like which will be described later can be displayed in the finder 34. The strobe 36 functions by emitting light when energy stored in a capacitor (not shown) is supplied to the discharge tube 36a.
[0019]
The imaging control unit 40 includes a zoom driving unit 42, a focus driving unit 44, an aperture driving unit 46, a shutter driving unit 48, an imaging system CPU 50 that controls them, a distance measuring sensor 52, and a photometric sensor 54. Each of the driving units such as the zoom driving unit 42 has driving means such as a stepping motor. In response to pressing of a release switch 114 described later, the distance measuring sensor 52 measures the distance to the subject, and the photometric sensor 54 measures the subject brightness. The measured distance data (hereinafter simply referred to as “distance data”) and subject luminance data (hereinafter simply referred to as “photometry data”) are sent to the imaging system CPU 50. The imaging system CPU 50 adjusts the zoom magnification and focus of the photographing lens 22 by controlling the zoom drive unit 42 and the focus drive unit 44 based on photographing information such as a zoom magnification designated by the user.
[0020]
The imaging system CPU 50 determines the aperture value and the shutter speed based on the RGB digital signal integrated value of one image frame, that is, the AE information. According to the determined value, the aperture driving unit 46 and the shutter driving unit 48 adjust the aperture amount and open / close the shutter 26, respectively.
[0021]
The imaging system CPU 50 also controls the light emission of the strobe 36 based on the photometric data, and simultaneously adjusts the aperture amount of the aperture 26. When the user instructs to capture an image, the CCD 30 starts to accumulate charges, and the accumulated charges are output to the imaging signal processing unit 32 after the shutter time calculated from the photometric data has elapsed.
[0022]
The processing unit 60 includes a main CPU 62 that controls the entire digital camera 10, particularly the processing unit 60 itself, a memory control unit 64, a YC processing unit 70, an optional device control unit 74, a compression / decompression processing unit 78, and communication that are controlled thereby. An I / F unit 80 is included. The main CPU 62 exchanges necessary information with the imaging CPU 50 by serial communication or the like. The operation clock of the main CPU 62 is given from the clock generator 88. The clock generator 88 also provides clocks with different frequencies to the imaging system CPU 50 and the display unit 100, respectively.
[0023]
The main CPU 62 is provided with a character generation unit 84 and a timer 86. The timer 86 is backed up by the backup power source 136 and always counts the date and time. From this count value, information on the shooting date and time information and other time information are given to the main CPU 62. The character generation unit 84 generates character information such as a shooting date and time and a title, and the character information is appropriately combined with the shot image.
[0024]
The memory control unit 64 controls the nonvolatile memory 66 and the main memory 68. The non-volatile memory 66 includes an EEPROM (electrically erasable and programmable ROM), a FLASH memory, and the like, and should be retained even when the power of the digital camera 10 is turned off, such as setting information by a user and adjustment values at the time of shipment. Data is stored. In some cases, the non-volatile memory 66 may store a boot program or a system program for the main CPU 62. On the other hand, the main memory 68 is generally composed of a relatively inexpensive memory having a large capacity, such as a DRAM. The main memory 68 has a function as a frame memory for storing data output from the imaging unit 20, a function as a system memory for loading various programs, and other functions as a work area. The nonvolatile memory 66 and the main memory 68 exchange data with each part inside and outside the processing unit 60 via the main bus 82.
[0025]
The YC processing unit 70 performs YC conversion on the digital image data, and generates a luminance signal Y and color difference (chroma) signals BY and RY. The luminance signal and the color difference signal are temporarily stored in the main memory 68 by the memory control unit 64. The compression / decompression processor 78 sequentially reads out the luminance signal and the color difference signal from the main memory 68 and compresses them. The data thus compressed (hereinafter simply referred to as “compressed data”) is written to a memory card which is a type of option device 76 via the option device control unit 74.
[0026]
The processing unit 60 further has an encoder 72. The encoder 72 receives the luminance signal and the color difference signal, converts them into a video signal (NTSC or PAL signal), and outputs the video signal from the video output terminal 90. When a video signal is generated from data recorded in the option device 76, the data is first supplied to the compression / decompression processing unit 78 via the option device control unit 74. Subsequently, the data that has undergone the necessary expansion processing in the compression / expansion processing unit 78 is converted into a video signal by the encoder 72.
[0027]
The option device control unit 74 performs necessary signal generation, logic conversion, voltage conversion, etc. between the main bus 82 and the option device 76 in accordance with the signal specifications recognized by the option device 76 and the bus specifications of the main bus 82. . The digital camera 10 may support a standard I / O card conforming to PCMCIA, for example, in addition to the memory card described above as the optional device 76. In this case, the option device control unit 74 may be configured by a PCMCIA bus control LSI or the like.
[0028]
The communication I / F unit 80 performs control such as protocol conversion according to communication specifications supported by the digital camera 10, such as USB, RS-232C, Ethernet, and the like. The communication I / F unit 80 includes a driver IC as necessary, and communicates with an external device including a network via the connector 92. In addition to such standard specifications, a configuration may be adopted in which data is exchanged with an external device such as a printer, a karaoke machine, or a game machine using an original I / F.
[0029]
The display unit 100 includes an LCD monitor 102 and an LCD panel 104. The LCD monitor 102 and the LCD panel 104 are respectively controlled by a monitor driver 106 and a panel driver 108 which are LCD drivers. In the present embodiment, the LCD monitor 102 and the LCD panel 104 use the white LED 101 as a backlight. The LED 101 is supplied with a constant current from a power supply circuit device 134 in the power supply unit 130. The LCD monitor 102 is provided on the back of the camera with a size of about 2 inches, for example, and the current shooting / playback mode, zoom magnification for shooting / playback, battery level, date / time, mode setting screen, subject image, etc. Is displayed. The LCD panel 104 is a small black and white LCD, for example, provided on the top surface of the camera, and simply displays information such as image quality (FINE / NORMAL / BASIC, etc.), strobe light emission / flash inhibition, standard number of shoots, number of pixels, battery capacity, etc. .
[0030]
The operation unit 110 includes mechanisms and electric members necessary for the user to set or instruct the operation of the digital camera 10 and its mode. The power switch 112 determines whether to turn on or off the power of the digital camera 10. The release switch 114 has a two-step pushing structure of half-pressing and full-pressing. As an example, AF and AE are locked when pressed halfway, and a captured image is captured when pressed fully, and is recorded in the main memory 68, optional device 76, etc. after necessary signal processing, data compression, and the like. In addition to these switches, the operation unit 110 may accept settings using a rotary mode dial, a cross key, and the like, which are collectively referred to as a function setting unit 116 in FIG. Examples of operations or functions that can be specified by the operation unit 110 include “file format”, “special effect”, “print”, “decision / save”, “display switching”, and the like. The zoom switch 118 determines the zoom magnification.
[0031]
The main operation of the above configuration is as follows.
[0032]
First, the power switch 112 of the digital camera 10 is turned on, and power is supplied from the power supply unit 130 to each part of the camera. The main CPU 62 reads the state of the function setting unit 116 to determine whether the digital camera 10 is in the shooting mode or the playback mode.
[0033]
When the camera is in the shooting mode, the main CPU 62 monitors the half-pressed state of the release switch 114. When the half-pressed state is detected, the main CPU 62 obtains photometry data and distance measurement data from the photometry sensor 54 and the distance measurement sensor 52, respectively. The imaging control unit 40 operates based on the obtained data, and adjustments such as focus and aperture of the taking lens 22 are performed. When the adjustment is completed, a character such as “Standby” is displayed on the LCD monitor 102 to notify the user, and then the release switch 114 is fully pressed. When the release switch 114 is fully pressed, the shutter 26 is closed after a predetermined shutter time, and the accumulated charge in the CCD 30 is swept out to the imaging signal processing unit 32. Digital image data generated as a result of processing by the imaging signal processing unit 32 is output to the main bus 82. The digital image data is temporarily stored in the main memory 68, then processed by the YC processing unit 70 and the compression / decompression processing unit 78, and recorded in the option device 76 via the option device control unit 74. The recorded image is displayed on the LCD monitor 102 in a frozen state for a while, and the user can know the captured image. This completes a series of shooting operations.
[0034]
On the other hand, when the digital camera 10 is in the playback mode, the main CPU 62 reads the last photographed image from the main memory 68 via the memory control unit 64 and displays it on the LCD monitor 102 of the display unit 100. In this state, when the user instructs “forward” or “reverse” on the function setting unit 116, images taken before and after the currently displayed image are read and displayed on the LCD monitor 102.
[0035]
FIG. 2 is a circuit diagram of the power supply circuit device 134 according to the present invention. The power supply circuit device 134 includes a control unit 150, a constant current circuit 170, a constant voltage circuit 190, and a switching unit. In FIG. 2, the left side of the line AA is a configuration inside the integrated circuit (IC), and the right side is a configuration outside the integrated circuit (IC). The power supply circuit device 134 has a function of the constant current circuit 170 capable of supplying a constant current to the backlight LED 101 of the liquid crystal monitor (panel) and a function of the constant voltage circuit 190 capable of supplying a constant voltage. I have a match. When the power supply circuit device 134 is used as a constant voltage circuit, the transistor 162 functions as a switching element.
[0036]
The control unit 150 includes a transistor 152, an AND gate 156, and a duty ratio control unit 154. The control unit 150 is supplied with a selection signal from the main CPU 62 (see FIG. 1) instructing which of the constant current circuit 170 or the constant voltage circuit 190 is to be selected. The selection signal is supplied to the transistor 152. The transistor 152 is an npn type, and outputs an output signal from the collector to the AND gate 156 based on the selection signal. The duty ratio control unit 154 outputs a duty ratio signal having a desired duty ratio to the AND gate 156 in order to control the duty ratio of the signal output from the AND gate 156. Another control signal may be output to the AND gate 156.
[0037]
The transistor 172 and the transistor 162 can realize a switching circuit. In the illustrated configuration, the transistor 172 is a pnp type and the transistor 162 is an npn type, but in another embodiment, the transistors 172 and 162 are of the same type, and one of the transistors 172 or 162 is An inverter may be provided before the input.
[0038]
The transistor 172 determines the conduction state between the first reference voltage source and the output port 182 based on the input signal input to the base. The transistor 162 determines a conduction state between the second reference voltage source and the output port 182 based on the input signal input to the base. As shown in the figure, the emitter of the transistor 172 is connected to an LED power supply provided outside the integrated circuit device (IC). The emitter of the transistor 162 is grounded. In this embodiment, the transistor 172 determines a conduction state between the LED power source and the output port 182, and the transistor 162 determines a conduction state between the ground and the output port 182. When switch 164 is on and switch 180 is off, transistors 172 and 162 connected in parallel function as a switching circuit and based on the duty ratio signal supplied from AND gate 156, transistor 172 or 162 Either one of them conducts.
[0039]
The constant current circuit 170 includes the transistor 172, the resistor 174, the error amplifier 176, and the comparison voltage source 178 described above. When the power supply circuit device 134 functions as the constant current circuit 170, the transistor 172 functions not as one switching element in the switching circuit but as a constant current control element that varies the collector output in accordance with the output of the error amplifier 176. To do. Thus, the transistor 172 in this embodiment can be used as either a switching element or a constant current control element. The resistor 174 has a predetermined resistance value R, and is provided to provide a corresponding voltage corresponding to the current value of the current output from the output port 182. That is, the resistor 174 can monitor the current value of the current output from the output port 182 and indicate a voltage corresponding to the monitored current value. This corresponding voltage is input to the inverting input of an error amplifier 176 that is a comparator. Further, a voltage signal having a predetermined comparison voltage Vref is supplied from the comparison voltage source 178 to the non-inverting input of the error amplifier 176. The error amplifier 176 compares the corresponding voltage with the comparison voltage Vref and outputs an analog signal corresponding to the difference.
[0040]
The constant voltage circuit 190 includes a filter 192, a transistor 194, a protection circuit 196, and resistors 198 and 200. The filter 192 includes a coil and a capacitor. The constant voltage circuit 190 can generate a predetermined constant voltage using the output voltage output from the output port 182.
[0041]
Transistor 194 receives a voltage signal from output port 182 when switch 166 is on. The transistor 194 opens and closes the gate based on the voltage signal, and the capacitor of the filter 192 is charged based on the opening and closing of the gate. The voltage of the capacitor is divided by the resistors 198 and 200 and fed back to the duty ratio control unit 154. The duty ratio control unit 154 adjusts the duty ratio of the duty ratio signal supplied to the transistors 162 and 172 constituting the switching circuit to a desired one based on the fed back voltage.
[0042]
The switching unit includes a constant current / constant voltage circuit switching unit 160 and switches 164, 166 and 180. The switch 164 has a function of determining whether to supply the duty ratio signal output from the control unit 150 to the transistor 172. The switch 180 has a function of determining whether to supply the analog signal output from the error amplifier 176 to the transistor 172. The switch 166 has a function of determining whether to supply the output of the output port 182 to the constant voltage circuit 190. The switching unit can selectively realize the function of either the constant current circuit 170 or the constant voltage circuit 190 based on the output signal from the transistor 152. Specifically, the constant current / constant voltage circuit switching unit 160 receives the output signal from the transistor 152 and turns on / off the switches 164, 166, and 180, whereby the power supply circuit device 134 is connected to the constant current circuit. Alternatively, it functions as a constant voltage circuit.
[0043]
When the power supply circuit device 134 is used as a constant current circuit, the switches 164 and 166 are turned off and the switch 180 is turned on. At this time, the analog signal is supplied to the transistor 172 and the duty ratio signal is not supplied to the transistor 172. Conversely, when the power supply circuit device 134 is used as a constant voltage circuit, the switches 164 and 166 are turned on and the switch 180 is turned off. At this time, the duty ratio signal is supplied to the transistor 172, and the analog signal is not supplied to the transistor 172. As described above, the switching unit has a function of causing the transistor 172 to output one of the duty ratio signal and the analog signal as an input signal of the transistor 172.
[0044]
A specific operation of the power supply circuit device 134 in the present embodiment will be described. First, a selection signal that determines whether the power supply circuit device 134 is used as a constant current circuit or a constant voltage circuit is input to the base of the transistor 152 of the control unit 150. In the following description, the selection signal is divided into a case where the selection signal is H (high) and a case where the selection signal is L (low).
[0045]
When the selection signal is a logical value H, the transistor 152 is turned on and becomes conductive. As a result, since the emitter of the transistor 152 is grounded, the collector output of the logical value L is supplied to the AND gate 156 and the constant current / constant voltage circuit switching unit 160. The AND gate 156 always outputs a logical value L, and the transistor 162 is turned off.
[0046]
The switching unit switches each switch so that the power supply circuit device 134 functions as a constant current circuit. When the constant current / constant voltage circuit switching unit 160 receives the output of the transistor 152 having the logic value L, the constant current / constant voltage circuit switching unit 160 turns off the switches 164 and 166 and turns on the switch 180.
[0047]
The transistor 172 determines a conduction state between the first reference voltage source and the output port 182 based on an input signal input to the base. In addition, a corresponding voltage corresponding to the current value of the current output from the output port 182 is given by the resistor 174 having a predetermined resistance value R. This corresponding voltage is compared with a predetermined comparison voltage Vref in the error amplifier 176. The error amplifier compares the corresponding voltage with the comparison voltage Vref and outputs an analog signal corresponding to the difference. The analog signal is input to the base of the transistor 172 as an input signal. If there is a difference between the corresponding voltage and the comparison voltage Vref, the error amplifier 176 adjusts the level of the analog signal so that the corresponding voltage and the comparison voltage Vref are equal. As a result, a constant current indicating the current value of Vref / R is output from the output port 182.
[0048]
In this manner, the power supply circuit device 134 according to the present embodiment can function as a constant current circuit when the selection signal is the logical value H. The constant current generated in this way is supplied to the LED 101 to realize a stable operation of the LED 101.
[0049]
Next, when the selection signal is a logical value L, the transistor 152 is turned off. As a result, a signal of a logical value H is supplied to the AND gate 156 and the constant current / constant voltage circuit switching unit 160.
[0050]
The switching unit switches each switch so that the power supply circuit device 134 functions as a constant voltage circuit. When the constant current / constant voltage circuit switching unit 160 receives the signal of the logical value H, it turns on the switches 164 and 166 and turns off the switch 180.
[0051]
The transistor 172 determines a conduction state between the first reference voltage source and the output port 182 based on an input signal input to the base. The transistor 162 determines a conduction state between the ground and the output port 182 based on an input signal input to the base. Duty ratio control unit 154 outputs a duty ratio signal having a desired duty ratio to AND gate 156. AND gate 156 outputs this duty ratio signal to transistors 172 and 162.
[0052]
According to the illustrated configuration, the transistor 172 is turned on with a logic value L, and the transistor 162 is turned on with a logic value H. The transistor 172 forms a switching circuit together with the transistor 162, and either the transistor 172 or the transistor 162 is in a conductive state during the operation of the power supply circuit device 134. Therefore, one output of the transistor 172 or 162 is supplied from the output port 182 to the constant voltage circuit 190 based on the duty ratio of the duty ratio signal. At this time, a signal having the same duty ratio as the duty ratio signal is output from the output port 182. The constant voltage circuit 190 outputs a predetermined constant voltage from the output terminal 202 using the output voltage output from the output port 182 based on this duty ratio.
[0053]
In this way, the power supply circuit device 134 according to the present embodiment can function as a constant voltage circuit when the selection signal is the logical value L. The constant voltage generated in this way may be supplied to the backup power source 136, for example.
[0054]
When incorporated in a digital camera, the power supply circuit device 134 functions as a constant current circuit that turns on the LED 101 when the digital camera operates, and functions as a constant voltage circuit that supplies a constant voltage to the backup power source 136 when the operation ends. May be. In addition, the power supply circuit device 134 according to the present invention can be used not only for a digital camera but also for a portable device including a liquid crystal panel or other devices.
[0055]
As is apparent from the above description, according to the present invention, a power supply circuit device incorporating a constant current circuit and a constant voltage circuit can be provided. As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements are also included in the technical scope of the present invention.
[0056]
【The invention's effect】
According to the present invention, it is possible to provide a power supply circuit device that can be used by switching between a constant current circuit or a constant voltage circuit.
[Brief description of the drawings]
FIG. 1 shows a configuration of a digital camera 10 according to an embodiment.
FIG. 2 is a circuit diagram of a power supply circuit device 134 according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Digital camera, 20 ... Imaging unit, 22 ... Shooting lens, 24 ... Aperture, 26 ... Shutter, 28 ... Optical LPF, 30 ... CCD, 32 ... Image pick-up signal processing section 34 .. finder 36... Strobe 36 a .. discharge tube 40... Image pick-up control unit 42 .. zoom drive section 44. ..Aperture drive unit, 48 ... Shutter drive unit, 50 ... Imaging system CPU, 52 ... Distance sensor, 54 ... Photometric sensor, 60 ... Processing unit, 62 ... Main CPU , 64 ... Memory control unit, 66 ... Non-volatile memory, 68 ... Main memory, 70 ... YC processing unit, 72 ... Encoder, 74 ... Optional device control unit, 76 ...・ Optional equipment, 78 ... Decompression / decompression processing unit, 80 ... Communication I / F unit, 82 ... Main bus, 84 ... Character generation unit, 86 ... Timer, 88 ... Clock generator, 90 ... Video output Terminals, 92 ... Connectors, 100 ... Display units, 101 ... LEDs, 102 ... LCD monitors, 104 ... LCD panels, 106 ... Monitor drivers, 108 ... Panel drivers, 110 ... Operation unit 112 ... Power switch 114 ... Release switch 116 ... Function setting unit 118 ... Zoom switch 130 ... Power supply unit 132 ... Battery 134 .. Constant current / constant voltage circuit device, 136... Backup power supply, 150... Control unit, 152. AND gate 160 ... constant current / constant voltage switching unit 162 ... transistor 164 ... switch 166 ... switch 170 ... constant current circuit 172 ... transistor 174 .. Resistor, 176... Error amplifier, 178... Comparison voltage source, 180... Switch, 182... Output port, 190 .. Constant voltage circuit, 192. -Transistors, 196 ... protection circuit, 198 ... 200 ... resistor, 202 ... output terminal

Claims (8)

A first transistor for determining a conduction state between the first reference voltage source and the output port based on the input signal;
A second transistor for determining a conduction state between the second reference voltage source and the output port based on the input signal;
Desired to force out the duty ratio signal having a duty ratio, and the conducted to control part of one of the first transistor or the second transistor based on the duty ratio signal,
When the duty ratio signal is input to the first transistor capacitor and the second transistor, on the basis of the duty ratio of the duty ratio signal, using the output voltage output from the output port, a predetermined constant voltage A constant voltage circuit for generating
A resistor for providing a corresponding voltage corresponding to the current value of the current output from the output port;
By comparing the comparison voltage of the corresponding voltage and Jo Tokoro, a comparator for outputting an analog signal corresponding to a difference between said corresponding voltage and said predetermined comparison voltage,
One of the duty ratio signal or said analog signal as said input signal, e Bei a switching unit for outputting to the first transistor,
Said first transistor, when the switching unit is to output the analog signal to the first transistor, in response to said analog signals, power supply characterized that you vary the output current output from the output port Supply circuit device. The first reference voltage source supplies a predetermined positive voltage;
The power supply circuit device according to claim 1, wherein the second reference voltage source is a ground. The constant voltage circuit is:
A charged capacitor based on the output voltage output from the output port;
Two resistors for dividing the voltage of the capacitor;
Have
2. The power supply according to claim 1, wherein the control unit feeds back a voltage divided by the two resistors and adjusts a duty ratio of the duty ratio signal based on the fed back voltage. Supply circuit device. The switching unit is
A first switch for determining whether to supply the duty ratio signal to the first transistor;
A second switch for determining whether to supply the analog signal to the first transistor;
The power supply circuit device according to claim 1, further comprising: a circuit switching unit that turns on one of the first switch and the second switch. The switching unit further includes a third switch that determines whether to supply the output of the output port to the constant voltage circuit ,
5. The power supply circuit device according to claim 4, wherein the circuit switching unit turns on the third switch when turning on the first switch and turning off the second switch. 6. And circuitry cooperates formed outside, a current product circuit device you supplying a constant current,
A first transistor for determining a conduction state between the first reference voltage source and the output port based on the input signal;
Based on the entering force signal, a second transistor and the second reference voltage source determining the conduction state of the output port,
Desired to force out the duty ratio signal having a duty ratio, and the conducted to control part of one of the first transistor or the second transistor based on the duty ratio signal,
A comparator that compares a corresponding voltage corresponding to the current value of the current output from the output port with a predetermined comparison voltage, and outputs an analog signal corresponding to a difference between the corresponding voltage and the predetermined comparison voltage ;
A switching unit that outputs one of the duty ratio signal or the analog signal as the input signal to the first transistor;
Wherein the first transistor and the second transistor, when the switching unit is to output the previous Symbol duty No. Hishin before Symbol first transistor capacitor and the second transistor, leaving the output voltage corresponding to the duty ratio Outputs from the force port,
Said first transistor, when the switching unit is to output the previous Symbol analog signal before Symbol first transistor, integrated circuit and outputs the output current corresponding to the analog signal from the previous SL output port apparatus. The switching unit is
A first switch for determining whether to supply the duty ratio signal to the first transistor;
A second switch for determining whether to supply the analog signal to the first transistor;
The integrated circuit device according to claim 6, further comprising: a circuit switching unit that turns on one of the first switch and the second switch.   The switching unit further includes a third switch that determines whether to supply the output of the output port to an external constant voltage circuit,
  8. The integrated circuit device according to claim 7, wherein the circuit switching unit turns on the third switch when turning on the first switch and turning off the second switch.

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