Abstract:
To prevent temporary reduction of battery voltage when driving a shutter, an exposure control drive apparatus is provided with a boosting circuit for boosting a voltage of the battery and outputting a boosted voltage. A capacitor is charged by the boosted voltage for driving an actuator of an exposure control mechanism. A detecting circuit detects a current flowing in the boosting circuit and a control circuit controls operation of the boosting circuit in accordance with a magnitude of the detected value so that the boosting circuit is prevented from boosting the battery voltage when the detected current exceeds a predetermined level and is permitted to boost the battery voltage when the detected current is below the predetermined level. In this manner, the current flowing from the battery is prevented from exceeding a maximum level.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an exposure control drive apparatus. 
     Conventionally, an actuator such as a motor or the like for driving a member for controlling an exposure device such as a shutter or a diaphragm is driven by using a battery power source via a regulator as shown by FIG.  14 . 
     FIG. 14 shows an example of a conventional digital still camera. In the drawing, a regulator REG 1  stably supplies a regulated output voltage of a battery E to a control circuit (hereinafter, referred to as “CPU”)  100 , a light measuring circuit (hereinafter, referred to as “AE”)  2 , a distance measuring circuit (hereinafter, referred to as “AF”)  3 , a photographing unit (hereinafter, referred to as “CCD”)  4  including CCD(s) as photographing elements, a CCD drive circuit (hereinafter, referred to as “CCDDR”), an image signal processing circuit and a drive voltage generating circuit and an electronic viewfinder (hereinafter, referred to as “EVF”)  5  including a liquid crystal panel for displaying a photograph captured by the CCD  4 , a liquid crystal panel drive circuit and a drive voltage generating circuit. 
     The CPU  100  comprises a CPU, ROM and RAM and controls various operations in accordance with operation programs stored in ROM. A stroboscopic device  6  comprises a booster circuit and a stroboscopic light emitting unit and is controlled by the CPU  100 . 
     A motor driver DRV  200  comprises transistors Tr 11  through Tr 14  and diodes D 11  through D 14  for supplying current to a coil La of a motor  9  for driving members for exposure control such as the shutter or the diaphragm. Current supplied to the coil La is supplied from the battery E via a regulator REG 300 . 
     A voltage detecting circuit VDT 0  detects the voltage of the battery E and generates an output for detecting battery rundown when the voltage of the battery E becomes proximate to a minimum voltage guaranteeing proper operation of the CPU  100 . The CPU  100  generates a low battery alarm at a display unit (not illustrated) in accordance with the battery rundown detected output and prevents the shutter from being released by making a release switch (not illustrated) inoperable. 
     Generally, when power source voltage is lowered, a control circuit such as the CPU  100  undergoes erroneous operation or becomes inoperable and when a battery is used as a power source, the larger the consumed current, the lower the battery voltage becomes due to the internal resistance of the battery. 
     According to the example of FIG. 14, in order to avoid operational failure of the CPU  100  due to lowering of the battery voltage, the voltage of the battery E is monitored by the voltage detecting circuit VDT 0  and when the battery voltage becomes proximate to the minimum voltage guaranteeing proper operation of the CPU  100 , a battery low alarm is displayed and the shutter is prevented from being released. That is, the “battery rundown” is determined at a time point at which the battery voltage becomes proximate to the minimum voltage guaranteeing proper operation of the CPU  100 . 
     According to the above construction having the battery voltage monitoring function, there is a case in which by virtue of the consumed current flowing in a circuit which is temporarily operated, that is, by virtue of a temporary increase in the consumed current, the battery voltage decreases to proximate the minimum voltage guaranteeing proper operation of the CPU  100  and battery rundown is determined although there still is an allowance actually in the capacity of the battery. 
     Particularly, in the case of a digital still camera, there are many cases where an electronic viewfinder comprising a photographing unit having CCDs or a liquid crystal panel is used, where the battery is used as the power source for such a viewfinder. There is a case in which such a viewfinder is operated in photographing, particularly in determining composition. When the shutter is driven under this state, the consumed current is temporarily increased and accordingly., there is a significant possibility of producing the above-described erroneous determination. 
     Recently, in order to avoid the above-described drawback in a digital still camera, it has been devised that for example, in charging a stroboscope device, simultaneous drive of a plurality of circuits is avoided as much as possible such that operation of the liquid crystal panel of the electronic view finder is stopped to thereby lower a peak current value of the battery E. 
     However, even when various circuits are prevented from being driven simultaneously as much as possible, there are still present circuits which must be driven simultaneously in view of the mechanism and in that case, the peak current of the battery E is naturally increased and there is a problem of determining “battery rundown” even with a battery in which only a short time period has elapsed from the start of use. 
     SUMMARY OF THE INVENTION 
     The present invention has been devised to overcome the forgoing drawbacks. According to an aspect of the invention, there is provided an exposure control drive apparatus comprising a booster circuit for boosting voltage of a battery, a capacitor charged via the booster circuit, an actuator for driving an exposure control member with the capacitor as a power source, a detecting circuit for detecting a value in accordance with a current flowing in the booster circuit, and a control circuit for controlling operation of the booster circuit in accordance with a magnitude of the detected value. Therefore, a magnitude of current flowing from the battery can be controlled. Therefore, for example, a peak value of the current flowing from the battery can be restricted and temporary voltage drop of the battery can be restrained. 
     When the control circuit controls the operation of the booster circuit such that the detected value does not exceed a predetermined value, for example, the peak value of the current flowing from the battery can be restricted and temporary voltage drop of the battery can be restrained. 
     It is preferable that the booster circuit includes a booster coil and a switching transistor and outputs a boosted voltage by a switching operation of the switching transistor, and the control circuit controls the switching operation of the switching transistor in accordance with the magnitude of the detected value. 
     When the control circuit controls a pulse width of a switching pulse specifying the switching operation of the switching transistor in accordance with the magnitude of the detected value, individual pulse widths can be switched and accordingly, a value of the current flowing from the battery can be finely controlled. 
     The booster circuit may include a resistor in which the on current of the switching transistor flows, and the detecting circuit may detect voltage generated by flowing the on current in the resistor. 
     When the booster circuit includes a resistor in which on current of the switching transistor flows, and the detecting circuit detects a sum of voltages generated by flowing the on current in the resistor and the saturated voltage of the switching transistor generated when the switching transistor flows the on current, the saturated voltage of the switching transistor can be used as a bias voltage and accordingly, the detection level can be shifted. 
     There may also be constructed a circuit in which the booster circuit includes a booster coil and a switching transistor and outputs a boosted voltage by a switching operation of the switching transistor, a collector of the switching transistor is connected to one end of the capacitor via a diode, an emitter of the switching transistor is connected to the other end of the capacitor and the detecting circuit detects voltage generated in a resistor provided between the emitter of the switching transistor and a low potential side of the battery. In this case, the detected voltage is increased or reduced retardedly from on or off of the switching transistor by influence of the capacitor and becomes easy to detect. 
     It is preferable that the duty cycle of the switching pulse is equal to or larger than 50%. 
     The booster circuit may be prohibited from executing a boosting operation in driving the actuator and/or at a desired time. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a circuit diagram showing an embodiment of the invention; 
     FIG. 2 is a view showing details of essential portions of FIG. 1; 
     FIG. 3 is a timing chart for explaining operation of FIG. 1; 
     FIG. 4 is a timing chart for explaining operation of FIG. 1; 
     FIG. 5 is a circuit diagram showing another embodiment of the invention; 
     FIG. 6 is a timing chart for explaining operation of FIG. 5; 
     FIG. 7 is a circuit diagram showing still another embodiment of the invention; 
     FIG. 8 is a timing chart for explaining operation of FIG. 7; 
     FIG. 9 is a circuit diagram showing essential portions of still another embodiment of the invention; 
     FIG. 10 is a circuit diagram showing essential portions of still another embodiment of the invention; 
     FIG. 11 is a circuit diagram showing essential portions of still another embodiment of the invention; 
     FIG. 12 is a timing chart for explaining operation of the still another embodiment of the invention; 
     FIG. 13 is a timing chart for explaining operation of the still another embodiment of the invention; and 
     FIG. 14 is a circuit diagram showing a conventional example. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A specific explanation will be given of the invention based on an embodiment with reference to the attached drawings as follows. 
     FIG. 1 shows an example of applying the invention to a digital still camera. In the drawing, elements or portions having constitutions the same as those in FIG. 14 are labelled with the same notations. 
     In the drawing, the control circuit (hereinafter, referred to as “CPU”)  1  comprises a CPU, ROM and RAM and controls various operations in accordance with operational programs stored in the ROM. 
     As an example of an actuator, the motor  9  is adopted in this example, a drive circuit DRV 8  comprises transistors Tr 1  through Tr 4  and diodes D 11  through D 14 , gates (control terminals) of the transistors Tr 1  through Tr 4  are supplied with operation control signals DR from the CPU  1 , and the motor  9  for driving a member A for exposure control, mentioned later, is driven by controlling the coil La of the motor  9 . By selectively activating the transistors Tr 1  through Tr 4  and changing a direction of conducted current of the coil La of the motor  9 , forward and reverse magnetic forces are generated. The coil La of the motor  9  is driven with the charge voltage of a capacitor C 2  as a power source. 
     A converter  7  serving as a voltage boosting circuit comprises a capacitor C 1 , resistors R 1  and R 2 , a switching transistor TR 1 , a diode D 1  and a booster coil L 1  for supplying an electromotive force generated in the booster coil L 1  in accordance with the ON/OFF state of the switching transistor TR 1  to the capacitor C 2  via the diode D 1  to thereby charge the capacitor C 2 . 
     A voltage detecting circuit VDT 1  comprises resistors R 3 , R 4  and R 5 , a variable resistor VR 1 , a Zener diode Z, a capacitor C 3  and a comparator CMP 1  having a hysteresis characteristic. The comparator CMP 1  compares a voltage Vm′ produced by dividing a charge voltage Vm of the capacitor C 2  by the resistors R 3  and R 4  and the variable resistor VR 1  with reference voltage Vth 1  set by the Zener diode Z and the capacitor C 3 , outputs an “H” level from a terminal DW when the voltage Vm′ is equal to or lower than the reference voltage Vth 1  and outputs an “L” level from the terminal DW when the voltage Vm′ becomes equal to or higher than voltage Vmax produced by adding a hysteresis voltage ΔVh to the reference voltage Vth 1 . 
     A voltage detecting circuit VDT 2  comprises resistors R 6  and R 7 , a variable resistor VR 2 , a capacitor C 4  and a comparator CMP 2 , and compares a voltage Vr generated in the resistor R 2  in the converter  7  with reference voltage Vth 2  set by the resistors R 6  and R 7  and the variable resistor VR 2  by the comparator CMP 2  and outputs an “H” level when the voltage Vr becomes equal to or higher than the reference voltage Vth 2 . A one-shot pulse generating circuit  10  outputs one pulse having a predetermined pulse width to a terminal  0 VR when an “H” level is output from the voltage detecting circuit VDT 2 . The voltage Vr generated at the resistor R 2  is proportional to the magnitude of the ON current of the switching transistor TR 1  in the converter  7  and the magnitude of the ON current of the switching transistor TR 1  corresponds to current Iin flowing out from the battery E. 
     A converter control circuit  11  comprises an inverter  11   a , gate circuits  11   b ,  11   c  and  11   d , and inputs an output of the voltage detecting circuit VDT 1 , the pulse OVR and a reference booster signal cp 0 , a booster permitting signal Sb and a booster control signal Sa from the CPU  1  and controls the ON/OFF state of the switching transistor TR 1  in the converter  7  by an output of the gate circuit  11   d . Further, the output of the gate circuit  11   d  constitutes a switching pulse. When restriction of current consumed from the battery E is not needed, the booster control signal Sa uses the reference booster signal cp 0  as a switching pulse cp as it is to thereby shorten a time period required for boosting. For example, when the capacitor C 2  is initially charged by turning ON the power source of the digital still camera, the reference booster signal cp 0  is used as it is as the switching pulse cp by the booster control signal Sa. A display unit  12  carries out a display of “battery rundown” alarm. 
     FIG. 2 shows the motor  9  and the member A for exposure control. In this example, there is used a shutter which also serves as a diaphragm as the member A for exposure control. In the drawing, the motor  9  is constituted by a rotor R, a stator S and the coil La. The stator S is provided with pole portions S 1  and S 2 , and an N pole and an S pole are respectively produced by switching a direction of electricity conducted to the coil La in forward and reverse directions. Thereby, the rotor R can be rotated in both forward and reverse directions. 
     Sectors A 2  and A 3  for opening and closing a shutter opening A 1  by being driven by rotating the motor  9 , are symmetrically arranged with respect to the shutter opening A 1 . The sector A 3  is supported pivotably around a shaft A 4  projected from a base plate (not illustrated). The sector A 2  is supported pivotably around a shaft A 5  fixedly press-fitted to the rotor R, and a sector opening and closing lever A 6  is pivotably supported around the shaft A 5  at an upper face of the sector A 2 . An arm portion A 7  of the sector opening and closing lever A 6  is engaged with an engaging pin A 8  provided at the base plate, and a sector opening and closing lever pin A 9  of the sector opening and closing lever A 6  is axially attached to the sector A 2  and engaged with a groove portion A 3   a  of the sector A 3  to thereby drive the sectors A 2  and A 3 . The sector opening and closing lever A 6  is normally urged in the clockwise direction by a spring A 10 . In this example, when electricity is supplied to the coil La in the forward direction, that is, when the transistors Tr 1  and Tr 4  are turned ON and the transistors Tr 2  and Tr 3  are turned OFF, the shutter A which also serves as a diaphragm is opened to thereby open the shutter opening A 1 , photographing light reaches CCDs in the CCD  4  and when electricity is supplied to the coil La in the reverse direction, that is, when the transistors Tr 2  and Tr 3  are turned ON and the transistors Tr 1  and Tr 4  are turned OFF, the shutter A which also serves as a diaphragm is closed to thereby close the shutter opening A 1 . 
     Next, an explanation will be given of an outline of the operation with reference to FIG.  3 . Further, it is assumed that the reference booster signal cp 0  is output from the CPU 1 , the booster permitting signal Sb is at an “H” level and the booster control signal Sa is at an “L” level. 
     When an exposure operation is executed in accordance with operation of the release switch (not illustrated) and the drive circuit DRV 8  is operated with the capacitor C 2  as power source and the motor  9  starts driving (refer to t′), the charge voltage Vm of the capacitor C 2  is lowered and voltage Vm′ which is the divided voltage of the charge voltage Vm is also lowered by that amount. 
     When the voltage Vm′ becomes equal to or lower than the reference voltage Vth 1  (refer to t 0 ), the voltage detecting circuit VDT 1  outputs an “H” level signal to the terminal DW, the gate circuit  11   c  is opened and the reference booster signal cp 0  is output from the gate circuit  11   c.    
     On this occasion, when the voltage Vr across the resistor R 2  is smaller than the reference voltage Vth 2 , the output of the comparator CMP 2  becomes “L” in level, the one-shot pulse generating circuit  10  does not generate a pulse and the output of the inverter  11   a  becomes “H” and accordingly, the reference booster signal cp 0  is output from the output terminal cp of the gate circuit  11   d . Therefore, the switching transistor TR 1  is turned ON or OFF based on the reference booster signal cp 0  and when the switching transistor TR 1  is switched from ON to OFF, the capacitor C 2  is charged by a counter electromotive force produced at the booster coil L 1 . 
     When the charging operation has progressed and the counter electromotive force of the booster coil L 1  is increased, current Iin consumed from the battery E is increased and the voltage of the battery E is lowered. 
     Hence, in this example, with regard to a reduced voltage state of the battery E, the reduced voltage state of the battery E is detected by detecting current flowing in the converter  7 , specifically, by detecting a voltage (the voltage of the resistor R 2 ) the magnitude of which is changed in proportion to the current flowing in the converter, and when the detected voltage exceeds a predetermined value, the boosting operation of the converter  7  is restrained and the magnitude of current flowing out from the battery E is restrained. 
     Next, a detailed description will be given of operation of the above-described circuit with reference to FIG. 4, which is a detailed timing diagram of a time period before reaching times t′ through t 1  of FIG.  3 . In the drawing, times t′ and t 0  are the same as the times t′ and to of FIG. 3, notations OVR, cp and DW show voltage waveforms of the terminal OVR, the terminal cp and the terminal DW of FIG.  1  and notations Vr, Iin, cp 0 , DR and Vm′ respectively designate the voltage Vr, the current Iin, the reference booster signal cp 0 , the operation control signal DR and the voltage Vm′ of FIG.  1 . 
     As mentioned above, when the exposure operation is i executed in accordance with operation of the release switch (not illustrated) the drive circuit DRV 8  is operated by the operation control signal DR with the capacitor C 2  as a power source and the motor  9  starts driving (refer to t′), the charge voltage Vm of the capacitor C 2  is lowered and the voltage Vm′ which is the divided voltage of the charge voltage Vm is also lowered by that amount. 
     When the voltage Vm′ becomes equal to or lower than the reference voltage Vth 1  (refer to t 0 ), the terminal DW becomes “H” in level and the reference booster signal cp 0  is output from the gate circuit  11   c  (refer to t 41 ). 
     On this occasion, when the applied voltage Vr of the resistor R 2  is smaller than the reference voltage Vth 2 , the output of the comparator CMP 2  becomes “L”, the one-shot pulse generating circuit  10  does not generate a pulse, the output of the inverter  11   a  becomes “H” and accordingly, the reference booster signal cp 0  is output from the output terminal cp of the gate circuit  11   d . Therefore, the switching transistor TR 1  is turned ON or OFF based on the reference booster signal cp 0  and the capacitor C 2  is charged by the counter electromotive force produced at the booster coil L 1  when the switching transistor TR 1  is switched from ON to OFF. 
     When the above-described charging operation has progressed and the counter electromotive force of the booster coil L 1  is increased, the current Iin consumed from the battery E is increased and in accordance therewith, ON current flowing to the switching transistor TR 1  when the switching transistor TR 1  is turned ON is increased, and the applied voltage Vr of the resistor R 2  is increased (refer to t 41  through t 42 ). 
     When the applied voltage Vr of the resistor R 2  becomes equal to or larger than the reference voltage Vth 2 , the output of the comparator CMP 2  becomes “H” in level and in accordance therewith, the one-shot pulse generating circuit  10  outputs the pulse OVR (refer to t 42 ). 
     The pulse OVR is inverted by the inverter  11   a , the gate circuit  11   d  is closed by the inverted signal and the “H” level of the reference booster signal cp 0  output to the terminal cp is cut by the time period of the pulse OVR. By cutting the “H” level during the time period of the pulse OVR, the voltage of the booster coil L 1  is lowered and in accordance therewith, the consumed current Iin from the battery E is lowered (refer to t 42  through t 44 ). 
     When the pulse OVR has terminated, the output of the inverter  11   a  returns to “H”, the gate circuit  11   d  is opened and accordingly, similar to the above-described operation, the reference booster signal cp 0  is output to the terminal cp and the booster operation is carried out similar to the above-described operation (refer to t 44  through t 45 ). 
     At subsequent times, the operation is carried out similar to that described above, at every time at which the voltage Vr exceeds the reference voltage Vth 2 , the pulse OVR is output and the boosting operation is prohibited during that time period. 
     In this way, the current flowing from the battery E to the converter  7  is detected based on a value in correspondence with the current value, and more specifically, a voltage value in proportion to the current value, and the operation of the converter  7  is controlled in accordance with the magnitude of the detected value. Accordingly, the magnitude of the current flowing out of the battery E can be controlled. Therefore, for example, a peak value of the current flowing out of the battery E can be restricted and a temporary voltage drop of the battery E can be restrained. Further, when individual pulse widths of pulses at an “H” level of the reference booster signal cp 0  are controlled to reduce as in this example, a value of the current flowing out from the battery E can finely be controlled. 
     Further, the pulse width of the pulse OVR can pertinently be changed in accordance with the reference booster signal cp 0 . 
     Next, an explanation will be given of another embodiment with reference to FIG.  5 . In FIG. 5, notation  11   f  designates a flip-flop and elements which are the same or similar to those in FIG. 1 are designated with the same notations. Further, in this example, the reduced voltage state of the battery E is detected by detecting voltage Vrh applied to the resistor R 2  and the switching transistor TR 1 , so that when the detected voltage exceeds a predetermined value during a time period in which the switching transistor TR 1  is turned ON, the boosting operation of the converter  7  is restrained and the magnitude of the current flowing out of the battery E is restrained. Further, a reference voltage Vth 3  compared by the comparator CMP 2  is made higher than the reference voltage Vth 2  shown in FIG.  1 . 
     Next, an explanation will be given of the operation with reference to FIG.  6 . In this example, an explanation will be given based on differences in operation from that of FIG.  1 . 
     When the operation control signals DR become “H” and the motor  9  starts driving with the capacitor C 2  as a power source (refer to t′), the charge voltage of the capacitor C 2  is lowered, the gate circuit  11   c  is opened by an “H” level output of the voltage detecting circuit VDT 1  and the reference booster signal cp 0  is output from the terminal cp (refer to t 61 ). 
     The voltage of the booster coil L 1  is increased by the output of the reference booster signal cp 0  and in accordance therewith, the voltage Vrh during the time period in which the switching transistor TR 1  is turned ON (hereinafter, simply referred to as “voltage Vrh”) is also increased (refer to t 61  through t 62 ). Further, the flip-flop  11   f  is reset by an “L” output of the reference booster signal cp 0 . 
     When the voltage Vrh becomes equal to or higher than the reference voltage Vth 3 , the voltage detecting circuit VDT 2  makes the terminal OVR 0  “H” in level and in accordance therewith, the Q terminal of the flip flop  11   f  becomes “L” in level, the gate circuit  11   d  is closed, the reference booster signal cp 0  to the terminal cp stops being output (refer to t 62 ) and the voltage Vrh is reduced (refer to t 62  through t 63 ). 
     The flip flop  11   f  is reset by “L” of the reference booster signal cp 0  and operation similar to the above-described is repeated (refer to t 63  and thereafter). 
     In this manner, the reduced voltage state of the battery E is detected by detecting the voltage Vrh applied to the resistor R 2  and the switching transistor TR 1 , and when the detected voltage exceeds a predetermined value, the boosting operation of the converter  7  is restrained, the magnitude of the current consumed from the battery E is restrained and accordingly, there is achieved an effect similar to that in the example of FIG. 1, an inversion level of voltage compared and detected by the comparator CMP 2  can be shifted upwardly from that in the case of FIG. 1 by the saturated voltage of the switch transistor TR 1  and accordingly, there is no need for using a construction which can detect a very small voltage as the comparator CMP 2  as in FIG.  1  and low cost implementation is achieved. 
     In accordance with the above-described embodiments, the reduced voltage state of the battery E is detected by detecting the voltage of the resistor R 2  or the voltage of the resistor R 2  and the switching transistor TR 1 . When the detected voltage exceeds a predetermined value, the boosting operation of the converter  7  is restrained and the magnitude of the current flowing out of the battery E is restrained. 
     With reference to FIG. 7, an embodiment will be described in which the emitter of the switching transistor TR 1  is connected to low potential sides of the capacitors C 1  and C 2  and a voltage across a resistor R 52  provided between a terminal N 1  and a low potential side of the power source is detected to thereby detect the reduced voltage state of the battery E. When the detected voltage exceeds a predetermined value, the boosting operation of the converter  7  is restrained to thereby restrain the magnitude of the current consumed from the battery E. 
     In FIG. 7, elements which are the same or similar to those in FIG. 1 are designated by the same reference numerals. In FIG. 7, a comparator CMP 21  in the voltage detecting circuit VDT 2  is provided with hysteresis, compares voltage Vri generated at the terminal N 1  with reference voltage Vth 4  set by the resistors R 6  and R 7  and the variable resistor VR 2 , outputs an “H” level when the voltage Vri becomes equal to or higher than the reference voltage Vth 4  and outputs an “L” level when the voltage Vri becomes equal to or lower than voltage Vth 5  produced by subtracting the hysteresis voltage ΔVha from the reference voltage Vth 4 . 
     Next, an explanation will be given of operation of FIG. 7 with reference to FIG.  8 . Further, in this example, an explanation will be given centering on differences in operation from that of FIG.  1 . 
     When the operation control signals DR become “H” and the motor  9  starts driving with the capacitor C 2  as a power source (refer to t′), the charge voltage of the capacitor C 2  is lowered, the gate circuit  11   c  is opened by the output of the voltage detecting circuit VDT 1  and the reference booster signal cp 0  is output from the terminal cp (refer to t 81 ). 
     The voltage of the booster coil L 1  is increased by the output of the reference booster signal cp 0  and in accordance therewith, the voltage Vri across terminals of the resistor R 52  is also increased (refer to t 81  through t 82 ). When the voltage Vri becomes equal to or higher than the reference voltage Vth 4 , the voltage detecting circuit VDT 2  makes the terminal OVR “H” in level and in accordance therewith, the gate circuit  11   d  is closed and the reference booster voltage cp 0  to the terminal cp stops being output (refer to t 82 ). 
     At this time, an amount of current change in accordance with the turning OFF of the switching transistor TR 1 , that is, an alternating current component flows to the terminal N 1  via the capacitors C 2  and C 1  and accordingly, the voltage Vri is reduced comparatively gradually (refer to t 82  through t 83 ). 
     When the voltage Vri becomes equal to or lower than the voltage Vth 5  produced by subtracting the hysteresis voltage ΔVha from the reference voltage vth 4 , the voltage detecting circuit VDT 2  makes the terminal OVR “L” in level and starts the above-described charging operation again. Thereafter, the above-described operation is repeated. 
     In this way, the emitter of the switching transistor TR 1  is connected with the low potential side of the capacitor C 2  and the voltage of the resistor R 52  provided between the terminal N 1  and the low potential side of the power source is detected to thereby detect the reduced voltage state of the battery E. When the detected voltage exceeds the predetermined value, the boosting operation of the converter  7  is restrained, the magnitude of the current consumed from the battery E is restrained and therefore, the magnitude of the current flowing out from the battery E can be controlled. Therefore, for example, the peak value of the current flowing out from the battery E can be restricted and the temporary voltage drop of the battery E can be restrained. Further, when the individual pulse width of the pulse at an “H” level of the reference booster signal cp 0  is controlled to reduce as necessary as in this example, the amount of the current flowing out of the battery E can be finely controlled. Further, even when the switching transistor TR 1  is turned OFF, the voltage of the terminal N 1  is gradually reduced and accordingly, when the voltage reducing time period is made to specify the time period of prohibiting the pulse at the “H” level of the reference booster signal cp 0 , there is no need for providing the one-shot pulse generating circuit as in the case of FIG.  1  and simplification of the circuit construction is achieved. 
     According to the respective examples of FIGS. 1,  5  and  7 , depending on the manner of use, there is a possibility in which the charge voltage of the capacitor C 2  becomes lower than the voltage of the battery E and in this case, current flows automatically from the battery to the capacitor C 2  and accordingly, there is a case in which it is difficult to restrain the peak value of the current flowing out of the battery E in driving the actuator (motor). In such a case, a converter shown in FIG. 9 may be used in place of the converter  7  in FIGS. 1 and 5 and a converter shown in FIG. 10 may be used in place of the converter  7  of FIG.  7 . Further, in FIGS. 7 and 8, elements which are the same or similar to as those in FIGS. 1 and 5 are denoted by the same reference numerals and voltages generated at the terminal E, the terminal cp, the terminal Vm, the terminal Vr and the terminal Vri respectively correspond to voltages E, cp, Vm, Vr and Vri respectively generated in FIGS. 1,  5  and  7 . An explanation will be given of FIGS. 9 and 10 as follows. 
     In FIG. 9, reference numeral  7   a  designates a transformer, reference numeral R 8  designates a resistor and reference numeral C 5  designates a capacitor. In this case, even when the charge voltage of the capacitor C 2  becomes lower than the voltage of the battery E, the battery E and the capacitor C 2  are separated by the transformer  7   a  and accordingly, current does not flow from the battery E to the capacitor C 2  and the above-described problem is not posed. 
     In FIG. 10, notation TR 1  designates a transistor for switching and notation R 9  designates a resistor and in this case, the battery E and the capacitor C 2  are separated by the switching transistor TR 1  and accordingly, even when the charge voltage of the capacitor C 2  becomes lower than the voltage of the battery E, current does not flow from the battery E to the capacitor C 2  and the above-described problem is not posed. 
     Although according to the above-described respective examples, the reference booster signal cp 0  is output from the CPU  1 , an explanation will be given of an example in which the converter per se is provided with an oscillating function and the reference booster signal cp 0  need not be supplied from the CPU  1  in reference to FIG. 11 as follows. In this example, there is used a publicly-known ringing choke converter as the converter  7 . Output voltage is stabilized by a Zener diode Zdc, a diode Dc and a capacitor Cc, and start and stop of oscillation is controlled by making a transistor Trc turn ON or OFF by a signal input via a terminal CNT. Further, in the drawing, elements which are the same or similar to those in FIG. 1 are designated with the same reference numerals, reference numeral  7   a  designates a transformer having windings P 1  (primary winding), P 2  (base winding) and P 3  (secondary winding), notations Rb 1  and Rb 2  designate resistors and notation Cb designates a capacitor. 
     Also in this case, the battery E and the capacitor C 2  are separated from each other by the transformer  7   a  and accordingly, even when the charge voltage of the capacitor C 2  becomes lower than the voltage of the battery E, current does not flow from the battery E to the capacitor C 2  and the above-described problem is not posed. 
     As in the above-described respective examples, the charge voltage of the capacitor C 2  can be used in driving the motor for driving the shutter A which serves also as a diaphragm (exposure control member) and accordingly, the current flowing from the battery E can be reduced and the time during which the battery voltage is temporarily lowered by driving the motor  9  can be reduced. Therefore, in the case in which the above-described circuit construction is used in a camera having a function of determining battery rundown when, for example, the battery voltage becomes smaller than a predetermined value, driving the motor  9  for driving the shutter A which serves also as a diaphragm (exposure control member), does not cause the problem of voltage drop in the battery so that a battery in which only a small time period has elapsed from the start of use is deemed to have undergone “battery rundown”. This effect becomes particularly significant when the above-described circuit is used in a digital still camera in which CCDs or an electronic viewfinder is operated in driving the motor for driving the exposure control member. That is, according to such a digital still camera, driving of the motor for driving the exposure control member is executed simultaneously with operation of the CCDs or the electronic viewfinder and in driving the motor, the battery voltage is temporarily and rapidly lowered, however, when the above-described circuit is used, the rapid lowering of the battery voltage can be reduced. Therefore, the problem in which a relatively new battery is deemed to have been rundown is overcome. 
     Further, although according to the above-described respective examples, the converter  7  is driven in driving the motor  9 , the operation of the converter  7  may be stopped in driving the motor  9  as shown in FIG. 12 by selectively outputting the booster control signal Sa and the booster permitting signal Sb from the CPU  1 , or the converter  7  may be prevented from being operated in driving the motor  9  and during predetermined time period thereafter as shown by FIG.  13 . Further, in the case of operating the converter  7  as shown by FIG. 12 in driving the motor  9 , the booster permitting signal Sb may be made “L” or an output of the reference booster signal cp 0  may be stopped and in the case of operating the converter  7  as shown in FIG. 13, in driving the motor  9  and during a predetermined time period thereafter, the booster permitting signal Sb may be made “L” in level or output of the reference booster signal cp 0  may be stopped. 
     Further, although an explanation has been given of the shutter which also serves as a diaphragm having two positions of open and close in the above-described examples, the invention is not limited thereto but is applicable to a diaphragm or a shutter having a plurality of positions. 
     Further, the actuator is not limited to the motor of a single coil type but a stepping motor for driving a plurality of coils or other kinds of actuator, for example, a plunger may be used. 
     Further, the exposure control member is not limited to the above-described configuration. For example, there may be used a member of changing a diaphragm aperture or a member switching to insert or not to insert a member having a different transmitted light amount as in an ND filter. 
     According to the present invention, electric charge for charging the capacitor can be supplied as current for operating the actuator for driving the exposure control member in photographing a picture in which current is mostly needed and accordingly, current flowing out from the battery can be reduced in photographing a picture. 
     Further, by controlling the magnitude of the current flowing from the battery, the peak value of the current flowing from the battery can be restricted and temporary and rapid voltage drop of the battery can be restrained. 
     When the operation of the booster circuit is controlled such that the detected value does not exceed a predetermined value, for example, restriction of the peak value of the current flowing from the battery and restraint of temporary voltage drop of the battery can effectively be controlled. 
     Further, when the pulse width of the switching pulse for specifying the switching operation of the switching transistor is controlled in accordance with the magnitude of the detected value, the individual pulse width can be switched and accordingly, the value of the current flowing out from the battery can finely be controlled. 
     When the booster circuit includes the resistor in which ON current of the switching transistor flows and the detecting circuit detects the sum of the voltage generated by flowing the ON current in the resistor and the saturated voltage of the switching transistor generated when the switching transistor flows the ON current, the saturated voltage can be used as a bias voltage and therefore, the detection level can be shifted. 
     There may be constructed a circuit in which the booster circuit includes the booster coil and the switching transistor, the booster voltage is output by the switching operation of the switching transistor, the collector of the switching transistor is connected to one end of the capacitor via the diode, the emitter of the switching transistor is connected to other end of the capacitor and the voltage generated at the resistor provided between the emitter of the switching transistor and low potential side of the battery is detected. In this case, the detected voltage is increased or reduced retardedly from ON or OFF of the switching transistor by influence of the capacitor and is easy to detect.