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BACKGROUND OF THE INVENTION
This invention relates to a light supply device for an endoscope, and more
particularly to a light supply device which supplies an endoscope with a
light of desired intensity and has a prescribed insulation withstand
voltage property.
An endoscope light supply device is generally included in medical electric
equipment. Therefore, an endoscope light supply device should meet an item
included in the safety regulations of various countries as well as those
of international scope (e.g. UL, IEC, etc.), namely, a specification
related to the insulation withstand voltage. This insulation withstand
voltage specification prescribes that the abovementioned endoscope light
supply device needs to be provided with an insulation withstand voltage
property of at least 5,000 volts.
The conventional endoscope light supply device comprises a patient circuit
connected to an endoscope to be introduced into a patient's coeliac cavity
and a primary circuit directly connected to a commercial A.C. power
source. A flash tube for emitting a light to photograph an affected
portion of the patient's coeliac cavity is connected to the primary
circuit, and actuated in response to a signal transmitted from the patient
circuit. Further, to assure the aforesaid insulation withstand voltage
property, the patient circuit and primary circuit are optically connected
together and yet electrically isolated by means of an optoisolator.
With the prior art endoscope light supply device, however, the optoisolator
for connecting the patient circuit to the primary circuit has a low
withstand voltage. Where, therefore, a high voltage of, for example, 5,000
volts is impressed between the patient circuit and primary circuit, the
optoisolation is very likely to be destroyed. Viewed this way, the
conventional endoscope light supply device has the drawbacks that it does
not fully meet the insulation withstand voltage specification included in
the international safety regulations, and can not be regarded as
completely safe for the patient, for example.
A pulse transformer acting as magnetic coupling means which might replace
the optoisolator still has the drawbacks that the pulse transformer having
a large size unavoidably renders an endoscope light supply device bulky;
leads to an increase in the production cost of the above-mentioned device;
and is unadapted to be used with an endoscope light supply device demanded
to quickly process a signal, because the pulse transformer transmits a
signal at a slower rate than the optoisolator.
It is accordingly the object of this invention to provide a light supply
device for an endoscope which is quickly actuated and which is extremely
safe for the human body.
SUMMARY OF THE INVENTION
To attain the above-mentioned object, this invention provides an endoscope
light supply device which comprises a first circuit to be connected to the
endoscope, a second circuit to be connected to a commercial A.C. power
source, and a signal transfer means having a plurality of stages of
optical coupling means provided between the first circuit and the second
circuit for electrically insulating the first and second circuits from
each other and transferring signals between the first and second circuits.
This invention can be more fully understood from the following detailed
description when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block circuit diagram showing the manner in which a
first embodiment of a light supply device embodying this invention is
connected to an endoscope;
FIG. 2 schematically indicates the arrangement of a power supply circuit
set in an endoscope light supply device;
FIG. 3 sets forth the arrangement of an electric circuit of a control
section provided in the endoscope light supply device of FIG. 1;
FIG. 4 shows an arrangement of an electric circuit of a control section
provided in a second embodiment of this invention;
FIG. 5 is an arrangement of an electric circuit of a control section
provided in a third embodiment of this invention; and
FIG. 6 schematically shows the arrangement of a modification of the
electric circuit of FIG. 2.
DETAILED DESCRIPTION
With an endoscope light supply device (FIGS. 1 to 3) according to a first
embodiment of this invention, an endoscope 10 includes an insertion
section 12, control section 14 and eyepiece section 16. The insertion
section 12 is formed of a flexible tube for introduction into the coeliac
cavity of the human body. The control section 14 is connected to a light
supply device 20 through a universal cord 18. A light guide 22 formed of
an optical fiber bundle extends through the insertion section 12, control
section 14 and universal cord 18. One end portion of the light guide 22 is
disposed at the open end of the control section 12. The other end portion
24 of the light guide 22 is inserted into the light supply device 20. An
image guide 26 also formed of an optical fiber bundle extends through the
insertion section 12 and control section 14. An object lens 28 is set
close to the distal end of the insertion section 12, that is, the distal
end of the image guide 26. A beam splitter 30 formed of a rectangular
prism is provided in the eyepiece section 16 close to the proximal end of
the image guide 26. An optoelectric transducing element 31 and eyepiece 32
are set adjacent to the beam splitter 30. A light beam conducted through
the image guide 26 is diverted in two directions by the beam splitter 30.
One portion of the light beam is delivered to the optoelectric transducing
element 31. The other portion of the light beam is sent to the eyepiece
32. An endoscope camera 34 is detachably fitted to the eyepiece section
16. A photographic film 36, shutter 38, and synchronizing contact switch
40 are received in the endoscope camera 34. Reference numeral 42 denotes
the surface of, for example, a patient's coeliac cavity.
The endoscope light supply device 20 comprises an illumination lamp 44 for
emitting an observation light having a prescribed quantum, a reflection
mirror 45 and a flash tube 46 for irradiating a photographic light having
a larger quantum than the observation light. The observation light and
photographic light are selectively transmitted to the endoscope 10 by a
light-transmitting section 47. A light path-switching mirror 48 and
light-condensing lens 49 (simply referred to as "a condenser") are
provided between the proximal end 24 of the light guide 22 and flash tube
46. The illumination lamp 44 is connected to the first output terminals of
a power supply circuit 50. The second output terminal of the power supply
circuit 50 is connected to a solenoid or an electromagnet 53 through an
electromagnet driving circuit 52. The electromagnet 53 is disposed near
the light path-switching mirror 48. The light path-switching mirror 48 is
normally inclined at an angle of, for example, 45.degree. at a point
facing the proximal end 24 of the light guide 22, so that an observation
light emitted from the illumination lamp 44 can be directed to the
proximal end of the light guide 22. Where, at the time of photographing,
the electromagnet 53 is energized through the electromagnet driving
circuit 52, then the light path-switching mirror 48 is lifted to cause a
photographic light emitted from the flash tube 46 to be transmitted
straight to the proximal end 24 of the light guide 22 through the
condenser 49.
The control section 54 includes a patient circuit 56, intermediate circuit
58 and primary circuit 60. The first input terminals of the patient
circuit 56 are connected to the optoelectric transducing element 31 held
in the eyepiece section 16 of the endoscope 10 through the universal cord
18. The second input terminals of the patient circuit 56 are connected to
the synchronizing contact switch 40 of the endoscope camera 34 similarly
through the universal cord 18. An area defined between the output terminal
of the patient circuit 56 and the input terminal of the intermediate
circuit 58 and an area defined between the output terminal of the
intermediate circuit 58 and the input terminal of the primary circuit 60
are electrically isolated and yet optically connected by means of, for
example, the latter described optoisolator. One output terminal of the
primary circuit 60 is optically connected to the other input terminal of
the electromagnet driving circuit 52 by means of the later described
optoisolator. The other output terminals of the primary circuit 60 are
connected to the flash tube 46. The third input terminal of the patient
circuit 56 and the other input terminal of the intermediate circuit 58 are
respectively connected to the third and fourth output terminals of the
power supply circuit 50. An input terminal of the power supply circuit 50
and an input terminal of the primary circuit 60 are connected to a
commercial A.C. power source (not shown) through a cord plug 62.
Additionally, one terminal of the cord plug 62 is connected to a metal
housing of the light supply device 20.
As seen from FIG. 2, the power supply circuit 50 is arranged with a first
transformer T.sub.1 for supplying electric power on the patient circuit 56
and a second transformer T.sub.2 for supplying electric power on the
intermediate circuit 58. The primary windings 64, 65 of the first and
second transformers T.sub.1, T.sub.2 are connected to the cord plug 62
(FIG. 1) in mutually parallel relationship. The first transformer T.sub.1
includes secondary windings 66, 67, 68. The secondary winding 66 is
connected to the input terminal of a full-wave rectifier 69 . The output
terminal of the full-wave rectifier 69 is connected to a smoothing
capacitor 70, a bypass capacitor 71, and known voltage regulated circuit
(hereinafter referred to as "a constant voltage circuit") 72. Accordingly,
an output voltage V.sub.1 of +5 volts is produced at one terminal of the
constant voltage circuit 72. The other terminal of the full-wave rectifier
69 is grounded to earth indicated by G.sub.1. The other secondary windings
67, 68 of the first transformer T.sub.1 are connected to known full-wave
rectifier 74 formed of four diodes, known constant voltage circuits 76,
77, smoothing capacitors 78, 79, and bypass capacitors 80, 81. The
secondary windings 67, 68 are jointly grounded to the earth G.sub.1.
Accordingly, an output voltage V.sub.2 of +15 V and an output voltage
V.sub.3 of -15 V are respectively produced at the output terminals of the
constant voltage circuits 76, 77.
The second transformer T.sub.2 includes secondary windings 83, 84. The
secondary winding 83 is connected to the illumination lamp 44. The
secondary winding 84 is connected to the input terminals of a full-wave
rectifier 87 through a resistor 86. A zener diode 88, known constant
voltage circuit 90, a smoothing capacitor 94, and a bypass capacitor 95
are connected to the output terminal of the full-wave rectifier 87.
Accordingly, an output voltage V.sub.4 of +5 V is produced at one output
terminal of the constant voltage circuit 90. The other output terminal of
the full-wave rectifier 87 is grounded to the other earth G.sub.2 which is
electrically separated from the earth G.sub.1. The secondary winding 84 is
also connected to the input terminal of another full-wave rectifier 96
connected in parallel with the full-wave rectifier 87. The output terminal
of the full-wave rectifier 96 is connected to three diodes 97, 98, 99 and
three capacitors 100, 101, 102 in the known manner. As a result, a triple
rectified voltage is generated across the capacitor 102. The electromagnet
driving circuit 52 is arranged with a series circuit consisting of an NPN
type transistor 104 and the phototransistor 107 included in the later
described optoisolator 106. This optoisolator 106 is connected between the
patient circuit 56 and the NPN type transistor 104. The collector of the
transistor 104 is connected to one terminal of the capacitor 102 at which
a triple rectified voltage is produced. A phototransistor 107 is connected
between the base of the transistor 104 and the other end of the capacitor
102. A resistor 108 is connected between the collector and base of the
transistor 104. The above-mentioned electromagnet 53 is connected between
the emitter of the transistor 104 and phototransistor 107.
Referring now to the control section 54 shown in detail in FIG. 3, the
patient circuit 56 includes an exposure control circuit 110 connected to
the optoelectric element 31 set in the endoscope 10, flash synchronize
circuit 111 connected to the synchronizing contact switch 40 and
electromagnet signal-generating circuit 112. With the exposure control
circuit 110, the input terminals of an operation amplifier 114 are
connected to the optoelectric transducing element 31. The operation
amplifier 114 converts an output current from the optoelectric transducing
element 31 into a voltage signal. A resistor 116 is connected between a
minus terminal of the input terminals and the output terminal of the
operation amplifier 114. The output terminal is connected to one of the
input terminals (a minus terminal) of an integrator 120 formed of an
operation amplifier through another resistor 118. The other input terminal
(a plus terminal) of the integrator 120 is connected to the other input
terminal (a plus terminal) of the operation amplifier 114. An
integration-starting FET 122 and integration capacitor 124 are connected
in mutual parallel relationship between the minus terminal of the
integrator 120 to which the resistor 118 is connected and the output
terminal of the integrator 120. The output terminal of the integrator 120
is connected to one of the input terminals (a minus terminal) of a
comparator 128 through a resistor 126. For example, five resistors 129,
130, 131, 132, 133 are connected to the minus input terminal of the
comparator 128 mutually parallel relationship. These resistors are
connected at one end to a changeover switch 134, whose input terminal is
impressed with an output voltage V.sub.2 from the power supply circuit 50.
The other input terminal (a plus terminal) of the comparator 128 is
directly connected to the other input terminal (the plus input terminal)
of the integrator 120. The threshold voltage level of the comparator 128
is defined by the changeover switch 134 in accordance with, for example,
the sensitivity of the film 36 of the endoscope camera 34, etc. The output
terminal of the compartor 128 is connected to the base of an NPN
transistor 138 through a resistor 136. The emitter of the transistor 138
is connected to the plus input terminal of the comparator 128. The
collector of the transistor 138 is connected to the cathode of a
light-emitting diode 142 of an optoisolator 140 which is provided between
the patient circuit 57 and intermediate circuit 58. The anode of the
light-emitting diode 142 is supplied with an output voltage V.sub.1 from
the power supply circuit 50 (FIG. 2) through a resistor 144.
The flash synchronize circuit 111 operated by the closure of the
synchronizing contact switch 40 and electromagnet signal-generating
circuit 112 cause one of the input terminals of a chattering-preventing
one-shot multivibrator 146 to be connected to one of the terminals of the
synchronizing contact switch 40 through an inverter 148. The one terminal
of the synchronizing contact switch 40 is impressed with an output voltage
V.sub.1 from the power supply circuit 50 (FIG. 2) through a resistor 150.
A capacitor 152 is connected in parallel to the multivibrator 146. One of
the terminals of the capacitor 152 is impressed with an output voltage
V.sub.1 from the power supply circuit 50 through a resistor 153. The
output terminal of the multivibrator 146 is connected to the base of an
NPN transistor 156 through a resistor 154. The emitter of the transistor
156 is directly connected to the other terminal of the synchronizing
contact switch 40 and multivibrator 146. The collector of the transistor
156 is connected to the cathode of a light-emitting diode 160 of an
optoisolator 158 which is also provided between the patient circuit 56 and
the intermediate circuit 58. The anode of the light-emitting diode 160 is
impressed with an output voltage V.sub.1 from the power supply circuit 50
through a resistor 162. The junction of the inverter 148 and resistor 150
is connected to the gate of the aforesaid FET 122 through two inverters
164, 165. Where an output signal from the synchronizing contact switch 40
is transmitted to the FET 122 through the inverters 164, 165, then the FET
122 is rendered nonconducting. At this time, the integrator 120 commences
the integration of an output voltage from the optoelectric transducing
element 31. The junction of the inverter 164 and resistor 150 is connected
to the base of an NPN transistor 170 through the other inverter 166 and
resistor 168. The emitter of the NPN transistor 170 is connected to the
emitter of the aforementioned transistor 156. The collector of the NPN
transistor 170 is connected to the cathode of a light-emitting diode 174
of the optoisolator 106. The anode of the light-emitting diode 174 is
impressed with an output voltage V.sub.1 from the power supply circuit 50
(FIG. 2).
The intermediate circuit 58 of the control section 54 includes a first
transmission circuit 178 for transmitting an output light signal from the
light-emitting diode 142 of the optoisolator 140 of the patient circuit 56
to the succeeding section and a second transmission circuit 180 for
transmitting an output light signal from the light-emitting diode 160 of
the optoisolator 158. The first transmission circuit 178 comprises a
phototransistor 182 set in the optoisolator 140 in a state facing the
light-emitting diode 142. The collector of the phototransistor 182 is
connected to the input terminals of a one-shot multivibrator 186 through
an inverter 184, and impressed with an output voltage V.sub.4 from the
power supply circuit 50 through a resistor 185. A capacitor 188 is
connected in parallel to the one-shot multivibrator 186. One terminal of
the capacitor 188 is similarly impressed with an output voltage V.sub.4
from the power supply circuit 50 through a resistor 189. The output
terminal of the multivibrator 186 is connected to the base of an NPN
transistor 192 through an inverter 190 and resistor 191. The emitter of
the NPN transistor 192 is connected to the emitter of the phototransistor
182 and one terminal of the multivibrator 186. The collector of the
transistor 192 is connected to the cathode of a light-emitting diode 196
of an optoisolator 194 which is provided between the intermediate circuit
58 and the primary circuit 60. The anode of the transistor 192 is
impressed with an output voltage V.sub.4 from the power supply circuit 50
through a resistor 198.
The multivibrator 186 is actuated upon receipt of an output signal from the
phototransistor 182 to generate a pulse signal for actuating the
optoisolator 194.
The second transmission circuit 180 includes a phototransistor 200 provided
in the optoisolator 158 in a state facing the light-emitting diode 160.
The collector of the phototransistor 200 is connected to the base of an
NPN transistor 212 through an inverter 202, two multivibrators 204, 206,
inverter 208 and resistor 210. The emitter of the NPN transistor 212 is
directly connected to the emitter of the phototransistor 200. The
collector of the NPN transistor 212 is connected to the cathode of a
light-emitting diode 216 of another optoisolator 214 which is also
provided between the intermediate circuit 58 and the primary circuit 60.
The anode of the light-emitting diode 216 is impressed with an output
voltage V.sub.4 from the power source 50 through a resistor 218. The
output voltage V.sub.4 is impressed on the collector of the
phototransistor 200 through a resistor 220 and also on one end of each of
capacitors 222, 224, respectively connected to the multivibrators 204, 206
through the corresponding resistors 226, 228. One multivibrator 204
concurrently acts as a timer for effecting the changeover of the operation
of the light path-switching mirror 48 (FIG. 1). The other multi-vibrator
206 is actuated in response to an output signal from the one multivibrator
204 to generate drive pulses having a short time width.
The primary circuit 60 includes the known auto-strobo circuit 230 and a
circuit for supplying the flash tube with electric power (hereinafter
referred to as "flash tube power supply circuit") 232. In the autostrobo
circuit 230, a phototransistor 234 is provided in the optoisolator 194 in
a state facing the light-emitting diode 196. The emitter and collector of
the phototransistor 234 are connected to the input terminals of a
thyristor trigger circuit 236 for impressing a firing voltage on the gate
of the later described quenching thyristor 252. Another phototransistor
238 is provided in another optoisolator 214 in a state facing the
light-emitting diode 216. The emitter and collector of the phototransistor
238 are connected to the corresponding input terminals of a trigger
circuit 240. One of the output terminals of the trigger circuit 240 is
connected to a trigger coil 242, and the other output terminal of the
trigger circuit 240 is connected to the input terminal of a thyristor
trigger circuit 243. One of the output terminals of the trigger coil 242
is connected to the trigger circuit 240 and thyristor trigger circuits
236, 243, and further directly to one terminal 66-2 of the primary winding
65 of the second transformer T.sub.2 of the power supply circuit 50 (FIG.
2), namely, to a commercial A.C. power source. The other output terminal
of the trigger coil 242 is connected to a trigger electrode of the flash
tube 46, one end of which is connected to the terminal 66-2 of the primary
winding 65 of the second transformer T.sub.2 through a resistor 245 and a
main thyristor 246. The gate of the main thyristor 246 is connected to the
other output terminal of the main thyristor trigger circuit 243. The other
end of the flash tube 46 is connected to one end of a parallel circuit of
a coil 248 and diode 249, and also to the aforesaid terminal 66-2 of the
primary winding 65 of the second transformer T.sub.2 through a resistor
250 and a quenching thyristor 252. The gate of the thyristor 252 is
connected to the other output terminal of the thyristor trigger circuit
236. A quenching capacitor 254 is connected between the anodes of the
thyristors 246, 252. A main capacitor 256 is connected between the
terminal 66-2 of the primary winding 65 of the second transformer T.sub.2
and the other end of a parallel circuit consisting of the coil 248 and
diode 249. Where, therefore, the phototransistor 238 receives an output
light signal from the light-emitting diode 216, then the trigger circuit
240 begins to be actuated to impress a firing gate voltage on the gate of
the main thyristor 246. At this time, the quenching thyristor trigger
circuit 236 starts actuation in response to an output signal from the
phototransistor 238 of the optoisolator 194 to impress a firing gate
voltage on the gate of a transmission thyristor 252.
The flash tube power supplying circuit 232 is connected to both terminals
66-1, 66-2 of the primary winding 65 of the second transformer T.sub.2 of
the power supply circuit 50, and further to a commercial A.C. source (not
shown). Namely, the input terminal of a charge control circuit 258 is
connected to the both terminal 66-1, 66-2 of the primary winding 65 of the
second transformer T.sub.2. TRIAC 260 is connected in parallel to the
charge control circuit 258. One of the terminals of TRIAC 260 is connected
to one end of a parallel circuit consisting of the coil 248 and diode 249,
that is, the cathode of the diode 249 through three series-connected
diodes 262, 263, 264. The cathode of the diode 249 is further connected to
the output terminal of the charge control circuit 258. A capacitor 266 is
connected in parallel to the diodes 262, 263. A capacitor 268 is connected
between the cathode of the diode 262 and said one end 66-2 of the primary
winding 65 of the second transformer T.sub.2. Therefore, TRIAC 260
connected to the charge control circuit 258 assures the constant voltage
charge of the main capacitor 256. The known triple rectifying circuit
formed of the diodes 262, 263, 264 and capacitors 266, 268 supplies the
main capacitor 256 with a charge voltage three times higher than the
commercial A.C. voltage.
Description is now given of the operation of an endoscope light supply
device which is the first embodiment of this invention. Where the release
button (not shown) of the endoscope camera 34 is depressed, then the
shutter 38 is opened, and the synchronizing contact switch 40 is closed.
An output signal from the closed switch 40 is transmitted to the patient
circuit 56 provided in the control section 54 of the light supply device
20. Accordingly, the optoisolator 106 is driven, and the electromagnet 53
(FIG. 2) is energized. The energized electromagnet 53 lifts the light
path-switching mirror 48 (FIG. 1). At this time, the one-shot
multivibrator 146 eliminates chattering noises included in an output
signal from the closed synchronizing contact switch 40. Thereafter said
output signal from the switch 40 is transmitted to the intermediate
circuit 58 as a flash tube-actuating signal through the optoisolator 158.
This flash tube-actuating signal is delayed by the one-shot multivibrator
204 and converted into a flash tube-actuating pulse signal by another
one-shot multivibrator 206. The pulse signal is transmitted to the primary
circuit 60 through the optoisolator 214, causing the trigger circuit 240
and main thyristor trigger circuit 243 to be actuated. As a result, an
output trigger voltage from the trigger circuit 240 is supplied to the
trigger electrode 244 of the flash tube 46. The main thyristor 246 is
fired by the main thyristor trigger circuit 243. As a result, the flash
tube 46 sends forth a photographic light having a prescribed luminosity.
The photographic light is transmitted straight to the distal end 24 of the
light guide 22 through the condenser 49 of FIG. 1, and then illuminates
the surface 42 of a patient's coeliac cavity through the light guide 22. A
light reflection from the surface 42 enters the beam splitter 30 through
the image guide 26. One portion of the light reflection divided by the
beam splitter 30 is projected on the film 36 through the eyepiece 32,
because the shutter 38 is opened. The other portion of the light
reflection divided by the beam splitter 30 enters the optoelectric
transducing element 31, an output signal from which is conducted to the
patient circuit 56 through the universal cord 18. An output signal from
the optoelectric transducing element 31 is amplified by the operation
amplifier 114 and then integrated by the integrator 120. Where an output
integrated voltage from the integrator 120 reaches a prescribed
illumination level or threshold level, then the comparator 128 is actuated
to drive the optoisolator 128 is transmitted to the one-shot multivibrator
186 of the intermediate circuit 58 through the optoisolator 140 as a
signal for stopping the operation of the flash tube 46. The flash
tube-stopping signal is converted into an illumination-stopping pulse by
the multivibrator 186, and supplied to the quenching thyristor trigger
circuit 236 of the autostrobo circuit 230. Accordingly, the quenching
thyristor trigger circuit 236 is actuated to render the quenching
thyristor 252 conducting. As a result, the main thyristor 246 is backward
biased by the discharge voltage of the quenching capacitor 254, rendering
the main thyristor 246 nonconducting. Therefore, the flash tube 46 ceases
to be quenched to emit a light.
Where the release button (not shown) of the endoscope camera 34 regains its
original position, then the synchronizing contact switch 40 is opened, and
the electromagnet 53 is deenergized, causing the light path-switching
mirror 48 to return to the normal position.
With the endoscope light supply device of this invention shown in FIGS. 1
to 3, the intermediate circuit 58 is connected between the patient circuit
56 and primary circuit 60. Means of optoisolator is provided not only
between the patient circuit 56 and intermediate circuit 58 but also
between the intermediate circuit 58 and primary circuit 60, thereby doubly
assuring electric insulation. Therefore high voltage impressed between the
patient circuit 56 and commercial A.C. power source is split into two
levels by one group of optoisolators 140, 158 and another group of
optoisolators 194, 214. Where, therefore, a high voltage of, for example,
at least 5,000 volts is impressed between the patient circuit 56 and
commercial A.C. power source, a voltage impressed on the optoisolators
140, 158, 194, 214 is reduced to about half the original voltage level,
that is, about 2,500 volts. Even where, therefore, the conventional
optoisolator is applied, the endoscope light supply device of this
invention is provided with a sufficiently high insulation property to
satisfy the aforementioned safety regulations, and proves completely safe
for the human body. Further, the present endoscope light source device
eliminates the necessity of applying a pulse transformer, is reduced in
manufacturing cost, and is reliably prevented from slowing down in the
operation speed.
FIG. 4 shows a second embodiment of the invention. In this embodiment a
control circuit 54 is provided with a flash tube control circuit 298. An
intermediate circuit 58 has a multivibrator 204, the output terminal of
which is connected to the base of an NPN transistor 306 through two
inverters 300 and 302 and through a resistor 304. The emitter of the
transistor 306 is connected to a point where the emitter of a transistor
212 is connected to the emitter of a phototransistor 200 of an
optoisolator 158. The collector of the NPN transistor 306 is connected to
the cathode of a photodiode 310 of the optoisolator 158. The anode of the
photodiode 310 is connected to receive via a resistor 312 the output
voltage V.sub.4 of such a power source circuit 50 as shown in FIG. 2.
In the optoisolator 158, a phototransistor 314 is disposed, facing the
photodiode 310. The phototransistor 314 is an element of a patient circuit
56. The collector of the phototransistor 314 is connected to receive via a
resistor 316 the output voltage V.sub.1 of the power source circuit 50.
The collector of the phototransistor 314 is connected through an inverter
318 to one of the two input terminals of an AND circuit 320. The other
input terminal of the AND circuit 320 is connected to the output terminal
of an inverter 165. The output terminal of the AND circuit 320 is
connected to the gate of the FET 122. The emitter of the phototransistor
314 is connected to the emitter of a transistor 156.
Except for the above-mentioned features the embodiment of FIG. 4 is the
same as that of FIG. 3. Like and the same elements are indicated in FIG. 4
at the same numerals as in FIG. 3, and their functions are not described
here.
Now it will be described how the second embodiment operates. With the
synchronizing contact switch 40 closed, the multivibrator 204 is started
to generate output signals. The output signals of the multivibrator 204
are supplied to said one input terminal of the AND circuit 320 through the
optoisolator 308 which is provided between the patient circuit 56 and the
intermediate circuit 58. Since the other input terminal of the AND circuit
320 receives an output signal of the synchronizing contact switch 40, the
AND circuit 320 is closed. As a result, the output signal of the
multivibrator 204 is supplied to the gate of the FET 122. The FET 122 is
made nonconductive, whereby the integrator 120 starts operating. In other
words, the integrator 120 of the patient circuit 56 is inhibited as long
as the multivibrator 204 of the intermediate circuit 58 remains to
operate. Hence, the integrator 120 does not unnecessarily operate in
response to leaked light into an endoscope 10.
FIG. 5 shows a third embodiment of the invention. In this embodiment a
control circuit 54 is provided with an improper exposure preventing
circuit 328. A charge control circuit 258 of a primary circuit 60 has a
terminal which is connected to a point where the cathode of a diode 264 is
connected to a main capacitor 256. This terminal is connected also to a
point where resistors 332, 334 and 336 are connected together. The other
end of the resistor 332 is connected via zener diode 338 to a terminal
66-2 of such a second transformer T.sub.2 as shown in FIG. 2 and also to
the positive input terminal of an operational amplifier 340. The other end
of the resistor 334 is connected via a resistor 342 to the terminal 66-2
of the second transformer T.sub.2 and also to the negative input terminal
of the operational amplifier 340. The output terminal of the operational
amplifier 340 is connected to the base of an NPN transistor 346 through a
resistor 344. The emitter of this transistor 346 is connected to the
terminal 66-2, and the collector thereof is connected to the cathode of a
photodiode 350 of an optoisolator 348. The anode of the photodiode 350 is
connected to the other end of the resistor 336 through a resistor 352. The
other end of the resistor 336 is connected to the terminal 66-2 via a
zener diode 354. This structure enables the operational amplifier 340 to
receive a bias voltage.
In the optoisolator 348 which connects an intermediate circuit 58 and the
primary circuit 60, a phototransistor 356 is disposed, facing the
photodiode 350. The collector of the phototransistor 356 is connected to
receive the output voltage V.sub.4 of such a power supply circuit 50 as
shown in FIG. 2. The collector of the phototransistor 356 is connected to
the base of an NPN transistor 364 through an inverter 360 and a resistor
362. The emitter of the transistor 364 is connected to the emitter of the
phototransistor 356, and the collector thereof is connected to the cathode
of a photodiode 368 of an optoisolator 366 which connects a patient
circuit 56 and the intermediate circuit 58. The anode of the photodiode
368 is connected to receive via a resistor 370 the output voltage V.sub.4
of the power source circuit 50.
In the optoisolator 366 a phototransistor 372 is disposed, facing the
photodiode 368. The emitter of the phototransistor 372 is connected to a
point where the emitters of NPN transistors 156 and 170 are connected. The
collector of the phototransistor 372 is connected to receive the output
voltage V.sub.1 of the power supply circuit 50. The collector of the
phototransistor 372 is connected via an inverter through one of the two
input terminals of an AND circuit 378. The other input terminal of the AND
circuit 378 is connected to one terminal of a synchronizing contact switch
40. The output terminal of the AND circuit 378 is connected to a point
where the input terminals of inverters 148, 164 and 166 are connected.
Except for the above-mentioned features the embodiment of FIG. 5 is the
same as that of FIG. 3. Like and the same elements are indicated in FIG. 5
by the same numerals as in FIG. 3, and they are not described here again.
Now it will be described how the third embodiment operates. A reference
voltage, which is determined by the zener diode 338, is applied to the
positive input te | | |
