JP2001025161A - Power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong backup time by means of a large capacity of accumulated element, in an electronic apparatus which possesses a load circuit, a main power source to supply a microcomputer with power, and the accumulative element to back up the microcomputer. SOLUTION: A power supply circuit possesses a main power supply line 16, which supplies a microcomputer 5 with the output of a main power source 1, a discharge line 19 which supplies the microcomputer 5 with the output of an accumulating element 8, a voltage regulator 3 which is interposed in the main power supply line 16, a normal charge line 20 which leads to the accumulative element 8 for backup from the voltage regulator 3, auxiliary charge lines 17 and 18 which lead to the accumulating element 8 from the main power source 1, and a transistor 13 which is interposed in the auxiliary charge lines 17 and 18, and the microcomputer 5 turns on or turns off the transistor 13, based on the operation state of a load circuit and the potential of the accumulating element 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic device such as a digital still camera, which includes a main power supply such as a battery, a control circuit including a microcomputer, a load circuit such as a strobe device, and a backup storage element such as a capacitor. The present invention relates to a power supply circuit that supplies power and supplies power from a backup power storage element to a control circuit when the voltage of a main power supply decreases.

[0002]

2. Description of the Related Art Conventionally, in a digital camera, FIG.
As shown in (1), an ASIC (51) for performing signal processing such as compression / expansion of video data, a DC / DC converter (52) constituting a power supply circuit, a strobe device (53) for emitting light at the time of shooting, and an operation state A load circuit such as a liquid crystal display (54), an operation key circuit (55) for generating a signal according to a key operation by a user, and a microcomputer (50) for controlling the operation of these load circuits are provided. ) Is mounted, and each load circuit and microcomputer from main power supply (1)
(50). When the output voltage of the main power supply (1) falls below the threshold value, power is supplied from the backup storage element (8) to the microcomputer (50) to control the microcomputer (50). The minimum power required for storage data retention, etc.).

An output terminal of the main power supply (1) is connected to one input terminal (a) of a power supply changeover switch (7) via a main power supply line (16), and an output of a backup power storage element (8). The end is connected to the other input terminal b of the power switch 7 via the discharge line 19, and the output terminal of the power switch 7 is connected to the microcomputer 5
0) is connected to the power supply terminal Vcc. A voltage regulator (3) is interposed in the main power supply line (16), and the voltage at the output terminal of the voltage regulator (3) is adjusted to 3.2V. The output terminal of the voltage regulator (3) is connected to the backup storage element (8) via the normal charging line (20). Normally, a backflow preventing diode (9) and a current limiting resistor (10) are interposed in the charging line (20).

A divided resistor circuit (2) formed by connecting two resistors in series is connected to an output terminal of the main power supply (1).
(50), the output voltage of the main power supply (1) is constantly monitored. A power supply voltage detection circuit (4) is connected to the output terminal of the main power supply (1), and when the power supply voltage detected by the power supply voltage falls below a predetermined threshold value (3.3 V),
A signal representing the state is created and supplied to the microcomputer (50), and a power switch (7)
As a first switching control signal. Further, a regulator output voltage detection circuit (6) is connected to an output terminal of the voltage regulator (3), and when the output voltage detected by the output terminal falls below a predetermined threshold (2.9V), the state of the output is detected. Is generated and a power switch
(7) is supplied as a second switching control signal. Furthermore,
A backup voltage detection circuit (11) is connected to the discharge line (19). When the backup voltage for the microcomputer (50) falls below a predetermined threshold (2.4 V), the reset circuit (12) operates. Then, the microcomputer (50) is reset.

In the power supply circuit of the digital still camera, when the output voltage Vo of the main power supply (1) is sufficiently high (Vo = 3.3 V to 6.5 V), the power supply voltage detection circuit
In response to the first switching control signal from (4), the power switch 7 is switched to the terminal a. In this state, the output voltage of the main power supply (1) is
Power supply switch after being adjusted to 3.2V
After (7), it is supplied to the microcomputer (50).
The output of the voltage regulator (3) is connected to the normal charging line (2
0), the power is supplied to the backup storage element (8), and the backup storage element (8) is charged.

In this state, if the output voltage of the voltage regulator (3) falls below 2.9 V, for example, when the power of the main power supply (1) is consumed, the second output from the regulator output voltage detection circuit (6) is generated. In response to the switching control signal, the power switch 7 is switched to the terminal b. As a result, the output of the backup storage element (8) is supplied to the microcomputer (50) via the power switch (7).

The discharge of the backup storage element (8) proceeds, and the voltage supplied to the microcomputer (50) becomes 2.
When the voltage falls below 4V, this is the backup voltage detection circuit (11)
And the microcomputer (50) is reset by the reset circuit (12). This prevents runaway of the microcomputer (50).

[0008]

In order to extend the backup time by the backup storage element (8) as much as possible, the capacity of the backup storage element (8) may be increased. Since a current limiting resistor (10) is connected to (8), a long time is required to charge the backup storage element (8) to a predetermined potential, and the backup storage element (8) is If the backup is started in a state where the battery is not charged to the potential, there is a problem that a desired backup time cannot be obtained.

Therefore, an object of the present invention is to extend the backup time by rapidly charging the backup storage element (8) even when a large-capacity backup storage element (8) is employed in the power supply circuit. It is to plan.

[0010]

According to the present invention, there is provided an electronic apparatus comprising:
A load circuit that performs a predetermined operation when supplied with power, a control circuit that controls the operation of the load circuit, a main power supply (1) that supplies power to the load circuit and the control circuit, and a main power supply
(1) a backup power storage element (8) for supplying power required for control operation to the control circuit when the output voltage drops.

In the above electronic device, the power supply circuit is
A main power supply line (16) for supplying the output of the main power supply (1) to the control circuit, and a backup storage element (8)
A discharge line (19) for supplying the output of the
Power supply switching means for switching between a main power supply line (16) and a discharge line (19) and connecting to a control circuit; and a voltage regulator (3) interposed in the main power supply line (16)
A normal charging line (20) from the output terminal of the voltage regulator (3) to the backup storage element (8);
An auxiliary charging line (17) (18) extending from the output end of (1) to the backup storage element (8), and switching means interposed in the auxiliary charging line (17) (18), Power supply (1)
The switching control of the power supply switching means is performed in accordance with the output voltage of the power storage device, and the opening and closing of the switching means is controlled based on the operation state of the load circuit and the potential state of the output terminal of the backup storage element (8).

Specifically, the control circuit determines a normal operation state in which the power consumption of the load circuit increases and an operation halt state in which the power consumption of the load circuit decreases. The control signal for closing the opening / closing means is supplied to the opening / closing means on condition that the potential at the output terminal of (8) is equal to or lower than a predetermined threshold.

In the power supply circuit of the present invention, when the output voltage of the main power supply (1) is sufficiently high, the power supply switching means is switched to the main power supply (1).
In this state, after the output voltage of the main power supply (1) is adjusted by the voltage regulator (3), it is supplied to the control circuit via the power supply switching means. When the power of the main power supply (1) is consumed and the output voltage of the voltage regulator (3) falls below a predetermined threshold, the power supply switching means is switched to the backup power storage element (8). Thus, the output of the backup storage element (8) is supplied to the control circuit via the power supply switching means.

The output of the voltage regulator (3) is supplied to the backup storage element (8) via the normal charging line (20), and the backup storage element (8) is charged.
Here, when the load circuit is in the operation halt state with low power consumption and the potential of the output terminal of the backup power storage element (8) is equal to or lower than a predetermined threshold, the opening / closing means is closed and the main power supply ( Output of 1) is auxiliary charging line (17) (18)
Through the auxiliary charging line (1) at the same time as charging by the normal charging line (20).
7) Charging according to (18) is performed. At this time, the main power supply
Since the output voltage of (1) is higher than the output voltage of the voltage regulator (3), the backup storage element (8) is rapidly charged.

In a normal operation state in which the power consumption of the load circuit increases, the opening / closing means is opened and all the power from the main power supply (1) is supplied to the voltage regulator (3).
There is no shortage of power to be supplied to the load circuit. or,
Even in the operation halt state in which the power consumption of the load circuit is reduced, when the potential of the output terminal of the backup storage element (8) exceeds a predetermined threshold, the opening / closing means is opened and the auxiliary charging line (17) is opened. Backup storage element according to (18)
Since the charging of (8) is stopped, the backup storage element
There is no fear that an excessive voltage is applied to (8).

[0016]

According to the power supply circuit for an electronic device of the present invention, even when a large-capacity backup storage element (8) is provided, the backup storage element (8) is charged at a higher voltage than before. As a result, quick charging is possible.
Further, by providing a large-capacity backup electricity storage element (8), a longer backup time than before can be obtained.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a digital still camera shown in FIG. 2 will be specifically described with reference to the drawings. In the digital still camera according to the present invention, as shown in FIG. 1, an ASIC (51), a DC / DC
Converter (52), strobe device (53), liquid crystal display (54),
The load circuit such as the operation key circuit (55) is a microcomputer
(5), and usually supplies power of a main power supply (1) composed of a battery or an AC adapter to each load circuit and the microcomputer (5). When the output voltage of the main power supply (1) drops, the power of the backup storage element (8) composed of an electrolytic capacitor is supplied to the microcomputer (5).
Control operation (5) (timer operation, retention of stored data, etc.)
The minimum power required for

An output terminal of the main power supply (1) is connected to one input terminal a of a power supply changeover switch (7) via a main power supply line (16), and an output of a backup power storage element (8). The end is connected to the other input terminal b of the power supply changeover switch (7) via the discharge line (19), and the output terminal of the power supply changeover switch (7) is connected to the microcomputer.
It is connected to the power supply terminal Vcc of (5). A voltage regulator (3) is interposed in the main power supply line (16), and the voltage at the output terminal of the voltage regulator (3) is adjusted to 3.2V. The output terminal of the voltage regulator (3) is connected to the backup storage element (8) via the normal charging line (20). Normally, a backflow preventing diode (9) and a current limiting resistor (10) are interposed in the charging line (20).

A divided resistor circuit (2) formed by connecting two resistors in series is connected to an output terminal of the main power supply (1), and a divided voltage obtained from a middle point between the two resistors is monitored by a voltage monitor. line
The output voltage of the main power supply (1) is supplied to the microcomputer (5) via (23) and is constantly monitored. A power supply voltage detection circuit (4) is connected to an output terminal of the main power supply (1). When the power supply voltage detected by the power supply voltage falls below a predetermined threshold (3.3 V), the state is indicated. A signal is created and supplied to the microcomputer (5), and is also supplied to the power switch (7) as a first switching control signal. Further, a regulator output voltage detection circuit (6) is connected to an output terminal of the voltage regulator (3), and when the output voltage detected by the output terminal falls below a predetermined threshold (2.9V), the state of the output is detected. Is generated and supplied to the power switch 7 as a second switching control signal. Furthermore, discharge line (19)
Is connected to a backup voltage detection circuit (11). When the backup voltage for the microcomputer (5) falls below a predetermined threshold value (2.4 V), the reset circuit (12) is activated to operate the microcomputer. Reset (5).

The above configuration is the same as that of the conventional digital still camera shown in FIG. 2, but in the digital camera according to the present invention, the output terminal of the main power supply (1) is connected to the auxiliary charging lines (17) (18). ), The backup storage element (8)
It is connected to the. The auxiliary charging lines (17) and (18) include a switching transistor (13), a current limiting resistor (14), and a backflow prevention diode (15). The auxiliary charging line (17) on the main power supply (1) side is connected to the emitter of the switching transistor (13), and the auxiliary charging line (18) on the side of the backup storage element (8) is connected to the collector of the switching transistor (13). Connected to. The base of the switching transistor (13) is connected to the microcomputer (5) via the control line (21), and the microcomputer (5) turns on / off the switching transistor (13) by the control line (21). Off control is possible.

The midpoint between the current limiting resistor (14) and the backflow preventing diode (15) is connected to a microcomputer (5) via a voltage monitoring line (22). Is based on the voltage Vm obtained from the voltage monitoring line (22) and the voltage Vo of the main power supply (1) obtained from the voltage monitoring line (23). It is possible to estimate the potential Vc. For example, a current flowing through the current limiting resistor (14) of the auxiliary charging line (18) is calculated from the two voltages, and a voltage drop due to the backflow prevention diode (15) is estimated from the calculation result. ) Can be derived. The microcomputer (5) controls on / off of the switching transistor (13) as described later, based on the operation state of the digital still camera and the voltage Vc at the output terminal of the backup storage element (8). It is.

In the digital still camera of the present invention, when a power switch (not shown) is turned on, a normal operation state is set, and electric power is supplied to each load circuit and the microcomputer (5), so that photographing, Image recording,
It is possible to reproduce images and the like. In the normal operation state, the switching transistor (13) is always turned off. Here, when the output voltage Vo of the main power supply (1) is sufficiently high (Vo = 3.3V to 6.5V), the power supply changeover switch () is supplied by the first changeover control signal from the power supply voltage detection circuit (4). 7) is switched to the terminal a. In this state, the output voltage of the main power supply (1) is
After being adjusted to 3.2 V by (3), the voltage is supplied to the microcomputer (5) via the power switch (7). In this way, all the power from the main power supply (1) is supplied to the voltage regulator (3), so that the power required for normal operation of the digital still camera does not run short.

When the output voltage of the voltage regulator (3) falls below 2.9 V due to the consumption of the power of the main power supply (1) or the stop of the power supply from the main power supply (1), Regulator output voltage detection circuit
In response to the second switching control signal from (6), the power switch (7) is switched to the terminal b. Thus, the output of the backup storage element (8) is supplied to the microcomputer (5) via the power switch (7). The output of the voltage regulator (3) is supplied to the backup storage element (8) via the normal charging line (20), and the backup storage element (8) is charged.

The discharge of the backup storage element (8) proceeds, and the voltage supplied to the microcomputer (5) becomes 2.
When the voltage falls below 4V, this is the backup voltage detection circuit (11)
And the microcomputer (5) is reset by the reset circuit (12). This prevents runaway of the microcomputer (5).

Thereafter, when the output voltage Vo of the main power supply (1) recovers to 3.3 V or more by replacing the battery or the like,
The state is detected by the power supply voltage detection circuit (4), and by the first switching control signal from the power supply voltage detection circuit (4),
The power switch 7 is switched to the terminal a, and the power of the main power supply 1 is supplied to the microcomputer 5.

When a power switch (not shown) is turned off, an operation pause state is set, and the microcomputer is turned off.
Power is supplied only to (5), and the power required for the minimum control operation such as the timer operation and the retention of stored data is covered.

When the output voltage Vo of the main power supply (1) is sufficiently high (Vo = 3.3V to 6.5V), the power supply voltage detection circuit
In response to the first switching control signal from (4), the power switch 7 is switched to the terminal a. In this state, the output voltage Vo of the main power supply (1) is
After being adjusted to 3.2 V by (3), the voltage is supplied to the microcomputer (5) via the power switch (7).

When the output voltage of the voltage regulator (3) falls below 2.9 V due to the consumption of the power of the main power supply (1) or the stop of the power supply from the main power supply (1), Regulator output voltage detection circuit
In response to the second switching control signal from (6), the power switch (7) is switched to the terminal b. As a result, the output voltage Vc of the backup storage element (8) passes through the power switch (7) and is supplied to the microcomputer.
(5). The output of the voltage regulator (3) is supplied to the backup storage element (8) via the normal charging line (20), and the backup storage element (8) is charged.

In the idle state, the switching transistor (13) is on / off controlled as described later. That is, when the potential of the output terminal of the backup storage element (8) detected by the microcomputer (5) is less than or equal to 3.2 V, the switching transistor (13) is turned on and the main power supply (1) is turned on. The output of the auxiliary charging line
Through (17) and (18), the battery is supplied to the backup storage element (8), and is charged by the auxiliary charging lines (17) and (18) simultaneously with charging by the normal charging line (20). At this time, the output voltage Vo (3.3 V to 6.5 V) of the main power supply (1) is higher than the output voltage (3.2 V) of the voltage regulator (3). Will be charged.

On the other hand, when the potential at the output terminal of the backup storage element (8) detected by the microcomputer (5) exceeds a predetermined threshold, the switching transistor (13) is set to OFF, Auxiliary charging line (1
7) The charging of the backup storage element (8) by (18) is stopped. Therefore, there is no possibility that an excessive voltage exceeding the threshold value is applied to the backup storage element (8).

In the digital still camera according to the present invention, even when a large-capacity backup storage element (8) is provided, the backup storage element (8) is a conventional voltage storage element.
Since the battery is charged at a voltage (3.3 V or higher) higher than (3.2 V or lower), quick charging is possible.

FIG. 3 shows the change over time of the output voltage when the backup storage element 8 composed of a capacitor is discharged. As shown in the figure, when the discharge is started from the output voltage V1, the voltage first drops to V2 due to the internal resistance of the capacitor, and then the voltage gradually decreases to the lower limit voltage V3 at which the microcomputer (5) can operate. The backup of the microcomputer (5) can be performed until the number of times reaches (5). In the digital still camera of the present invention, since the backup storage element (8) is charged to the voltage V1 'higher than before, a longer backup time (T1 to T2') than before can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a digital still camera according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of a conventional digital still camera.

FIG. 3 is a graph showing a time change of an output potential of a backup storage element.

[Explanation of symbols]

 (1) Main power supply (2) Divider resistance circuit (3) Voltage regulator (4) Power supply voltage detection circuit (5) Microcomputer (6) Regulator output voltage detection circuit (7) Power switch (8) Backup storage element ( 11) Backup voltage detection circuit (12) Reset circuit (13) Switching transistor (16) Main power supply line (17) Auxiliary charge line (18) Auxiliary charge line (19) Discharge line (20) Normal charge line (21) Control Line (22) Voltage monitoring line (23) Voltage monitoring line

Continued on the front page F term (reference) 5C022 AA13 AB15 AC11 AC31 AC32 AC69 AC73 5G003 AA04 BA02 CA11 CC02 DA02 DA05 FA08 GC05 5G015 GB06 HA13 JA05 JA34 JA53 JA60 KA05 5G065 AA00 DA02 EA02 GA06 HA17 JA02 JA07 KA02 LA01 MA10 NA01

Claims (2)

[Claims] 1. A load circuit that performs a predetermined operation when supplied with power, a control circuit that controls the operation of the load circuit,
Main power supply (1) for supplying power to load circuit and control circuit
And a backup power storage element (8) for supplying power required for a control operation to the control circuit when the output voltage of the main power supply (1) decreases. ) Output to the control circuit, a main power supply line (16), and a backup storage element
Discharge line for supplying the output of (8) to the control circuit (19)
Power supply switching means for switching between a main power supply line (16) and a discharge line (19) to connect to a control circuit, and a voltage regulator interposed in the main power supply line (16)
(3), a normal charging line (20) from the output terminal of the voltage regulator (3) to the backup storage element (8), and an auxiliary from the output terminal of the main power supply (1) to the backup storage element (8). Charging line (17) (18) and auxiliary charging line (17) (18)
The control circuit comprises a main power supply.
The switching control of the power supply switching means is performed according to the output voltage of (1), and the switching of the switching means is controlled based on the operation state of the load circuit and the potential state of the output terminal of the backup storage element (8). A power supply circuit, characterized in that: The control circuit determines a normal operation state in which the power consumption of the load circuit increases and an operation halt state in which the power consumption of the load circuit decreases, and in the operation halt state, controls the backup power storage element. 2. The power supply circuit according to claim 1, wherein a control signal for closing the opening / closing means is supplied to the opening / closing means on condition that the potential of the output terminal of the switching element is not more than a predetermined threshold value.