JP4039770B2 - Electronic equipment power supply circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power supply circuit of an electronic device that includes a battery such as a dry battery or a secondary battery and supplies electric power from the battery to a load, and in particular, to reduce an instantaneous decrease in battery voltage during a sudden load change. The present invention relates to a power supply circuit that can
[0002]
[Prior 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 incorporated as a main power source, and a capacitor (6) for memory backup of a microcomputer (3) as an auxiliary power source. ) Is built-in.
The output end 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) that stores electric power for light emission, and charging of the strobe capacitor is controlled by a load control signal C supplied from the microcomputer (3).
[0003]
A second power supply line (14) (15) branches off from the first power supply line (10), and the second power supply line (14) (15) is connected to 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 power supply voltage monitoring line (16) branches from the second power supply line (14), and the power supply voltage monitoring line (16) is connected to the microcomputer (3). Thereby, a battery check is performed by software of the microcomputer (3).
Further, the charging line 13 branches from the second power supply line 15 and the charging line 13 is connected to the memory backup capacitor 6 through the charging circuit 5, whereby the memory The backup capacitor (6) is charged.
[0004]
The output terminal of the memory backup capacitor (6) is connected to the power management circuit (4) through 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 the discharge line ( 12) and the second power supply line (15) to be supplied to the microcomputer (3) to back up the memory.
[0005]
[Problems to be solved by the invention]
In the digital still camera, when the strobe capacitor starts to be charged after the strobe device emits light, current suddenly flows from the battery (2) to the load (1), and the battery (2 ) Output voltage drops instantaneously.
[0006]
By the way, the output voltage of the battery (2) gradually decreases as the remaining capacity decreases as shown in FIG. 5, but even if the aforementioned sudden load fluctuation occurs when the remaining capacity is relatively large (in the figure). Arrow A), the decrease in the output voltage at that time is slight. However, if the above-mentioned sudden load fluctuation occurs when the remaining capacity becomes small (arrow A ′ in the figure), the decrease in output voltage at that time becomes large. As a result, there is a possibility that the output voltage is lower than the battery check voltage VS1 by software, and further lower than the reset voltage VS2 by hardware.
[0007]
When the output voltage of the battery (2) falls below the battery check voltage VS1 for a certain time or more, the microcomputer (3) determines that the battery life is reached and shifts to a corresponding processing operation.
However, when the drop in the output voltage of the battery (2) is momentary, the microcomputer (3) may not be able to detect this, and the output voltage of the battery (2) is also the reset voltage. When the voltage drops to VS2, the system is reset on the power management circuit (4) side, so that it can no longer be operated continuously.
As a result, the battery (2) must be replaced even though the battery (2) has not yet reached the end of its life.
[0008]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a power supply circuit for an electronic device that can reduce a sudden voltage drop of a battery when a load fluctuates and can fully use the battery until its lifetime.
[0009]
[Means for solving the problems]
A power supply circuit for an electronic device according to the present invention includes a load, a control circuit that performs a predetermined control operation, a battery that serves as a power source for the load and the control circuit, a storage element that serves as an emergency auxiliary power supply for the control circuit, and a battery And a power supply auxiliary line from the power storage element to the load, and an on / off switch means is interposed in the power supply auxiliary line to cause a sudden change in the load. When this occurs, the on / off switch means is turned on for a certain period from the time of occurrence of the load fluctuation.
[0010]
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 power storage element to the load is closed. As a result, in addition to the power of the battery, the power of the power storage element is supplied to the load, so that the burden on the battery due to a sudden load change is reduced. Therefore, even if the remaining capacity of the battery is small at that time, the decrease in the output voltage of the battery is slight, and there is almost no possibility that the output voltage falls below the reset voltage.
After that, when the on / off switch means is turned off, the supply of power from the power storage element to the load is stopped, but at that time, since the fluctuation of the load has already been settled, only by the power supply from the battery, The battery output voltage does not drop rapidly.
[0011]
In a specific configuration, the control circuit creates 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 as being supplied to the load, The timing generation means detects a load fluctuation occurrence point based on the load control signal, and creates a timing signal for turning on the on / off switch means for the predetermined period.
In the specific configuration, when a load control signal is supplied from the control circuit to the load and supply of power from the battery to the load is started, a large current instantaneously flows from the battery to the load, and a sudden load is applied. Although fluctuations occur, by turning on the on / off switch means for a certain period from that time point, a decrease in the output voltage of the battery due to a sudden load fluctuation is reduced.
[0012]
In addition, the second on / off switch means controlled by the timing signal is interposed in the discharge line from the storage element to the control circuit, and the on / off switch means is set off for the predetermined period.
Thereby, during the certain period, all the electric power of the power storage element is supplied to the load, and it is possible to cope with a large load fluctuation.
[0013]
【The invention's effect】
According to the power supply circuit for an electronic device according to the present invention, the 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 its lifetime. In addition, since the load on the battery at the time of a sudden load change is reduced by the electric power of the storage element serving as an emergency auxiliary power source for the control circuit, the storage element that is an existing resource can be effectively used.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention 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 has a built-in battery (2) such as a dry battery or a secondary battery as a main power source, and a memory backup for a microcomputer (3) as an auxiliary power source. A capacitor (6) is incorporated.
The output end 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) that stores electric power for light emission, and charging of the strobe capacitor is controlled by a load control signal C supplied from the microcomputer (3).
[0015]
From the first power supply line (10), a second power supply line (14) (15) and a power supply voltage monitoring line (16) branch, and the second power supply line (14) (15) is a microcomputer (3). The power supply voltage monitoring line (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) through a charging circuit (5) comprising a diode. As a result, the memory backup capacitor (6) is charged.
[0016]
The output terminal of the memory backup capacitor (6) is connected to the power management circuit (4) via the discharge line (12), and the first switch (8) made of a PNP transistor is interposed in the discharge line (12). is doing.
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 the discharge line ( 12) and the second power supply line (15) to be supplied to the microcomputer (3) to back up the memory.
[0017]
The output terminal of the memory backup capacitor (6) is connected to the first power supply line (10) via the power auxiliary line (11), and the power auxiliary line (11) includes a second NPN transistor. Two switches (9) are interposed.
The load control signal C output from the microcomputer (3) is supplied to the load (1) and simultaneously 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 sets the time constant for a certain time T by a resistor and a capacitor as shown in FIG. The load control signal C is switched from low (L) to high (H) by taking the exclusive OR of both the input signals as shown in FIG. A timing signal S that is high (H) for a certain time T from the time is generated.
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).
[0018]
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. , Supplied to load (1). As a result, the strobe capacitor is charged.
In addition, the load control signal C is input to the timing generation circuit (7) and subjected to the above-described signal processing, so that the charging of the strobe capacitor is constant as shown in FIG. 2 (b). A timing signal S that is high (H) for a time T 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) is switched from on (ON) to off (OFF) at the start of charging the strobe capacitor as shown in FIG. 2 (c), and is turned on again after the predetermined time has elapsed. Further, as shown in FIG. 2D, the second switch (9) is switched from OFF to ON at the start of charging of the strobe capacitor, and is turned OFF again after the predetermined time has elapsed.
[0019]
As described above, the first switch (8) is turned off and the second switch (9) is turned on for a certain period of time from the start of charging the strobe capacitor, thereby turning on the power management circuit from the memory backup capacitor (6). The power supply to (4) is blocked, and the entire power of the memory backup capacitor (6) is supplied to the load (1) through the power supply auxiliary line (11).
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, a large current flows instantaneously into the load (1), but this large load fluctuation is absorbed by the generated power of both the battery (2) and the memory backup capacitor (6), so the battery (2) There is no significant drop in the output voltage below the battery check voltage.
[0020]
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 load (1) has only the power generated by the battery (2). Will be supplied. At this time, since the generation period of the instantaneous inrush current to the strobe capacitor 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 There is no significant drop below the reset voltage.
[0021]
As described above, according to the charging circuit of the present invention, a 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 used up to the end of its life.
Furthermore, since the memory backup capacitor (6) is shared as an auxiliary power source for both the load (1) and the microcomputer (3), the memory backup capacitor (6) can be used effectively and the device body can be downsized. Is planned.
[0022]
In addition, each part structure of this invention is not restricted to the said embodiment, A various deformation | transformation is possible within the technical scope as described in a claim. Needless to say, 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 showing the operation of the power supply circuit.
FIG. 3 is a time chart showing the 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) First power supply line
(11) Power auxiliary line
(12) Discharge line
(13) Charging line
(14) Second power supply line
(15) Second power supply line
(16) Power supply voltage monitoring line

Claims (3)

A load, a control circuit that performs a predetermined control operation, a battery that is a power source for the load and the control circuit, a power storage element that is an emergency power source for the control circuit, and a charging circuit that charges the power storage element with the power of the battery In the provided electronic device, a power supply auxiliary line from the power storage element to the load is provided, and an on / off switch means is interposed in the power supply auxiliary line so that when a sudden change occurs in the load, from the time when the load change occurs. A power supply circuit, wherein the on / off switch means is turned on for a certain period. The control circuit creates 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 as being supplied to the load. 2. The power supply circuit according to claim 1, wherein a time point at which a load change occurs is detected based on a load control signal, and a timing signal for turning on the on / off switch means is generated for the predetermined period. The second on / off switch means controlled by the timing signal is interposed in the discharge line from the storage element to the control circuit, and the on / off switch means is set to be off for the predetermined period. The power supply circuit described in 1.

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