Photography – With power supply detail
Reexamination Certificate
2002-06-04
2004-05-04
Adams, Russell (Department: 2851)
Photography
With power supply detail
C396S303000
Reexamination Certificate
active
06731871
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photocoupler driving system and a camera using the system.
2. Description of the Related Art
Recent advances of semiconductor manufacturing processes have brought minuter elements for a CPU or the like to operate at high speed and with low power consumption. However, this has reduced an operating power supply voltage range and resistance to voltage of the element.
This tendency has been also found in CPUs used in cameras, and power consumption has been simultaneously reduced. In an electric circuit of the camera, an AF sensor which processes minute signals, or a flash control circuit which controls a high voltage power supply requires a high voltage (generally 5V), while a CPU which controls them, especially, a CPU using a high speed CPU core uses a low voltage core with minuter patterns to meet the operating speed. In this case, the CPU operates at a low power supply voltage different from a power supply voltage of the peripheral sensor or the like, and for such an electric circuit of the camera, it is necessary to prepare power supplies with different voltages and feed an optimal voltage from each power supply to the peripheral sensor or the like.
On the other hand, the camera uses a photocoupler such as a photointerrupter (PI) or a photoreflector (PR) for detecting opening of a shutter member, a position of a film in film feeding, a position of a photography lens barrel, or the like.
The photointerrupter includes an LED for light emission and a phototransistor for receiving a light emitted from the LED, and has a movable member which transmits and intercepts the light from the LED between the LED and the phototransistor. The photointerrupter detects whether the movable member intercepts the light, that is, the movable member is in a slit (between the LED and the phototransistor) of the photointerrupter, by energizing the LED on the light emission side and detecting the light emission of the LED with the phototransistor on the light receiving side.
The photoreflector detects whether the movable member is within a detecting range of the photoreflector, that is, whether the movable member is in a position where it reflects the light emission from the LED, by reflecting the light emission from the LED on the movable member and detecting the reflected light with the phototransistor on the light receiving side.
FIG. 7
shows an electric circuit of a camera including a photocoupler such as a photointerrupter or a photoreflector.
To an LED
105
a
of a photocoupler
105
, limited resistance
106
and a transistor for switching (switching transistor)
107
connect in series, and when the switching transistor
107
is switched on by an instruction from a CPU
101
, a substantially constant current feeds into the LED
105
a
. Therefore, the LED
105
a
emits a light and the phototransistor
105
b
receives the light from the LED
105
a.
On the other hand, detecting resistance
108
is incorporated between the phototransistor
105
b
and a GND, and when the phototransistor
105
b
receives the light from the LED
105
a
, a voltage in accordance with photocurrent from the phototransistor
105
b
is generated in the detecting resistance
108
. The generated voltage is A/D converted by an A/D converter
102
included in the CPU
101
and then detected as a digital value. The CPU
101
controls desired operations, for example, opening a shutter member or film feeding based on the detected results. The voltage generated in the detecting resistance
108
can be detected by a comparator or the like as well as the A/D converter.
When the phototransistor
105
b
receives no light from the LED
105
a
, no current passes through the phototransistor
105
b
, and the voltage generated in the detecting resistance
108
becomes zero.
On the other hand, when the phototransistor
105
b
receives the light from the LED
105
a
, the current starts passing through the phototransistor
105
b
, and as the current increases, the voltage generated in the detecting resistance
108
increases. When the current passing through the phototransistor
105
b
further increases, the voltage generated in the detecting resistance
108
approaches the power supply voltage, and the voltage generated in the detecting resistance
108
increases up to a saturation level of the phototransistor
105
b.
The LED
105
a
requires this forward voltage (Vf) of 1 to 2 V, and a voltage of 1 V for controlling energizing of the LED
105
a
on/off and driving a substantially constant current, so that the circuit including the LED
105
a
requires a total voltage of 2 to 3 V. On the other hand, an operation of the light receiving side (phototransistor
105
b
) is allowed with caution not to saturate the phototransistor
105
b.
Generally, when the photocoupler
105
is driven, a stabilized voltage is used as a power supply of the LED
105
a
or the phototransistor
105
b
instead of a direct battery voltage so as to prevent influence of fluctuations in power supply voltages due to changes in current consumption in driving the movable member (such as the shutter). Specifically, the battery voltage is increased and stabilized by a DC/DC converter, and the output of the DC/DC converter to be used as a power supply of an AF sensor or the like is used as a power supply of the LED
105
a
or the phototransistor
105
b
. The increased and stabilized voltage is generally set to 5 V.
However, if semiconductor devices such as a CPU have become minuter to reduce resistance to voltage thereof, semiconductor devices including the detecting resistance
108
for detecting output of the phototransistor
105
b
or a detecting circuit such as the A/D converter
102
(or a comparator) have also become minuter to reduce the operating power supply voltage and the resistance to voltage thereof, preventing the conventional power supply voltage of 5 V from being applied.
Thus, the power supply voltage of the semiconductor device including the detecting circuit has to be set to a low voltage value such as 3.3 V or 2.5 V, or further, 1.8 V. In this case, if the circuit is used where the power supply voltage on the light receiving side (phototransistor
105
b
) is set to a 5 V system as is conventional, no problem occurs when amount of received light of the phototransistor
105
b
is small, but the semiconductor device cannot function normally when the amount of received light increases and, for example, when the voltage generated in the detecting resistance
108
exceeds the power supply voltage of the semiconductor device.
To solve this problem, it is possible to take measures in respect of the circuit or the process such as building a limiter of the power supply voltage into the semiconductor device or increasing the resistance to voltage only in the detecting circuit, but this raises costs significantly and is difficult to achieve.
If the power supply voltage identical to that of the semiconductor device (low value power supply voltage) is used as the power supply for emitting and receiving light in the photointerrupter or the photoreflector, an output voltage in the circuit on the light receiving side does not exceed the resistance to voltage of the semiconductor device, and the above described problem of the semiconductor device not functioning normally does not occur, but it becomes difficult to ensure the voltage for driving the above described LED, disabling desired light emitting control.
SUMMARY OF THE INVENTION
The present invention has an object to provide a camera ensuring stable operations of a light emitting element forming a photocoupler and a processing circuit in which elements becomes minuter to reduce resistance to voltage.
In order to attain the above described object, a camera according to the invention includes:
a first power supply output circuit which outputs a first stabilized power supply voltage;
a second power supply output circuit which outputs a second stabilized power supply voltage lower than the first power supply voltage;
a photocoupler w
Kitani Kazunari
Kosaka Takashi
Ohtsuka Masanori
Adams Russell
Canon Kabushiki Kaisha
Robin Blecker & Daley
Smith Arthur A
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