JPH0121486B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply control circuit for a camera, and particularly to a power supply control circuit that controls power supply to a photometry circuit of a camera.

Conventionally, as a circuit that controls power supply to a photometry circuit included in an exposure control circuit, etc., power supply to the photometry circuit is started by pressing the shutter release button halfway, etc.
There are devices that operate the photometry circuit for a certain period of time and then automatically stop the power supply after the certain period of time has elapsed. In this way, wastage of power due to forgetting to turn off the power switch, etc. is prevented.

However, such a power supply control circuit can be used for multi-mode exposure control, i.e. automatic exposure control modes such as shutter speed priority, aperture priority, program, etc.
When used in a photometry circuit capable of manual exposure control, the following problems arise. In manual exposure control mode, it takes a long time to manually set the aperture value and shutter speed, while in automatic exposure control mode, the operation can be completed in a short time. However, the power supply holding time during which the conventional power supply control circuit as described above supplies power to the photometric circuit and operates it is constant regardless of the mode. Assuming that this power supply holding time is simply the average value of the time required in each mode, in manual exposure control mode, the power supply to the photometry circuit will be stopped while manually operating the aperture value and shutter speed setting components. However, in the case of automatic exposure control mode, the photometry circuit is unnecessarily supplied with power even after the operation is completed.

An object of the present invention is to obtain a power supply control circuit for a camera that eliminates the above-mentioned drawbacks by switching the time from the start to the stop of power supply to the photometry circuit to an appropriate length according to the set exposure control mode. It is in.

The drawings illustrate embodiments of the invention. The photometric circuit 1 is supplied with power from a power supply Vcc via a first power switch _SW1 . NOR circuit NOR, AND circuit AND ₁ ~
AND ₄ , a counter consisting of flip-flops FF ₁ to FF ₄ , and an oscillator OSC are connected to the timer circuit 2.
Configure. This timer circuit 2 is supplied with power via a second power switch _SW2 . Operating switch SW ₃
turns ON in conjunction with pressing the shutter release button halfway, etc.
become. OR circuit 3 consists of two diodes. When the operating switch SW 3 is turned on by pressing the shutter release button halfway, this OR circuit ₃ turns on the first and second power switches SW ₁ and SW ₂ to supply power to the photometry circuit 1 and the timer circuit 2. Let it start. Thereby, the photometric circuit 1 starts operating. However, since the timer circuit 2 has been reset via the switch _SW3 at this time, timing does not start.
Also, the output of timer circuit 2 in this reset state is sent to switches SW ₁ and SW ₂ via OR circuit 3.
Turn it ON to maintain power supply to the photometry circuit 1 and timer circuit 2. Therefore, even if the shutter release button is then released from the halfway press and the switch SW ₃ is turned off, the power to the photometry circuit 1 is maintained. On the other hand, when this switch SW ₃ is turned OFF, the timer circuit 2 is
The reset is released, time measurement starts, and after a predetermined time measurement, output is generated and switches SW ₁ and SW ₂
is turned OFF to stop power supply to the photometric circuit and timer circuit 2 itself, rendering these circuits inoperable.
Note that the length of time measured by the timer circuit 2 is determined by switches SW ₄ to _{SW 7} , which are linked to the settings of manual exposure control, shutter speed priority automatic exposure control, aperture priority automatic exposure control, and program automatic exposure control, respectively. Then, the light metering circuit 1 and the timer circuit 2 are operated for the time required for each control mode. Further, the switches SW ₁ and SW ₂ can be constituted by well-known electric switches such as transistors.

Next, the operation will be explained.

Turn on the operating switch SW ₃ by pressing the shutter release button halfway.
An H level voltage is applied to the switches SW ₁ and SW 2 via SW ₃ and the OR circuit 3, and the switches _{SW 1 and} SW ₂
is turned ON, power supply to the photometry circuit 1 and timer circuit 2 is started, and the photometry circuit 1 starts photometry.
However, at this time, the H level voltage is applied to the flip-flops _FF1 to _FF4 of the timer circuit ₂ via the switch SW3.
The output of flip-flops _FF1 to _FF4 becomes L, and the AND circuit
The outputs of AND ₁ to _{AND 4} also become L, and the output of the NOR circuit becomes H. Therefore, the H output of this NOR circuit NOR is sent to the switches SW ₁ and SW ₂ via the OR circuit 3.
is turned on to maintain the operation of photometry circuit 1 and timer circuit 2. Next, release the shutter release button halfway and turn switch SW ₃ to OFF. The power supply to the photometric circuit 1 and timer circuit 2 in this state is as follows:
It is maintained by the H output of the NOR circuit NOR. On the other hand, flip-flops _FF1 to _FF4 are released from reset by turning off switch _SW3 , and begin counting the output of oscillator OSC. At this time, it is assumed that, for example, a program automatic exposure control mode that does not require manual settings of aperture value or shutter speed is selected, and switch SW ₇ is turned on.
In this case, one input of AND gate AND ₄ becomes H, so the first pulse from oscillator OSC causes the output of flip-flop FF ₄ to become H.
The output of the AND gate _AND4 becomes H, and the output of the NOR gate NOR becomes L. Also, switch SW ₃ is already turned off. Therefore, the output of the OR circuit 2 also becomes L, and the switches SW ₁ and SW ₂ are turned OFF. Therefore, power supply to the photometric circuit and timer circuit 2 is stopped, and these circuits become inoperable. That is, in the program mode, the power supply holding time of the exposure control circuit is set to be the shortest.

Also, if manual exposure control mode is selected and switch SW ₄ is ON, the AND gate
Since one input of AND ₁ becomes H, when the output of flip-flop FF ₁ becomes H, the AND gate becomes H.
As in the previous case, the output of the NOR gate NOR becomes L, the output of the OR circuit 3 becomes L, switches SW ₁ and SW ₂ are turned OFF, and power is supplied to the photometry circuit 1 and timer circuit 2. stop. Here flip-flop FF ₄ ~ FF ₁ is the oscillator OSC
Since outputs _are generated by dividing the output _of
It will be faster than FF ₂ and FF ₃ . Therefore, the time from the start to the stop of photometry is the longest in the manual exposure control mode. This time is determined in consideration of the time required to manually set both the aperture value and the shutter speed, so that the power supply to the photometry circuit 1 is not cut off during the manual setting. Also, when shutter priority mode is set, switch SW ₅
However, when aperture priority mode is set, switch SW ⁶
are each turned on. The power supply holding time to the photometry circuit 1 is set to a length that allows manual setting of the shutter speed in the former case and aperture value in the latter case. In this embodiment, a flip-flop is used as the frequency dividing circuit, but if any frequency dividing circuit is used, it is possible to arbitrarily set the time in each mode.

As described above, according to the present invention, the time from the start to the stop of power supply to the photometric circuit is switched to match the set exposure mode. Therefore,
Since power supply is not stopped and the photometry circuit becomes inoperable while setting the aperture value or shutter speed, operability is improved, and power is saved because no more power is supplied than necessary.

[Brief explanation of drawings]

The drawings are diagrams showing embodiments of the invention. [Explanation of symbols of main parts], Photometric circuit...1,
Operating switch... _SW3 , timer circuit...2, power switch... _SW1 , _SW2 , switching circuit... _SW4 ~
_SW7 .

Claims (1)

[Claims] 1. Starting time measurement in response to the operation of an operation switch,
A timer circuit that generates a timing completion signal when the counting time has elapsed; a power switch that is inserted into the power supply path to the photometry circuit of the camera and becomes non-conductive in response to the timing completion signal; and a power switch that responds to the selection of an exposure control mode. When the manual exposure control mode is selected, the time measured by the timer circuit is set to the first time, and when the automatic exposure control mode is selected, the time measured by the timer circuit is set to the first time. 1. A power supply control circuit for a camera, comprising: a clock time switching circuit that switches to a second time shorter than the current time. 2 Start timing according to the operation of the operating switch,
A timer circuit that generates a timing completion signal when the counting time has elapsed; a power switch that is inserted into the power supply path to the photometry circuit of the camera and becomes non-conductive in response to the timing completion signal; and a power switch that responds to the selection of an exposure control mode. When the shutter priority or aperture priority automatic exposure control mode is selected, the time measured by the timer circuit is set as the first time, and when the program automatic exposure control mode is selected, the time measured by the timer circuit is set as the first time. A power supply control circuit for a camera, comprising: a clock time switching circuit that switches a clock time to a second time shorter than the first time.