JP5471654B2 - Power supply device and display device - Google Patents

Description

  The present invention relates to a power supply device and a display device.

  In recent years, with the increase in the operating speed of personal computers, the spread of network infrastructure, the increase in capacity and price of data storage, information such as documents and images provided on printed paper on paper has become easier to use electronic information. The opportunity to obtain and browse the electronic information is increasing more and more.

  In order to browse such electronic information, conventional liquid crystal displays and CRTs, and in recent years, light-emitting displays such as organic EL displays are mainly used. However, especially when the electronic information is document information, it is necessary to keep an eye on the document information for a relatively long time. As a disadvantage of a general light-emitting display, eyes flicker due to flickering, inconvenient to carry, and reading It is known that the posture is limited and the power consumption increases when reading for a long time.

  An electrochemical display method is known as a display method for solving these drawbacks, and as an example, an electrodeposition method (hereinafter abbreviated as ED method) using dissolution precipitation of a metal or a metal salt is known. Yes. (For example, refer to Patent Documents 1 and 2.)

  The ED display element can be driven at a low voltage of 3V or less, can be realized with a simple cell configuration, and has excellent display quality (bright paper-like white and firm black). Yes.

  When driving an electrochemical display element such as an ED system, a constant voltage equal to or higher than a threshold value is applied to both ends of the electrochemical display element for a certain period of time. The display state can be controlled by voltage or time.

Japanese Patent No. 3428603 JP 2003-241227 A

  In a display device in which a plurality of these electrochemical display elements are arranged in a matrix, the current when starting to drive the display device is large. Particularly in the case of the ED method, since a dissolution of metal or metal salt is used, a large current of several amperes (A) flows at the beginning of voltage application, and the peak current for driving the display device is very large. Become.

  On the other hand, as the dissolution or precipitation of the metal or metal salt of each electrochemical display element proceeds, the current for driving the display device decreases and becomes a small current of about 0.1 to 1A.

  For this reason, a display device using these electrochemical display elements is required to have a power source capable of supplying an output current of about 0.1 A to 10 A with high energy conversion efficiency. In particular, in the case of a battery-driven portable display device, a power source capable of supplying power with high energy conversion efficiency under all load conditions is desired from the viewpoint of extending battery life and reducing battery size.

  However, it is difficult to achieve high energy conversion efficiency in such a wide load current range in the conventional power supply circuit.

  The present invention has been made in view of the above problems, and an object thereof is to provide a power supply device having high energy conversion efficiency in a wide load current range and a display device including the power supply device.

  The object of the present invention can be achieved by the following constitution.

1. A power supply device that switches an input voltage based on a control pulse, rectifies the switched power, and outputs a DC voltage,
A plurality of switching circuits configured to maximize energy conversion efficiency at different load currents,
Voltage control for controlling to apply the control pulse to a switching circuit having the highest energy conversion efficiency among the plurality of switching circuits to output a predetermined DC voltage based on information for predicting a load current of the power supply device And
A power supply device comprising:

2. The voltage controller is
2. The power supply device according to 1, wherein the frequency of the control pulse is changed based on information for predicting the input voltage so that high energy conversion efficiency can be obtained.

3. A display device having a plurality of display elements and displaying an image by applying power to each display element,
The power supply device according to 1 or 2,
A current prediction unit for predicting a load current of the power supply device;
Have
The voltage controller is
Based on the information for predicting the load current of the power supply device from the current prediction unit, the control pulse is applied to the switching circuit with the highest energy conversion efficiency among the plurality of switching circuits, and the predetermined DC voltage is output. A display device characterized by controlling as described above.

4). A voltage predicting unit for predicting future changes in the input voltage;
The voltage controller is
4. The display device according to 3, wherein the frequency of the control pulse is changed based on information for predicting the input voltage from the voltage predicting unit so that energy conversion efficiency of the power supply device is increased.

5. The current prediction unit
5. The display device according to 3 or 4 above, wherein how the load current of the power supply device changes in the future is predicted based on image data to be displayed next.

6). An input voltage detector for detecting the input voltage;
The voltage prediction unit
Predicting how the input voltage will change in the future based on information on the input voltage detected by the input voltage detector and information on load current of the power supply device predicted by the current predictor. The display device according to any one of 3 to 5, wherein:

7). A brightness detection unit for detecting the brightness of the surroundings of the display device;
7. The display device according to 6, wherein the input voltage is predicted to change in the future based on information on brightness detected by the brightness detection unit.

  The power supply device according to the present invention is a switching device having the highest energy conversion efficiency among a plurality of switching circuits designed to maximize the energy conversion efficiency at different load currents based on information predicting the load current of the power supply device. A control pulse is applied to the circuit to output a predetermined DC voltage.

  Therefore, it is possible to provide a power supply device with high energy conversion efficiency in a wide load current range and a display device including the power supply device.

It is a figure which shows the general view of the display apparatus 100 which concerns on embodiment of the display apparatus of this invention. 1 is a schematic cross-sectional view showing a basic configuration of an ED type electrochemical display element 1 used in a display device 100 in the present embodiment. 3 is a diagram for explaining a relationship between a time during which a writing voltage is applied to the electrochemical display element 1 and a display density D. FIG. It is a figure which shows the electrical constitution of the display apparatus 100 in this embodiment. It is a figure for demonstrating the internal structure of the display control part 11 in this embodiment, and the internal structure of the power supply device 150. FIG. It is a circuit block diagram of the power supply device 150 of this embodiment. 3 is a graph showing an example of a relationship between load current and efficiency of a first switching circuit 130 and a second switching circuit 131. 3 is a time chart showing a change in voltage of each part when an image is displayed on the electrochemical display element 1. It is a graph which shows the load current of the power supply device 150 in the case of changing all the electrochemical display elements 1 of the display screen 50 from black of the minimum density | concentration D0 to black of the maximum density | concentration D10. It is a graph which shows the load current of the power supply device 150 in the case of making all the electrochemical display elements 1 of the display screen 50 into the gray of density D6 from white of the minimum density. A power supply for changing the 2/3 electrochemical display element 1 of the display screen 50 from white with the lowest density to gray with the density D6 and 1/3 electrochemical display element 1 from white with the lowest density to black with the density D10. 3 is a graph showing a load current of the device 150. It is a flowchart of an operation button interruption processing routine. It is a flowchart of a timer interruption processing routine. It is a time chart of each part at the time of image writing.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is an external view showing an example of a display device according to an embodiment of the present invention.

  The display device 100 is, for example, a tablet PC, an electronic book, or a PDA, and displays data such as images and characters stored in the memory 10 (see FIG. 5) on the display screen 50. The display screen 50 uses an electrochemical display element 1 (see FIG. 2), which is a memory-type display element capable of displaying gray scales from white to black. The operation unit 42 is provided with a forward button 43 and a reverse button 44 which are mechanical switches. For example, when the user presses the forward button 43, the data on the next page of the data displayed on the display screen 50 is read from the memory 10 and displayed. Similarly, when the user presses the reverse button 44, the data of the page before the data displayed on the display screen 50 is read from the memory 10 and displayed.

  In FIG. 1, the upper layer of the display screen 50 is a touch panel 40. After switching to the handwriting mode by an input operation on the touch panel 40, the user designates a position or an area on the screen and performs handwriting input. The input operation to the touch panel 40 may use a stylus pen, or may directly operate the touch panel 40 with a finger or the like.

  FIG. 2 is a schematic cross-sectional view showing a basic configuration of an ED type electrochemical display element 1 used in the display device 100. 2A shows a state in which black is displayed by the electrochemical display element 1, and FIG. 2B shows a state in which white is displayed.

  The ED electrochemical display element 1 shown in FIG. 2 holds an electrolyte 31 between a transparent ITO (tin-doped indium oxide) electrode 32 and a silver electrode 30. A power source 34 is connected to the ITO electrode 32 and the silver electrode 30. The user observes the electrochemical display element 1 from the ITO electrode 32 side.

  As shown in FIG. 2A, when a negative voltage is applied to the ITO electrode 32 from the power source 34 to the silver electrode 30, a current flows in the direction of the arrow in the figure, and silver contained in the electrolyte 31 is deposited on the ITO electrode 32 side. A reaction occurs. Hereinafter, the negative voltage applied to the ITO electrode 32 is referred to as a write voltage.

  35 is precipitated silver, and the precipitated silver 35 absorbs light, so that the concentration of the electrochemical display element 1 viewed from the ITO electrode 32 side is increased. Reference numeral 36 schematically shows dissolved silver. On the silver electrode 30 side, a phenomenon occurs in which the precipitated silver is dissolved in the electrolyte 31.

  When a positive voltage is applied to the ITO electrode 32 from the power source 34 to the silver electrode 30 as shown in FIG. 2B, a current flows in the direction of the arrow in the figure, and silver dissolution reaction occurs on the ITO electrode 32 side. Hereinafter, the positive voltage applied to the ITO electrode 32 is referred to as an erasing voltage. In the state of FIG. 2A, silver deposited on the ITO electrode 32 side dissolves in the electrolyte 31, and when an erasing voltage is applied for a certain period of time, a light diffusing substance (for example, titanium oxide particles) mixed in the electrolyte 31. As a result, the electrochemical display element 1 viewed from the ITO electrode 32 side becomes white in the initial state.

  The electrolyte 31 contained in the electrochemical display element 1 can be prepared by, for example, phase inversion of silver from a silver salt aqueous solution to a non-aqueous silver salt solution. Such an aqueous silver salt solution can be prepared by dissolving a known silver salt in water.

  FIG. 3 is a view for explaining the relationship between the time for applying the write voltage to the electrochemical display element 1 and the display density D. In FIG.

  In FIG. 3, the horizontal axis represents Tx, the time for applying the writing voltage, and the vertical axis 0 to 10 represents the display density value D. 0 is the minimum display density (white) of the electrochemical display element 1, and 10 is the maximum display density (black) of the electrochemical display element 1. In this embodiment, 11 gradation levels from 0 to 10 are displayed. To do. As shown in FIG. 3, in the electrochemical display element 1 of this embodiment, when a predetermined write voltage is applied, the display density D increases according to the write time Tx.

  4 and 5 are diagrams showing the configuration of the display device according to this embodiment. Although FIG. 4 shows the configuration of only 3 rows × 3 columns of pixels for simplification of description, in order to display an image on the display screen 50, more n rows × m columns of pixels are used. For example, if the XGA display screen 50 is configured, the number of pixels is 1024 × 768.

  FIG. 5 is a diagram for explaining the internal configuration of the display control unit 11 and the internal configuration of the power supply device 150.

Although illustration of the power supply device 150 is omitted in FIG. 4, the power supply V _{DD of the} display device 100 is supplied from the power supply device 150 as illustrated in FIG. 5. The display controller 11 and the like are supplied with a power source Va from a stabilized power source (Reg.) 136. The stabilized power supply 136 and the power supply device 150 are driven by the battery 135.

  In FIG. 4, each pixel includes an electrochemical display element 1, a drive transistor 2, and a switching transistor 4. In FIG. 4, each of the electrochemical display elements 1 of the pixels of n rows × m columns is denoted as Pnm. For example, the electrochemical display element 1 of the pixel in the first row and first column is expressed in order as P11, and the electrochemical display element 1 of the pixel in the second row and second column is expressed as P12.

  Reference numerals 5a, 5b, and 5c denote scanning lines that connect the gates of the switching transistors 4 and the gate drivers 12 of the pixels arranged in the row direction to each other. Reference numerals 8a, 8b, and 8c denote signal lines that connect the sources of the switching transistors 4 of the pixels arranged in the column direction and the source driver 14 to each other. The gate driver 12 controls on / off of the switching transistor 4 by selectively outputting the output voltages G1, G2, and G3 to the scanning lines 5a, 5b, and 5c based on the control of the display control unit 11. The row to which the control voltage is applied to the driving transistor 2 is selected. The drain of the driving transistor 2 is connected to the silver electrode 30 of the electrochemical display element 1 of each pixel, and the source is grounded by the GND bus 6.

  The source driver 14 has a driver circuit for each of the signal lines 8a, 8b, and 8c, and outputs output voltages S1, S2, and S3 to the signal lines 8a, 8b, and 8c based on the control of the display control unit 11. The driver circuit of the source driver 14 is an on / off binary driver, and outputs a control voltage Vs input to the source driver 14 or 0V which is an off voltage based on the control of the display control unit 11.

  The control voltage power supply 15 outputs the control voltage Vs based on the control of the display control unit 11 and supplies it to the source driver 14.

The bus lines 7a, 7b, and 7c are connected to the ITO electrode 32 of the electrochemical display element 1 of each pixel for each row, and one end thereof is connected to the common power supply 13. Common power supply 13 outputs a common voltage V _C is positive or negative voltage by a command of the display control unit 11.

  When the output voltages S1, S2, and S3 of the source driver 14 are Vs, which is an on-voltage, when the switching transistor 4 is turned on, Vs is applied to the gate of the driving transistor 2, and the driving transistor 2 is turned on and the electrochemical display element. 1 is applied with a common voltage Vc. After that, even when the switching transistor 4 is turned off, the driving transistor 2 is kept on by the stray capacitance of the gate.

  When the output voltages S1, S2, and S3 of the source driver 14 are 0V that is an off voltage, when the switching transistor 4 is turned on, 0V is applied to the gate of the drive transistor 2, and the drive transistor 2 is turned off.

  The memory 10 includes a recording medium such as a ROM (Read Only Memory) or a flash memory.

  The first frame memory 60 and the second frame memory 61 are frame memories for one screen each having a storage area corresponding to the number of pixels of the display screen 50. The first frame memory 60 stores a display density value X as first image data to be displayed on the display screen 50 next time by the electrochemical display element 1. The second frame memory 61 stores a display density value Y as second image data currently being displayed on the display screen 50 by the electrochemical display element 1. In the drawing, the first frame memory 60 and the second frame memory 61 are denoted as FM1 and FM2, respectively.

  The touch panel controller 41 drives the touch panel 40 according to a command from the display control unit 11, and transmits input position information read from the touch panel 40 to the display control unit 11.

  The display control unit 11 includes a CPU and the like, and controls the entire display device 100 based on a program.

  The brightness detection unit 46 is a sensor circuit made of, for example, a photodiode or a phototransistor, and is attached to the casing of the display device 100 to detect the brightness around the display screen 50.

  The illumination part 45 consists of white LED etc., for example, and illuminates the display screen 50 whole.

  The internal configurations of the display control unit 11 and the power supply control unit 110 will be described with reference to FIG.

  The display control unit 11 includes a CPU 98 (central processing unit), a RAM 97 (Random Access Memory), a ROM 96 (Read Only Memory), and the like, and reads a program stored in the ROM 96 as a nonvolatile storage unit to the RAM 97. Each part of the display device 100 is controlled according to the program.

  In FIG. 5, the density-specific pixel number calculation unit 80, the current prediction unit 81, the voltage prediction unit 82, the voltage application control unit 83, and the input voltage detection unit 84 described in the CPU 98 are each realized by executing a program by the CPU 98. The function to be performed is shown as a function block. In the present embodiment, these functional blocks are realized by software, but may be realized by hardware.

  Based on the first image data stored in the first frame memory 60, the density-specific pixel number calculation unit 80 calculates the number of pixels for each display density to be displayed in the next image display.

  The current prediction unit 81 predicts a future current consumption of the display device 100, that is, a load current of the power supply device 150, based on the number of pixels calculated by the density-specific pixel number calculation unit 80.

  The voltage predicting unit 82 predicts the future voltage of the battery 135, that is, the input voltage of the power supply device 150, from the information on the voltage of the battery 135 detected by the input voltage detecting unit 84 and the brightness detected by the brightness detecting unit 46. .

  The voltage application control unit 83 controls the drive transistor 2 via the gate driver 12 and the source driver 14 so as to apply the erase voltage or the write voltage to each electrochemical display element 1 based on the first image data. . The voltage application control unit 83 performs control so that a voltage is applied during a desired number of frame periods according to an image to be displayed on each electrochemical display element.

  The input voltage detector 84 detects the voltage of the battery 135, that is, the input voltage of the power supply device 150, from the digital output value of the A / D converter 85 connected to the battery 135.

  The power supply device 150 of this embodiment includes a power supply control unit 110, a first switching circuit 130, a second switching circuit 131, and an A / D converter 122.

  The power control unit 110 includes a CPU 111 (central processing unit), a RAM 120 (Random Access Memory), a ROM 121 (Read Only Memory), and the like, and reads a program stored in the ROM 121 as a nonvolatile storage unit to the RAM 120. Each part of the power supply apparatus 150 is controlled according to the program.

  In FIG. 5, the voltage control unit 112 described in the CPU 111 shows functions realized by execution of a program by the CPU 111 as functional blocks. In the present embodiment, these functional blocks are realized by software, but may be realized by hardware.

  The communication unit 160 is provided in the communication unit 161 of the display control unit 11 in order to receive information and instructions from information. The communication unit 160 and the communication unit 161 are connected by a communication line, and synchronous serial communication such as I2C is performed in both directions.

  The first switching circuit 130 and the second switching circuit 131 are configured such that energy conversion efficiency (hereinafter also referred to as efficiency) is maximized at different load currents.

The voltage control unit 112 applies the control pulse to the more efficient one of the first switching circuit 130 or the second switching circuit 131 based on the information for predicting the load current, and the first switching circuit whose output side is connected. One of 130 and the second switching circuit 131 is controlled to output a predetermined DC voltage V _DD . The control of the voltage control unit 112 will be described in detail later.

The input sides of the first switching circuit 130 and the second switching circuit 131 are connected to the battery 135. The output voltages V _DD of the first switching circuit 130 and the second switching circuit 131 are converted to digital values by the A / D converter 122 and fed back to the voltage control unit 112.

  The A / D converter 122 samples in synchronization with the control pulse.

  A more detailed configuration of the power supply apparatus 150 will be described with reference to FIG. FIG. 6 is a circuit block diagram of the power supply device 150 of the present embodiment.

  The first switching circuit 130 and the second switching circuit 131 are switching circuits used in a known step-down synchronous rectification switching power supply, and both have the same circuit configuration. The first switching circuit 130 and the second switching circuit 131 of FIG. 6 include interface (I / F) sections 140 and 141 and FETs (electric effect transistors) 142, 143, 144 and 145, coils 146 and 147, capacitors 148, respectively. 149.

  Each part will be described by taking the first switching circuit 130 as an example.

  The interface unit 140 is provided for level conversion of the control pulses PWM1a and PWM1b output from the power supply control unit 110 so that the gate terminals of the FETs 142 and 144 can be controlled.

  The FET 142 is turned on and off between the drain and the source by the level-converted control pulse PWM1a.

  The FET 144 is turned on and off between the drain and the source by the level-converted control pulse PWM1b.

  The FET 142 and the FET 144 are controlled to be alternately turned on and off by the power supply control unit 110.

  The coil 146 and the capacitor 148 are smoothing circuits.

  The second switching circuit 131 has the same configuration and will not be described.

  Thus, although the circuit configurations of the first switching circuit 130 and the second switching circuit 131 are the same, the components are selected so that the efficiency is maximized at different load currents.

  The relationship between load current and efficiency will be described using the graph shown in FIG. FIG. 7A shows an example of the load current and efficiency characteristics of the first switching circuit 130, and FIG. 7B shows an example of the load current and efficiency characteristics of the second switching circuit 131. In either case, the input voltage is 8V and the output voltage is 1.5V.

  In the display device 100 of the present embodiment, the load current fluctuates to about 0.1 to 10 A. Therefore, the first switching circuit 130 has a high efficiency with the load current of 1 to 10 A, and the second switching circuit 131 has the load current of 0.1. Designed for high efficiency between ˜1A.

  The first switching circuit 130 performs PWM control at a frequency of 300 KHz to 1 MHz using a coil 146 capable of outputting a large current of about several tens to several hundreds μH, for example, as in the characteristic example of FIG. A maximum efficiency of 90% can be obtained with a load current of 10 A. However, since the self-circuit loss is large in the low current region (1 A or less), the efficiency drops to about 50%.

  For example, the second switching circuit 131 performs PWM control at a frequency of 300 KHz or less using a coil 147 of about 0.1 to several μH, so that a maximum of 90 at a load current of 0.8 A as shown in FIG. % Efficiency is obtained. However, a large current of 1 A or more cannot be output.

  In the present embodiment, since the first switching circuit 130 and the second switching circuit 131 are switched and controlled according to the predicted load current, the efficiency is as high as 80% or more in a wide load current range of 0.1 to 1A. Can be realized.

  In addition, since the energy conversion efficiency of the power supply device 150 is reduced due to fluctuations in the input voltage, it is necessary to consider this point.

  The coil ripple current is expressed by the following formula (1).

ΔI _L = output voltage / (control pulse frequency × inductance) × (1−output voltage / input voltage) (1)
Here, if the input voltage increases and ESR loss ripple current [Delta] I _L increases and the core losses capacitor inductor increases, efficiency decreases. On the other hand, by increasing the control pulse frequency, the ripple current can be reduced and the efficiency reduction can be suppressed.

  The voltage control unit 112 of the present embodiment changes the frequency of the control pulse so as to obtain high efficiency based on information for predicting the load current as will be described in detail later.

  Next, control when displaying an image on the display device 100 of the present invention in the page feed mode will be described with reference to FIG.

  FIG. 8 is a time chart showing a change in voltage of each part when an image is displayed on the electrochemical display element 1. FIG. 8 illustrates a page feed mode in which writing is performed after an erase voltage is applied to the electrochemical display element 1 to erase images of all the electrochemical display elements 1.

First, the voltages V _P11 , V _P21 , and V _P31 applied to P11, P21, and P31 in the first column will be described using the time chart of FIG. The horizontal axis of the time chart of FIG. 8 is a time axis, and F _W 1 to F _W 5 represent the first frame to the fifth frame. N expressed as F _W N is a frame number, and represents the number of frame periods from the start of writing. In the page feed mode, the common voltage V _C is V _cb as shown in FIG.

T _{0 to} t ₅ are the start timings of the first to sixth frames.

In the time chart of FIG. 8, only F _W 5 is displayed to simplify the drawing.

First, the output voltages G1, G2, and G3 of the gate driver 12 in each frame _FW will be described.

When the output voltage G1 in the first row of the gate driver 12 becomes “H” during ΔT, the switching transistor 4 in the first row is turned on. Then, the gate voltages of the drive transistors 2 connected to P11, P12, and P13 in the first row are set to the outputs S1, S2, and S3 of the source driver 14, respectively, and are held in stray capacitances (not shown). Therefore, when the switching transistor 4 is turned on when the output of the source driver 14 is V _S1 , the driving transistor 2 is turned on. Next, when the output of the source driver 14 is 0 V, the driving transistor 2 is turned on until the switching transistor 4 is turned on. Keeps the on state.

  Next, the output voltage G2 of the second row of the gate driver 12 becomes “H” during ΔT, and the gate voltages of the driving transistors 2 connected to P21, P22, and P23 of the second row are respectively those of the source driver 14. The outputs S1, S2, and S3 are set and held in a stray capacitance (not shown). Similarly, the gate voltages of the drive transistors 2 connected to the P31, P32, and P33 in the third row are also set to the outputs S1, S2, and S3 of the source driver 14, respectively, and held in stray capacitances (not shown).

  Outputs S1, S2, and S3 of the source driver 14 are set according to a display density value X that is a density of an image displayed on the electrochemical display element 1.

  The operation of the example of FIG. 8 will be described.

In the frame _{F W 1~F W 5, P11,} P21, the driving transistor 2 is connected to P31 is turned on, _{V cb} is applied to P11, P21, P31.

  In addition, although the electrochemical display element 1 in the first column has been described, a voltage is similarly applied to the electrochemical display elements 1 in other columns.

  In this way, the electrochemical display element 1 is sequentially scanned, and a voltage corresponding to the display image X is applied for a predetermined frame period.

  Next, a specific example of the load current of the power supply device 150 when an image is displayed on the display screen 50 will be described with reference to FIGS. 9, 10, and 11.

FIG. 9 is a graph showing the load current of the power supply device 150 when all the electrochemical display elements 1 on the display screen 50 are changed from white having the lowest density D0 to black having the highest density D10. Rapidly load current from the start timing t ₀ of the first frame is increased, a peak between t ₁ and t _2. The peak current is about 10A. After that, the load current decreases gradually to substantially zero at the timing t ₁₀ to the end of the 10th frame in which all of the electrochemical display element 1 becomes a black maximum density.

FIG. 10 is a graph showing the load current of the power supply device 150 when all the electrochemical display elements 1 on the display screen 50 are changed from white having the lowest density to gray having the density D6. The period from t ₀ to t ₆ is the same as that in FIG. 9, and the load current becomes almost zero at the timing t ₆ when the fifth frame in which the density D6 becomes gray is finished.

FIG. 11 shows that the 2/3 electrochemical display element 1 of the display screen 50 is changed from white having the lowest density to gray having the density D6, and the electrochemical display element 1 having 1/3 is changed from white having the lowest density to black having the density D10. It is a graph which shows the load current of the power supply device 150 in the case of doing. between t ₀ of _{t 6} are the same as FIG. 9, _{t 6} thereafter becomes a load current of 1/3 of the example of FIG. Load current 1A decreases at and then gradually less at t _6, the load current at the timing t ₁₀ becomes substantially zero.

  Thus, the load current of the power supply device 150 varies greatly with time depending on the image data displayed on the display screen 50. In the present invention, the number of pixels (number of electrochemical display elements 1) is calculated for each display density from the image data displayed on the display screen 50, and information for predicting a change in load current is obtained from the number of pixels for each display density. .

  Hereinafter, description will be made along the flowcharts of FIGS. 12 and 13 with reference to the time chart of FIG.

Note that image writing is performed in units of frame periods, and the frame periods are represented by F _W N (N is a frame number).

  When the operator presses the forward button 43 or the reverse button 44 of the operation unit 42, an interrupt signal is transmitted from the operation unit 42 to the display control unit 11, and the display control unit 11 starts an operation button interrupt processing routine shown in FIG. Is done.

  The display control unit 11 erases and initializes the entire screen, and then step S101 is executed.

  S 101: A step of designating a page from which image data is read from the memory 10 and writing the display density value X of the page to the first frame memory 60.

  The CPU 71 designates a page from which image data is read from the memory 10 and writes the display density value X of the page to the first frame memory 60.

  For example, when the operator presses the forward button 43 of the operation unit 42, the CPU 98 updates the page designation read from the memory 10 from the first page to the second page, and the image data (display density of the display density) stored in the second page. Value X) is written into the first frame memory 60.

  S102: This is a step of calculating the number of pixels for each display density from the image data in the first frame memory 60.

  The density-specific pixel number calculation unit 80 calculates the number of pixels for each display density from the image data in the first frame memory 60.

  For example, the density-specific pixel number calculation unit 80 calculates the number of pixels with a display density of 10 and the number of pixels with a display density of 9 in order.

S103: a step of transmitting the switching timing _{T Y.}

The current predicting unit 81 calculates the load current of the power supply device 150 of each frame as shown in FIGS. 9 to 11 from the number of pixels for each display density calculated by the pixel number for each density calculating unit 80, and the first switching circuit 130. determining the switching timing _{T Y} to switch to the second switching circuit 131 from. In this embodiment, the first switching circuit 130 has a high efficiency of 1 to 10A and the second switching circuit 131 has a high efficiency of 0.1 to 1A. Will switch.

  An example will be described with reference to the time chart of FIG.

  FIG. 14A shows that the 2/3 electrochemical display element 1 of the display screen 50 is changed from white having the lowest density D0 to gray having the density D6 and 1/3 electrochemical display element 1 being the lowest, as in FIG. It is a graph which shows the load current of the power supply device 150 in the case of changing from density white to black of density D10.

This step is executed at a timing of t _A at least 10 ms before t ₀ , and the current prediction unit 81 calculates a predicted value of the load current as shown in FIG. Beyond the 1A immediately after _{t 0,} in this example, the switching timing _{T Y} switching from the first switching circuit 130 to the second switching circuit 131 since below again 1A at the timing _{t 6} is a timing _{t 6.}

Current prediction unit 81, the switching timing _{T Y} is transmitted from the communication unit 161 the information indicating that _{t 6} to the communication unit 160.

Note that when most of the electrochemical display elements 1 are white with the minimum density D0, the load current is 1 A or less immediately after the start of writing, so the switching timing T _Y = 0 for switching from the first switching circuit 130 to the second switching circuit 131, That is, the second switching circuit 131 is used from the beginning.

Power supply control unit 110 which has received the information of the switching timing T _Y controls the application of the control pulse becomes the switching timing T _Y switch to the second switching circuit 131.

  S104: This is a step of detecting the battery voltage.

  Input voltage detector 84 detects the voltage of battery 135, that is, the input voltage of power supply device 150.

  S105: This is a step of detecting brightness.

  The brightness detection unit 46 detects ambient brightness.

S106: A step of determining whether the battery voltage E after a predetermined time is equal to or less than _ETH .

The voltage predicting unit 82 determines the predetermined time from the battery voltage E (input voltage) detected by the input voltage detecting unit 84, the load current predicted by the current predicting unit 81, and the brightness information detected by the brightness detecting unit 46. to predict the battery voltage E after, determines whether the E _TH below.

  The battery voltage E after a predetermined time can be predicted from the current input voltage and the predicted value of the load current after the predetermined time. When the brightness detection unit 46 detects that the brightness is lower than the predetermined brightness, the CPU 98 turns on the illumination unit 45 and the load current increases. Therefore, the voltage prediction unit 82 also increases this increase when the battery voltage E is predicted. Consider.

If: E _TH, (step S106; Yes), the process proceeds to step S107.

S107: This is a step of transmitting a prediction of E ≦ _ETH .

The voltage prediction unit 82 transmits prediction information of E ≦ E _TH from the communication unit 161 to the communication unit 160 of the power supply device 150.

The power supply apparatus 150 that has received the prediction information that the future battery voltage E ≦ E _TH sets the frequency of the control pulse to a high frequency. FIG. 14 shows an example in which E ≦ E _TH is predicted after a predetermined time at the timing t _A , and the power supply apparatus 150 sets the frequency of the control pulse to a high frequency as shown in FIG.

When it exceeds E _TH, (step S106; No), the process proceeds to step S108.

S108 is a step of transmitting a prediction of E> E _TH .

The voltage prediction unit 82 transmits prediction information of E> E _TH from the communication unit 161 to the communication unit 160 of the power supply device 150.

The power supply apparatus 150 that has received the prediction information that the future battery voltage is E> E _TH sets the frequency of the control pulse to a low frequency. FIG. 14 is an example in which E> E _TH is predicted after a predetermined time at the timing of t ₃ , and the power supply apparatus 150 sets the frequency of the control pulse to a low frequency as shown in FIG. 14 (d).

  S107: This is a step of displaying an image.

  The voltage application control unit 83 writes an image by applying a voltage to a predetermined electrochemical display element 1 based on the image data in the first frame memory 60 in the procedure for writing the image described with reference to FIG.

  When the writing is finished, the image data in the first frame memory 60 is transferred to the second frame memory 61, and the process is finished.

  This is the end of the description of the flowchart of FIG.

  In the present embodiment, the voltage predicting unit 82 uses the input voltage detected by the input voltage detecting unit 84 and the information on the brightness detected by the brightness detecting unit 46 and the prediction of the load current predicted by the current predicting unit 81 in the future. When the input voltage is predicted but the illumination unit 45 is not provided, the brightness information is not necessary. Also, since it is difficult to predict brightness and battery voltage after a long time, it is desirable to review the input voltage prediction in a short period.

  For example, the prediction of the battery voltage may be reviewed by a timer interruption at each frame start timing in the procedure shown in FIG.

  FIG. 13 is a flowchart of the timer interrupt processing routine. The processing procedure is the same as S104 to S108 in FIG.

  The present invention is not limited to the step-down synchronous rectification type as in the embodiment, and can be applied to a step-up or step-up / step-down type power supply device as long as it is a switching power supply.

  In the present embodiment, an example in which control is performed by two CPUs of the display control unit 11 and the power supply control unit 110 has been described. However, control by one CPU is also possible.

  The procedure described with reference to the flowchart of FIG. 12 can also be applied when deleting an image.

  That is, if the density-specific pixel number calculation unit 80 calculates the number of pixels for each display density from the image data in the second frame memory 61, and the current prediction unit 81 predicts the load current while setting all the pixels to the display density D0. good. The power supply device 150 can switch between the first switching circuit 130 and the second switching circuit 131 based on the prediction of the load current at the time of image erasure.

  As described above, according to the present embodiment, it is possible to provide a power supply device with high energy conversion efficiency in a wide load current range and a display device including the power supply device.

DESCRIPTION OF SYMBOLS 1 Electrochemical display element 2 Drive transistor 4 Switching transistor 5a, 5b, 5c Scan line 7a, 7b, 7c Bus line 8a, 8b, 8c Signal line 10 Memory 11 Display control part 12 Gate driver 13 Common power supply 14 Source driver 30 Silver electrode DESCRIPTION OF SYMBOLS 31 Electrolyte 32 ITO electrode 34 Power supply 45 Illumination part 46 Brightness detection part 80 Pixel number calculation part by density 81 Current prediction part 82 Voltage prediction part 83 Voltage application control part 84 Input voltage detection part 110 Power supply control part 112 Voltage control part 135 Battery 136 Stabilized power supply 150 Power supply

Claims (5)

A display device having a plurality of display elements and displaying an image by applying power to each display element,
A power supply device that switches an input voltage based on a control pulse, rectifies the switched power, and outputs a DC voltage ;
Next, a pixel number calculation unit for each density that calculates the number of pixels for each display density from image data to be displayed;
A current prediction unit for predicting a load current of the power supply device;
Have
The power supply device
A plurality of switching circuits configured to maximize energy conversion efficiency at different load currents,
Voltage control for controlling to apply the control pulse to a switching circuit having the highest energy conversion efficiency among the plurality of switching circuits to output a predetermined DC voltage based on information for predicting a load current of the power supply device And
I have a,
The current prediction unit
Predicting how the load current of the power supply device will change from the number of pixels for each display density calculated by the density-specific pixel number calculation unit,
The voltage controller is
Based on the information for predicting the load current of the power supply device from the current prediction unit, the control pulse is applied to the switching circuit with the highest energy conversion efficiency among the plurality of switching circuits, and the predetermined DC voltage is output. A display device characterized by controlling as described above . The voltage controller is
The display device according to claim 1, wherein the frequency of the control pulse is changed based on information for predicting the input voltage so that high energy conversion efficiency can be obtained. A voltage predicting unit for predicting future changes in the input voltage;
The voltage controller is
Based on the information to predict the input voltage from the voltage prediction unit, the frequency of the control pulses to claim 1 or claim 2, characterized in that changing to the energy conversion efficiency increases of the power supply device The display device described. An input voltage detector for detecting the input voltage;
The voltage prediction unit
Predicting how the input voltage will change in the future based on information on the input voltage detected by the input voltage detector and information on load current of the power supply device predicted by the current predictor. The display device according to any one of claims 1 to 3 . A brightness detection unit for detecting the brightness of the surroundings of the display device;
The display device according to claim 4 , wherein the input voltage is predicted to change in the future based on information on brightness detected by the brightness detection unit.

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