JP2000358338A - Power circuit of electronic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce abrupt voltage drop in a battery by installing an auxiliary power line which runs from a power storage element to a load, placing an on/off switching means in the auxiliary power line, and keeping the on/off switching means on for a certain period after an occurrence of fluctuation in the load. SOLUTION: When the strobe device of a digital still camera is made to flash by photographing operation and its strobe capacitor is discharged, a microcomputer 3 produces a load control signal C, supplies it to a load 1, and charges the strobe capacitor. A first switch 8 is changed over from on to off, when the charging of the strobe capacitor is started and is turned on again, when a fixed time has elapsed. A second switch 9 is changed over from off to on, when the charging of the strobe capacitor is started and is turned off again, when the fixed time has elapsed. Thus battery output voltage drop is reduced of large fluctuation in load, and the battery can be used up to completely until its service life is spent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit of an electronic device which includes a battery such as a dry battery or a secondary battery and supplies power from the battery to a load. The present invention relates to a power supply circuit capable of reducing a temporary decrease.

[0002]

2. Description of the Related Art For example, in a digital still camera, as shown in FIG. 4, a battery (2) such as a dry battery or a secondary battery is built in as a main power supply, and a memory backup of a microcomputer (3) is used as an auxiliary power supply. Capacitor (6) is built-in. The output terminal of the battery (2) is connected to the load (1) via a first power supply line (10).
Connected to the flash device. The strobe device has a built-in strobe capacitor (not shown) for storing power for light emission, and charging of the strobe capacitor is controlled by a load control signal C supplied from a microcomputer (3).

[0003] A second power supply line (14) (15) branches from the first power supply line (10), and the second power supply line (14) (1).
5) is connected to the microcomputer (3). Second
A power management circuit (4) is interposed in the power supply lines (14) and (15), and the supply of power to the microcomputer (3) is managed by the circuit. A power supply voltage monitoring line (16) branches from the second power supply line (14), and the power supply voltage monitoring line (16) is a microcomputer.
Connected to (3). As a result, a battery check is performed by the software of the microcomputer (3). Further, a charging line (13) branches from the second power supply line (15), and the charging line (13) is connected to a memory backup capacitor (6) via a charging circuit (5). The backup capacitor (6) is charged.

The output terminal of the memory backup capacitor (6) is connected to a power management circuit via a discharge line (12).
Connected to (4). Power management circuit (4)
Constantly monitors the output voltage of the battery (2), and when the output voltage drops abnormally, the power stored in the memory backup capacitor (6) is transferred to the discharge line (1).
The power is supplied to the microcomputer 3 via 2) and the second power supply line 15 to back up the memory.

[0005]

In the above-mentioned digital still camera, when the flash device starts charging after the flash device emits light, current suddenly flows from the battery (2) to the load (1). Due to a sudden load change, the output voltage of the battery (2) decreases instantaneously.

By the way, the output voltage of the battery (2) is
As shown in FIG. 5, it gradually decreases as the remaining capacity decreases.
Even if the abrupt load fluctuation described above occurs when the remaining capacity is relatively large (arrow A in the figure), the output voltage at that time decreases only slightly. However, if the above-mentioned sudden load fluctuation occurs when the remaining capacity becomes small (arrow A 'in the figure), the output voltage at that time becomes large. As a result, the output voltage may be lower than the battery check voltage VS1 by software, and may be lower than the reset voltage VS2 by hardware.

When the output voltage of the battery (2) falls below the battery check voltage VS1 for a certain period of time or more, the microcomputer (3) judges that the battery life has expired and shifts to a corresponding processing operation. However, when the output voltage of the battery (2) decreases instantaneously, the microcomputer (3) may not be able to detect this, and the output voltage of the battery (2) may be reduced to the reset voltage. When the voltage drops to VS2, the system is reset on the power management circuit (4) side.
It can no longer be operated continuously. As a result, the battery (2) must be replaced even though the life of the battery (2) has not yet reached.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a power supply circuit of an electronic device which can reduce a sudden voltage drop of a battery at the time of a load change and can fully use the battery up to its life.

[0009]

According to the present invention, there is provided a power supply circuit for an electronic device, comprising: a load; a control circuit for performing a predetermined control operation;
It has a battery serving as a power supply for a load and a control circuit, a storage element serving as an emergency auxiliary power supply for the control circuit, and a charging circuit for charging the storage element with the power of the battery. A power supply auxiliary line is provided, and an on / off switch means is interposed in the power supply auxiliary line. When a sudden change occurs in the load, the on / off switch means is turned on for a certain period from the time when the load change occurs. I do.

In the power supply circuit of the present invention, when a sudden change occurs in the load, the on / off switch means is turned on, and the power supply auxiliary line from the storage element to the load is closed. As a result, the load is supplied with the electric power of the power storage element in addition to the electric power of the battery, so that the load on the battery caused by a sudden load change is reduced. Therefore, even if the remaining capacity of the battery is reduced at that time, the output voltage of the battery is slightly reduced, and there is almost no possibility that the output voltage falls below the reset voltage. Thereafter, when the on / off switch means is turned off, the supply of power from the power storage element to the load is stopped. At this point, however, the load has already fluctuated, so that only the power supply from the battery can be used. The output voltage of the battery does not drop sharply.

In a specific configuration, the control circuit generates a load control signal for starting the supply of power from the battery to the load, and the load control signal is supplied to the timing generation means at the same time when the load control signal is supplied to the load. The timing generation means detects a time point at which a load change occurs based on the load control signal, and creates a timing signal for turning on the on / off switch means for the predetermined period. In this specific configuration, when a load control signal is supplied from the control circuit to the load and the supply of power from the battery to the load is started, a large current flows instantaneously from the battery to the load, and a sudden load Fluctuations occur, but by turning on the on / off switch for a certain period from the time, a decrease in the output voltage of the battery due to a sudden load fluctuation is reduced.

Further, a second on / off switch controlled by the timing signal is interposed in the discharge line from the storage element to the control circuit, and the on / off switch is set to off for the predetermined period. Is done. Thus, during the certain period, all the power of the power storage element is supplied to the load, and it is possible to cope with a large load change.

[0013]

According to the power supply circuit of an electronic device according to the present invention, a decrease in the battery output voltage at the time of a large load change is reduced, so that the battery can be used up to the end of its life. In addition, since the load on the battery at the time of a sudden load change is reduced by the power of the storage element serving as an emergency auxiliary power supply of the control circuit, the existing storage element, which is an existing resource, can be effectively used.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a digital still camera will be specifically described below with reference to the drawings. As shown in FIG. 1, the digital still camera according to the present invention incorporates a battery (2) such as a dry battery or a secondary battery as a main power supply, and a memory backup of a microcomputer (3) as an auxiliary power supply. Capacitor
(6) is built-in. An output terminal of the battery (2) is connected to a strobe device serving as a load (1) via a first power supply line (10). The strobe device has a built-in strobe capacitor (not shown) for storing power for light emission, and charging of the strobe capacitor is controlled by a load control signal C supplied from a microcomputer (3).

A second power supply line (14) (15) and a power supply voltage monitoring line (16) branch off from the first power supply line (10), and the second power supply line (14) (15) is a microcomputer. Power supply voltage monitoring line connected to the power input terminal of (3)
(16) is connected to the power supply voltage monitoring terminal of the microcomputer (3). A power management circuit (4) is interposed in the second power supply lines (14) and (15), and the supply of power to the microcomputer (3) is managed by the circuit. A charging line (13) branches from the second power supply line (15), and the charging line (13) is connected to a memory backup capacitor (6) via a charging circuit (5) including a diode. As a result, the memory backup capacitor (6) is charged.

The output terminal of the memory backup capacitor (6) is connected to a power management circuit via a discharge line (12).
(4), and a first switch (8) composed of a PNP transistor is interposed in the discharge line (12).
The power management circuit (4) constantly monitors the output voltage of the battery (2). When the output voltage drops abnormally, the power stored in the memory backup capacitor (6) is transferred to a discharge line ( The power is supplied to the microcomputer (3) via the second power supply line (12) and the second power supply line (15) to back up the memory.

The output end of the memory backup capacitor (6) is connected to a first power supply line (10) via a power supply auxiliary line (11).
A second switch (9) composed of an NPN transistor is interposed. The load control signal C output from the microcomputer (3) is supplied to the load (1) and at the same time is input to the timing generation circuit (7). The timing generation circuit (7) uses the load control signal C shown in FIG. 3 (a) as one input signal and, as shown in FIG. 3 (b), converts the load control signal into a time constant for a fixed time T by a resistor and a capacitor. The load control signal C is switched from low (L) to high (H) by taking the exclusive OR of both input signals as shown in FIG. A timing signal S which becomes high (H) for the predetermined time T from the time is created. The timing signal S output from the timing generation circuit (7) is supplied to the base of the first switch (8) and to the base of the second switch (9).

In the digital still camera of the present invention, when the strobe device emits light by the photographing operation and the strobe condenser is discharged, the microcomputer
(3) creates the load control signal C shown in FIG. 2 (a) and supplies it to the load (1). As a result, the strobe capacitor is charged. Further, the load control signal C is input to the timing generation circuit (7) and subjected to the above-described signal processing, so that the charge is kept constant from the time when the charging of the strobe capacitor is started, as shown in FIG. High for time T
A timing signal S serving as (H) is created, and the timing signal is supplied to the bases of the first switch (8) and the second switch (9). As a result, the first switch (8)
As shown in FIG. 2 (c), at the start of charging the strobe capacitor, the state is switched from ON (ON) to OFF (OFF), and after a lapse of the predetermined time, it is turned ON again. Also, the second switch (9)
As shown in FIG. 2D, the flash capacitor is switched from off to on at the start of charging, and is turned off again after the predetermined time has elapsed.

As described above, the first switch (8) is turned off and the second switch (9) is turned on for the predetermined time from the start of charging the strobe capacitor, so that the memory backup capacitor (6) is turned off. The power supply to the power management circuit (4) is blocked, and the entire power of the memory backup capacitor (6) is supplied to the power supply auxiliary line (1).
It is supplied to the load (1) via 1). As a result,
The power of the battery (2) and the power of the memory backup capacitor (6) are simultaneously supplied to the load (1), and charging of the strobe capacitor is started. At this time, load
Although a large current flows into (1) instantaneously, this large load fluctuation is absorbed by the power generated by both the battery (2) and the memory backup capacitor (6).
A large drop below the battery check voltage does not occur in the output voltage of the battery (2).

Thereafter, when the timing signal S switches from high to low, the first switch (8) is turned on, the second switch (9) is turned off, and the battery (2) is connected to the load (1).
Only the generated power is supplied. At this time, since the period during which the instantaneous rush current to the strobe capacitor has occurred has ended, the current flowing from the battery (2) to the load (1) is stable, and therefore, the output voltage of the battery (2) is reduced. No significant drop below the reset voltage occurs.

As described above, according to the charging circuit of the present invention,
The decrease in the output voltage of the battery due to a sudden load change is reduced, thereby preventing an unexpected system reset. In addition, the battery can be fully used up to its life. In addition, memory backup capacitors
Since (6) is shared as an auxiliary power source for both the load (1) and the microcomputer (3), the memory backup capacitor (6) can be effectively used, and the size of the apparatus body can be reduced.

The configuration of each part of the present invention is not limited to the above embodiment, and various modifications can be made within the technical scope described in the claims. In addition, it goes without saying that the present invention can be applied not only to a digital still camera but also to various electronic devices including a liquid crystal backlight, a motor, and the like as a load.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a power supply circuit of an electronic device according to the present invention.

FIG. 2 is a time chart illustrating an operation of the power supply circuit.

FIG. 3 is a time chart illustrating an operation of the timing generation circuit.

FIG. 4 is a diagram showing a configuration of a conventional power supply circuit.

FIG. 5 is a graph showing a decrease in output voltage of a battery.

[Explanation of symbols]

 (1) Load (2) Battery (3) Microcomputer (4) Power management circuit (5) Charging circuit (6) Memory backup capacitor (7) Timing generation circuit (8) First switch (9) Second switch (10 ) 1st power supply line (11) auxiliary power line (12) discharge line (13) charging line (14) 2nd power supply line (15) 2nd power supply line (16) power supply voltage monitoring line

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 5/232 H04N 5/232 Z F-term (Reference) 2H053 AA04 AC22 BA00 BA10 DA03 2H054 AA01 5C022 AA13 AB15 AC00 AC69 AC73 5G015 FA13 GB06 HA16 JA07 JA19 JA34 JA53 JA62 5G065 BA02 DA01 DA04 EA02 HA01 JA02 KA02 KA06 MA07 MA10 NA04 NA06

Claims (3)

[Claims] 1. A load, a control circuit controlling a predetermined control operation, a battery serving as a power supply of the load and the control circuit, a power storage element serving as an emergency power supply of the control circuit, and charging the power storage element with the power of the battery. In an electronic device provided with a charging circuit, a power supply auxiliary line from a power storage element to a load is provided, and on / off switch means is interposed in the power supply auxiliary line. A power supply circuit characterized in that the on / off switch means is turned on for a certain period from the time when the fluctuation occurs. 2. The control circuit generates a load control signal for starting supply of power from a battery to a load, and the load control signal is supplied to a timing generation unit at the same time as the load control signal is supplied to the load. 2. The power supply circuit according to claim 1, wherein the timing generation means detects a time point at which a load change occurs based on the load control signal, and generates a timing signal for turning on an on / off switch means for the predetermined period. 3. A discharge line from a storage element to a control circuit includes a second on / off switch controlled by the timing signal, and the on / off switch is set to off for the predetermined period. The power supply circuit according to claim 2, wherein