Photography – With object illumination for exposure – With insulated gate bipolar transistor
Reexamination Certificate
2000-12-27
2002-04-30
Gray, David M. (Department: 2851)
Photography
With object illumination for exposure
With insulated gate bipolar transistor
C396S006000, C396S206000
Reexamination Certificate
active
06381414
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an oscillation circuit and a strobe circuit, which employs the oscillation circuit, and which is suitably incorporated into lens-fitted film units.
Conventionally, some of the lens-fitted film units, in each of which a non-exposed film is incorporated in advance of putting them on the market, also incorporate a strobe device, which emits a strobe light from a light emitting tube, such as a xenon lamp, etc., by means of charging/discharging actions of a capacitor when capturing an image.
In the abovementioned lens-fitted film unit incorporating strobe device, a light-emitting action of an indicating lamp, such as a light emitting diode, a neon tube, etc., notifies the user of the completion of the discharging action of the capacitor.
An example of the conventional strobe circuits incorporated in the abovementioned lens-fitted film units will be detailed in the following, referring to FIG.
11
.
As shown in
FIG. 11
, the conventional strobe circuit comprises boosting-up circuit
101
for boosting up a source voltage of battery BT to a predetermined voltage necessary for the light-emitting action of strobe-lighting tube Xe, strobe-lighting circuit
102
for charging main-capacitor MC with the high voltage generated by boosting-up circuit
101
to emit a strobe light from strobe-lighting tube Xe, and neon lamp activating circuit
103
for activating the illumination of neon lamp NE, either when charging operation for main-capacitor is completed or when the user forgets to turn off a strobe-switch operating section (not shown in the drawings), mounted in the lens-fitted film unit, so as to warn the user.
Battery BT is coupled to boosting-up circuit
101
through switch SW
1
(a power switch), which is one of main switch MSW, serving as a double-pole single-throw switch, to be turned on or off by the operating action for the strobe-switch operating section.
The boosting-up circuit
101
comprises oscillation transistor Q, oscillation transformer TR
1
and resistor R
1
.
Oscillation transformer TR
1
is composed of primary winding W
1
and secondary winding W
2
for boosting up the voltage of battery BT. Oscillation transistor Q and oscillation transformer TR
1
constitutes a self-running blocking oscillator, which starts oscillating action by turning on main switch MSW and continues its oscillation under the direct current fed from battery BT, so that an alternate current flowing through primary winding W
1
induces an alternate high-voltage, corresponding to the winding number ratio of primary winding W
1
and secondary winding W
2
, at both terminals of secondary winding W
2
.
Secondary winding W
2
of oscillation transformer TR
1
is coupled to main-capacitor MC (for instance, an electrolytic capacitor) and trigger-capacitor TC, included in strobe-lighting circuit
102
, through rectifying diode D, so that the rectifying diode D rectifies alternate high-voltage induced in secondary winding W
2
and the rectified current flows into main-capacitor MC and trigger-capacitor TC to charge them.
Strobe-lighting circuit
102
comprises main-capacitor MC, strobe-lighting tube Xe, trigger-switch TSW, which turns on and off in conjunction with movements of shutter blinds, trigger-coil TR
2
composed of primary winding W
11
and secondary winding W
12
, resistor R
2
, trigger-capacitor TC, neon lamp NE, which emits a light when the charge voltage of main-capacitor MC reaches a predetermined voltage, and resistor R
4
serially connected to neon lamp NE.
Cathode K and anode A of strobe-lighting tube Xe are coupled to negative pole (−) and positive pole (+) of main-capacitor MC, respectively, and gate G is coupled to secondary winding W
12
of trigger-coil TR
2
.
Further, the strobe circuit comprises oscillation stoppage circuit
104
for stopping unnecessary oscillating action of transistor Q when main-capacitor MC is completely charged and for stopping the power supply to boosting-up circuit
101
from battery BT.
Oscillation stoppage circuit
104
comprises oscillation-suppressing transistor Q
11
, resistor R
11
, and zener diode ZD.
The emitter and the collector of oscillation-suppressing transistor Q
11
are coupled to the base of oscillation transistor Q and switch SW
2
of main switch MSW, respectively, while the high-voltage generated by boosting-up circuit
101
is applied to the base of oscillation-suppressing transistor Q
11
through zener diode ZD and resistor R
11
.
The operations of the abovementioned strobe circuit, mainly the operations of oscillation stoppage circuit
104
, will be described as follow.
When turning on switch SW
1
and switch SW
2
by operating main switch MSW, oscillation transistor Q starts to oscillate, and the high-voltage, boosted by boosting-up circuit
101
, charges main-capacitor MC.
At the same time, the high-voltage, boosted by boosting-up circuit
101
, is applied to zener diode ZD.
When the charged voltage of main-capacitor MC exceeds the zener voltage of zener diode ZD, zener diode ZD turns on, resulting in a conductive state of oscillation-suppressing transistor Q
11
. Then, oscillation transistor Q turns off, since the conductive state of oscillation-suppressing transistor Q
11
lowers the base potential of oscillation transistor Q, the base of which is coupled to the emitter of oscillation-suppressing transistor Q
11
.
As a result, the oscillating action of oscillation transistor Q is automatically stopped, and the power supply, fed from battery BT to boosting-up circuit
101
, is also cut off to stop the unnecessary charge current flowing into main-capacitor MC. The conventional technology mentioned above is also set forth in Tokkaihei 11-183975.
According to the strobe circuit having conventional oscillation stoppage circuit
104
mentioned above, it is possible to automatically stop the oscillating action of oscillation transistor Q, to prevent excessive charging operation to main-capacitor MC and to prevent unnecessary power dissipation of battery BT when the user forgets to turn off main switch MSW.
In the conventional strobe circuit mentioned above, however, since many parts, including relatively expensive parts such as oscillation-suppressing transistor Q
11
and zener diode, are employed for oscillation stoppage circuit
104
, there have been problems that man-hours for assembling the lens-fitted film unit and its cost tend to increase.
SUMMARY OF THE INVENTION
To overcome the abovementioned drawbacks in conventional strobe circuits, it is an object of the present invention to provide a strobe circuit, which makes it possible to conduct a timer operation (automatic stopping operation after a predetermined time) and/or an intermittent oscillating operation by adding a small number of parts, and which is suitably employed for lens-fitted film units.
Further, it is another object of the present invention to provide a strobe circuit, which makes it possible to restrict an increase of man-hours for assembling it and to prevent a power dissipation of the power source when the user forgets to turn off the main switch.
Accordingly, to overcome the cited shortcomings, the abovementioned objects of the present invention can be attained by a lens-fitted film unit, a strobe circuit and an oscillation circuit, described as follow.
(1) A lens-fitted film unit incorporating a strobe device, comprising: a main body; a photographic film loaded in advance in the main body; a shutter; a photographic lens; and a strobe circuit included in the strobe device, the strobe circuit comprising, a boosting-up circuit including a DC power source, an oscillation transistor, an oscillation transformer having a primary winding and a secondary winding, and a rectifying element for rectifying an electronic current induced at the secondary winding of the oscillation transformer, an oscillation controlling circuit for controlling a base potential of the oscillation transistor, and a strobe lighting circuit including a main-capacitor charged by the electronic current rectified by the rectifying element
Blackman Rochelle
Cantor & Colburn LLP
Konica Corporation
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