JP2000347255A - Charge control circuit for stroboscopic device and camera provided with the circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To completely use up a battery until its life by restraining the lowering of the output voltage of the battery associated with charging in a charge control circuit charging a stroboscopic capacitor by supplying the power of the battery to a stroboscope charging circuit through a current control circuit. SOLUTION: This circuit is equipped with a monitor circuit 5 always monitoring the output voltage of the battery 1 in real time, a microcomputer 6 generating a PWM signal S1 for lowering the charge current of the stroboscopic capacitor 4 as an output voltage value monitored by the circuit 5 gets lower in accordance with the output voltage value, and a smoothing circuit 7 smoothing the PWM signal outputted from the microcomputer 6 and supplying it to the current control circuit 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge control circuit for charging a strobe device with electric power obtained from a battery such as a dry battery or a secondary battery, and a camera including the same.

[0002]

2. Description of the Related Art Conventionally, in a strobe device such as a digital still camera, as shown in FIG. 7, electric power generated by a battery (1) is supplied to a strobe charging circuit (11) via a current control circuit (10). Charging a strobe capacitor (not shown), an output voltage of the battery (1) is detected by a voltage detection circuit (12), and the detection signal is supplied to a current control circuit (10). Controls the charging current of the strobe capacitor.

As a control method of the charging current, a difference between an output voltage value when the battery (1) is not loaded and an output voltage value when the load is connected to the battery (1) is detected before charging the strobe capacitor, and based on the detected value. A method is known in which the remaining capacity of the battery (1) is estimated and the charging current is determined according to the estimated value of the remaining capacity (Japanese Patent Application Laid-Open No. 2-93442 [G03B15 /
05]). In this control method, the charging current during the charging period is always maintained at a constant value.

[0004]

The output voltage of the battery gradually decreases as shown in FIG. 8 as the remaining capacity decreases. However, when the remaining capacity is relatively large, it is assumed that the load for strobe charging is applied. However, the decrease in output voltage during charging is slight. However, if the load of strobe charging is applied when the remaining capacity becomes small, the decrease in the output voltage during charging becomes large.

However, in the strobe device employing the conventional charge control method shown in FIG. 7, the charge current is determined prior to the strobe charge, and the charge current is maintained during the charge period. When charging is performed by a battery, the voltage drop from the start of charging to the end of charging becomes large, and as shown in FIG.
There is a possibility that the voltage falls below S1 and further falls below a reset voltage VS2 caused by hardware.

When the output voltage of the battery has fallen below the battery check voltage VS1 for a certain period of time or more, it is determined that the battery has reached the end of its life, and the process proceeds to a corresponding processing operation. Further, when the output voltage of the battery drops to the hard reset voltage VS2, the system is reset, and the operation cannot be continued any longer. As a result, the battery must be replaced even though the battery has not reached its life.

In a conventional digital still camera, if the strobe device is charged while the backlight of the image display device is lit, the load for lighting the backlight and the load for charging the strobe overlap. There is a problem that the output voltage of the battery is significantly reduced and the life of the battery is shortened.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a charge control circuit for a strobe device capable of suppressing a decrease in battery output voltage due to strobe charging and allowing the battery to be fully used up to its life. Another object of the present invention is to suppress a decrease in the battery output voltage even when a strobe device is charged while a backlight of an image display device is turned on in a camera having a strobe device. It is to provide a camera that can do it.

[0009]

A charge control circuit according to the present invention uses a current control circuit to convert electric power obtained from a battery (1).
A charge control circuit for supplying a strobe charging circuit (3) through (2) to charge the strobe device; a voltage monitoring means for constantly monitoring the output voltage of the battery (1) in real time; Charging current control means for generating a control signal for reducing the charging current of the strobe device as the output voltage value decreases according to the output voltage value monitored by the monitoring means, and supplying the control signal to the current control circuit (2); It has.

In the charge control circuit of the present invention, the output voltage of the battery (1) is constantly monitored in real time during the charging period of the strobe device, and the charging current of the strobe device decreases as the output voltage value decreases. Therefore, even when the remaining capacity of the battery (1) is small, the load on the battery (1) is reduced,
A decrease in the output voltage of the battery (1) is suppressed.

In a specific configuration in which the charge control circuit according to the present invention is applied to a camera, the apparatus further includes a control means for a backlight lighting circuit (8) for lighting a backlight (9) of an image display device to be provided. The backlight control means includes:
During the charging period of the strobe device, a brightness control signal for reducing the light emission brightness of the backlight (9) as the output voltage value decreases according to the output voltage value monitored by the voltage monitoring means is generated. Lighting circuit
Supply to (8).

According to the camera of the present invention, even if the strobe device is charged while the backlight (9) is turned on, the output voltage value of the battery (1) is low during the charging period of the strobe device. As the control for lowering the light emission brightness of the backlight (9) is performed as
The load of (1) is only the lighting of the backlight (9), and there is no great difference from the load when the strobe device is not charged. Even when the remaining capacity of the battery (1) is small, the load of the battery (1) is small. The lowering of the output voltage of 1) is suppressed.

[0013]

According to the charge control circuit of the strobe device according to the present invention, a decrease in the battery output voltage due to the strobe charging is suppressed, and the battery can be fully used up to its life. In the camera according to the present invention,
Even when the strobe device is charged while the backlight of the image display device is turned on, the decrease in the battery output voltage is slight.

[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. In the digital still camera according to the present invention,
As shown in FIG. 1, electric power generated by a battery (1) is supplied to a strobe charging circuit (3) via a current control circuit (2).
Strobe condenser by strobe charging circuit (3)
(4) is charged. The output voltage of the battery (1) is constantly monitored in real time by the monitor circuit (5), and the output voltage value obtained by this is input to the microcomputer (6) and used for controlling the charging current.

The microcomputer (6) has a battery
According to the output voltage value of (1), as the output voltage value increases, a PWM signal S1 having a large duty is generated as shown in FIG. 2A, and conversely, as the output voltage value decreases,
As shown in FIG. 2B, a PWM signal S1 having a small duty is used.
And supplies it to the smoothing circuit (7) shown in FIG. Here, the microcomputer (6) generates a PWM signal having a duty substantially proportional to the output voltage Vo of the battery (1), for example, as shown in FIG.

The smoothing circuit (7) is a microcomputer
The PWM signal S1 supplied from (6) is smoothed,
(a) Create a DC reference voltage signal Vr as shown in (b),
The current is supplied to the current control circuit (2). In the current control circuit (2),
The output voltage Vo of the battery (1) is converted into a charging current Is according to the magnitude of the reference voltage signal Vr, and is supplied to a strobe charging circuit (3). Here, the current control circuit (2) determines the charging current I that is substantially proportional to the reference voltage Vr as shown in FIG.
generate s. As a result, the strobe condenser (4) is charged with the charging current Is.

As shown in FIG. 1, a backlight (9) is connected to an output terminal of the battery (1) via a backlight lighting circuit (8). Microcomputer (6)
Generates a PWM signal S2 having a predetermined duty and supplies it to the backlight lighting circuit (8) when the strobe condenser (4) is not charging. PWM shown in 2 (a) and (b)
Similarly to the signal S1, a PWM signal S2 whose duty becomes smaller as the output voltage value of the battery (1) becomes lower is created and supplied to the backlight lighting circuit (8). The backlight lighting circuit (8) is provided with an output voltage V of the battery (1).
o is converted into a drive pulse having a duty corresponding to the PWM signal S2, and is supplied to the backlight (9). As a result, the backlight (9) is turned on with a luminance corresponding to the duty of the PWM signal S2.

In the above digital still camera, after the strobe device emits light and the condenser (4) discharges,
The microcomputer (6) sets P for the smoothing circuit (7).
The supply of the WM signal S1 is started. Thus, the strobe capacitor (4) is charged with the current Is according to the magnitude of the reference voltage signal Vr. That is, when the output voltage Vo of the battery (1) is high, a large reference voltage signal Vr is generated as shown in FIG.
strobe condenser with high charging current Is according to r
(4) is charged, but when the output voltage Vo of the battery (1) is low, a small reference voltage signal Vr is generated as shown in FIG. 2A, and a low charging current corresponding to the reference voltage signal Vr is generated. The flash capacitor (4) is charged by Is. Therefore, when charging the strobe condenser (4) in a state where the remaining capacity of the battery (1) is small, the charging current Is decreases, and the load on the battery (1) is reduced.
This suppresses a sharp drop in the output voltage of the battery (1).

Further, with the backlight (9) turned on,
When charging the strobe condenser (4), use the microcomputer during the charging period of the strobe condenser (4).
(6) PWM based on the output voltage Vo of the battery (1)
The signal S2 is supplied to the backlight lighting circuit (8). As a result, the backlight (9) is adjusted to have a brightness corresponding to the duty of the PWM signal S2. That is, when the output voltage Vo of the battery (1) is high, a driving pulse having a large duty is supplied to the backlight (9),
The backlight (9) emits light with high brightness, but the battery
When the output voltage Vo of (1) is low, a drive pulse having a small duty is supplied to the backlight (9), and the backlight (9) emits light with low luminance. Therefore, when the strobe condenser (4) is charged in a state where the remaining capacity of the battery (1) is small, the power consumed for turning on the backlight is reduced, and the load on the battery (1) is reduced. The rapid drop of the output voltage in (1) is suppressed.

In the digital still camera, the strobe condenser is charged using the signal processing period after photographing, so that there is no problem even if the brightness of the backlight is reduced during charging.

FIGS. 4 to 6 each show a more specific configuration of the charge control circuit. The output voltage of the battery (1) is monitored by voltage dividing resistors R1 and R2. P output from microcomputer (6)
The WM signal S1 is smoothed by a low-pass filter including a resistor R3 and a capacitor C1. In order to generate the charging current Is, a current control circuit (21) of a PWM chopper drive system with a small loss is employed, and a current detection resistor R4 is connected to an output terminal of the current control circuit (21). Thus, the detection signal is fed back to the current control circuit (21).

In the circuit shown in FIG. 4, a flat backlight (91) is employed as the backlight. The backlight lighting PWM signal S2 output from the microcomputer (6) is used as a synchronization signal by the inverter circuit (8).
Supplied to 2). The inverter circuit (82) is a DC voltage V supplied from the battery (1) via the constant voltage circuit (81).
d is an AC drive pulse V corresponding to the PWM signal S2.
c and is supplied to the flat backlight (91). As a result, the flat backlight (91) receives the PWM signal S2.
Is lit at a luminance corresponding to the duty.

In the circuit shown in FIG. 5, an edge light (92) having a fluorescent tube disposed at an edge portion is employed as a backlight. The backlight PWM signal S2 output from the microcomputer (6) is smoothed through a low-pass filter including a resistor R5 and a capacitor C2, and a reference signal obtained by this is converted to a constant voltage circuit.
(83). The constant voltage circuit (83) is a battery (1)
Is converted into a voltage corresponding to the reference signal,
Supply it to the inverter circuit (84). As a result, the inverter circuit (84) generates an AC drive pulse corresponding to the duty of the PWM signal S2 and supplies it to the edge light (92). As a result, the edge light (92) outputs the PWM signal S2
Is lit at a luminance corresponding to the duty.

Further, in the circuit of FIG. 6, a plurality of LEDs (93) connected in series are employed as a backlight. The backlight lighting PWM signal S2 output from the microcomputer (6) is smoothed through a low-pass filter including a resistor R6 and a capacitor C3, and the reference signal obtained by this is supplied to a constant current circuit (85). ing. The constant current circuit (85) converts the output voltage Vo of the battery (1) into a drive current according to the reference signal, and supplies the drive current to the LED (93). A current detection resistor R7 is connected to the LED (93), and the LED (93) and the resistor R7 are connected to the LED (93).
Is monitored by the constant current circuit (85), and the drive current to be supplied to the LED (93) is feedback-controlled. As a result, the LED (93)
The lighting is performed at a luminance corresponding to the duty of the M signal S2.

According to the camera provided with the charge control circuit of the present invention, a remarkable voltage drop accompanying strobe charging in a state where the remaining capacity of the battery is reduced is suppressed.
Further, during the strobe charging period, the difference between the battery output voltage in the steady load state and the battery output voltage in the charging load state is suppressed by reducing the lighting brightness of the backlight. As a result, there is no fear that the determination of the battery life is hastened, and it is possible to maximize the capacity of the battery.

[Brief description of the drawings]

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

FIG. 2 shows a PW created by a microcomputer.
FIG. 4 is a waveform diagram of an M signal.

FIG. 3 is a graph showing a relationship between a reference voltage input to a current control circuit and a charging current supplied to a strobe capacitor.

FIG. 4 is a block diagram showing a specific configuration of the circuit shown in FIG.

FIG. 5 is a block diagram showing another specific configuration of the circuit shown in FIG. 1;

FIG. 6 is a block diagram showing still another specific configuration of the circuit shown in FIG. 1;

FIG. 7 is a block diagram showing a configuration of a conventional charge control circuit.

FIG. 8 is a graph showing a change in battery output voltage.

FIG. 9 is a graph showing a relationship between an output voltage of a battery and a duty of a PWM signal generated by a microcomputer.

[Description of Signs] (1) Battery (2) Current control circuit (3) Strobe charging circuit (4) Strobe condenser (5) Monitor circuit (6) Microcomputer (7) Smoothing circuit (8) Backlight lighting circuit (9 ) Backlight

Claims (2)

[Claims] 1. A charge control circuit for charging a strobe device by supplying electric power obtained from a battery (1) to a strobe charging circuit (3) via a current control circuit (2). A voltage monitoring means for constantly monitoring the output voltage of the strobe device in real time; and a control signal for reducing the charging current of the strobe device as the output voltage value decreases according to the output voltage value monitored by the voltage monitoring means. And a charging current control means for supplying the charging current to the current control circuit (2). 2. An electric power obtained from a battery (1) is supplied to a strobe charging circuit (3) via a current control circuit (2) to charge a strobe device and to a backlight lighting circuit (8). Then, in a camera capable of turning on the backlight (9), a voltage monitor means for constantly monitoring the output voltage of the battery (1) in real time, and an output voltage value monitored by the voltage monitor means, Charge current control means for generating a control signal for reducing the charging current of the strobe device as the output voltage value decreases and supplying the control signal to the current control circuit (2); and voltage monitoring means during the charging period of the strobe device. According to the output voltage value to be monitored, a brightness control signal for reducing the emission brightness of the backlight (9) as the output voltage value decreases is created, Backlight lighting circuit
(8) A camera, comprising: a backlight control means for supplying to (8).