JP2001183728A - Electronic flash device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic flash device which is constituted so that the power consumption at initial charging is lowered and charging time is prevented from being prolonged and which is easily adjusted so that the desired power consumption and the desired charging time are obtained. SOLUTION: By turning on/off an FET 31 by a driving pulse signal, pulse voltage given to a primary coil is repeatedly applied. In order to control the maximum value of a primary current flowing to the primary coil, the frequency of the driving pulse signal is set to be constant. Besides, the duty ratio of the driving pulse signal is set to be small at the initial charging and set to be large when charging voltage is high.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flash device.

[0002]

2. Description of the Related Art When performing flash photography, it is necessary to charge a main capacitor to a high voltage in advance. For this reason, a strobe device mounted on a camera or the like includes a charging circuit that converts a low voltage of a battery or the like into a high voltage as a power source and charges a main capacitor with the high voltage. The charging circuit includes a self-excited type and a separately excited type.

In a separately-excited charging circuit, an oscillating transformer having a primary coil and a secondary coil, a semiconductor switching element connected to a battery as a primary coil and a power supply, a rectifier, and a rectifier connected to the secondary coil via the rectifier. A basic component includes a main capacitor, a drive pulse signal generation circuit for generating a drive pulse signal for turning on / off the semiconductor switching element, and the like. At the time of charging, the semiconductor switching element is repeatedly turned on by the drive pulse signal
By turning on / off, a current is intermittently supplied to the primary coil to generate a high AC voltage in the secondary coil, and the secondary current flowing at the high voltage is supplied to the main capacitor through the rectifier.

In this separately-excited charging circuit, a drive pulse signal having a constant frequency is usually given to a semiconductor switching element. However, when given a drive pulse signal in this way, as shown in FIG. 9, the maximum value I _max of the primary current flowing through each ON the semiconductor switching element is connected as a load to the secondary side of the oscillating transformer The charge voltage changes in accordance with the charged voltage of the main capacitor, and becomes extremely large in the initial stage of charging when the charged voltage is as low as 0 V to several tens V.

[0005] Therefore, in the initial stage of charging, the current consumption of the battery increases, and as a result, the output voltage of the battery significantly decreases, and the voltage required for the operation of other circuits such as a camera equipped with a strobe device. May not be obtained, and the device itself may malfunction. Further, a problem may occur that the device is reset when the output voltage of the battery drops once.

[0006] To prevent such inconvenience, varying the frequency of the drive pulse signal, by utilizing the fact that the maximum value I _max of the primary current changes accordingly, the power supply voltage in the initial stage of charging What is necessary is just to set the frequency of the drive pulse signal so that the drop is at a level that does not cause any problem. However, in this case, a problem such as a longer charging time occurs. For this reason, for example, in the early stage of charging, the frequency of the drive pulse signal is increased, the primary current is suppressed to reduce the power supply voltage drop, and thereafter the frequency of the drive pulse signal is reduced to prevent a longer charging time. There is a charging circuit.

[0007]

[SUMMARY OF THE INVENTION However, there is no linear relationship between the maximum value I _max of the frequency and the primary current of the drive pulse signal. For this reason, in order to obtain an appropriate current consumption and charging time, it is necessary to repeat an experiment to determine an appropriate frequency, and it takes time to determine the frequency of the driving pulse signal, and the development cost of the strobe device is increased. There was a problem that invites a rise.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a strobe device capable of easily performing adjustment for obtaining appropriate current consumption and charging time.

[0009]

In order to achieve the above object, according to the first aspect of the present invention, an excitation pulse generating circuit is provided.
A charging voltage detecting means for detecting a charging voltage of the main capacitor; a voltage control type which is turned on / off in response to a drive pulse signal and which is turned on to connect a primary coil and a power supply to apply a pulse voltage to the primary coil A semiconductor switching element, generates and outputs a drive pulse signal having a constant frequency, and, based on the detection result of the charging voltage detecting means, a pulse voltage having a narrow pulse width when the charging voltage of the main capacitor is low; And a driving pulse signal generating means for switching a duty ratio of the driving pulse signal so as to apply a pulse voltage having a wide pulse width to the primary coil when the charging voltage is high.

According to the second aspect of the present invention, the minimum duty ratio of the drive pulse signal is caused by the primary current flowing from the primary coil when the voltage control type semiconductor switching element is driven by the drive pulse signal. The loss in the voltage-controlled semiconductor switching element is determined so as to be less than the maximum allowable loss of the voltage-controlled semiconductor switching element, and the charging voltage of the main capacitor is equal to or less than a predetermined voltage including zero by the charging voltage detecting means. Is detected, the driving pulse signal is switched to the driving pulse signal having the minimum duty ratio.

According to the third aspect of the present invention, the voltage-controlled semiconductor switching element is a MOS field-effect transistor. According to the fourth aspect of the present invention, the duty ratio of the drive pulse signal is set in three or more steps according to the charging voltage of the main capacitor. According to the fifth aspect of the present invention, the charging voltage is provided by providing storage means for storing the duty ratio of the drive pulse signal, and performing digital processing on the drive pulse signal generation means based on the duty ratio stored in the storage means. , A drive pulse signal having a duty ratio corresponding to the driving pulse signal is generated.

[0012]

FIG. 2 shows an instant camera incorporating a strobe device embodying the present invention. On the front surface of the camera body 2, a collapsible lens barrel 3, a light projecting window 4 for automatic focusing, and a light receiving window 5 are provided. The lens barrel 3 holds a photographing lens 6, and a light metering window 7 for measuring the brightness of the subject and a strobe light receiving window 8 are provided on the front surface of the lens barrel 3. A release button 10 is provided on the grip unit 9. Above the release button 10, a strobe light emitting unit 11 of a strobe device and a finder 1 are provided.
2 are provided. On the upper surface of the camera body 2, a main switch button 13, a setting button 14, an LCD 1
5, an outlet 16 is provided.

The inside of the grip portion 9 is a battery chamber, into which a battery 17 (see FIG. 3) is loaded as a power source for the instant camera. The battery 17 is, for example, a battery in which four AA-size dry batteries with a nominal voltage of 1.5 V are connected in series.

Each time the main switch button 13 is pressed, the power of the instant camera is switched on and off alternately. When the power is turned on, the lens barrel 3 is extended to a photographing position protruding forward from the retracted position shown in the drawing, and becomes ready for photographing. When the power is turned off, the lens barrel 3 is returned to the retracted position, and no photographing is performed even if the release button 10 is pressed.

In the back of the light projecting window 4 and the light receiving window 5, a light transmitter and a light receiver for distance measurement are incorporated, and in the rear of the light measuring window 7, a light receiving element for photometry is arranged. Further, a light receiving sensor for automatic light control is arranged behind the strobe light receiving window 8.

When the release button 10 is half-pressed, distance measuring light is projected from the distance measuring light projector toward the object, and the reflected light is received by the light receiver to measure the object distance. The luminance of the subject is measured by the light receiving element through. Subsequently, when the release button 10 is fully pressed, the focusing of the photographing lens 6 is performed in accordance with the measured subject distance, and the opening and closing control of the shutter blades is performed based on the measured subject brightness, and instantaneous control is performed. Exposure to the film 18 is performed.

When the subject brightness is below a predetermined level,
In synchronization with opening and closing of the shutter blades, strobe light is emitted from the strobe light emitting unit 11 toward the subject. Then, the strobe light reflected by the subject is received by the light receiving sensor for automatic light control, and the strobe light emission is stopped when the amount of received light reaches a predetermined level.

The exposed instant film 18 is discharged from the discharge port 16. At the time of this discharge, the instant film 18 is moved to the discharge port 1 by the developer pod 18a.
6 ruptured by a pair of developing rollers provided in the back,
The developing solution contained in the developing solution pod 18a is developed inside. As a result, the instant film 18
Is completed, and after a lapse of a predetermined time, a printed photograph is obtained.

By operating the setting button 14, various settings such as exposure correction can be performed. The LCD 15 displays information necessary for photographing, such as exposure correction, the number of remaining instant films, and the remaining battery power.

FIG. 3 shows a main configuration of the instant camera.
Shown in The microcomputer 20 includes a CPU, an interface for inputting and outputting signals and data to and from each unit, and an A / D converter, which will be described later, on a single chip. The microcomputer 20 includes a ROM 21 and a RAM 2
2. The EEPROM 23 is connected.

The microcomputer 20 has a ROM 21
The operation of the entire instant camera is controlled according to the sequence program stored in. Also, this ROM
In 21, boundary voltage data D _ref1 and prescribed charging voltage data D _ref2 described later are written in advance. RAM 22
Is used as a work memory in which data necessary for performing the sequence is temporarily written. EEPROM2
In 3, a duty ratio of a drive pulse signal for driving the charging circuit is written as data.

When the power is on, the power supply circuit 24 converts the output voltage of the battery 17 into a constant drive voltage and outputs it. The drive voltage output from the power supply circuit 24 is kept constant even if the input-side voltage and the output-side load slightly fluctuate. Each part of the microcomputer 20, the instant camera (not shown) such as a shutter mechanism and an auto-focus mechanism operates by receiving the driving voltage. When the power is off, the power supply circuit 24 is not operated in order to suppress the power consumption, and the output voltage of the battery 17 is output as it is and supplied to the microcomputer 20. Thus, the microcomputer 20 operates in the sleep state by this voltage. In the sleep state, only a minimum necessary circuit such as a calendar circuit and a power ON / OFF detection circuit in the microcomputer 20 is operated.

The reset circuit 25 outputs a reset signal for resetting the microcomputer 20 with an appropriate delay after the output voltage of the power supply circuit 24 changes and exceeds a predetermined voltage. Thus, when the battery 17 is loaded into the instant camera and power supply is started, the microcomputer 20 is reset by a reset signal from the reset circuit 25.

The clock signal generation circuit 26 generates a clock signal having a constant frequency and sends it to the microcomputer 20. Based on the clock signal from the clock signal generation circuit 26, the microcomputer 20
Various signals for operating each unit are generated, and each unit is operated in synchronization.

The strobe device includes a charging circuit including a MOS type FET (field effect transistor) 31, an oscillation transformer 32, a rectifying diode 33 and the like, a main capacitor 34, a strobe discharge tube 35, a trigger circuit 36, and an automatic light control device. , A light control circuit 38, a charging voltage detection circuit 39, and the like.

The charging circuit is of a separately-excited type which performs a charging operation by a driving pulse signal output from the microcomputer 20. The charging circuit converts the output voltage of the battery 17 to a high voltage and sets the main capacitor 34 to a high voltage. Charge.
The oscillation transformer 32 includes a primary coil 32a and a secondary coil 32b inductively coupled to each other. Primary coil 32
a has one end connected to the positive electrode of battery 17 and the other end connected to FE.
It is connected to the drain terminal of T31. FET31
Has its source terminal connected to the negative electrode of the battery 17. The FET 31 has a gate terminal connected to a resistor 40a.
To the charge control terminal of the microcomputer 20 via
Further, it is connected to the negative electrode of the battery 17 via the resistor 40b and is grounded. Thereby, the gate voltage is applied to the FET 31 in response to the drive pulse signal output from the charge control terminal of the
N, OFF.

When the FET 31 is turned on, the output voltage of the battery 17 is applied to the primary coil 32a as a pulse voltage (excitation pulse), and a primary current (excitation current) that increases in proportion to time flows. As a result, the oscillation transformer 32 is excited. After the FET 31 is turned on,
If it is set to FF, a secondary current flows through the secondary coil 32b so as to maintain the same ampere turn as the primary current just before the OFF, and this is supplied to the main capacitor 34 via the rectifying diode 33. Thus, the main capacitor 34 is charged.

In this strobe device, in the prior art, in the initial stage of charging in which a very large large current flows as the primary current, a drive pulse signal having a small duty ratio is used to drive the FET 31.
ON / OFF to keep the maximum value of the primary current small, and after the charging voltage becomes high, the FET 31 is turned ON / OFF with a drive pulse signal having a relatively large duty ratio to charge efficiently. , So that the charging time is not long.

In this example, the MOS FET 31 which is a voltage-controlled semiconductor switching element is used as a switching element for applying a pulse voltage to the primary coil 32a. It is also possible to use a transistor. However, when combined with a device that outputs high and low voltages as an output signal, such as the microcomputer 20, a circuit or the like that supplies a drive current necessary for turning on the bipolar transistor is provided between the microcomputer and the bipolar transistor. It must be provided between them. The bipolar transistor is a MOS type F
Since the switching speed of transition from ON to OFF is relatively slow compared to ET and the loss is large, the primary current of the oscillation transformer 32 must be increased in order to shorten the charging time. As a result, the size of the bipolar transistor is increased, which hinders miniaturization of the strobe device and the instant camera.

Therefore, according to the present invention, a MOS-type FET 31 which is a voltage-controlled semiconductor switching element is used, which can be directly driven by an output signal of the microcomputer 20, and the size of the apparatus can be reduced. It is made to be advantageous.

A charging voltage detection circuit 39 is connected to the main capacitor 34. The charging voltage detection circuit 39
The resistors 39a and 39b connected in series and the capacitor 3
9c. Resistor 39 connected in series
a and 39 b are connected in parallel to the main capacitor 34. The resistors 39a and 39b are connected to the main capacitor 34.
Is divided and output, and the detection voltage V _CHG proportional to the charging voltage V _MC of the main capacitor 34 is output to the microcomputer 20. The microcomputer 20 detects the charging voltage V _MC from the detection voltage V _CHG, and based on the detection result, controls charging start and stop so as to maintain the charging voltage V _MC at the specified charging voltage V _ref2 ,
At the time of charging, the duty ratio of the drive pulse signal is switched according to the charging voltage V _MC .

The strobe discharge tube 35 includes a strobe light emitting unit 1
1 are arranged. The strobe discharge tube 35 is connected in parallel with a main capacitor 34, and an IGBT whose ON / OFF is controlled by a dimming circuit 38 is connected between the main capacitor 34 and the strobe discharge tube 35.
38a is connected. The IGBT 38a is turned on (conduction state) prior to strobe light emission.

A synchro signal synchronized with the opening and closing of shutter blades is input from the shutter device 41 to the trigger circuit 36 when flash light emission is performed. When the sync signal is input, the trigger circuit 36 applies a trigger voltage to the strobe discharge tube 35. As a result, the IGB turned ON
The electric charge of the main capacitor 34 is discharged by the strobe discharge tube 35 through T38a, and strobe light emission is started. The strobe light emitted from the strobe discharge tube 35 is
The light is emitted from the strobe light emitting unit 11 toward the subject.

The dimming circuit 38 turns on the IGBT 38a prior to flash emission as described above. Further, from the moment when the strobe discharge tube 33 emits light, the light receiving sensor 37 receives the strobe light reflected by the subject and integrates the light amount. At the moment when the integrated amount reaches a predetermined level, the IGBT 3
8a is turned off to stop strobe light emission. Thereby, the irradiation amount of the strobe light is automatically adjusted so that the exposure amount by the strobe light becomes appropriate.

FIG. 1 shows functional blocks of a microcomputer 20 according to the present invention. Microcomputer 2
0 is a drive pulse signal generating means, and FET3
1 and the charging voltage detection circuit 39 constitute an excitation pulse generation circuit. The detection voltage V _CHG output from the charging voltage detection circuit 39 is
The data is digitally converted by the D converter 20a and becomes voltage data D _CHG according to the voltage value. The voltage data D _CHG is supplied to the first determination unit 20b and the second determination unit 20c.
Sent to

The first judging means 20b includes an A / D converter 20
A magnitude relationship between the voltage data D _CHG from a and the boundary voltage data D _ref1 read from the ROM 21 is determined, and a duty ratio based on the determination result is read from the EEPROM 23 and set in the control signal generation means 20d. The boundary voltage data D _ref1 is determined in accordance with the upper limit value (hereinafter, referred to as a boundary voltage V _ref1 ) of the charging voltage V _MC of the main capacitor 34 which is considered to be in the initial stage of charging. Incidentally, the boundary voltage V _ref1 is less of course than the prescribed charging voltage V _{re f2.} .

In the EEPROM 23, the duty ratio of the drive pulse signal is converted into data and written as described above. In this example, the EEPROM 23, the duty ratio F ₁ for charging the initial used when a low charging voltage V _MC, when the high charge voltage V _MC (hereinafter, referred to as a steady state) and the duty ratio F ₂ used for Is written. Duty ratio F ₁ is smaller than the duty ratio F _2.

The data stored in the EEPROM 23 is not limited to the data obtained by converting the duty ratio of the drive pulse signal into data. For example, the ratio of the high-low binary pulse width of the drive pulse signal which indirectly expresses the duty ratio is used. Alternatively, the drive pulse signal period T and the pulse width of “H level” may be converted into data.

The first judging means 20b _{calculates the} voltage data D _CHG
Is smaller than or equal to the boundary voltage data D _ref1 , that is, when the charging voltage V _MC is lower than or equal to the boundary voltage V _ref1 ,
From EPROM23 reads the duty ratio F ₁ for charging the initial, voltage data D when _CHG is larger than the comparison voltage data D _ref1, i.e. the charge voltage V _MC is a boundary voltage V _{re f1}
When higher than reads the duty ratio F ₂ for the steady from EEPROM 23, and sets the control signal generating means 20d them.

The second determining means 20c is for controlling the output of the drive pulse signal so as to keep the charging voltage V _MC of the main capacitor 34 at the specified charging voltage V _ref2 . The second determining means 20c determines the magnitude relationship between the voltage data D _CHG and the specified charging voltage data D _ref2 corresponding to the specified charging voltage V _ref2 , and when the voltage data D _CHG is smaller than the specified charging voltage data D _ref2. That is, the control signal is output from the control signal generating means 20d only when the charging voltage V _MC is lower than the specified charging voltage V _ref2 .

The control signal generating means 20d generates a control signal having a constant period T, that is, a constant frequency f (= 1 / T), based on the clock signal from the clock signal generating circuit 25. Further, the control signal generating means 20d performs digital processing based on the set duty ratio so that the ratio of the pulse width of "L level" to the cycle T of the control signal becomes equal to the set duty ratio. Then, a control signal is generated.

The C-MOS circuit 20e converts a control signal into a voltage signal for driving the FET 31, that is, a drive pulse signal, and includes an enhancement type N-channel FET 43a and a P-channel FET 43b as is well known. . This C-MOS circuit 20e
When the control signal is at "L level", the FET 43a
Is turned off and the FET 43b is turned on, so that the drive pulse signal is set at “H level”. When the control signal is at “H level”, the FET 43a is turned on and the FET 43b is turned on.
The drive pulse signal becomes “L level” by being FF.
And

Thus, only when the charging voltage V _MC of the main capacitor 34 is lower than the specified charging voltage V _ref1 ,
A drive pulse signal is output from the charge control terminal of the microcomputer 20 to the FET 31 and the main capacitor 34
Is charged. The FET 31 is turned on when the drive pulse signal is at “H level”, and is turned off when it is at “L level”.

When the charging voltage V _MC is equal to or lower than the boundary voltage V _ref1 , as shown in FIG. 4A, the FET 31 is turned ON / OFF by the driving pulse signal having the duty ratio F ₁ for initializing charging.
It is turned off. This drive pulse signal has a signal level changed in a cycle T and a pulse width of “H level” in one cycle T is “Tw ₁ ”.

Further, when the charging voltage V _MC is higher than the boundary voltage V _ref2 , as shown in FIG. 4B, the FET 31 is turned on by the driving pulse signal having the duty ratio F ₂ for the steady state.
N / OFF. This steady-state drive pulse signal is
The signal level is changed at the same cycle T as the drive pulse signal for initial charging, but the pulse width of “H level” in one cycle T is “Tw ₂ ”, which is wider than “Tw ₁ ”. ing. That is, Deyuti ratio F ₁ is smaller than the duty ratio F _2, the excitation pulse in the initial stage of charging is smaller than that for the steady state.

FIG. 5 shows the relationship between the maximum value of the primary current flowing through the primary coil 32a during charging and the pulse width of the drive pulse signal. When the FET 31 is turned on, the primary current increases in proportion to the time t. At this time, the rate of increase of the primary side current increases as the charging voltage V _MC of the main capacitor 34 decreases, but under a constant charging voltage V _MC , the rate of increase is constant, and the primary side current in one cycle T is increased. the maximum value I _max of the pulse width of the excitation pulse, i.e. proportional to the pulse width of the drive pulse signal. The relationship between the charging voltage V _MC and the rate of increase can be relatively easily obtained using the inductance of the oscillation transformer 32 or the like.

Therefore, if the desired magnitude of the primary current at an arbitrary charging voltage V _MC is set, the duty ratio of the drive pulse signal corresponding to the desired primary current can be obtained by calculation. That is, it is not necessary to determine the duty ratios F ₁ and F ₂ of the drive pulse signal for setting the appropriate current consumption and charging time by experiments or the like, and the driving pulse signals can be obtained easily.

Next, the operation of the above configuration will be described. At the time of manufacturing the instant camera, the duty ratios F ₁ , F
EEPROM2 in which data of ₂ is written in advance
30 is built into the instant camera. of course,
The duty ratios F ₁ , F
₂ may be written as data.

Since the duty ratios F ₁ and F ₂ are obtained by the calculation as described above, an experiment for determining the duty ratios F ₁ and F ₂ is unnecessary, and the development and design period can be shortened. .

Further, when the excitation pulse generating circuit is constituted by an analog circuit as in the prior art, in order to adjust the charging characteristics such as the power consumption at the initial stage of charging and the charging completion time to the desired one, the excitation It is necessary to change the circuit constants of the pulse generation circuit, for example, to adjust the capacitance and resistance of the capacitor. However, in this strobe device, each duty ratio F stored in the EEPROM 23 is used.
₁ and F ₂ , the driving pulse signal is generated by digital processing.
A drive pulse signal having an accurately adjusted duty ratio can be obtained only by writing data obtained by converting each of the duty ratios F ₁ and F ₂ into the ROM 23. Therefore, no special adjustment work is required at the time of manufacture by the manufacturer.

Further, the duty ratio may be stored in a ROM or the like. However, if the electrically rewritable EEPROM 23 is used as described above, even if the duty ratio needs to be adjusted, an external computer can be used. Automatic adjustment of the duty ratio can be easily performed.

When the battery 17 is loaded in the instant camera, the output voltage of the battery 17 is output from the power supply circuit 24 as it is. Upon receiving the power supply from the power supply circuit 24, the microcomputer 20 starts operating in the sleep state. At this time, the operation of the microcomputer 20 may become unstable due to the voltage fluctuation accompanying the loading of the battery 17. However, when the reset signal from the reset circuit 25 is input to the microcomputer 20 with an appropriate delay from the time when the output voltage from the power supply circuit 24 reaches the predetermined voltage, the microcomputer 20 Since the microcomputer 20 is reset once after loading, the microcomputer 20 operates stably.

When the main switch button 13 is operated,
With this operation, the power is turned on and the microcomputer 2
The power supply circuit 24 is operated by the instruction of 0. As a result, the output voltage of the battery 17 is converted into a predetermined drive voltage by the power supply circuit 24 and supplied to each unit.
A value of 0 shifts from the sleep state to the normal state, and the other parts become operable. After the start of the supply of the driving voltage, the collapsible mechanism (not shown) is operated, the lens barrel 3 is extended to the photographing position, and the apparatus enters a photographing standby state in which the instant camera can photograph.

When the power is turned on, the microcomputer
The computer 20 is, as shown in FIG.
The control of charging the sensor 34 is started. Microcomputer
The A / D converter 20a operates the A / D converter 20a to detect the charging voltage.
Detection voltage V from output circuit 39 _CHGSampling digital
And the charge voltage V of the main capacitor 34_MCIn response
Detection voltage data D_CHGGet.

The obtained detected voltage data D _CHG is sent to the first judging means 20b and the second judging means 20c.
The magnitude relationship is determined for each of the boundary voltage data D _ref1 and the specified charging voltage data D _ref2 read from No. 1. First, the first determination means 20b determines the magnitude relationship between the detected voltage data D _CHG and the boundary voltage data D _ref1 , that is, the charging voltage V _MC of the main capacitor 34 and the boundary voltage V _ref1.
The magnitude relationship with _ref1 is determined, and based on the determination result, _{one of} the duty ratio F ₁ and the duty ratio F ₂ is read out from the EEPROM 23 and set in the control signal generating means 20d.

After setting the duty ratio, the detection voltage
Data D_CHGAnd specified charging voltage data D _ref2Relationship with
That is, the charging voltage V_MCAnd specified charging voltage V_MCRelationship with
Is determined, and control signal generating means is provided based on the determination result.
Whether the control signal is output from 20d is controlled.

In the case where the charging voltage V _MC is 0 V, for example, immediately after the start of use of the instant camera, the charging voltage V _MC is lower than the specified charging voltage V _MC and the boundary voltage when V _ref1 or less, based on the first determination determining means 20b, a duty ratio F ₁ is read from the EEPROM 23, which is set in the control signal generating means 20d. Next, based on the determination by the second determination unit 20c, the output of the control signal from the control signal generation unit 20d is started and sent to the C-MOS circuit 20e.

[0058] Thus, C-MOS from circuit 20e outputs driving pulse signal for charging the initial duty ratio F _1, ON FET 31 is repeated in this driving pulse signal
/ OFF. Each time the drive pulse signal becomes "H level", the FET 31 is turned on, a pulse voltage is applied to the primary coil 32a, and a primary current that increases in proportion to time at an increasing rate corresponding to the charging voltage V _MC is generated. Then, the oscillation transformer is excited. Then, when the drive pulse signal becomes “L level” and the FET 31 is turned off, the secondary coil 3 is controlled to maintain the same ampere turn as the primary side current.
The secondary side current flows through 2b, which is the rectifying diode 33.
Is supplied to the main capacitor 34 to charge the main capacitor 34. When the FET 31 is repeatedly turned on / off in response to the drive pulse signal, the charge of the main capacitor 34 gradually increases.

As described above, the main capacitor 34
During the charging, the sampling by the A / D converter 20a and the determination by the first and second determination means 20b and 20c are repeatedly performed.

The charging of the main capacitor 34 proceeds, and
Voltage V_MCIs the boundary voltage V_ref1, The A / D converter 2
Voltage data D obtained from 0a_CHGIs the comparison voltage data
TA D _ref1Larger than. Then, the first determining means 20
b, the duty ratio F from the EEPROM 23_TwoRead
And the duty ratio F₁Generate control signal instead of
It is set in the means 20d.

[0061] Thus, from the C-MOS circuit 20e outputs driving pulse signal for steady state became duty ratio F _2, FET 31 is ON / O in this driving pulse signal
FF is performed. Each time the drive pulse signal in this case becomes "H" level, a pulse voltage is applied to the primary coil 32a is ON the FET 31, increases in proportion to the time rate of increase corresponding to the charge voltage V _MC The primary current flows, and the oscillation transformer is excited. When the FET 31 is turned off, a secondary current flows through the secondary coil 32b, and the main capacitor 34 is charged.

Further, when the charging of the main capacitor 34 proceeds and the charging voltage V _MC becomes equal to or higher than the specified charging voltage V _{ref2, the} detected voltage data D _{CH G} obtained from the A / D converter 20a becomes the specified charging voltage data D _{CH G. Since it is equal to} or greater than _ref2 , the transmission of the control signal from the control signal generation means 20d is stopped by the second determination means 20c. As a result, the output of the drive pulse signal stops, and the charging of the main capacitor 34 stops.

When the charging voltage V _MC of the main capacitor 34 becomes lower than the specified charging voltage V _ref2 due to spontaneous discharge or internal discharge of the main capacitor 34 after the charging is stopped, transmission of the drive pulse signal is resumed, and the main capacitor 34 is turned off. The battery is charged to the specified charging voltage V _MC . As a result, the charging voltage V _MC is maintained at the specified charging voltage V _MC . Since the decrease in the charging voltage V _MC due to such spontaneous discharge is gentle, while the power is on, the charging voltage V _MC slightly drops below the charging voltage V _MC , that is, drops to the boundary voltage V _ref1 . The charging is resumed upon detection of a decrease in the charging voltage V _MC without any problem. Therefore, in this case, the duty ratio F
_The FET 31 is turned on by the drive pulse signal for steady state ₂
N / OFF is performed and charging is performed.

On the other hand, when the charging voltage V _MC of the main capacitor 34 suddenly drops to near 0 V due to strobe light emission, or when the charging voltage V _MC drops below the boundary voltage V _ref1 while the power is turned off, Is turned on, the charging voltage V _MC is equal to or lower than the boundary voltage V _ref1 , so that the FET 31 is first turned on / off by the drive pulse signal for initializing the charge having the duty ratio F _1.
Then, charging is performed. When the charging voltage V _MC exceeds the boundary voltage V _ref1 by this charging, the FET 31 is turned on / off by the steady-state driving pulse signal, and charging is performed.

As described above, at the beginning of charging when the charging voltage V _MC is low, the driving pulse signal having a small duty ratio causes
1 is turned ON / OFF and the pulse width of the excitation pulse is narrowed, so that the primary side current, that is, the consumed current, can be suppressed to a small value. It does not work. In addition, since the output voltage of the battery does not greatly decrease and the output voltage from the power supply circuit 24 does not decrease,
Since the reset circuit 25 does not output a reset signal, there is no problem that the microcomputer 20 is reset during charging.

When the charging voltage V _MC of the main capacitor 34 exceeds the boundary voltage V _ref1 , the FET 31 is turned on / off by a driving pulse signal having a large duty ratio.
F, the charging is performed efficiently by widening the pulse width of the excitation pulse, so that the time to reach the specified charging voltage _Vref2 does not become long.

In the above embodiment, the duty ratio of the drive pulse signal is switched between two stages, but may be switched between three or more stages. Of course, the relationship between the duty ratio for an arbitrary charging voltage and the maximum value of the primary current has linearity in the drive pulse signal having a constant cycle, so that a desired form of change in the maximum value of the primary current can be obtained. Each duty ratio can be easily obtained.

FIGS. 7 and 8 show an example in which an accident due to heat generation of the FET is prevented. Except as described below, the configuration is the same as that of the above-described embodiment, and the same components are denoted by the same reference numerals and described.

The microcomputer 20 switches and outputs three types of drive pulse signals having the duty ratios F _{3 to} F ₄ shown in FIG. 7 in accordance with the charging voltage V _MC of the main capacitor 34, and turns ON / OFF the FET 31. .

When the charging voltage V _MC of the main capacitor 34 is _{equal to} or lower than the boundary voltage V _ref3 , the FET 31 is turned on by a signal with a drive pulse having a duty ratio F ₃ shown in FIG.
/ OFF. In the same manner as the initial charge duty ratio F ₁ in the above embodiment, the maximum value I
In order to reduce the _max, the duty ratio F ₃ is small. Further, the duty ratio F ₃ is set to satisfy the following condition. P _D > ((V _O / (r _BTT + R ₁ + R _DS )) × k) ² × R _DS ×
F ₃

The symbols in the above formula are as follows. P _D : Allowable loss of FET 31 (rated drain loss) V _O : Maximum open voltage that battery 17 can take r _BTT : Internal resistance of battery 17 R ₁ : Winding resistance of primary coil 32a R _DS : Drain-source of FET 31 F ₃ : Duty ratio of drive pulse signal k: Coefficient of 1 or less obtained by measuring the primary current waveform of actual machine

[0072] Incidentally, as is the dissipation P _D ambient temperature becomes higher becomes smaller, because the power dissipation P _D of FET31 that varies with the ambient temperature, the value of the duty ratio F ₃ satisfying the conditional expression strobe device since changes according to the environmental temperature to be used may be determined a value of the duty ratio F ₃ for example ambient temperature using the flash device is assumed, or on the basis of the maximum temperature of the environment temperature to ensure the normal operation of the device.

When the charging voltage V _MC is _{equal to} or lower than the boundary voltage V _ref3 , the FET 31 is driven by a driving pulse signal having a duty ratio F ₃ satisfying the above-mentioned conditional expression.
2 is short-circuited or opened, and even if the detected charging voltage V _MC is continuously 0 V and the FET 31 is driven for a long time by the driving pulse signal of the duty ratio F ₃ , Loss is the allowable loss P
_D to make it less than _D ,
The accident caused by the heat generation in T31 is prevented from occurring.

The charging voltage V of the main capacitor 34
When _MC is lower than the high boundary voltage V _ref4 than the boundary voltage V _ref3, while as the maximum value I _max of the primary-side current does not become excessive, in order to shorten the charging time, FIG. 7
As shown in (b), the FET31 the drive pulse signal of a large duty ratio F ₄ than the duty ratio F ₃ O
N / OFF. Furthermore, when the charging voltage V _MC of the main capacitor 34 is higher than the boundary voltage V _{re f4} is, for more efficient charging time, as shown in FIG. 7 (c), FET 31, the duty ratio F ₄ It turned ON / OFF by a drive pulse signal having a duty ratio F ₅ is greater than.

The microcomputer 20 stops sending the drive pulse signal after a time T _d, for example, about 20 ms _, from the time point when the charging voltage V _MC of the main capacitor 34 detects that the charging voltage V _MC has reached the specified charging voltage V _ref2 . The magnitude relationship between each of the boundary voltages V _ref3 , V _ref4 and the specified charging voltage V _ref2 is as follows.
“0V <V _ref3 <V _ref4 <V _ref2 ”.

The specified charging voltage V _ref2 , each boundary voltage V _ref3 ,
V _ref4, the duty ratio F ₃ to F _5, and the frequency f of the drive pulse signals are respectively data of EEPROM2
3 so that changes can be easily made.

Next, the operation of the above configuration will be described with reference to FIG.
I will explain it. For example, charging voltage V _MCIs the boundary voltage V_ref3
In the case where charging is started from the following state, EEPRO
From M23, frequency f and duty ratio F_ThreeIs read
It is. Then, the frequency f and the duty ratio F_ThreeDriving pal
Signal from the microcomputer 20 to the FET 31.
And the FET 31 repeats based on this drive pulse signal.
It is turned ON / OFF repeatedly, and the secondary that flows with it
The main capacitor 34 is supplied by the secondary current from the coil 32b.
Is charged.

When the charging of the main capacitor 34 proceeds and the charging voltage V _MC exceeds the boundary voltage V _ref3 , the _{EEPROM 2}
3 duty ratio F ₄ is read from the frequency f, FET 31 in the driving pulse signal having a duty ratio F ₄ is ON / O
FF is performed, and charging of the main capacitor 34 is continued.
Further, when the charging of the main capacitor 34 proceeds and the charging voltage V _MC exceeds the specified charging voltage V _ref4 , the EEPR
OM23 duty ratio F ₅ is read from the frequency f, the FET31 the drive pulse signal having a duty ratio F ₅ is ON / OFF, charging Meinkodensa 34 is further continued.

The charging voltage V _MC is equal to the specified charging voltage V
_When it is detected that _ref2 has been reached, the time T _d
After elapse of, the microcomputer 20 stops outputting the drive pulse signal and stops charging the main capacitor 34.

As described above, the main capacitor 34 is switched while the duty ratio of the drive pulse signal is sequentially switched.
Of the rectifier diode 34, a disconnection between the secondary coil 32b and the main capacitor 34, or the like, in which the secondary circuit of the oscillation transformer 32 is short-circuited or opened. If the secondary circuit is short-circuited or open,
The charging voltage V _MC of the main capacitor 34 becomes 0V. Further, since the charging of the main capacitor 34 is not performed, the output of the drive pulse signal is continued, and the FET 31 is turned ON / OFF for a long time.

Further, in the case where a failure occurs such that the secondary side circuit is short-circuited or opened,
Since most or all of the energy of the oscillation transformer 32 excited by the primary current flowing through the primary coil 32a is not consumed on the secondary side of the oscillation transformer 32, the oscillation transformer 32 is magnetically saturated.

If the secondary circuit is short-circuited or open
The charging voltage V_MCDriven against
When the duty ratio of the pulse signal is large,
Magnetic saturation occurs even when the pulse width is wide.
However, when the oscillation transformer 32 is magnetically saturated as described above,
, While the FET 31 is ON, the battery
17, primary coil 32a, primary circuit of FET31
Is the voltage of the battery 17, the internal resistance r of the battery, the primary coil
32a winding resistance R₁, FET 31 on-resistance R _DSBy
Large primary current flows, and the FET 31 is turned on.
The resistance generates heat with a relatively large amount of heat.

[0083] The magnetic saturation occurs in the case of a large duty ratio of the drive pulse signal to the charge voltage V _MC, be slightly larger than the allowable loss P _D calorific value (loss) per unit time at this time, When the secondary circuit is normal, the charging voltage V _MC rises, and magnetic saturation is eliminated in a relatively short time. When the secondary side circuit is short-circuited or open, magnetic saturation is not eliminated and large heat generation continues for a long time.
Failure or accident due to this heat generation.

However, in the strobe device of the present invention, when the charging voltage V _MC of the main capacitor 34 becomes _lower than the boundary voltage V _ref3 during charging, the microcomputer 20 outputs a drive pulse signal having a duty ratio F _3. Since the FET 31 is turned ON / OFF by the drive pulse signal, when it is detected that the secondary circuit is short-circuited or opened and the charging voltage V _MC becomes 0 V as described above, the FET 31 sets the above condition. It is ON / OFF of a driving pulse signal having a duty ratio F ₃ satisfying the formula. As a result, the FET 31 is turned on / off in a state where the heat generation amount (loss) per unit time is smaller than the permissible loss P _D , so that the secondary circuit is short-circuited or open, and the FET 31 is turned on / off. Even if the OFF operation is performed for a long time, no failure of the FET 31 or an accident due to heat generation occurs.

An example in which the present invention is applied to a strobe device mounted on an instant camera has been described. However, the strobe device of the present invention is mounted on various cameras such as a camera using a 135-type photographic film and a digital still camera. It can also be used for strobe devices that are used in cameras and strobe devices that are mounted on cameras and used.

[0086]

As described above, according to the strobe device of the present invention, the drive pulse signal for turning on and off the voltage-controlled semiconductor switching element for applying the pulse voltage to the primary coil is made constant in frequency, When the charging voltage of the main capacitor is low, the pulse width of the pulse voltage is narrowed, and when the charging voltage is high, the pulse width is widened to switch the duty ratio.
Since it is possible to prevent an increase in the charging time of the main capacitor while reducing the power consumption at the initial stage of charging, and to easily obtain a duty ratio necessary for achieving a desired power consumption and charging time. In addition, the design and development period of the strobe device can be shortened. Also, MOS
By using a voltage-controlled semiconductor switching element such as a FET, it can be directly driven by a microcomputer or the like, and the number of parts can be reduced, and the loss can be reduced, so that the device can be downsized. Can be achieved.

Further, when the voltage-controlled semiconductor switching element is driven by the drive pulse signal, the drive pulse is controlled so that the loss in the voltage-controlled semiconductor switching element caused by the flow of the primary current is less than the maximum allowable loss. Since the minimum duty ratio of the signal is determined, and the drive pulse signal having the minimum duty ratio is used to drive the voltage-controlled semiconductor switching element when the charging voltage of the main capacitor is equal to or less than a predetermined voltage including zero, the secondary control is performed due to failure. Even if the side circuit is short-circuited or opened, the voltage-controlled semiconductor switching element does not break down or generate heat to cause an accident.

[Brief description of the drawings]

FIG. 1 is a functional block showing functions of a microcomputer.

FIG. 2 is a perspective view showing an appearance of an instant camera equipped with a strobe device embodying the present invention.

FIG. 3 is a circuit diagram showing a configuration of an instant camera.

FIG. 4 is a waveform diagram showing driving pulse signals at the time of initial charging and at the time of steady state.

FIG. 5 is a waveform diagram showing a relationship between a maximum value of a primary current and a pulse width of a drive pulse signal.

FIG. 6 is a flowchart showing a procedure at the time of charging.

FIG. 7 is a drive pulse signal waveform diagram in an example in which the duty ratio of the drive pulse signal is switched in three stages.

FIG. 8 is a graph showing a relationship between a charging voltage and a duty ratio of a driving pulse.

FIG. 9 is a graph showing a relationship between a conventional maximum value of a primary current and a charging voltage.

[Explanation of symbols]

 17 Battery 20 Microcomputer 23 EEPROM 34 Main capacitor 32 Oscillation transformer 31 FET 39 Charge voltage detection circuit

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Katsumi Motomura 3-13-45 Izumi, Asaka-shi, Saitama F-Term within Fuji Photo Film Co., Ltd. (Reference) 2H053 AA03 BA01 3K098 AA20

Claims (5)

[Claims] An oscillation transformer having a primary coil and a secondary coil inductively coupled to each other, an excitation pulse generating circuit for repeatedly applying a pulse voltage to the primary coil, and a strobe discharge tube connected to the secondary coil to emit light. A strobe device comprising: a main capacitor charged for charging; and the excitation pulse generation circuit is turned on / off in response to a drive pulse signal, and turned on. A voltage-controlled semiconductor switching element that connects the primary coil and a power supply to apply a pulse voltage to the primary coil by generating a drive pulse signal having a constant frequency, and outputs the drive pulse signal.
Based on the detection result of the charging voltage detection means, when the charging voltage of the main capacitor is low, a pulse voltage with a narrow pulse width, and when the charging voltage is high, a pulse voltage with a wide pulse width is applied to the primary coil, A driving pulse signal generating means for switching a duty ratio of the driving pulse signal. 2. The voltage control circuit according to claim 1, wherein the minimum duty ratio of the drive pulse signal is such that the voltage control generated by a primary current flowing from the primary coil when the voltage control type semiconductor switching element is driven by the drive pulse signal. It is determined that the loss in the type semiconductor switching element is less than the maximum allowable loss of the voltage controlled type semiconductor switching element, and the charging voltage of the main capacitor is equal to or less than a predetermined voltage including zero by the charging voltage detecting means. 2. The strobe device according to claim 1, wherein when detected, the drive pulse signal is switched to the drive pulse signal having the minimum duty ratio. 3. The strobe device according to claim 1, wherein the voltage-controlled semiconductor switching element is a MOS field-effect transistor. 4. The duty ratio of the driving pulse signal is
The strobe device according to any one of claims 1 to 3, wherein the strobe device is set in three or more stages according to a charging voltage of the main capacitor. 5. A storage unit for storing a duty ratio of the drive pulse signal, wherein the drive pulse signal generation unit performs digital processing based on the duty ratio stored in the storage unit, thereby obtaining the charging voltage. The strobe device according to any one of claims 1 to 4, wherein a drive pulse signal having a duty ratio according to the following is generated.