JP4136471B2 - Strobe device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement of a strobe device mounted on or attached to a camera.
[0002]
[Prior art]
Conventionally, for example, in Japanese Patent Application Laid-Open No. 6-504182, a so-called continuous mode operation is performed in which the on-time of the primary circuit is set to a predetermined length and the current level of the secondary circuit is controlled to a predetermined current level. A technique for charging is disclosed.
[0003]
However, in order to shorten the release time lag, the predetermined current level of the secondary side circuit is increased (in a state where the residual energy of the transformer is larger) and the battery current is increased (Vbat (continuous strong) in FIG. 13). When the battery is exhausted at the end of charging and the impedance of the battery increases, the battery voltage rapidly drops during strobe charging, and there is a possibility that the operation guarantee voltage (Vbat_th in the figure) of the microcomputer cannot be guaranteed.
[0004]
In order to solve this, Japanese Patent Publication No. 6-504182 discloses a technique for changing a predetermined current level of the secondary circuit according to the battery voltage. As shown in FIG. 13, the operation guarantee voltage of the microcomputer can be guaranteed even in a consumable battery by weakening the continuity at the end of charging (Vbat (continuous weak in the figure)).
[0005]
[Problems to be solved by the invention]
However, in the circuit configuration shown in FIG. 14 disclosed in the embodiment of the above-mentioned Japanese translation of PCT publication No. 6-504182, the comparator 102 is included in the secondary current detection circuit 101 that detects the current flowing in the secondary side circuit. Needed. Therefore, it is necessary to incorporate the comparator in the control IC or mount a comparator element.
[0006]
Further, a resistor 103 for detecting current provided in the secondary current detection circuit 101 is connected between GND and the transformer 104, and a detection voltage is detected at a position V in FIG. Therefore, V generated in the resistor 103 while the secondary current is flowing becomes a negative potential with respect to GND. Therefore, the comparison voltage Vref of the comparator 101 needs to be set to a minus potential, and a power supply configuration having a minus potential that constitutes the comparison voltage Vref is also required as a power source of the camera. Further, in order to change the predetermined current level of the current flowing through the secondary circuit, it is necessary to change the comparison voltage Vref, and a multiplexer is required to change the comparison voltage Vref, which increases the circuit scale. There was a problem.
[0007]
(Object of invention)
An object of the present invention is to provide a strobe device capable of performing an efficient charging operation according to a battery voltage and guaranteeing the operation of a circuit with a simple circuit configuration.
[0008]
[Means for Solving the Problems]
  To achieve the above objective,The present inventionIsCharged by secondary current of flyback converterA main capacitor and a first switch element for turning on and off the primary current of the flyback converter;The base is connected to the negative electrode of the main capacitor, the emitter is connected to the negative electrode of the battery as a power source, and the collector is connected to the auxiliary power source via a resistorTransistor,And a first resistor connected between the base and emitter of the transistor,Depending on the potential of the collectorSecondary current detection means for detecting whether or not the secondary current of the flyback converter has dropped below a predetermined current; and by detecting that the secondary current has dropped below a predetermined current, 1 switch element to drive the primary currentTurn onA strobe device having primary drive control means, wherein the predetermined current level of the secondary currentBut, Determined by the resistance value between the base and emitter of the transistor, and the first resistance of the secondary current detecting meansOn the other hand, a series circuit of the second resistor and the second switch element is connected in parallel.,When it is detected by the battery check means that the voltage of the battery as the power source is equal to or higher than a predetermined voltage, the second switch element is turned on, and when it is detected that the voltage is lower than the predetermined voltage, Turning off the second switch element;SaidBetween base and emitter of transistorThe strobe device changes the resistance value and switches the predetermined current level of the secondary current.
[0009]
  To achieve the same purpose,The present inventionIsCharged by secondary current of flyback converterA main capacitor and a first switch element for turning on and off the primary current of the flyback converter;The gate is connected to the negative electrode of the main capacitor, the source is connected to the negative electrode of the battery as a power source, and the drain is connected to the auxiliary power source via a resistor.Field effect transistor,And a first resistor connected between the gate and source of the field effect transistor,Depending on the potential of the drainSecondary current detection means for detecting whether or not the secondary current of the flyback converter has dropped below a predetermined current; and by detecting that the secondary current has dropped below a predetermined current, 1 switch element to drive the primary currentTurn onA strobe device having primary drive control means, wherein the predetermined current level of the secondary currentBut, Determined by the resistance value between the gate and the source of the field effect transistor, and the first resistance of the secondary current detection meansOn the other hand, a series circuit of the second resistor and the second switch element is connected in parallel.,When it is detected by the battery check means that the voltage of the battery as the power source is equal to or higher than a predetermined voltage, the second switch element is turned on, and when it is detected that the voltage is lower than the predetermined voltage, Turn off the second switch element,Between the gate and source of the field effect transistorThe strobe device changes the resistance value and switches the predetermined current level of the secondary current.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on illustrated embodiments.
[0012]
(First embodiment)
FIG. 1 is a block diagram showing a circuit configuration of a strobe device equipped with a flyback converter and a camera according to a first embodiment of the present invention.
[0013]
First, the configuration on the strobe device side will be described.
[0014]
In FIG. 1, 101 is a battery as a power source, 101 a is a battery internal resistance, 130 is a capacitor connected in parallel with the battery 101, and 150 is a battery check circuit that detects the battery state of the battery 101.
[0015]
Reference numeral 106 denotes a transformer, which accumulates energy in the core by passing current through a loop of the positive electrode of the battery 101, the primary winding, the FET 107, which will be described later, and the negative electrode of the battery 101, and generates back electromotive force with the energy. Reference numeral 107 denotes an FET that drives a current of the primary winding of the transformer 106. A resistor 131 pulls down the gate of the FET 107.
[0016]
  Reference numeral 109 denotes a main capacitor, which accumulates electric charges. Reference numeral 108 denotes a high voltage rectifier diode, whose anode is connected to the beginning of the secondary winding of the transformer 106 and whose cathode is connected to the anode of the main capacitor 109. 120 is a transistor, and 123 is a resistor connected between the base and emitter of the transistor 120. Reference numeral 124 denotes a resistor, one side of which is connected to the base of the transistor 120 and the other side is connected to the drain of the FET 125 described later. 125 is an FET, the drain is connected to the resistor 124, and the source is connected to the emitter of the transistor 120. By turning on the FET 125, the resistor 124 can be connected in parallel to the resistor 123. 122 is a resistor, one side of the transistor 120collectorAnd an input terminal of the control IC 105 to be described laterdAnd the other side is pulled up to the auxiliary power source Vcc. A resistor 126 pulls down the gate of the FET 125.
[0017]
The transistor 120, the resistor 122, and the resistor 123 constitute a secondary current detection circuit that detects whether or not the secondary current flowing through the secondary winding of the transformer 106 has become a predetermined current or less. Further, the resistor 124, the FET 125, and the resistor 126 constitute a circuit for switching the predetermined current of the secondary current according to the battery voltage.
[0018]
133 is a resistor. Reference numeral 136 denotes a thyristor. A resistor 137 and a capacitor 138 are connected in parallel between the gate and the cathode, and the gate is connected to the connection terminal f of the control IC 105 via the resistor 139. Reference numeral 135 denotes a trigger coil. Reference numeral 134 denotes a trigger capacitor, which is inserted on the primary side of the trigger coil 135.
[0019]
The resistor 133, trigger capacitor 134, trigger coil 135, thyristor 136, resistor 137, capacitor 138, and resistor 139 constitute a known trigger circuit.
[0020]
  Reference numeral 111 denotes a discharge tube, which receives a trigger voltage from the trigger circuit and emits light by charges accumulated in the main capacitor 109. 112 isCharge voltage detection circuitIt is connected to an A / D converter 105b in the control IC 105 described later and detects the voltage accumulated in the main capacitor 109.
[0021]
Next, the configuration on the camera side will be described.
[0022]
A control IC 105 controls a camera sequence such as photometry, distance measurement, lens drive, film feeding, and a strobe device. Reference numeral 105a denotes a microcomputer provided in the control IC 105, which has a RAM as storage means and controls the camera sequence. Reference numeral 105b denotes an A / D converter that digitizes the input voltage. A timer 105c measures the time for driving the primary current.
[0023]
Reference numeral 102 denotes a shutter driving device that drives the shutter, and reference numeral 103 denotes a constant voltage circuit that supplies control power as a power source to each circuit block. Reference numeral 113 denotes a photometric device that detects subject brightness. Reference numeral 114 denotes a distance measuring device that detects the distance to the subject. Reference numeral 115 denotes a lens driving device, which drives the photographing lens based on the detection result from the distance measuring device 114 and focuses the subject on the film surface. Reference numeral 116 denotes a film driving device that performs auto-loading, winding and rewinding of the film. Reference numeral 117 denotes a main switch for setting the camera in a shooting preparation state, and 118 (hereinafter referred to as SW1) is a switch that is turned on by the first stroke of the shutter button. When the switch SW1 is turned on, an electric circuit in the camera is activated. Detection such as photometry and distance measurement is started. Reference numeral 119 (hereinafter referred to as SW2) is a switch that is turned on by the stroke of the shutter button, and the photographing sequence is started when the switch SW2 is turned on.
[0024]
Next, the operation of the camera including the booster circuit in the strobe device according to the first embodiment of the present invention will be described with reference to the flowcharts of FIGS.
[0025]
First, the main sequence will be described with reference to the flowchart of FIG.
[0026]
First, in step S401, it is detected whether or not the main switch 117 is turned on. If it is detected that the main switch 117 is turned on, the process proceeds to step S402, where a battery check (BC) is performed by the battery check circuit 150 to determine whether the battery voltage of the camera is sufficient for camera operation. It memorize | stores in RAM in the microcomputer 105a. Then, in the next step S403, it is determined from the BC result obtained in the above step S402 whether or not the battery voltage is operable. If the battery voltage is operable (BCOK), the step is performed. The process proceeds to S404, and if the voltage is not operable, the process returns to step S401.
[0027]
If the operation proceeds to step S404 assuming that the battery voltage is operable, the photometry device 113 is operated to detect the subject luminance, and the obtained photometry result is stored in the RAM in the microcomputer 105a. In the next step S405, it is determined whether or not the photometric result obtained in step S404 is a value that requires strobe light emission for photographing. When the flash emission is unnecessary and the flash charging is not required, the main sequence is terminated. On the other hand, if it is determined in step S405 that the luminance is necessary for strobe light emission, the process proceeds to step S406, and strobe charging is performed in the flash mode.
[0028]
Here, the details of the flash mode in step S406 will be described with reference to the flowchart of FIG.
[0029]
When the flash mode is entered, first, in step S201, the charging voltage of the main capacitor 109 is detected based on the output of the A / D converter 105b in the control IC 105 by the voltage via the charging voltage detection circuit 112 of FIG. The detection result is stored in the RAM in the microcomputer 105a. Then, in the next step S202, it is determined whether or not charging is complete based on the detection result performed in step S201. As a result, if it is determined that the charging is completed, the process proceeds to step S211, a flag indicating completion of charging is set, the charging timer is stopped in the next step S212, and the charging sequence is terminated.
[0030]
If it is determined in step S202 that charging has not been completed, the process proceeds to step S203, a battery check (details will be described later) is performed, and if the battery voltage is equal to or higher than a predetermined voltage (BCH), the process proceeds to step S204. The FET 125 is turned on, and the process proceeds to step S206. On the other hand, if the voltage is less than the predetermined voltage, the FET 125 is turned off and the process proceeds to step S206.
[0031]
In step S206, a charge timer for measuring the charge time is started and strobe charge is started.
[0032]
Here, the circuit operation at the time of strobe charging will be described based on the timing chart of FIG.
[0033]
3A shows a case where the battery voltage is higher than a predetermined voltage and the FET 125 of FIG. 1 is on, that is, the resistor 124 is connected in parallel between the base and emitter of the transistor 120, and FIG. This shows a case where the battery voltage is lower than the predetermined voltage and the FET 125 is off, that is, the resistor 124 is not connected in parallel between the base and emitter of the transistor 120.
[0034]
First, each signal in the timing charts of FIGS. 3A and 3B will be described.
[0035]
  In the figure, “primary current” indicates the current flowing in the primary winding of the transformer 106, “secondary current” indicates the current flowing in the secondary winding of the transformer 106, “FETGATE” indicates the gate input signal of the FET 107, “transistor” “Base-emitter” indicates the base-emitter voltage of the transistor 120, respectively. The “secondary current IC input signal” indicates a secondary current detection signal in which the collector of the transistor 120 and the resistor 122 are connected to each other and the control IC 105 is connected. Correspondingly, the resistor 124 is connected between the base and emitter of the transistor 120 by the on / off signal of the gate signal of the FET 125 (in other words, the resistor 124 is connected in parallel to the resistor 123).DoIt is for switching whether or not.
[0036]
Next, the circuit operation shown in the timing chart of FIG.
[0037]
A predetermined oscillation signal (timing (1) of “FETGATE”) is given from the control IC 105 to the gate of the FET 107 via the connection terminal b. Then, when a high level signal is given to the control electrode of the FET 107, a current flows through the loop of the positive electrode of the battery 101, the primary winding of the transformer 106, the drain-source of the FET 107, and the negative electrode of the battery 101 (“primary current” (1) to (2) timing). For this reason, an induced electromotive force is generated in the secondary winding of the transformer 106. However, since the polarity of this current is blocked by the high-voltage rectifier diode 108, the excitation current does not flow from the transformer 106 and energy is generated. Accumulated in the core in the transformer 106. This energy storage (current drive) is performed for a predetermined time (until the timing of “FETGATE” (2)) measured by the charge timer from the start of driving.
[0038]
If the current is driven until a predetermined time here, the gate of the FET 107 is set to the low level to turn the FET 107 off (timing (2) of “FETGATE”), and the current is cut off to make it non-conductive. As a result, a counter electromotive force is generated in the secondary winding of the transformer 106. This counter electromotive force flows as a secondary current from the transformer 106 in a loop of the high voltage rectifier diode 108, the main capacitor 109, the transistor 120, the resistor 123, and the resistor 124 (the timing of (2) to (3) of the "secondary current". ), Electric charge is accumulated in the main capacitor 109.
[0039]
A potential difference is generated between the resistor 123 and the resistor 124 due to the generation of the secondary current. When this potential difference reaches Vbe of the transistor 120 (timing “2” of “transistor base-emitter voltage”), the transistor 120 is turned on and the secondary current IC input pulled up by the resistor 122 at Vcc is input. The signal becomes low level (timing (2) of “secondary current IC input signal”) simultaneously with the start of the discharge of the secondary current.
[0040]
Next, the energy stored in the transformer 106 is released, and the secondary current flowing through the transistor 120, the resistor 123, and the resistor 124 is lowered to a predetermined current (Vbe voltage) (“3 of transistor base-emitter voltage”). ) (Secondary current (3) timing), the secondary current IC input signal that was kept at the low level when turned on is inverted from the low level to the high level (“secondary current”). Current IC input signal (3) timing). In response to the inversion of the secondary current IC input signal from the low level to the high level, the control IC 105 generates a high level signal again at the gate of the FET 107 and makes the FET 107 conductive again (“ FETGATE "timing (1)), energy is stored in the transformer 106 for a predetermined time. Then, after a predetermined time has elapsed, the FET 107 is turned off by a low level signal. As a result, the stored energy is released from the transformer 106 and the main capacitor 109 is charged.
[0041]
Next, the circuit operation shown in the timing chart of FIG.
[0042]
A predetermined oscillation signal (timing (1) of “FETGATE”) is given from the control IC 105 to the gate of the FET 107 via the connection terminal. Then, when a high level signal is given to the control electrode of the FET 107, a current flows through the loop of the positive electrode of the battery 101, the primary winding of the transformer 106, the drain-source of the FET 107, and the negative electrode of the battery 101 (“primary current” (1) to (2) timing). For this reason, an induced electromotive force is generated in the secondary winding of the transformer 106. However, since the polarity of this current is blocked by the high-voltage rectifier diode 108, the excitation current does not flow from the transformer 106 and energy is generated. Accumulated in the core in the transformer 106. This energy storage (current drive) is performed for a predetermined time (until the timing of “FETGATE” (2)) from the start of driving.
[0043]
  When the current is driven until a predetermined time, the gate of the FET 107 is set to a low level to turn off the FET 107 (timing 2 of “FETGATE”), thereby cutting off the current and turning it off. As a result, a counter electromotive force is generated in the secondary winding of the transformer 106. This back electromotive force is converted into a secondary current from the transformer 106 by a high voltage rectifier diode 108, a main capacitor 109, a transistor 120, andLoop of resistor 123The electric charge is accumulated in the main capacitor 109.
[0044]
A potential difference is generated in the resistor 123 due to the generation of the secondary current. When this potential difference reaches Vbe of the transistor 120 (timing “2” of “transistor base-emitter voltage”), the transistor 120 is turned on and the secondary current IC input pulled up by the resistor 122 at Vcc is input. The signal becomes low level (timing (2) of “secondary current IC input signal”) simultaneously with the start of the discharge of the secondary current.
[0045]
Next, the energy stored in the transformer 106 is released, and the secondary current flowing through the transistor 120 and the resistor 123 is reduced to a predetermined current (Vbe voltage) (the timing of (3) of “transistor base-emitter voltage”. ) (Timing of “secondary current” (3)), the secondary current IC input signal that has been maintained at the low level when turned on is inverted from the low level to the high level (“secondary current IC input”). Signal (3) timing). In response to the inversion of the secondary current IC input signal from the low level to the high level, the control IC 105 generates a high level signal again at the gate of the FET 107 and makes the FET 107 conductive again as in the case of the primary current driving described above. The energy is stored in the transformer 106 for a predetermined time at the timing (1) of “FETGATE”. Then, after a predetermined time has elapsed, the FET 107 is turned off by a low level signal. As a result, the stored energy is released from the transformer 106 and the main capacitor 109 is charged.
[0046]
By the way, as for the predetermined current of the secondary current, the current generated by the current flowing through the resistor 123 reaches the base-emitter voltage Vbe of the transistor 120 and the resistor 122 pulled up to Vcc is connected. The sum of the base currents at which the collector is low. For example, when the resistor 122, which is a pull-up resistor, is 1 kΩ and the current flowing through the collector of the transistor 120 is assumed to be 5 cc,
(5-Vce) / 1000
However, Vce (collector-emitter voltage) at this time is a very low voltage. Therefore,
5/1000 = 5mA
It will be about. Therefore, the base current is about 0.17 mA when hfe of the transistor 120 is about 30. At this time, assuming that the current flowing through the primary winding is 3A (timing (2) of “primary current” in FIG. 3), the peak of the secondary current is in the ratio of turns between the primary winding and the secondary winding (Retio). For example, when the secondary winding is “20” with respect to the primary winding “1”, the current is about 150 mA. In the case of a predetermined current that detects about 50 mA, which is about 1/3 of the peak of the secondary current, the influence of the base current of the transistor 120 is extremely small in setting the predetermined current, and can be ignored. Often,
Predetermined current = Vbe / (base-emitter resistance)
It can be set with. For example, in FIG. 3A, when the predetermined current is set to 50 mA, which is about 1/3, and in FIG. 3B, when the predetermined current is set to 15 mA, which is about 1/10, if Vbe is 0.6 V, FIG. In FIG. 3A, the resistance between the base and the emitter is 12Ω, and in FIG. 3B, the resistance between the base and the emitter is 40Ω.
[0047]
Here, since the FET 125 is turned off in FIG. 3B, the resistance between the base and the emitter is only the resistance 123, and the resistance 123 becomes 40Ω. 3A, since the FET 125 is turned on, the resistance between the base and the emitter is determined by the parallel resistance of the resistor 123 and the resistor 124 (more precisely, the series resistance of the resistor 124 and the on-resistance of the FET 125) The resistance 124 becomes about 15Ω.
[0048]
As described above, the charging speed can be controlled by switching the predetermined current level of the secondary current only by turning on / off the FET 125. Therefore, when the battery voltage is higher than the predetermined voltage, the primary current (battery current) is increased (by increasing the predetermined current of the secondary current) as shown in FIG. If the battery voltage is low, the primary voltage is reduced (by reducing the predetermined secondary current) as shown in FIG. 3B, and the battery voltage is lowered. However, it is possible to guarantee the operation of the circuit. That is, if it demonstrates using FIG. 13, it can prevent that a battery voltage falls below Vbat_th irrespective of the battery voltage at that time.
[0049]
Here, the FET 125 is used as a changeover switch having a predetermined current level, but this changeover switch may be a transistor 128 as shown in FIG.
[0050]
Further, in the detection of the secondary current when energy remains in the transformer 106 as in the charging method of the present embodiment, the energy that generates noise in the transformer 106 is naturally increased. Therefore, as shown in FIG. 9, in the case where the anode of the high-voltage rectifier diode 108 is connected to the negative electrode of the battery 101 and the cathode is connected to one end of the transformer 106, the transformer 106 at the start of driving the primary current. The oscillating current due to the stray capacitance on the primary side of the secondary current is riding on the resistor 123 (not shown) of the secondary current detection circuit that detects the secondary current. For this reason, the circuit configuration as shown in FIG. 1 is desirable in which the oscillating current loop generated when the primary current is simultaneously driven is blocked by the high voltage rectifier diode 108.
[0051]
Each signal waveform in the configuration of FIGS. 9 and 1 is shown in the figure. In the case of the circuit configuration of FIG. 9, the signal waveform is as shown in FIG. 8, and the circuit configuration of FIG.
[0052]
In the signal waveform of FIG. 8, the signal between the base and emitter of the transistor is directly subjected to the vibration current noise caused by the stray capacitance on the primary side of the transformer generated at the start of the primary current drive, and the noise exceeds Vbe. ing. Therefore, the secondary current IC input signal, which is a collector signal, has reached a state where the detection signal causes false detection as shown in FIG.
[0053]
On the other hand, in the waveform of FIG. 7 according to the present embodiment, the signal between the base and the emitter of the transistor 120 is the noise of the oscillating current due to the stray capacitance on the primary side of the transformer 106 generated when the primary current drive is started. The high voltage rectifier diode 108 is blocked. Therefore, the noise does not exceed Vbe, and as the secondary current IC input signal as a collector signal, a signal having no malfunction as shown in FIG. 7 is obtained, and the circuit can be stably operated.
[0054]
Returning to the description of the flowchart of FIG. 5, when the operation proceeds to step S <b> 208, the charging voltage is detected based on the output of the A / D converter 105 b in the control IC 105 as in step S <b> 201, and the detection result is sent to the CPU 105. Stored in the internal RAM. In the next step S209, it is determined whether or not the charging voltage detected in step S208 has reached the voltage for completion of charging. If not, the process proceeds to step S213, and the charging started in step S206 is performed. It is determined whether the timer has counted a predetermined time (counted up). As a result, if the charging timer has been counted up, the process proceeds to step S214 to stop the above charging operation, and in the subsequent step S215, set the incomplete charging flag, and reset the charging timer in the next step S212. To complete the charging sequence.
[0055]
If the charging timer has not counted up, the process returns to step S207, the same operation as described above is repeated, and if it is determined in step S209 that the charging is completed, the process proceeds to step S210, the charging operation is stopped, and step S211 is performed. In step S212, the charging completion flag is set and the charging timer ends the charging sequence and the main sequence in FIG. 2 ends.
[0056]
Next, the release sequence will be described with reference to FIG.
[0057]
First, in step S101, the microcomputer 105a is initialized. Then, in the next step S102, the state of various switches is detected, and in the subsequent step S103, it is detected whether or not the switch SW1 is turned on from the detected switch state. As a result, if the switch SW1 is not turned on, the process returns to step S102. If the switch SW1 is turned on, the process proceeds to step S104, a battery check is performed in the same manner as step S402 in FIG. 2, and the result is stored in the RAM. . Then, in the next step S105, it is determined whether or not the camera is operable voltage from the battery stored in the RAM. If it is operable voltage, the process proceeds to step S106, and operation is impossible. If so, the process returns to step S102.
[0058]
When the process proceeds to step S106 assuming that the battery is sufficient, the distance measuring device 114 is operated to detect the distance to the subject, and the distance measurement result is stored in the RAM in the microcomputer 105a. In the subsequent step S107, the photometric device 113 is operated to detect the subject brightness, and the result (photometric result) is stored in the RAM in the microcomputer 105a in the same manner as the distance measurement result. Then, in the next step S108, based on the photometric result detected in step S107, whether or not strobe charging is necessary (based on whether the subject brightness is so dark that it requires strobe light emission) or not. Make a decision. In other words, if the subject brightness is so dark as to require strobe light emission and the strobe is not sufficiently charged, the process proceeds to step S109. If the flash does not need to be emitted, the process immediately proceeds to step S111. When the strobe needs to emit light, the shooting situation is dark or the backlight is in the backlit state.
[0059]
If it proceeds to step S109 because strobe light emission is necessary, the flash mode is entered and the charging sequence described in the flowchart of FIG. 5 is performed. When this charging sequence ends, the process proceeds to step S110, where it is determined whether or not the strobe charging is completed. This determination is to check the state of the flag indicating whether or not the charging is OK in the charging sequence in step S109. If the charging is OK, that is, if the charging is completed, the process proceeds to an on standby state of the switch SW2 in step S111. . If the charging is not completed with NG, the process returns to step 102, and the same operation is repeated thereafter.
[0060]
The process proceeds to the standby state of the switch SW2 in step S111. If it is detected that the switch SW2119 is turned on, the process proceeds to step S112, and the lens driving device 115 is driven according to the distance measurement result obtained in step S106 to drive the photographing lens. Take control. In the next step S113, the shutter drive control is performed using the shutter drive device 102 in accordance with the photometric result obtained in step S107. At this time, if strobe light emission is necessary, strobe light emission is performed according to the operation of the trigger circuit 110 that receives a trigger signal from the control IC 105.
[0061]
In step S114, lens reset is performed to return the lens at the focal position to the initial position of the lens. In the next step S115, the film driving device 116 controls the film feeding to the next photographing frame, and in the subsequent step S116, it is determined whether or not the strobe precharge is performed. Here, the case where the strobe precharge is not performed is a case where the result determined in step S108 based on the result of the photometry performed in step S107 is not the strobe shooting mode. In this case, step S102 is performed. Return to.
[0062]
Further, the strobe precharge is performed in the strobe flash shooting mode. In this case, the process proceeds to step S117, and the flash mode similar to step S406 in FIG. 2 is executed. After the camera sequence is completed, the switch SW1 is turned on in step S102.
[0063]
According to the first embodiment described above, the main capacitor 109, the first switch element (FET 107) for turning on and off the primary current of the flyback converter (transformer 106), the transistor 120, and the transistor 120 A secondary current detecting means comprising a first resistor (resistor 123) connected between the base and the emitter, and detecting whether or not the secondary current of the flyback converter has dropped below a predetermined current; And a primary drive control means (control IC 105) for driving the first switch element to turn on the primary current and start strobe charging when it is detected that the secondary current has dropped below a predetermined current. The predetermined current level of the secondary current is determined by a resistance value between a base and an emitter of the transistor 120, and A second switch element (FET 125 or transistor 128) capable of connecting a second resistor 124 in parallel with the first resistor of the current detection means, and performing on / off control of the second switch element; The resistance value is changed to switch the predetermined current level of the secondary current.
[0064]
When the battery voltage is equal to or higher than a predetermined voltage, the second switch element is turned on, and the second resistor is connected in parallel to the first resistor, thereby reducing the resistance value to the predetermined current. On the other hand, when the battery voltage is less than a predetermined voltage, the second switch element is turned off and the resistance value is increased without connecting the second resistance in parallel with the first resistance. Thus, the predetermined current is reduced.
[0065]
Therefore, when the battery voltage is higher than the predetermined voltage, the resistance value between the base and the emitter of the transistor 120 is small and the predetermined secondary current is large, so that charging can be performed at high speed. Is lower than the predetermined voltage, the resistance value between the base and emitter of the transistor 120 is large and the predetermined current of the secondary current is small, so the charging speed is slow, but the battery voltage falls below the operation guarantee voltage of the control IC 105. Circuit operation can be guaranteed. In other words, an efficient charging operation according to the battery voltage and a guarantee of the circuit operation can be performed by a simple circuit configuration whether or not the resistors are connected in parallel.
[0066]
Specifically, conventionally, a comparator for detecting a secondary current must be built in the control IC, a comparator element must be mounted, and the comparison voltage Vref of the comparator is set to a negative potential. As a power supply, a power supply having a negative potential constituting the comparison voltage Vref must be configured, and further, a multiplexer for changing the comparison voltage Vref as the secondary current changes to a predetermined current level must be provided. However, in the first embodiment, since the predetermined secondary current can be changed only by changing the resistance value between the base and emitter of the transistor 120, the circuit configuration is greatly simplified. Is done.
[0067]
(Second Embodiment)
FIG. 10 is a block diagram showing a circuit configuration of a strobe device equipped with a flyback converter according to a second embodiment of the present invention. The same parts as those in FIG. .
[0068]
In FIG. 10, a portion different from the configuration in FIG. 1 is provided with an FET 127 instead of the transistor 120 in FIG. 1. Therefore, the resistor 123 is connected between the gate and source of the FET 127. The anode of the constant voltage diode 140 is connected to the source of the FET 127 and the cathode is connected to the gate.
[0069]
2, 4, and 5 are the same as those in the first embodiment, and thus description thereof is omitted.
[0070]
Next, the operation of the flyback converter will be described based on the timing chart of FIG.
[0071]
FIG. 11A shows a case where the battery voltage is higher than a predetermined voltage and the FET 125 is turned on, that is, the resistor 124 is connected in parallel between the gate and source of the FET 127, and FIG. This shows a case where the voltage is lower than the voltage and the FET 125 is off, that is, the resistor 124 is not connected in parallel between the gate and the source of the FET 127.
[0072]
First, each signal shown in the timing charts of FIGS. 11A and 11B will be described.
[0073]
In the figure, “primary current” indicates the current flowing through the primary winding of the transformer 106, “secondary current” indicates the current flowing through the secondary winding of the transformer 106, and “FETGATE” indicates the gate input signal of the FET 105. . “FET gate voltage” indicates the gate-source voltage of the FET 127. The “secondary current IC input signal” indicates a secondary current detection signal in which the drain of the FET 127 and the resistor 122 are connected and connected to the control IC 105. The “resistance switch” corresponds to the FET 125, and switches whether the resistor 124 is connected between the gate and the source of the FET 127 according to an ON / OFF signal of the FET 125.
[0074]
Next, the circuit operation shown in the timing chart of FIG.
[0075]
A predetermined oscillation signal (timing (1) of FETGATE) is given from the control IC 105 (not shown in FIG. 10) in the camera control circuit 200 to the gate of the FET 107 via the connection terminal b. As a result, a high level signal is applied to the gate of the control electrode of the FET 107, whereby a current flows in the positive loop of the battery 101, the primary winding of the transformer 106, the drain-source of the FET 107, and the negative loop of the battery 101 (primary current). (1) to (2) timing). For this reason, an induced electromotive force is generated in the secondary winding of the transformer 106. Since the polarity of this current is blocked by the high-voltage rectifier diode 108, no excitation current flows from the transformer 106, and the energy is Accumulated in the core in the transformer 106. This energy storage (current drive) is performed for a predetermined time (until the timing of FETGATE (2)) from the start of driving.
[0076]
When the current is driven until a predetermined time here, the gate of the FET 107 is set to low level to turn the FET 107 off (timing (2) of FETGATE), and the current is cut off to make it non-conductive. As a result, a counter electromotive force is generated in the secondary winding of the transformer 106. This back electromotive force flows as a secondary current (secondary current (2) to (3) timing) from the transformer 106 in a loop of the high voltage rectifier diode 108, the main capacitor 109, the resistor 123, and the resistor 124. The charge is accumulated in the.
[0077]
The secondary current IC input signal causes a potential difference between the resistor 123 and the resistor 124 due to the generation of the secondary current. When this potential difference causes the gate of the FET 127 to reach the predetermined voltage Vgs (the timing of (2) of the FET gate voltage), the FET 127 is turned on, and the secondary current IC input signal that has been pulled up by the resistor 122 at Vcc is At the same time as the discharge of the secondary current starts, the level becomes low (timing (2) of the secondary current IC input signal). At this time, the gate-source voltage of the FET 127 is configured not to rise above the predetermined voltage Vzd by the constant voltage diode 140 connected between the gate and source of the FET 127.
[0078]
Next, the energy stored in the transformer 106 is released, and becomes lower than the zener voltage Vzd of the constant voltage diode 140 due to the decrease in the secondary current flowing through the resistor 123, the resistor 124, and the constant voltage diode 140 (the FET gate voltage). (Timing (3)), the gate-source voltage of the FET 127 gradually decreases. Then, the secondary current is reduced to a predetermined current (Vgs voltage) (the timing of (4) timing of the FET gate voltage) (the timing of (4) timing of the secondary current), and is turned on to maintain the low level. The secondary current IC input signal is inverted from the low level to the high level (timing (4) of the secondary current IC input signal).
[0079]
  In response to the inversion of the secondary current IC input signal from the low level to the high level, the control IC 105 generates a high level signal again at the gate of the FET 107, and the FET 107 is turned on again (FETGATE as in the case of the primary current driving described above). The energy is stored in the transformer 106 for a predetermined time. Then, after a predetermined time has elapsed, a low level signal causes the FET 107 toTheThe stored energy is released from the transformer 106 as non-conduction, and the main capacitor 109 is charged.
[0080]
Next, the circuit operation shown in the timing chart of FIG.
[0081]
A predetermined oscillation signal (timing (1) of FETGATE) is given to the gate of the FET 107 from the control IC 105 (not shown in FIG. 10) in the camera control circuit 200 via the connection terminal. Therefore, when a high-level signal is applied to the control electrode of the FET 107, a current flows through the loop of the positive electrode of the battery 101, the primary winding of the transformer 106, the drain-source of the FET 107, and the negative electrode of the battery 101 (▲ 1 of the primary current). Timing of ▼ to ▲ 2). For this reason, an induced electromotive force is generated in the secondary winding of the transformer 106. However, since the polarity of this current is blocked by the high-voltage rectifier diode 108, no excitation current flows from the transformer 106, and the energy Is accumulated in the core in the transformer 106. This energy storage (current drive) is performed for a predetermined time (time of FETGATE {circle around (2)}) counted by a timer from the start of driving.
[0082]
When the current is driven until a predetermined time here, the gate of the FET 107 is set to the low level, the FET 107 is turned off (timing (2) of FETGATE), and the current is cut off to make it non-conductive. As a result, a counter electromotive force is generated in the secondary winding of the transformer 106. This back electromotive force flows as a secondary current (secondary current (2) to (4) timing) from the transformer 106 through a loop of the high voltage rectifier diode 108, the main capacitor 109 and the resistor 123, and the main capacitor 109 is charged. Accumulated.
[0083]
A potential difference is generated in the resistor 123 due to the generation of the secondary current. When this potential difference causes the gate of the FET 127 to reach the predetermined voltage Vgs (timing (2) of the source voltage of the FET 127), the FET 123 is turned on and the secondary current IC input signal pulled up by the resistor 122 at Vcc. Becomes low level (timing (2) of the secondary current IC input signal) almost simultaneously with the start of secondary current discharge. At this time, the gate-source voltage of the FET 127 is configured not to rise above the predetermined voltage Vzd by the constant voltage diode 140 connected between the gate and source of the FET 127.
[0084]
Next, the energy stored in the transformer 106 is released, and becomes lower than the zener voltage Vzd of the constant voltage diode 140 due to the decrease in the secondary current flowing through the resistor 123 and the constant voltage diode 140 ((3) of the FET source voltage). ), The gate-source voltage of the FET 127 gradually decreases. Then, the secondary current is reduced to a predetermined current (Vgs voltage) (the timing of the FET gate voltage (4)) (the timing of the secondary current (3)), so that the low level is maintained at the time of ON. The secondary current IC input signal is inverted from low level to high level (second timing of secondary current IC input signal (4)). In response to the inversion of the secondary current IC input signal from the low level to the high level, the control IC 105 generates a high level signal again at the gate of the FET 107, and again turns on the FET 107 (FETGATE) in the same manner as the primary current drive described above. The energy is stored in the transformer 106 for a predetermined time. Then, after a predetermined time has elapsed, the FET 107 is made non-conductive by a low level signal, the stored energy is released from the transformer 106, and the main capacitor 109 is charged.
[0085]
By the way, the predetermined current of the secondary current in the second embodiment of the present invention is a current at which the voltage generated by the current flowing through the resistor 123 reaches the gate-source voltage Vgs of the FET 127.
[0086]
For example, when Vgs is 1.5 V, assuming that the current is 3A at the peak flowing through the primary winding at this time (the timing of (2) of the primary current in FIGS. 11A and 11B), the transformer The peak of the secondary current flowing through 106 (the timing of (2) of the secondary current in FIGS. 11A and 11B) depends on the turn ratio of the primary winding to the secondary winding, for example, 2 When the winding of the next winding is “20” with respect to the primary winding “1”, it is about 150 mA.
[0087]
When 50 mA, which is about 1/3 of the peak of the secondary current, is set as the predetermined current, the predetermined current can be set by “predetermined current = Vgs / resistance 123”. For example, in FIG. 11A, when the predetermined current is set to 50 mA, which is about 1/3, and in FIG. 11B, when the predetermined current is set to 15 mA, which is about 1/10, Vgs is set to 1.5V. In FIG. 11A, the gate-source resistance of the FET 127 is 30Ω, and in FIG. 11B, the gate-source resistance is 100Ω.
[0088]
In FIG. 11B, since the FET 125 is turned off, the resistance between the gate and the source is only the resistance 123, and the resistance 123 is set to 100Ω. In FIG. 11A, since the FET 125 is on, the resistance between the gate and the source is determined by the parallel resistance of the resistor 123 and the resistor 124 (more precisely, the series resistance of the resistor 124 and the on-resistance of the FET 125). The resistor 124 is set to about 50Ω.
[0089]
As described above, the charging speed can be controlled by switching the predetermined current level of the secondary current only by turning on / off the FET 125. Therefore, when the battery voltage is high, as shown in FIG. 11A, the battery current can be increased to quickly charge the battery. On the other hand, when the battery voltage is low, switching to a state in which the battery current is reduced as shown in FIG. 11B makes it possible to guarantee the operation of the circuit even when the battery is exhausted.
[0090]
Similar to the first embodiment, the resistance changeover switch may be a transistor instead of the FET 125.
[0091]
  Also, this second embodimentInWhile the secondary current is flowing, the gate voltage of the FET 127 rises to Vzd. At this time, the gate potential of the thyristor 136 also rises to Vzd. When Vzd is a voltage higher than the power supply voltage of the camera, a reverse current flows through the camera control circuit 200 via the resistor 139. Therefore, when Vzd is a voltage higher than the power supply voltage of the camera, a diode 141 is inserted between the connection terminal f of the camera control circuit 200 and the resistor 139 as shown in FIG. It is desirable to prevent current.
[0092]
Similarly to the first embodiment described above, the connection configuration of the secondary current discharge loop is composed of the high-voltage rectifier diode 108, the main capacitor 109, and the resistor 123 from the transformer 106 as described above. Yes. By configuring the secondary current discharge loop in this way, the signal between the gate and source of the FET 127 is not directly subjected to the noise of the transformer 106, but is blocked by the high voltage rectifier diode 108, and the noise exceeds Vgs. There will be no state. Therefore, the secondary current IC input signal, which is a drain signal, can be obtained without causing a malfunction, and the circuit can be stably operated.
[0093]
According to the second embodiment, the main capacitor 109, the first switch element (FET 107) for turning on and off the primary current of the flyback converter (transformer 106), the FET 127, and the gate of the FET 127- A secondary current detecting means comprising a first resistor (resistor 123) connected between the sources and detecting whether or not the secondary current of the flyback converter has dropped below a predetermined current; and the secondary current And a primary drive control means (control IC 105) for driving the first switch element to turn on the primary current and start strobe charging when it is detected that the current drops below a predetermined current, The predetermined current level of the secondary current is determined by a resistance value between a gate and a source of the FET 127, and the secondary current detecting unit A second switch element (FET 127) capable of connecting the second resistor 124 in parallel with the first resistor, and performing on / off control of the second switch element to change the resistance value and to change the secondary current The predetermined current level is switched.
[0094]
When the battery voltage is equal to or higher than a predetermined voltage, the second switch element is turned on, and the second resistor is connected in parallel to the first resistor, thereby reducing the resistance value to the predetermined current. When the battery voltage is less than a predetermined voltage, the second switch element is turned off and the resistance value is increased without connecting the second resistor in parallel to the first resistor. The predetermined current is reduced.
[0095]
  Therefore, the same effect as the first embodiment can be obtained.
  (Correspondence between the present invention and the embodiment)
  1 corresponds to the first switch element of the present invention, the resistor 123 corresponds to the first resistor of the present invention, and the resistor 124 corresponds to the second resistor of the present invention. In addition, FIG., FET125 in FIG.OrTransistor 128 of FIG.Is the second switching element of the present invention, and the FET 127 of FIG.3Respectively).The battery check circuit 150 corresponds to the battery check means of the present invention.
[0096]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a strobe device that can perform an efficient charging operation according to the battery voltage and guarantee the operation of the circuit with a simple circuit configuration.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a circuit configuration of a camera and a strobe device according to a first embodiment of the present invention.
FIG. 2 is a flowchart showing an operation of the camera according to the first embodiment of the present invention.
FIG. 3 is a timing chart during a charging operation according to the first embodiment of the present invention.
FIG. 4 is a flowchart showing a series of photographing operations of the camera according to the first embodiment of the present invention.
FIG. 5 is a flowchart showing a charging operation according to the first embodiment of the present invention.
6 is a block diagram showing an example in which a part of the circuit configuration of the strobe device of FIG. 1 is changed.
7 is a timing chart during a charging operation when the circuit configuration of FIG. 6 is used.
8 is a timing chart during a charging operation when the circuit configuration of FIG. 9 is used.
9 is a block diagram illustrating an inappropriate example in which a part of the circuit configuration of the strobe device of FIG. 1 is changed.
FIG. 10 is a block diagram showing a circuit configuration of a strobe device according to a second embodiment of the present invention.
FIG. 11 is a timing chart during the charging operation according to the second embodiment of the present invention.
12 is a block diagram showing an example in which a part of the circuit configuration of the strobe device of FIG. 10 is changed.
FIG. 13 is a timing chart for explaining a charging operation changed according to a conventional battery voltage.
FIG. 14 is a block diagram showing a circuit configuration of a main part of a conventional strobe device.
[Explanation of symbols]
101 battery
105 Control IC
106 transformer
108 diode
109 Main capacitor
112 Charge voltage detection circuit
120 transistors
123 resistance
124 resistance
125 FET
127 FET
128 transistors
140 constant voltage diode
150 Battery check circuit

Claims (4)

A main capacitor charged by the secondary current of the flyback converter ;
A first switch element for turning on and off the primary current of the flyback converter;
A transistor having a base connected to the negative electrode of the main capacitor, an emitter connected to the negative electrode of a battery as a power source, and a collector connected to an auxiliary power source via a resistor , and a transistor connected between the base and emitter of the transistor A secondary current detecting means for detecting whether or not the secondary current of the flyback converter has dropped below a predetermined current by the potential of the collector ;
A strobe device having primary drive control means for driving the first switch element to turn on the primary current by detecting that the secondary current has dropped below a predetermined current,
The predetermined current level of the secondary current is determined by a resistance value between a base and an emitter of the transistor,
For the first resistance of the secondary current detecting means, a series circuit of a second resistor and a second switch element is connected in parallel,
When it is detected by the battery check means that the voltage of the battery as the power source is equal to or higher than a predetermined voltage, the second switch element is turned on, and when it is detected that the voltage is lower than the predetermined voltage, A strobe device that turns off the second switch element, changes a resistance value between a base and an emitter of the transistor, and switches the predetermined current level of the secondary current. When the battery voltage is equal to or higher than a predetermined voltage, the second switch element is turned on and the second resistor is connected in parallel to the first resistor, thereby reducing the resistance value between the base and the emitter of the transistor. And increasing the predetermined current,
When the battery voltage is less than a predetermined voltage, the second switch element is turned off, and the resistance value between the base and emitter of the transistor is increased without connecting the second resistor in parallel to the first resistor. The strobe device according to claim 1, wherein the predetermined current is reduced. A main capacitor charged by the secondary current of the flyback converter ;
A first switch element for turning on and off the primary current of the flyback converter;
A field effect transistor having a gate connected to the negative electrode of the main capacitor, a source connected to a negative electrode of a battery as a power source, and a drain connected to an auxiliary power source via a resistor, and between the gate and source of the field effect transistor A secondary current detecting means, comprising: a first resistor connected; and detecting whether or not the secondary current of the flyback converter has dropped below a predetermined current by the potential of the drain;
A strobe device having primary drive control means for driving the first switch element to turn on the primary current by detecting that the secondary current has dropped below a predetermined current,
The predetermined current level of the secondary current is determined by a resistance value between a gate and a source of the field effect transistor,
A series circuit of a second resistor and a second switch element is connected in parallel to the first resistor of the secondary current detecting means ,
When it is detected by the battery check means that the voltage of the battery as the power source is equal to or higher than a predetermined voltage, the second switch element is turned on, and when it is detected that the voltage is lower than the predetermined voltage, A strobe device, wherein the second switch element is turned off to change a resistance value between a gate and a source of the field effect transistor to switch the predetermined current level of the secondary current . When the battery voltage is equal to or higher than a predetermined voltage, the second switch element is turned on and the second resistor is connected in parallel to the first resistor, whereby the resistance value between the gate and the source of the field effect transistor is set. Increase the predetermined current to a smaller value,
When the battery voltage is less than a predetermined voltage, the resistance value between the gate and source of the field effect transistor is set without turning off the second switch element and connecting the second resistor in parallel with the first resistor. The strobe device according to claim 3, wherein the strobe device is increased and the predetermined current is decreased .

Images