JP2005339987A - Light emitting device for photography and camera having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform quickly stroboscope charge at the time of speed-light photographing, irrespective of a temperature in the environment of using a camera. <P>SOLUTION: The digital camera 10 comprises a stroboscope circuit 20, a light-emitting portion 26 and a temperature detector 28 for detecting the temperature in the environment of using the camera 10. When stroboscope charging operation for speed-light photography is performed, the duty factors of a series of pulse signals transmitted to the MOSFET of the stroboscope circuit 20 are determined for a normal temperature (A) or for a low temperature (B). The pulse signals are outputted to the MOSFET, based on the determined duty factors, and the duty factors are gradually switched with the increase of a charging voltage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a strobe device that emits an auxiliary light source during photographing, and more particularly to a strobe circuit that boosts a battery power supply voltage using a transistor and charges the battery.

In a normal camera, a strobe device using a transistor such as a MOSFET is mounted. The current is supplied to the transistor provided on the primary side, the power supply voltage is boosted, and the charge is supplied by the capacitor provided on the secondary side. Accumulated. During charging, a series of pulse signals are output so as to control the ON / OFF of the transistors, and the duty ratio of the pulse signals is switched as the charging voltage increases (see, for example, Patent Document 1). When the user performs a release operation, discharge light is emitted in accordance with the release operation.
Japanese Unexamined Patent Publication No. 7-85888 (FIG. 6)

  When the temperature in the operating environment at the time of flash photography is low, such as below freezing, the charging time becomes longer than the charging period at room temperature due to the increase in internal resistance of the battery and the discharge characteristics. As a result, it is not possible to shoot promptly at the time of strobe shooting, and there is a situation where a photo opportunity is missed.

  The light emitting device for photographing according to the present invention is a device that illuminates a subject when photographing with a camera, and includes a booster circuit, PWM control means, and light emitting means. The boosting circuit includes a boosting transformer, a transistor provided on the primary side of the transformer, and a charging capacitor provided on the secondary side of the transformer, and boosts the power supply voltage of the battery to charge the capacitor. For example, a DC-DC converter is applied as the booster circuit.

  The PWM control means sends a series of pulse signals for controlling the ON / OFF operation of the transistor to the transistor in order to perform PWM control of the operation of the transistor. Along with the ON / OFF operation of the transistor, a current flows to the primary side of the transformer, and accordingly, a current flows to the secondary side of the transformer to charge the capacitor. The PWM control means switches the duty ratio of a series of pulse signals as the secondary side charging voltage rises in order to flow a current suitable for the charging voltage to the primary side of the transformer. The light emitting means emits light by discharge light emission based on the electric charge accumulated in the capacitor.

  The light emitting device for photographing includes a temperature detector that detects the temperature at the time of photographing. Here, the air temperature at the time of shooting is defined so as to include all of the outside air temperature, the battery temperature of the camera, and the temperature inside the camera when the camera is used. For example, the battery temperature is detected. The PWM control means outputs a series of pulse signals in accordance with the temperature at the time of photographing so as to increase the duty ratio with respect to a decrease in temperature. That is, the value of the duty ratio at a low temperature is increased as compared with the temperature during normal use. Increasing the value of the duty ratio increases the amount of current flowing on the primary side of the booster circuit. As a result, the secondary side charging period does not become long even in a low temperature state.

  The PWM control means may switch the duty ratio stepwise as the charging voltage increases. At this time, the duty ratio at each stage is changed in accordance with the temperature so as to suppress the decrease in the transformer current on the primary side due to the decrease in the camera temperature. For example, a series of duty ratios that change in a stepwise manner as the charging voltage rises and a stepwise change in values depending on the temperature are stored in the memory, and from the series of duty ratios, What is necessary is just to provide the duty ratio setting means which sets a set of duty ratios according to the detected temperature. The PWM control means outputs a series of pulse signals based on the set set duty ratio. Dividing into at least two temperature ranges (for example, a first temperature range and a second temperature range), a series of duty ratios may be determined. For example, the low temperature range is set to 0 degrees or less, and the normal temperature range is set to above 0 degrees.

  A program of the present invention is a light emission control program in a light emitting device for photographing, and includes a step-up transformer, a transistor provided on the primary side of the transformer, and a charging capacitor provided on the secondary side of the transformer. A series of pulse signals for controlling the ON / OFF operation of the transistor is sent to the booster circuit that boosts the power supply voltage of the battery and charges the capacitor to the transistor. The PWM control means for switching the duty ratio and the series of duty ratios in which the value changes stepwise as the charging voltage rises and the stepwise value changes depending on the temperature, the detected temperature is changed to the detected temperature. A duty ratio setting means for setting a set of corresponding duty ratios is made to function.

  The camera of the present invention includes a battery, a boosting transformer, a transistor provided on the primary side of the transformer, and a charging capacitor provided on the secondary side of the transformer, and boosts the power supply voltage of the battery. A booster circuit for charging the capacitor, a PWM control means for sending a series of pulse signals for controlling the ON / OFF operation of the transistor to the transistor, and switching the duty ratio of the series of pulse signals as the secondary charging voltage rises, and an auxiliary A light source, a light emitting unit that emits light based on the electric charge accumulated in the capacitor, and a temperature detector that detects a temperature at the time of shooting, and the PWM control unit has a duty against a decrease in temperature according to the temperature at the time of shooting. A series of pulse signals are output so as to increase the ratio.

  As described above, according to the present invention, strobe charging can be performed quickly at the time of flash photography regardless of the temperature in the camera usage environment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram of a digital camera according to the present embodiment.

  The digital camera 10 is a digital camera that can record a still image or display a recorded image. When the main switch S1 is turned on by the user's ON operation on a power button (not shown), power is supplied from the battery 14 to each circuit.

  When the photometry switch S2 is turned on by half-pressing a release button (not shown), the brightness of the subject is detected by the photometry control unit 42, and an aperture value and a shutter speed corresponding to the brightness of the subject are calculated. . Then, when the release switch S3 is turned on by a full pressing operation of the release button, a shutter (not shown) opens and closes for a predetermined time. A subject image is formed on the light receiving surface of the CCD 32 by the light passing through the photographing optical system 49, and an image signal corresponding to the subject image is read from the CCD 32. The image signal read from the CCD 32 is processed in the signal processing circuit 36, and after being compressed, the image data is recorded in the memory 52 in the memory card format. When the playback mode is set by the user, the recorded image data is read and the recorded image is displayed on the LCD 38.

  The digital camera 10 is provided with a system control circuit 12 that controls the entire camera 10 and incorporates a CPU 41 and a memory such as a ROM 43 that stores a program for controlling the operation of the camera, data relating to flash photography, and the like. The system control circuit 12 outputs control signals to the CCD drive circuit 34, LCD drive unit 40, photometric control unit 42, focus adjustment control unit 44, lens drive unit 46, shutter drive unit 48, pulse generator 50, and the like. When the power is turned on, power is supplied through a regulator 16 that stabilizes the voltage.

  When the strobe switch S4 is turned on by a user's strobe button (not shown) operation, power is supplied to the strobe circuit 20. The strobe circuit 20 includes a booster 22 and a voltage detector 24, boosts the power supply voltage of the battery 14, and charges it. The light emitting section 26 is provided with a discharge tube filled with xenon gas, and discharges light (flashes) based on the charge charged in the strobe circuit 20. When the release switch S3 is turned on, a trigger signal is output from the system control circuit 12 to the light emitting unit 26, and flash photography is performed by synchronizing the light emission operation with the photographing operation. The voltage detector 24 in the strobe circuit 20 detects the charging voltage in the strobe circuit 20.

  The temperature detector 28 provided with the thermistor detects the temperature of the battery 14, thereby detecting the internal temperature of the camera 10, that is, the temperature in the environment where the camera 10 is used.

  FIG. 2 is a circuit diagram of the strobe circuit 20.

  The strobe circuit 20 is a DC-DC converter including a step-up transformer 13. An N-channel MOSFET 15 is provided on the primary side of the transformer 13, and a strobe charging capacitor C <b> 3 is provided on the secondary side. The strobe circuit 20 is a flyback booster circuit, and a capacitor C1 is connected in parallel to the MOSFET 15 and a capacitor C2 is connected in parallel to the capacitor C3.

  A series of pulse signals sent from the system control circuit 12 is input between resistors R1 and R2 connected to the gate G side of the MOSFET 15 in accordance with a pulse waveform according to a predetermined duty ratio as will be described later. As a result of the MOSFET 15 performing an ON / OFF operation based on a series of pulse signals, magnetic energy is generated by a current change on the primary side of the transformer 13, and a current flows on the secondary side by mutual induction.

A voltage higher than the power supply voltage V ₀ of the battery 14 is charged in the capacitor C3 by the ON / OFF operation of the MOSFET 15 and the actions of the diodes D1, D2 and the capacitors C1, C2. As time elapses, the power supply voltage V ₀ is gradually increased, and finally the capacitor C3 is charged up to a voltage (shooting voltage) necessary for flash photography. Potential at the anode AD between the resistors R4, R5 corresponds to the potential of the capacitor C3, resistors R3, R4 and divided voltage V _c at the resistor R5 is detected by the system control circuit 12.

  FIG. 3 is a flowchart showing strobe light emission processing executed in the system control circuit 12. FIG. 4 is a diagram showing a current flowing on the primary side and a charging voltage on the secondary side during the charging period. FIG. 5 is a diagram showing a duty ratio that is switched in stages during the charging period.

  In step S101, it is determined whether or not the strobe button has been pressed by the user. If it is determined that the strobe button has been pressed, it is determined in step S102 whether or not strobe photography is possible, that is, whether or not the remaining amount of the battery 14 is sufficient to allow strobe photography. If it is determined that the flash photography is not possible, the processing routine ends. On the other hand, if it is determined that the flash photography is possible, the process proceeds to step S103, and the temperature inside the camera, that is, the temperature in the use environment is detected by the temperature detection circuit 28. In step S104, it is determined whether or not the temperature is 0 degrees or less.

FIG. 4 shows a pulse waveform pattern of a series of pulse signals output to the MOSFET 15 during the charging period in the strobe circuit 20. Since the charging voltage of the secondary side it is necessary to increase the current amount of the primary along with the increase, the duty ratio is switched stepwise as the charging voltage V _c of the secondary side is increased. Here, the period until full charge from 0V to 330V is divided into seven stages, and a switching voltage is set for each stage. These series of pulse waveform patterns are stored in the ROM 43 in advance.

  If it is determined in step S104 that the temperature is not less than 0 degrees, the process proceeds to step S106, and the first PWM waveform pattern (A) for room temperature (here, a range above 0) is set. On the other hand, if it is determined that the temperature is 0 degrees or less, the process proceeds to step S105, and the second PWM waveform pattern (B) for low temperature (range of 0 degrees or less) is set. In the second PWM pattern (B), the overall duty ratio is higher than that in the first PWM waveform pattern (A). Specifically, the duty ratio in the fourth to seventh stages is set large. When step S105 or step S106 is executed, the process proceeds to step S107.

In step S107, the charge voltage V _c of the secondary side is detected. In step S108, a series of pulse signals are output to the MOSFET 15 according to the set PWM waveform pattern (A) / (B). During the charging period, the secondary side charging voltage V _c is constantly monitored, and when the charging voltage V _c reaches the switching voltage, a pulse signal based on the duty ratio in the next stage is output. In FIG. 5, the primary-side current value I and the secondary-side charging voltage V _c from the start of charging are represented over time. When step S108 is executed, the process proceeds to step S109.

In step S109, it is determined whether or not the release button is pressed halfway and the photometric switch S2 is turned on. If it is determined that the metering switch is not in the ON state, the process returns to step S107. On the other hand, the photometric switch S2 when it is determined that the ON state, the process proceeds to step S110, the charge voltage V _c is whether flash photography possible voltages is determined. If it is determined in step S110 that the flash photography is not possible, the process returns to step S107, and steps S107 to S110 are repeatedly executed until the flash charging is completed. As a result, the duty ratio of the pulse signal increases stepwise.

  On the other hand, if it is determined in step S110 that the flash photography is possible, the process proceeds to step S111, display processing for notifying the completion of charging is performed, and whether the release button is fully pressed and the release switch S3 is turned on. Is judged. If it is determined that the release switch S3 is not in the ON state, the process returns to step S109. On the other hand, when it is determined that the release switch S3 is in the ON state, the process proceeds to step S112, and a trigger signal is sent to the light emitting unit 26. The light emitting unit 26 emits light based on the trigger signal.

  FIG. 6 is a diagram showing capacity characteristics associated with battery discharge. FIG. 7 is a diagram showing the internal resistance of the battery.

In FIG. 6, the number of times the camera is used and the battery voltage associated therewith are graphed, and the voltages V ₁ , V ₂ , and V ₃ when used under conditions of 25 degrees, 0 degrees, and −10 degrees are curves. It is represented. As shown in FIG. 6, the discharge characteristics of the battery differ depending on the temperature, and the lower the temperature, the faster the remaining amount of battery decreases. FIG. 7 shows changes in the internal resistance of the battery due to temperature changes, and the internal resistance increases as the temperature decreases.

  FIG. 8 is a diagram showing the current value flowing on the primary side in the strobe circuit 20 according to temperature. FIG. 9 is a diagram showing the secondary side charging voltage in the strobe circuit 20 according to temperature.

8, the normal temperature and the current I _s of the primary side of (25 degrees in this case), are shown a low temperature and the current I _L on the secondary side of the (here 0 °) it is. Since the duty ratio is increased at low temperatures, the switching timing of the ON / OFF operation of the MOSFET 15 is shortened. As a result, the amount of current flowing through the coil of the transformer 13 on the primary side increases, and the amount of current does not drop much compared to that at room temperature. FIG. 8 shows the current I ′ _L when the PWM waveform pattern at normal temperature shown in FIG. 4 is used at low temperature.

In FIG. 9, the charging voltage V _{s at} normal temperature and the charging voltage V _{L at} low temperature based on the amount of current shown in FIG. 8 are shown over time. Since a large amount of current flows on the primary side by increasing the duty ratio at low temperatures, the locus of the charging voltage VL is hardly different from the locus of the charging voltage Vs. FIG. 9 shows the charging voltage V ′ _L when the PWM waveform pattern at normal temperature shown in FIG. 4 is used at low temperature.

  As described above, according to the present embodiment, the camera 10 includes the strobe circuit 20 and the light emitting unit 26, and the temperature detector 28 that detects the air temperature in the usage environment of the camera. When a strobe charging operation is performed for strobe shooting, the duty ratio of a series of pulse signals sent to the MOSFET 15 of the strobe circuit 20 is set to room temperature (A) or low temperature (B). Then, a pulse signal is output based on the determined duty ratio, and the duty ratio is switched stepwise as the charging voltage increases.

  Since the pulse signal is set in accordance with the temperature, even in a situation where the battery performance deteriorates because the temperature is low, the flash photography can be performed with the charging period substantially the same as the charging period at room temperature.

  In the present embodiment, the temperature range is divided into two temperature ranges with reference to 0 degrees, but the duty ratio may be set in a plurality of ranges. Further, the duty ratio may be set to be changed continuously. Alternatively, the PWM waveform pattern may be changed once by setting the PWM waveform pattern and then detecting the temperature during charging.

  The temperature of the outside air inside and outside the camera 10 may be detected, and the temperature in the camera operating environment (when using the battery) may be detected.

  A strobe circuit other than this embodiment may be used, and any booster circuit that can be boosted and charged by PMW control, such as a booster circuit using a transistor other than a MOSFET or a forward booster circuit, may be used. Moreover, you may apply to other cameras and imaging devices, such as a silver salt camera.

It is a block diagram of the digital camera which is this embodiment. It is a circuit diagram of a strobe circuit. It is the flowchart which showed the flash light emission process performed in a system control circuit. It is the figure which showed the electric current which flows into the primary side in a charging period, and the charging voltage of a secondary side. It is the figure which showed the duty ratio switched in steps in a charging period. It is the figure which showed the capacity | capacitance characteristic accompanying discharge of a battery. It is the figure which showed the internal resistance of the battery. It is the figure which showed the electric current value which flows into the primary side in a strobe circuit according to temperature. It is the figure which showed the charging voltage of the secondary side in a strobe circuit according to temperature.

Explanation of symbols

10 Digital Camera 12 System Control Circuit 13 Booster Transformer 14 Battery 15 MOSFET (Transistor)
20 Strobe circuit (boost circuit)
26 Light emitting part (light emitting means)
28 Temperature detector (temperature detection circuit)
43 ROM (memory)

Claims (6)

A boosting circuit having a boosting transformer, a transistor provided on the primary side of the transformer, and a charging capacitor provided on the secondary side of the transformer, and boosting a power supply voltage of a battery to charge the capacitor When,
PWM control means for sending a series of pulse signals for controlling the ON / OFF operation of the transistors to the transistors and switching the duty ratio of the series of pulse signals as the secondary side charging voltage rises;
A light emitting means for emitting light based on the electric charge accumulated in the capacitor;
A temperature detector that detects the temperature during shooting,
The imaging light-emitting device, wherein the PWM control unit outputs a series of pulse signals so as to increase a duty ratio with respect to a decrease in temperature according to a temperature at the time of imaging.   The PWM control means switches the duty ratio in stages as the charging voltage increases, and changes the duty ratio in each stage so as to suppress a decrease in the primary transformer current due to a decrease in camera temperature. The light emitting device for photographing according to claim 1. A memory that can store a series of duty ratios whose values change stepwise as the charging voltage rises, and whose stepwise value changes depending on the temperature,
A duty ratio setting means for setting a set of duty ratios according to the detected temperature from the set of duty ratios;
The light emitting device for photographing according to claim 1, wherein the PWM control unit outputs the series of pulse signals based on a set of set duty ratios.   4. The photographing light-emitting device according to claim 3, wherein the set of duty ratios is determined according to at least two temperature ranges. A light emission control program in a light emitting device for photographing,
A boosting circuit having a boosting transformer, a transistor provided on the primary side of the transformer, and a charging capacitor provided on the secondary side of the transformer, and boosting a power supply voltage of a battery to charge the capacitor On the other hand, a PWM control means for sending a series of pulse signals for controlling the ON / OFF operation of the transistors to the transistors and switching the duty ratio of the series of pulse signals as the secondary side charging voltage rises;
A set of duty ratios corresponding to the detected temperature is set from a series of duty ratios that change stepwise as the charging voltage rises and change stepwise depending on the temperature. A program characterized by causing the duty ratio setting means to function. Battery,
A step-up transformer having a step-up transformer, a transistor provided on the primary side of the transformer, and a charging capacitor provided on the secondary side of the transformer, boosting the power supply voltage of the battery and charging the capacitor Circuit,
PWM control means for sending a series of pulse signals for controlling the ON / OFF operation of the transistors to the transistors and switching the duty ratio of the series of pulse signals as the secondary charging voltage rises;
An auxiliary light source;
A light emitting means for emitting light based on the electric charge accumulated in the capacitor;
A temperature detector that detects the temperature during shooting,
The camera according to claim 1, wherein the PWM control means outputs a series of pulse signals so as to increase a duty ratio with respect to a decrease in temperature according to a temperature at the time of photographing.

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