JP3847646B2 - Camera with flash - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a camera with a flash that operates with a rechargeable battery, and more particularly to a camera with a flash that can save power in a rechargeable battery.
[0002]
[Prior art]
An increasing number of cameras use a rechargeable battery such as a nickel metal hydride battery. For example, the power source of a digital still camera is mostly a rechargeable battery, and when the battery is exhausted, it is not necessary to replace the battery like an alkaline battery. For this reason, it is necessary to aim at power saving of a rechargeable battery so that a battery may not run out on the way.
[0003]
The flash consumes the most power on the camera. When the flash is emitted, the flash light emitting capacitor is always fully charged. However, if shooting is stopped with the capacitor fully charged, a large amount of energy remains in the capacitor. The present situation is that the remaining energy of this capacitor is wasted due to natural discharge.
[0004]
By making available the residual energy of this capacitor, it is possible to save power for the rechargeable battery. For example, the conventional technique described in Japanese Patent Laid-Open No. 7-301843 has a wiring path that allows the camera motor to be driven by the energy of the capacitor, so that the remaining energy of the capacitor can be used effectively. Is possible.
[0005]
[Problems to be solved by the invention]
However, the above-described conventional technology is not a technology whose main purpose is to effectively use the remaining energy of the capacitor. Therefore, when the camera power is turned off when the capacitor is fully charged, the remaining energy of the capacitor is spontaneously discharged. Will be thrown away in vain.
[0006]
An object of the present invention is to provide a camera with a flash that does not waste energy remaining in a capacitor when the camera is turned off.
[0007]
[Means for Solving the Problems]
A camera with a flash that achieves the above object includes a rechargeable battery, a flash light emitting unit, a capacitor that supplies power to the flash light emitting unit, and a capacitor that boosts the output voltage of the rechargeable battery and charges the capacitor. a charging circuit, and chargeback circuit steps down the remaining voltage of the capacitor when the input of a power off command to a voltage value higher than the output voltage value of the rechargeable battery for charging the rechargeable power cell back to the rechargeable battery It is provided with. With this configuration, the energy remaining in the capacitor can be used effectively, and a larger number of images can be taken with a small battery capacity.
[0008]
Preferably, in the above, the capacitor charging circuit is configured to operate as the chargeback circuit. With this configuration, the number of circuit components is reduced, the manufacturing cost is reduced, and the installation space can be effectively used.
[0009]
More preferably, in the above, there is provided means for variably setting the step-down ratio of the chargeback circuit in accordance with the value of the residual voltage of the capacitor. With this configuration, the remaining energy of the capacitor can be efficiently returned to the rechargeable battery, and a further power saving effect can be obtained.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0011]
FIG. 1 is an external view of a camera with a flash according to an embodiment of the present invention. The digital still camera 1 according to this embodiment is equipped with a flash lamp 2 that can be housed in the camera body at the right shoulder corner when viewed from the front, and a lens mirror that houses a photographing lens in the center. A barrel 3 is provided.
[0012]
The lens barrel 3 is retracted into the camera body when the power of the camera 1 is turned off, and the front surface of the photographing lens is protected by a lens barrier (not shown), but is extended forward when the power is turned on, as shown in FIG. It becomes a state.
[0013]
An autofocus AF sensor 4, a photometric sensor 5, and a finder window 6 are provided above the lens barrel 3 of the camera body, and a two-stage shutter release provided at the top of the camera body. When the button 7 is half-pressed, the AF sensor 4 measures the distance to the subject, the photometric sensor 5 measures the brightness of the subject, and when the two-stage shutter release button 7 is fully pressed, the distance to the subject is measured. The lens barrel 3 is extended so as to be in focus, a shutter (not shown) is opened and closed, and photographing is performed.
[0014]
FIG. 2 is a functional configuration diagram of the imaging system and the control system of the digital still camera 1 described above. An image sensor and a control system of the digital still camera 1 are provided in the main body of the camera 1, and an image sensor 10 such as a CCD disposed on an optical path of a photographing lens provided in the lens barrel 3 is an image sensor 10. Is connected to the image pickup circuit 11 that takes
[0015]
The imaging circuit 11 includes an image memory 12, an external storage device 13 such as a memory card that is detachably attached to the digital still camera 1, a driving device for an LCD panel 15 provided on the back of the camera body, and a control CPU 16. Are interconnected via a bus 17.
[0016]
The main body of the digital still camera 1 is further provided with a flash control unit 18 that controls the light emission of the flash lamp 2, a zoom control unit 19, an automatic focus (AF) control unit 20, and an aperture control unit 21, These are controlled by the control CPU 16 based on a user instruction input from the photographing operation unit 22 including the shutter release button 7.
[0017]
The digital still camera 1 houses a rechargeable battery 30 such as a nickel metal hydride battery, and the driving voltages of the control units 18, 19,..., The circuits 11, 12,. Are generated from the output voltage of the rechargeable battery 30 and supplied to each.
[0018]
FIG. 3 is a detailed block diagram of the flash controller 18 shown in FIG. The flash control unit 18 includes a first conversion circuit 31 connected to the rechargeable battery 30, a xenon tube 32 serving as a light emitting unit of the flash lamp 2, and a capacitor 33 that stores electric charges for causing the xenon tube 32 to emit light. A trigger coil 35 connected to the output end of the capacitor 33 via a resistor 34 and applying a trigger signal to the xenon tube 32; and a light emission connected to the xenon tube 32 to cut off the current flow to the xenon tube 32 according to the detected light quantity. The stop switch 36, the second conversion circuit 37 connected to the capacitor 33, the transformation transformer 38 connecting the first conversion circuit 31 and the second conversion circuit 37, and the voltage at the output terminal of the capacitor 33 are detected. And a voltage detection circuit 39.
[0019]
The control CPU 16 takes in the detection voltage value of the voltage detection circuit 39 and outputs a control command to the first conversion circuit 31 and the second conversion circuit 37, and normally the first conversion circuit 31, the second conversion circuit 37, and the transformation transformer. As shown in detail later, the flash capacitor charging circuit composed of 38 is made to function as a chargeback circuit, and the rechargeable battery 30 is charged with the remaining energy of the capacitor.
[0020]
FIG. 4 is a flowchart showing a procedure in which the control CPU 16 controls the flash light emitting unit 18. When the camera power supply is turned on (step S1), first, charging of the capacitor 33 is started (step S2).
[0021]
The rechargeable battery 30 outputs a DC voltage of about 4.5 V, for example, and the control CPU 16 outputs a control command to the first conversion circuit 31 to intermittently convert the DC voltage into an AC voltage. The transformation transformer 38 boosts the voltage of 4.5V to the AC voltage of 300V, and the second conversion circuit 37 rectifies the AC voltage of 300V in response to a command from the control CPU 16 and charges the capacitor 33.
[0022]
When the charging of the capacitor 33 is finished in the next step S3, it is in a standby state until photographing, and then in step S4, it is determined whether or not photographing is performed. This determination is made based on whether or not the shutter release button 7 is fully pressed. When the shutter release button 7 is fully pressed, flash emission control is performed in step S5, and one shooting is completed.
[0023]
Although detailed illustration of the shooting procedure is omitted in FIG. 4, photometry and distance measurement are performed in the half-pressed state before the shutter release button 7 is fully pressed, and when the shutter release button 7 is fully pressed, the shooting is performed. The lens is extended to the in-focus position and the shutter is opened and closed, and then the photographing lens position is returned to the state shown in FIG.
[0024]
When the flash emission is performed in step S5, that is, when a current flows from the capacitor 33 to the xenon tube 32, the camera 1 detects the reflected light from the subject, and the flash emission amount becomes the emission amount necessary for the optimum exposure. When it is determined that the light has reached, the light emission stop switch 36 cuts off the current.
[0025]
For example, when shooting a distant view or when the surroundings are dark, it is necessary to emit a large amount of light. However, when shooting close-up or when the surroundings are bright, a small amount of light is sufficient. For this reason, the amount of residual energy of the capacitor 33 varies depending on the shooting distance and the like.
[0026]
In terms of the terminal voltage of the capacitor 33, the residual voltage of the capacitor 33 when full light emission is performed is about 50V, but the residual voltage after a close-up photographing of about several centimeters is about 280V. For this reason, after waiting for the next photographing, after step S5, the process returns to step S2 to start charging the capacitor 33, but the time required to fully charge the capacitor 33 differs depending on the previous light emission state.
[0027]
If it is determined in step S4 that the shutter release button 7 has not been fully pressed, the process proceeds from step S4 to step S6, and it is determined whether or not the user has turned off the power switch of the camera 1. If it is determined that the power switch is not turned off, the process returns to step S4 to wait for shooting.
[0028]
If it is determined in step S6 that the power switch has been turned off, in the present embodiment, the following steps S7, S8, and S9 are performed before step S10 that actually turns off the power of the camera 1. That is, in step S 7, the voltage detection circuit 39 detects the value of the terminal voltage of the capacitor 33.
[0029]
After about 5 seconds from shooting, since the capacitor 33 is in a fully charged state, its terminal voltage is constant at 300 V. However, as described above, the charging time required for full charging according to the previous light emitting state is as follows. Come different. For this reason, the terminal voltage of the capacitor 33 becomes an arbitrary value between 50V and 300V at the timing when the power switch is turned off.
[0030]
In the next step S 8, the control CPU 16 outputs a control command to the first conversion circuit 31 and the second conversion circuit 37, and sets the optimum conditions for charging back the remaining energy of the capacitor 33 to the rechargeable battery 30. I do. Then, in the next step S9, charge back from the capacitor 33 to the rechargeable battery 30 is performed.
[0031]
That is, the second conversion circuit 37 intermittently converts the output voltage (DC voltage) of the capacitor 33 into an AC voltage, and the first conversion circuit 31 converts the AC voltage obtained by stepping down the output voltage of the capacitor 33 from the transformer transformer 38. The rechargeable battery 30 is charged by rectifying it into a DC voltage.
[0032]
Since the value of the residual voltage of the capacitor 33 is not a constant value, it is necessary to control the step-down ratio of the transformer transformer 38. The step-up ratio of the transformer transformer 38 is set so as to boost the output voltage of the 4.5 V rechargeable battery to 300 V. Therefore, when the remaining voltage of the capacitor 33 is 300 V, the step-down ratio is the inverse of the step-up ratio. When stepped down, it becomes 4.5V.
[0033]
For this reason, when the remaining voltage of the capacitor 33 is 280 V, if the voltage is stepped down at this step-down ratio, the voltage value becomes lower than 4.5 V, and charging does not proceed when the rechargeable battery is in a state of nearly full charge. When the remaining voltage of the capacitor 33 is 50 V, the rechargeable battery 30 can be charged with the voltage value stepped down by this step-down ratio only when the rechargeable battery 30 is nearly empty.
[0034]
Therefore, in order to charge the rechargeable battery with the remaining voltage of the capacitor 33 under any condition, the voltage value is slightly higher than the output voltage value of the rechargeable battery 30, for example, a voltage value of 5 V or more or 10 V or more. It is necessary to step down.
[0035]
Therefore, in the present embodiment, a plurality of intermediate taps are provided on the input side and output side coils of the transformation transformer 38, respectively, and the first conversion circuit 31 and the second conversion circuit 37 to which the transformation transformer 38 is connected are controlled by the control CPU 16. In response to the command from the intermediate tap, the intermediate tap is selected so that the step-down ratio can be selected so that the optimum voltage value for charging the rechargeable battery 30 can be obtained.
[0036]
As a result, the output voltage value of the first conversion circuit 31 when charging back becomes an optimum voltage value for charging the rechargeable battery 30, and even when the residual voltage 33 of the capacitor 33 is as low as 50V, The remaining energy is reliably returned to the rechargeable battery 30.
[0037]
As described above, in this embodiment, since the function of charging back the energy remaining in the flash capacitor 33 to the rechargeable battery when the power-off command is input is provided, it is possible to save power of the rechargeable battery. This makes it possible to take a large number of images with a smaller battery capacity.
[0038]
In the above-described embodiment, the chargeback circuit is configured using the capacitor charging circuit (the first conversion circuit 31, the second conversion circuit 37, and the transformation transformer 38). However, the chargeback circuit is provided separately from the capacitor charging circuit. You may do it. However, a configuration in which the chargeback circuit shares the capacitor charging circuit is preferable because the number of parts is reduced, the manufacturing cost is reduced, and a narrow installation space of the camera can be effectively used.
[0039]
In the embodiments, a digital still camera has been described as an example. However, the present invention can also be applied to a film camera using a rechargeable battery. It should be noted that the numerical values such as 4.5V, 5V, 300V, 50V, and 280V used in the above description are for ease of explanation, and needless to say are merely examples.
[0040]
【The invention's effect】
According to the present invention, since the energy remaining in the flash light emitting capacitor is returned to the rechargeable battery, power can be saved in the rechargeable battery, and a large number of images can be taken with a smaller battery capacity. .
[Brief description of the drawings]
FIG. 1 is an external view of a digital still camera according to an embodiment of the present invention.
2 is a functional configuration diagram of the digital still camera shown in FIG. 1. FIG.
FIG. 3 is a detailed configuration diagram of a flash control unit shown in FIG. 2;
4 is a flowchart showing a processing procedure of a flash control unit shown in FIG. 3;
[Explanation of symbols]
1 Digital still camera 2 Flash lamp 16 Control CPU
18 Flash control unit 30 Rechargeable battery 31 First conversion circuit 32 Xenon tube 33 Capacitor for flash emission 37 Second conversion circuit 38 Transformer transformer 39 Voltage detection circuit

Claims (3)

A rechargeable battery, a flash light emitting unit, a capacitor that supplies power to the flash light emitting unit, a capacitor charging circuit that boosts the output voltage of the rechargeable battery and charges the capacitor, and upon input of a power-off command with flash, characterized in that a charge-back circuit for charging the rechargeable power battery back steps down the remaining voltage of the capacitor to a voltage value higher than the output voltage value of the rechargeable battery to the rechargeable battery camera.   The camera with flash according to claim 1, wherein the capacitor charging circuit is configured to operate as the chargeback circuit.   The camera with flash according to claim 1 or 2, further comprising means for variably setting the step-down ratio of the chargeback circuit in accordance with a value of a residual voltage of the capacitor.

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