JP7806568B2 - Display control device and electronic device - Google Patents

Description

The present invention relates to a display control device and an electronic device.

Conventionally, a technology has been known in which a device that operates on power supplied from a power source is provided with a capacitor that is charged by the power source, and in the event of a power outage, the power charged in the capacitor is used as an auxiliary power source to continue operating the device. Furthermore, Patent Document 1 discloses a technology that reduces the amount of power consumed per unit time of the power charged in the capacitor by operating the device's components in a manner that consumes less power during a power outage, thereby extending the operational time during a power outage.

JP 2011-254660 A

However, with the above-mentioned conventional technology, each component of the device continues to operate during a power outage, so the effectiveness of reducing power consumption per unit time is limited. This poses the problem of requiring a large capacity to ensure the desired operational time during a power outage.

The object of this invention is to provide a display control device and electronic device that can ensure the desired operational time during a power outage while minimizing increases in capacity.

In order to solve the above problems, a display control device according to the present invention comprises:
a determination means for determining whether a detected voltage corresponding to a charging voltage of a capacitor in an electronic device that is charged by a power source and supplies power when the power source is out of service, and a display means having a light source, is less than a reference voltage;
a control means for stopping the supply of power from the capacitor to the light source of the display means for lighting the light source when the determination means determines that the detected voltage is lower than the reference voltage; and
a logic operation means for outputting an output signal representing the logical product of a first signal relating to the determination result by the determination means and a second signal for turning on the light source;
Equipped with
the first signal has a first value corresponding to a true logical value when the determination means determines that the detected voltage is equal to or greater than the reference voltage, and has a second value corresponding to a false logical value when the determination means determines that the detected voltage is less than the reference voltage;
the control means controls the lighting operation of the light source based on the output signal output by the logical operation means.
It is characterized by:

In order to solve the above problems, the electronic device according to the present invention comprises:
The above display control device;
the capacitance;
the display means having the light source;
The present invention is characterized by comprising:

This invention makes it possible to ensure the desired operational time during a power outage while minimizing increases in capacity.

FIG. 2 is a block diagram showing the functional configuration of the electronic device. FIG. 2 is a circuit block diagram showing the configuration of a power supply unit and a display unit. FIG. 10 is a diagram illustrating a truth table of a logical product circuit. 10 is a flowchart showing the flow of an operation for dealing with an instantaneous power outage. 10 is a flowchart showing the flow of an operation for recovering from an instantaneous power failure. 10A to 10C are diagrams illustrating an example of transitions of a detected voltage, a first signal, a second signal, and an output signal during an instantaneous power outage response operation and an instantaneous power outage recovery operation. FIG. 10 is a circuit block diagram showing the configuration of a power supply unit and a display unit according to a comparative example. 10A and 10B are diagrams illustrating an example of transitions of a detected voltage and a second signal during an instantaneous power outage in a configuration of a comparative example.

The following describes an embodiment of the present invention with reference to the drawings.

<Configuration of electronic device>
FIG. 1 is a block diagram showing the functional configuration of an electronic device 1. As shown in FIG.
The electronic device 1 of this embodiment includes a CPU 11 (Central Processing Unit), a RAM 12 (Random Access Memory), a storage unit 13, a power supply unit 20, a display unit 30, an operation input unit 40, a communication unit 50, and a bus 60. The components of the electronic device 1 are connected via the bus 60. The electronic device 1 of this embodiment is an electronic dictionary that displays dictionary-related information and the like on the liquid crystal display 34 of the display unit 30 in response to input operations made to the operation input unit 40.

The CPU 11 is a processor (processing unit) that controls the operation of the electronic device 1 by reading and executing the program 131 stored in the storage unit 13 and performing various arithmetic processing. The electronic device 1 may have multiple processors (e.g., multiple CPUs), and the multiple processes performed by the CPU 11 of this embodiment may be executed by these multiple processors. In this case, the processing unit is made up of the multiple processors. In this case, the multiple processors may be involved in a common process, or the multiple processors may independently execute different processes in parallel.

RAM 12 provides working memory space for CPU 11 and stores temporary data.

The storage unit 13 is a non-transitory recording medium readable by the CPU 11 as a computer, and stores the program 131 and various data. The storage unit 13 includes a non-volatile memory such as a flash memory. The program 131 is stored in the storage unit 13 in the form of computer-readable program code. Data stored in the storage unit 13 includes setting data related to the operation settings of the electronic device 1 and dictionary data related to the contents of a dictionary.

The power supply unit 20 includes a battery 21 (power supply), a battery holder 211 , an auxiliary capacitor 22 (capacitor), and a power supply monitor 23 , and supplies operating power to each part of the electronic device 1 .
The display unit 30 includes a liquid crystal driver IC 31, a logical product circuit 32 (logical operation means), a light source driver IC 33 (control means), and a liquid crystal display 34 (display means). The liquid crystal display 34 has a light source 341. In response to a control signal transmitted from the CPU 11, the display unit 30 displays various information such as the contents of the dictionary and the status of the electronic device 1 on the liquid crystal display 34.
The display control device 100 is configured by the power supply monitoring unit 23 of the power supply unit 20 and the liquid crystal driver IC 31, the logical product circuit 32, and the light source driver IC 33 of the display unit 30.

FIG. 2 is a circuit block diagram showing the configuration of the power supply unit 20 and the display unit 30. As shown in FIG.
Hereinafter, the detailed configuration of the power supply unit 20 and the display unit 30 will be described with reference to FIG.

The battery 21 of the power supply unit 20 is loaded into a battery holder 211 provided inside the housing of the electronic device 1. The positive and negative electrodes of the battery 21 loaded into the battery holder 211 contact terminals on the battery holder 211, and the voltage of the battery 21 is supplied to each part of the electronic device 1 via a circuit connected to these terminals. In this embodiment, two 1.5V batteries connected in series are loaded into the battery holder 211, and a power supply voltage of 3V is supplied to each part of the electronic device 1. The power supply unit 20 may be equipped with a boost circuit that boosts the voltage of the battery 21, and the voltage boosted by this boost circuit may be supplied to each part of the electronic device 1.

The auxiliary capacitor 22 is electrically connected to the positive terminal of the battery holder 211, which contacts the positive electrode of the battery 21. The auxiliary capacitor 22 can be, for example, a ceramic capacitor, but is not limited to this. The auxiliary capacitor 22 is charged by the voltage of the battery 21 loaded in the battery holder 211, and functions as an auxiliary power source for the electronic device 1 when the battery 21 is temporarily removed from the terminal of the battery holder 211 (during a power outage), supplying a charging voltage corresponding to the amount of charge stored. For example, if the battery 21 is momentarily removed from the terminal of the battery holder 211 due to an external impact on the electronic device 1, the charging voltage of the auxiliary capacitor 22 is supplied to each part of the electronic device 1 instead of the power supply voltage of the battery 21 (power is supplied to each part of the electronic device 1 from the auxiliary capacitor 22).

The power supply monitoring unit 23 monitors the power supply voltage of the battery 21 and the charging voltage of the auxiliary capacitor 22, and outputs a signal related to the monitoring results. The power supply monitoring unit 23 includes a delay circuit 231 and a comparator 232 (discrimination means).

The delay circuit 231 is located between the positive terminal of the battery holder 211 and the comparator 232, and delays fluctuations in the voltage at the positive terminal of the battery holder 211 (hereinafter referred to as "power supply voltage VBAT") before outputting it to the comparator 232. Here, the power supply voltage VBAT is the power supply voltage of the battery 21 (and the voltage of the charged auxiliary capacitor 22) when a battery 21 is inserted in the battery holder 211, and is the charging voltage of the auxiliary capacitor 22 when the battery 21 is removed from the battery holder 211.

The delay circuit 231 includes a resistor 2311, a diode 2312, and a delay circuit capacitor 2313. The resistor 2311 and the diode 2312 are arranged in parallel between the positive terminal of the battery holder 211 and the delay circuit capacitor 2313, and are electrically connected to the positive terminal of the battery holder 211 and the delay circuit capacitor 2313.

When the battery 21 is removed from the terminal of the battery holder 211 and the power supply voltage VBAT drops, the charge stored in the delay circuit capacitance 2313 is gradually discharged via the resistor 2311. Therefore, the delay circuit 231 outputs a detection voltage VSENSE that delays the fluctuation of the power supply voltage VBAT by the delay time during which this discharge continues. Therefore, the detection voltage VSENSE corresponds to the power supply voltage VBAT (charging voltage). Furthermore, the delay time corresponds to the time constant RC of the delay circuit 231 (R is the resistance value of the resistor 2311, and C is the size of the delay circuit capacitance 2313).
On the other hand, when the contact between the terminal of the battery holder 211 and the battery 21 is restored while the delay circuit capacitance 2313 is discharged, the delay circuit capacitance 2313 is rapidly charged via the diode 2312, and the detection voltage VSENSE returns to the power supply voltage of the battery 21.

The comparator 232 receives the detection voltage VSENSE and a predetermined reference voltage VREF. In this embodiment, the reference voltage VREF is 2 V. However, this is an example and is not limited to this value. The comparator 232 determines whether the detection voltage VSENSE is less than the reference voltage VREF and outputs a first signal S1 related to the determination result. Specifically, if the detection voltage VSENSE is equal to or greater than the reference voltage VREF, the comparator 232 outputs a voltage "High" (hereinafter also simply referred to as "High"), and if the detection voltage VSENSE is less than the reference voltage VREF, the comparator 232 outputs a voltage "Low" (hereinafter also simply referred to as "Low"). Here, the voltage "High" is, for example, the positive power supply voltage input to the comparator 232, and the voltage "Low" is, for example, the negative power supply voltage (e.g., ground potential) input to the comparator 232. The "High" voltage corresponds to a first value corresponding to a true logical value (e.g., "1"), and the "Low" voltage corresponds to a second value corresponding to a false logical value (e.g., "0").

Next, the configuration of the display unit 30 will be described.
The liquid crystal display 34 of the display unit 30 includes an active matrix transmissive liquid crystal panel 342 and a backlight having a light source 341. Fig. 2 shows the display surface side of the liquid crystal panel 342 of the liquid crystal display 34. The backlight is provided on the opposite side (back side) of the liquid crystal panel 342 from the display surface side, and is not depicted in Fig. 2. Although Fig. 2 also shows the backlight light source 341 schematically within the area of the liquid crystal panel 342, this is for the sake of convenience; in reality, the light source 341 is provided inside the backlight located on the back side of the liquid crystal panel 342 and is not visible from the display surface side of the liquid crystal panel 342.

The liquid crystal panel 342 includes a liquid crystal layer sealed between two transparent substrates and polarizing plates sandwiching these two transparent substrates. The liquid crystal layer is driven for each pixel in response to the application of voltage to pixel electrodes arranged in a matrix on the opposing surfaces of the transparent substrates, thereby switching the transmission of light incident from the backlight on and off for each pixel to produce a display.

The backlight includes multiple light sources 341 (two in Figure 2) and a light guide plate that guides the light emitted from the light sources 341 in a planar form and diffuses it toward the display surface. The light sources 341 are elements that emit light with a brightness corresponding to the input drive current, such as LEDs (Light Emitting Diodes). The light emitted from the backlight toward the display surface enters the liquid crystal panel 342, and as described above, transmission is switched on/off for each pixel, resulting in a visible image.

The LCD driver IC 31 is mounted on the transparent substrate of the LCD panel 342 or on a circuit board electrically connected to the electrodes on the transparent substrate. In response to a control signal for controlling the LCD panel sent from the CPU 11, the LCD driver IC 31 applies a drive voltage to the pixel electrodes of the LCD panel 342 to drive the liquid crystal layer and display an image on the LCD display 34.

In addition, the LCD driver IC 31 outputs a second signal S2 to the AND circuit 32 to turn on (emit light from) the light source 341 at a specified brightness in response to a light source control signal (control command) sent from the CPU 11. In this embodiment, the second signal S2 is a binary signal that periodically switches between "High" and "Low" and is a PWM (pulse width modulation) signal that specifies the brightness of the light source 341 based on the duty ratio of the "High" period. In more detail, the second signal S2 indicates that the higher the duty ratio of the "High" period, the higher the lighting brightness of the light source 341. When the duty ratio of the "High" period is 0, i.e., is constant at "Low," the light source 341 is turned off (unlit). In this way, the second signal S2 is "Low" (second value corresponding to a false logical value) during the period when the light source 341 is not turned on, and is "High" (first value corresponding to a true logical value) during at least part of the period when the light source 341 is turned on. The liquid crystal driver IC 31 generates and outputs the second signal S2 with a duty ratio according to the control signal sent from the CPU 11.

The logical product circuit 32 (AND circuit) outputs the logical product of the signals input to the two input terminals IN0 and IN1.
FIG. 3 is a diagram showing a truth table of the AND circuit 32.
As shown in FIG. 3, the logical product circuit 32 outputs "H" when the signals input to the input terminals IN0 and IN1 are both "H (High)," and outputs "L" when at least one of the signals input to the input terminals IN0 and IN1 is "L (Low)."

2, the first signal S1 output from the comparator 232 is input to one input terminal IN0 of the logical product circuit 32, and the second signal S2 output from the LCD driver IC 31 is input to the other input terminal IN1. Therefore, the logical product circuit 32 outputs an output signal Sout representing the logical product of the first signal S1 and the second signal S2. More specifically, while the first signal S1 input to the input terminal IN0 is "High," i.e., while the detection voltage VSENSE is equal to or higher than the reference voltage VREF, the logical product circuit 32 outputs an output signal Sout corresponding to the same logical value as the second signal S2 input to the input terminal IN1 (in other words, the second signal S2 input to the input terminal IN1 is output as is as the output signal Sout). On the other hand, while the first signal S1 input to the input terminal IN0 is "Low," i.e., while the detection voltage VSENSE drops below the reference voltage VREF, the AND circuit 32 outputs a "Low" output signal Sout regardless of the value of the second signal S2 input to the input terminal IN1.

The light source driver IC 33 has an enable terminal CE (chip enable terminal, CE terminal) to which a signal for enabling the light source driver IC 33 is input, an output terminal VOUT electrically connected to the anode of the light source 341, and a feedback terminal VFB connected to the cathode of the light source 341. The light source driver IC 33 uses VDD input to the power supply terminal as the operating voltage of the light source driver IC 33, and generates the voltage at the output terminal VOUT by boosting the VDD voltage using a switching circuit according to the number of light sources. A potential difference is then generated between the output terminal VOUT and the feedback terminal VFB based on the duty ratio of the PWM signal input to the enable terminal CE, thereby supplying a drive current to the light source 341 to illuminate it. The light source driver IC 33 also adjusts the brightness of the light source 341 by adjusting the magnitude of this drive current. The VDD voltage is generated by boosting the voltage of the battery 21 using a boost circuit (not shown). "Enable" above means that a control signal from the CPU 11 or the like inputs "High" to the enable terminal CE, and an output signal corresponding to the input signal input to the enable terminal CE is output from the output terminal VOUT. In contrast, "not enable" means that a "Low" is input to the enable terminal CE, the switching circuit stops, the output terminal VOUT stops outputting, and no current flows between the output terminal VOUT and the feedback terminal VFB and the light source 341.

The output signal Sout output from the AND circuit 32 is input to the enable terminal CE.
The light source driver IC 33 is not activated while the "Low" output signal Sout continues to be input to the activation terminal CE, and during this period, no drive current is supplied to the light source 341, causing the light source 341 to be turned off.
Furthermore, the light source driver IC 33 is enabled in response to a "High" output signal Sout being input to the enable terminal CE. The light source driver IC 33 supplies the light source 341 with a drive current whose magnitude corresponds to the duty ratio of the period during which the output signal Sout is "H." That is, the light source driver IC 33 supplies the light source 341 with a drive current whose magnitude corresponds to the above duty ratio so that the light source 341 lights up with a brightness that corresponds to the duty ratio. FIG. 2 shows the voltage VLED+ at the output terminal VOUT and the voltage VLED- at the feedback terminal VFB when a drive current of such magnitude is being supplied to the light source 341.

Returning to Figure 1, the operation input unit 40 has at least one input device such as a keyboard, physical buttons, or a touch panel overlaid on the liquid crystal display 34 of the display unit 30, and outputs an operation signal to the CPU 11 in response to an input operation on the input device.

The communication unit 50 is composed of a network card or communication module, etc., and transmits and receives data to and from external devices in accordance with a specified communication standard.

The electronic device 1 may further include components not shown in FIG. 1. For example, it may include a speaker that outputs information related to the dictionary contents, such as the pronunciation of words, and a microphone that accepts voice input of instructions from the user.

<Electronic device operation>
Next, the operation of the electronic device 1 will be described, focusing on the control operation of the display unit 30 during a momentary power outage.

Generally, in electronic devices such as electronic dictionaries that run on battery power, if an external impact is applied (for example, if the electronic device is dropped on the floor), the battery may momentarily become detached from the terminals of the battery holder, causing a momentary power outage.If no measures are taken to prevent momentary power outages, the operation of the entire system of the electronic device will usually stop within a few hundred microseconds of the momentary power outage.
In response to this, in the past, in order to avoid such operational interruptions due to momentary power outages, a technology has been used in which a capacitor that functions as an auxiliary power source is provided in electronic devices, and in the event of a momentary power outage, the power stored in the capacitor allows the electronic devices to continue operating for a certain period of time.

However, in recent years, with electronic dictionaries and other electronic devices, the load has tended to increase as the system scale has grown, and the capacity required for auxiliary power supplies has also increased. Increasing the capacity of the auxiliary power supply increases the inrush current when a battery is inserted, increasing the risk of the fuse connected to the battery blowing, making safety measures necessary. Furthermore, the area occupied by the capacitance on the circuit board increases, hindering the ability to increase circuit density and leading to higher manufacturing costs.

Therefore, in the electronic device 1 of this embodiment, the auxiliary capacitor 22 that functions as an auxiliary power source is provided, and the operation of the display unit 30 during a momentary power outage is controlled so that a sufficient operating time is ensured with the small auxiliary capacitor 22. Specifically, when the detection voltage VSENSE falls below the reference voltage VREF due to a momentary power outage, the light source 341, which is a large power load on the auxiliary capacitor 22, is turned off.
In the following, first, the normal operation of the electronic device 1 will be described, and then the operation during a momentary power outage will be described.

(Normal operation)
During normal operation when the battery 21 is inserted in the battery holder 211, the auxiliary capacitor 22 and delay circuit capacitor 2313 are charged, and the power supply voltage VBAT is maintained at 3 V. Therefore, the detection voltage VSENSE also becomes 3 V, which is equal to or greater than the reference voltage VREF (2 V), causing the comparator 232 to output a "High" signal. This "High" output is input to the input terminal IN0 of the AND circuit 32, which then outputs the second signal S2 input to its input terminal IN1, i.e., the PWM signal for lighting the light source 341 at a specified brightness, as the output signal Sout. In response to the output signal Sout (PWM signal) being input to the enable terminal CE, the light source driver IC 33 supplies a drive current to the light source 341 of a magnitude that causes the light source 341 to light at a brightness corresponding to the duty ratio of the PWM signal. The light source 341 lights up in response to this drive current, and the display on the liquid crystal panel 342 of the liquid crystal display 34 becomes visible.

(Operation during momentary power outage)
Next, the operation of the electronic device 1 when a momentary power outage occurs (operation to cope with a momentary power outage) will be described with reference to the flowchart of FIG.
FIG. 4 is a flowchart showing the flow of operations for dealing with a momentary power outage.
It is assumed that the electronic device 1 is performing the above-described normal operation at the start of the instantaneous power outage response operation.

In momentary power outage response operation, when the battery 21 becomes detached from the terminal of the battery holder 211 and a momentary power outage occurs ("YES" in step S101), each part of the electronic device 1 (e.g., the CPU 11, the power supply monitoring unit 23 of the power supply unit 20, the display unit 30, the operation input unit 40, and the communication unit 50) operates using the power charged to the auxiliary capacitance 22. That is, power is supplied from the auxiliary capacitance 22 to the loads of each part of the electronic device 1 (the charge accumulated in the auxiliary capacitance 22 is discharged), and the charging voltage of the auxiliary capacitance 22, i.e., the power supply voltage VBAT, drops accordingly (step S102).

The delay circuit 231 outputs the detection voltage VSENSE, which is obtained by delaying the drop in the power supply voltage VBAT according to the time constant RC, to the comparator 232 (step S103). The comparator 232 determines whether the detection voltage VSENSE has dropped below the reference voltage VREF (2 V) (step S104). If it is determined that the detection voltage VSENSE has not dropped below the reference voltage VREF ("NO" in step S104) and the momentary power outage has not ended (i.e., contact between the terminals of the battery holder 211 and the battery 21 has not been restored) ("NO" in step S105), the output of the comparator 232 remains "High" and step S104 is executed again.

If it is determined that the detection voltage VSENSE has dropped below the reference voltage VREF ("YES" in step S104), the output of the comparator 232 switches to "Low" (step S106). While this "Low" output is input to the input terminal IN0 of the AND circuit 32, as described above, the AND circuit 32 outputs a "Low" output signal Sout regardless of the value of the second signal S2 input to the input terminal IN1 (step S107). Therefore, the input signal to the enable terminal CE of the light source driver IC 33 is fixed to "Low" (step S108). As a result, the light source driver IC 33 stops supplying drive current to the light source 341 (step S109). In other words, when the light source driver IC 33 determines that the detection voltage VSENSE corresponding to the charging voltage of the auxiliary capacitor 22 is less than the reference voltage VREF, it stops the supply of power from the auxiliary capacitor 22 to the light source 341 to turn on the light source 341. This turns off the light source 341 (step S110). With the light source 341 turned off, the transmissive mode display on the liquid crystal panel 342 of the liquid crystal display 34 becomes invisible (or difficult to view). Note that the liquid crystal panel 342 continues to operate at this time. When the light source 341 is turned off in step S110, the momentary power outage response process ends.

Since the power required to light the light source 341 accounts for a large proportion of the overall power consumption of the electronic device 1, stopping the power supply to the light source 341 as described above effectively reduces the amount of power consumed per unit time charged in the auxiliary capacitance 22. This extends the operational time of each component other than the light source 341 after the light source 341 is turned off, preventing the entire system of the electronic device 1 from shutting down in a short period of time. In this embodiment, the size of the auxiliary capacitance 22 is determined so that the operation of each component other than the light source 341 is maintained for at least 10 milliseconds after the start of a momentary power outage.

Incidentally, by providing delay circuit 231, if the duration from the occurrence of a momentary power outage to the end of the momentary power outage is approximately the time constant RC of delay circuit 231, the process does not proceed to the flow for stopping light source 341 (steps S106 to S110), and light source 341 continues to emit light. That is, even if a momentary power outage causes power supply voltage VBAT to drop (step S102), temporarily causing power supply voltage VBAT to fall below reference voltage VREF, contact between the terminals of battery holder 211 and battery 21 is restored and the momentary power outage ends (step S105) before the detected voltage VSENSE, delayed by delay circuit 231 by approximately the time constant RC, falls below reference voltage VREF ("NO" in step S104). This causes light source 341 to remain illuminated and return to normal operation (step S101). Specifically, the restored power supply voltage of the battery 21 rapidly charges the delay circuit capacitor 2313 via the diode 2312 shown in FIG. 2, causing the detection voltage VSENSE to return to the power supply voltage of the battery 21 (3 V) before it drops below the reference voltage VREF. Therefore, the output of the comparator 232 remains "High," and the light source 341 continues to emit light. This prevents the light source 341 from turning off due to an extremely short-term power outage or power supply voltage fluctuation, making the display on the LCD 34 unreadable. Furthermore, the time constant RC of the delay circuit 231 (i.e., the size of the resistor 2311 and/or the size of the delay circuit capacitor 2313) is set so that the light source 341 does not turn off due to a power outage or power supply voltage fluctuation of less than a desired length.

Next, the recovery operation (momentary power outage recovery operation) of the electronic device 1 when the momentary power outage ends after the light source 341 is turned off in step S110 above will be described with reference to the flowchart in Figure 5.

FIG. 5 is a flowchart showing the flow of the recovery operation after a momentary power outage.
At the start of the momentary power failure recovery operation, the electronic device 1 is in the state it was in at the end of the momentary power failure response operation. Therefore, at the start of the momentary power failure recovery operation, the detection voltage VSENSE is less than the reference voltage VREF, the delay circuit 231 and the logical product circuit 32 output "Low," the light source driver IC 33 is not enabled, and the light source 341 is turned off.

During momentary power outage recovery operation, when contact between the battery holder 211 terminal and the battery 21 is restored and the momentary power outage ends ("YES" in step S201), the auxiliary capacitor 22 is charged and the power supply voltage VBAT increases (step S202). Furthermore, the delay circuit capacitor 2313 is also rapidly charged via the diode 2312, causing the detection voltage VSENSE to increase.

Comparator 232 determines whether the detection voltage VSENSE has risen above the reference voltage VREF (2 V) (step S203). During the period in which it is determined that the detection voltage VSENSE has not risen above the reference voltage VREF ("NO" in step S203), the output of comparator 232 remains "Low" and step S203 is executed again.

If it is determined that the detection voltage VSENSE has risen above the reference voltage VREF ("YES" in step S203), the output of the comparator 232 switches to "High" (step S204). While this "High" output is being input to the input terminal IN0 of the AND circuit 32, as described above, the AND circuit 32 outputs the second signal S2 (PWM signal) output from the LCD driver IC 31 and input to the input terminal IN1 as the output signal Sout to the enable terminal CE of the light source driver IC 33 (step S205). This causes the light source driver IC 33 to resume supplying a drive current to the light source 341 (step S206). That is, based on the PWM signal input to the enable terminal CE, the light source driver IC 33 supplies a drive current of a magnitude that illuminates the light source 341 at a brightness corresponding to the duty ratio of the PWM signal. In response to this drive current, the light source 341 lights up (step S207), and the display on the LCD display 34 returns to a visible state. When the light source 341 lights up in step S207, the momentary power outage recovery process ends.

Figure 6 shows an example of the transitions of the detection voltage VSENSE, the first signal S1, the second signal S2, and the output signal Sout during momentary power outage response operation and momentary power outage recovery operation.

During the period from time t0 to time t1 in Figures 6(A) to 6(D), the battery 21 is properly inserted into the battery holder 211 and normal operation is occurring. Also, as shown in Figure 6(A), the detection voltage VSENSE during this period is maintained at 3V. Accordingly, as shown in Figure 6(B), the first signal S1 output by the comparator 232 during this period is "High." Therefore, the AND circuit 32 outputs the second signal S2 (Figure 6(C)) during this period as the output signal Sout (Figure 6(D)). The light source driver IC 33 supplies a drive current to the light source 341 that controls the brightness of the light source 341, depending on the duty ratio of the second signal S2 (output signal Sout) during this period, which is input to the enable terminal CE of the light source driver IC 33. As a result, the light source 341 lights up at a brightness determined by the duty ratio of the output signal Sout.

Assume that at time t1, the battery 21 becomes detached from the terminal of the battery holder 211, causing a momentary power outage. As shown in FIG. 6A, the detection voltage VSENSE begins to drop after time t1. Although not shown in FIG. 6, the drop in the detection voltage VSENSE immediately after the momentary power outage occurs is smoothed by the action of the delay circuit 231. Although the detection voltage VSENSE continues to drop from time t1 to time t2, it remains above the reference voltage VREF (2V). Therefore, as shown in FIG. 6B, the first signal S1 output by the comparator 232 remains "High" from time t1 to time t2, and the AND circuit 32 outputs the second signal S2 (FIG. 6C) unchanged as the output signal Sout (FIG. 6D) from time t1 to time t2. Therefore, a drive current is supplied from the light source driver IC 33 to the light source 341, and the light source 341 continues to light up at a brightness that corresponds to the duty ratio of the second signal S2 (output signal Sout) during the above period. Because the light source 341 is lit, the power that had been charged in the auxiliary capacitor 22 is consumed by the light source 341, and the power supply voltage VBAT and detection voltage VSENSE (Figure 6(A)) drop rapidly.

When the detection voltage VSENSE falls below the reference voltage VREF (2 V) at time t2, the first signal S1 (Figure 6(B)) output by the comparator 232 switches to "Low." In response, the output signal Sout (Figure 6(D)) output by the AND circuit 32 is fixed to "Low" regardless of the second signal S2. When this output signal Sout is input to the enable terminal CE of the light source driver IC 33, the light source driver IC 33 stops supplying drive current to the light source 341, turning off the light source 341. With the light source 341 turned off and the power consumed by the auxiliary capacitor 22 no longer being consumed by the light source 341, the rate at which the detection voltage VSENSE (Figure 6(A)) falls slows from time t2 onward. Furthermore, after time t2, all components of the electronic device 1, except for the light source 341, continue to operate. Therefore, even after time t2, the LCD driver IC 31 continues to output the second signal S2 (PWM signal) (Figure 6(C)).

At time t3, 10 milliseconds after time t1, the battery 21 returns to contact with the terminals of the battery holder 211, ending the momentary power outage. Furthermore, after time t3, the auxiliary capacitor 22 and delay circuit capacitor 2313 are charged by the power supply voltage of the battery 21, causing the detection voltage VSENSE (Figure 6(A)) to rise rapidly.

At time t4, when the detection voltage VSENSE (FIG. 6(A)) rises to the reference voltage VREF (2 V), the first signal S1 (FIG. 6(B)) output by the comparator 232 switches to "High." In response, the AND circuit 32 outputs the second signal S2 (FIG. 6(C)) as is as the output signal Sout (FIG. 6(D)). When this output signal Sout is input to the enable terminal CE of the light source driver IC 33, the light source driver IC 33 supplies a drive current to the light source 341, and the light source 341 resumes illumination at a brightness corresponding to the duty ratio of the second signal S2 (output signal Sout). This restores the electronic device 1 to a state where the display on the liquid crystal panel 342 of the liquid crystal display 34 is visible, and thereafter resumes normal operation.

<Comparative Example>
Next, the operation of a comparative example in which the light source 341 is not turned off will be described.

FIG. 7 is a circuit block diagram showing the configuration of the power supply unit 20 and the display unit 30 according to the comparative example.
The configuration of the comparative example corresponds to the configuration of the embodiment shown in Figure 2 , in which the comparator 232 and the logical product circuit 32 are omitted, and the second signal S2 output by the liquid crystal driver IC 31 is directly input to the enable terminal CE of the light source driver IC 33. In the configuration of the comparative example, even if the detection voltage VSENSE drops due to a momentary power outage, the second signal S2 continues to be input to the enable terminal CE of the light source driver IC 33. Therefore, the supply of drive current from the light source driver IC 33 to the light source 341 is not stopped, and the light source 341 continues to light even during the momentary power outage. Therefore, during the momentary power outage, the power of the auxiliary capacitor 22 continues to be consumed by the light source 341, the charging voltage (power supply voltage VBAT) of the auxiliary capacitor 22 drops rapidly, and the overall operation of the electronic device 1 stops prematurely.

8A and 8B are diagrams showing an example of transitions of the detected voltage VSENSE (FIG. 8A) and the second signal S2 (FIG. 8B) during an instantaneous power outage in the configuration of the comparative example.
In the comparative example, even after time t1 when the momentary power outage occurs, the light source driver IC 33 continues to supply a drive current to the light source 341 in response to the second signal S2, and the light source 341 continues to be illuminated. As a result, the detection voltage VSENSE ( FIG. 8A ), which corresponds to the charging voltage of the auxiliary capacitor 22, continues to rapidly decrease. At time t5, approximately 2 milliseconds after the momentary power outage occurs, when the detection voltage VSENSE drops to approximately 1.3 V, a predetermined system reset function is activated, and the entire system of the electronic device stops operating. After time t5, the CPU 11, the power supply monitoring unit 23 of the power supply unit 20, the display unit 30, the operation input unit 40, the communication unit 50, and other components stop operating. Therefore, as shown in FIG. 8B , after time t5, the output of the second signal S2 by the LCD driver IC 31 also stops.

Let's assume that the momentary power outage ends at time t6, which is after time t5. After time t6, the auxiliary capacitor 22 and delay circuit capacitor 2313 are charged by the power supply voltage of the battery 21, and the detection voltage VSENSE (Figure 8(A)) rises. However, because the system, including the CPU 11, remains stopped, the LCD driver IC 31 cannot output the second signal S2 (PWM signal). Therefore, the supply of drive current from the light source driver IC 33 to the light source 341 does not resume, and the light source 341 remains off.

In this way, in the comparative example configuration that does not have the comparator 232 and the logical product circuit 32, the light emission of the light source 341 is not stopped, so the system operation stops within a short time, such as 2 milliseconds, after the momentary power outage occurs, and operation does not resume even after the momentary power outage ends.
In contrast, in the configuration of this embodiment, as shown in Fig. 6, the light source 341 is turned off after time t2 when the detection voltage VSENSE (Fig. 6(A)) falls below the reference voltage VREF, thereby reducing the amount of power consumed per unit time by the entire electronic device 1, and as a result, it is possible to continue operating each component other than the light source 341 for a longer period of time than in the comparative example. Therefore, by turning the light source 341 back on after the momentary power outage ends, the display on the liquid crystal display 34 returns to a visible state, and normal operation can be resumed thereafter.

<Effects>
As described above, the display control device 100 according to this embodiment includes the electronic device 1 including the auxiliary capacitor 22 that is charged by the battery 21 and supplies auxiliary power during a power outage, and the liquid crystal display 34 having the light source 341. The electronic device 1 includes the comparator 232 (determination means) that determines whether the detection voltage VSENSE corresponding to the charging voltage of the auxiliary capacitor 22 is less than the reference voltage VREF, and the light source driver IC 33 (control means) that, when the comparator 232 determines that the detection voltage VSENSE is less than the reference voltage VREF, stops the supply of power from the auxiliary capacitor 22 to the light source 341 of the liquid crystal display 34 for lighting the light source 341. According to this, when the detection voltage VSENSE becomes less than the reference voltage VREF during a power outage, the supply of power to the light source 341, which is a large load, is stopped, thereby effectively reducing the amount of power consumed per unit time of the power charged in the auxiliary capacitor 22. This makes it possible to extend the operable time of each part of the electronic device 1 other than the light source 341 after the light source 341 is turned off, and to prevent the entire system of the electronic device 1 from shutting down in a short time during a power outage. Therefore, it is possible to secure a desired operable time during a power outage while suppressing an increase in the auxiliary capacitance 22.

The display control device 100 also includes a logical product circuit 32 (logical operation means) that outputs an output signal Sout representing the logical product of a first signal S1 related to the determination result by the comparator 232 and a second signal S2 for turning on the light source 341. The first signal S1 becomes "High" (a first value corresponding to a true logical value) when the comparator 232 determines that the detection voltage VSENSE is equal to or greater than the reference voltage VREF, and becomes "Low" (a second value corresponding to a false logical value) when the comparator 232 determines that the detection voltage VSENSE is less than the reference voltage VREF. The light source driver IC 33 controls the lighting operation of the light source 341 based on the output signal Sout output by the logical product circuit 32. As a result, when the detection voltage VSENSE is equal to or greater than the reference voltage VREF, the logical product circuit 32 outputs the second signal S2 (output signal Sout) for turning on the light source 341, and when the detection voltage VSENSE is less than the reference voltage VREF, the logical product circuit 32 does not output the second signal S2 (output signal Sout). Therefore, by operating the light source driver IC 33 based on the output signal Sout of the logical product circuit 32, it is possible to realize an operation of turning off the light source 341 when the detection voltage VSENSE is less than the reference voltage VREF.

The second signal S2 is "Low" during periods when the light source 341 is not turned on, and is "High" during at least part of the periods when the light source 341 is turned on. The AND circuit 32 outputs an output signal Sout whose value corresponds to the same logical value as the second signal S2 when the first signal S1 is "High," and outputs a "Low" output signal Sout when the first signal S1 is "Low." This makes it possible to achieve the operation of turning off the light source 341 when the detection voltage VSENSE falls below the reference voltage VREF through simple control of operating the light source driver IC 33 based on the output signal Sout of the AND circuit 32, which is "High" and "Low."

The output signal Sout is also input to the enable terminal CE of the light source driver IC 33, and the light source driver IC 33 is enabled in response to the input of a "High" output signal Sout to the enable terminal CE, thereby turning on the light source 341. This allows the light source driver IC 33 to appropriately control the light source 341 based on the output signal Sout of the AND circuit 32.

The second signal S2 is a signal that specifies the brightness of the light source 341. This allows the light source 341 to be lit at the desired brightness.

The second signal S2 is a signal that specifies the brightness of the light source 341 based on the duty ratio of the period during which it is "High." This allows the light source 341 to be lit at a desired brightness based on the second signal S2, which is made up of "High" and "Low."

In addition, a delay circuit 231 is provided between the auxiliary capacitor 22 and the comparator 232, which delays fluctuations in the charging voltage and outputs it to the comparator 232 as the detection voltage VSENSE. This means that even if a momentary power outage causes the charging voltage (power supply voltage VBAT) of the auxiliary capacitor 22 to temporarily fall below the reference voltage VREF, if the momentary power outage ends before the detection voltage VSENSE delayed by the delay circuit 231 falls below the reference voltage VREF, normal operation can be restored while the light source 341 remains lit. This prevents the occurrence of a malfunction in which the light source 341 goes out and the display on the LCD display 34 becomes unreadable due to an extremely short momentary power outage or fluctuations in the power supply voltage.

The electronic device 1 according to this embodiment also includes the display control device 100 described above, an auxiliary capacitance 22, and a liquid crystal display 34 having a light source 341. This makes it possible to ensure the desired operating time during a power outage while suppressing an increase in the auxiliary capacitance 22. Also, suppressing an increase in the auxiliary capacitance 22 makes it possible to keep the inrush current when the battery 21 is installed small. Furthermore, since it is possible to suppress an increase in the area occupied by the auxiliary capacitance 22 on the circuit board of the electronic device 1, it is possible to suppress an increase in the size of the electronic device 1 and an increase in manufacturing costs.

<Others>
The above description of the embodiment is merely an example of the display control device and electronic device according to the present invention, and the present invention is not limited to this.
For example, in the above embodiment, an electronic dictionary is used as an example of the electronic device 1, but the electronic device 1 is not limited to this. The electronic device 1 may be any device that includes a capacitor that functions as an auxiliary power source and a display unit that has a light source.

In addition, the light source 341 of the liquid crystal display 34 may be used as a front light that illuminates the liquid crystal panel 342 from the display surface side, instead of a back light that illuminates the liquid crystal panel 342 from the rear side.

In addition, in the above embodiment, a liquid crystal display 34 having a light source 341 was used as an example of the display means, but this is not limited to this. For example, the display means may be an organic EL (Electro Luminescence) display in which multiple pixels that emit light in response to a drive current are arranged. In this case, each pixel that makes up the organic EL display corresponds to a light source.

In addition, in the above embodiment, a PWM signal was used as an example of the second signal S2 for turning on the light source 341, but this is not limited to this. For example, the second signal S2 may be a binary signal that only instructs the light source 341 to be switched on and off.

Furthermore, in cases where it is acceptable for the light source 341 to be turned off during a short, momentary power outage, the delay circuit 231 may be omitted. In this case, the power supply voltage VBAT is input to the comparator 232 without being delayed. Furthermore, the power supply voltage VBAT corresponds to the "detection voltage."

Furthermore, the power source is not limited to a battery 21, but may be, for example, a commercial AC power source.

In addition, while the above embodiment illustrates an example in which the AND circuit 32 and the enable terminal CE of the light source driver IC 33 operate in positive logic, this is not limiting and they may operate in negative logic. That is, a voltage value corresponding to a first value corresponding to a true logical value (here, "0") may be set to "Low," and a voltage value corresponding to a second value corresponding to a false logical value (here, "1") may be set to "High." In this case, the AND circuit 32 outputs a "Low" output signal Sout when both the signals input to input terminals IN0 and IN1 are "Low," and outputs a "High" output signal Sout when at least one of the signals input to input terminals IN0 and IN1 is "High." Furthermore, the light source driver IC 33 turns off the light source 341 by not supplying a drive current to the light source 341 while the "High" output signal Sout continues to be input to the enable terminal CE, and is enabled in response to the input of the "Low" output signal Sout to the enable terminal CE, and supplies a drive current to the light source 341. More specifically, the light source driver IC 33 outputs a larger drive current as the duty ratio during the "Low" period is larger. Therefore, the second signal S2 in this case indicates that the lighting luminance of the light source 341 is increased as the duty ratio during the "Low" period is larger, and indicates that the light source 341 is turned off when the duty ratio during the "Low" period is 0, i.e., is constant at "High." Furthermore, the comparator 232 outputs "Low" when the detection voltage VSENSE is equal to or greater than the reference voltage VREF, and outputs "High" when the detection voltage VSENSE is less than the reference voltage VREF.

Furthermore, the logical operation means that outputs the output signal Sout representing the logical product of the first signal S1 and the second signal S2 is not limited to the logical product circuit 32 (AND circuit) shown in Figure 2, but can be any circuit that outputs a value according to the same truth table as the AND circuit.

Furthermore, the configuration of the delay circuit 231 is not limited to that shown in Figure 2, and can be any circuit (for example, an integrating circuit) that delays fluctuations in the power supply voltage VBAT and outputs the delay as the reference voltage VREF.

In addition, in the above embodiment, the supply of drive current from the light source driver IC 33 to the light source 341 was controlled by inputting the output signal Sout of the logical product circuit 32 to the enable terminal CE of the light source driver IC 33, but this is not limited to this. For example, the output signal Sout of the logical product circuit 32 may be used to control the on/off of the VDD voltage supplied to the power terminal of the light source driver IC 33. In this way, when the detection voltage VSENSE is equal to or greater than the reference voltage VREF, the VDD voltage is supplied to the light source driver IC 33 and a drive current is supplied to the light source 341. When the detection voltage VSENSE is less than the reference voltage VREF, the supply of the VDD voltage to the light source driver IC 33 is stopped and no drive current is supplied to the light source 341.

Furthermore, it goes without saying that the detailed configuration and detailed operation of each component of the electronic device 1 and display control device 100 in the above embodiment can be modified as appropriate without departing from the spirit and scope of the present invention.

Although the embodiments of the present invention have been described, the scope of the present invention is not limited to the above-described embodiments, but includes the scope of the invention described in the claims and its equivalents.
The inventions described in the claims originally attached to this application are as follows. The claim numbers described in the appendix are the same as those of the claims originally attached to this application.
[Note]
<Claim 1>
a determination means for determining whether a detected voltage corresponding to a charging voltage of a capacitor in an electronic device that is charged by a power source and supplies power when the power source is out of service, and a display means having a light source, is less than a reference voltage;
a control means for stopping the supply of power from the capacitor to the light source of the display means for lighting the light source when the determination means determines that the detected voltage is lower than the reference voltage; and
A display control device comprising:
<Claim 2>
a logical operation means for outputting an output signal representing a logical product of a first signal relating to the determination result by the determination means and a second signal for turning on the light source,
the first signal has a first value corresponding to a true logical value when the determination means determines that the detected voltage is equal to or greater than the reference voltage, and has a second value corresponding to a false logical value when the determination means determines that the detected voltage is less than the reference voltage;
the control means controls the lighting operation of the light source based on the output signal output by the logical operation means.
2. The display control device according to claim 1.
<Claim 3>
the second signal has the second value during a period when the light source is not turned on, and has the first value during at least a part of a period when the light source is turned on;
the logical operation means outputs the output signal having a value corresponding to the same logical value as the second signal when the first signal is the first value, and outputs the output signal having the second value when the first signal is the second value;
3. The display control device according to claim 2.
<Claim 4>
The output signal is input to an enable terminal of the control means,
the control means is enabled in response to the output signal of the first value being input to the enable terminal, and turns on the light source;
4. The display control device according to claim 3.
<Claim 5>
the second signal is a signal that specifies the brightness of the light source;
5. The display control device according to claim 2, wherein the display control device is a display control device for displaying a display image.
<Claim 6>
the second signal is a signal that specifies the brightness of the light source by a duty ratio of a period during which the second signal has the first value;
5. The display control device according to claim 3 or 4.
<Claim 7>
a delay circuit is provided between the capacitor and the discrimination means, which delays the fluctuation of the charging voltage and outputs the delayed fluctuation as the detection voltage to the discrimination means;
7. The display control device according to claim 1, wherein the display control device is a display control device for displaying a display image.
<Claim 8>
A display control device according to any one of claims 1 to 7;
the capacitance;
the display means having the light source;
An electronic device comprising:

1 Electronic equipment 11 CPU
12 RAM
13 Memory unit 131 Program 20 Power supply unit 21 Battery (power supply)
211 Battery holder 22 Auxiliary capacity (capacity)
23 Power supply monitor 231 Delay circuit 2311 Resistor 2312 Diode 2313 Delay circuit capacitance 232 Comparator (determining means)
30 Display unit 31 Liquid crystal driver IC
32 logical product circuit (logical operation means)
33 Light source driver IC (control means)
34 Liquid crystal display (display means)
341 Light source 342 Liquid crystal panel 40 Operation input unit 50 Communication unit 60 Bus 100 Display control device CE Validation terminal S1 First signal S2 Second signal Sout Output signal VBAT Power supply voltage (charging voltage)
VREF Reference voltage VSENSE Detection voltage

Claims (7)

a determination means for determining whether a detected voltage corresponding to a charging voltage of a capacitor in an electronic device that is charged by a power source and supplies power when the power source is out of service, and a display means having a light source, is less than a reference voltage;
a control means for stopping the supply of power from the capacitor to the light source of the display means for lighting the light source when the determination means determines that the detected voltage is lower than the reference voltage; and
a logic operation means for outputting an output signal representing the logical product of a first signal relating to the determination result by the determination means and a second signal for turning on the light source;
Equipped with
the first signal has a first value corresponding to a true logical value when the determination means determines that the detected voltage is equal to or greater than the reference voltage, and has a second value corresponding to a false logical value when the determination means determines that the detected voltage is less than the reference voltage;
the control means controls the lighting operation of the light source based on the output signal output by the logical operation means.
A display control device comprising: the second signal has the second value during a period when the light source is not turned on, and has the first value during at least a part of a period when the light source is turned on;
the logical operation means outputs the output signal having a value corresponding to the same logical value as the second signal when the first signal is the first value, and outputs the output signal having the second value when the first signal is the second value;
2. The display control device according to claim 1 . The output signal is input to an enable terminal of the control means,
the control means is enabled in response to the output signal of the first value being input to the enable terminal, and turns on the light source;
3. The display control device according to claim 2 . the second signal is a signal that specifies the brightness of the light source;
The display control device according to any one of claims 1 to 3 . the second signal is a signal that specifies the brightness of the light source by a duty ratio of a period during which the second signal has the first value;
4. The display control device according to claim 2 or 3 . a delay circuit is provided between the capacitor and the discrimination means, which delays the fluctuation of the charging voltage and outputs the delayed fluctuation as the detection voltage to the discrimination means;
The display control device according to any one of claims 1 to 5 . A display control device according to any one of claims 1 to 6 ;
the capacitance;
the display means having the light source;
An electronic device comprising: