JP4246903B2 - Flash light emitting circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flash light emitting circuit that emits flash light.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there has been known a camera that takes a picture by emitting flash light in synchronization with a shutter operation when subject brightness is insufficient. Such a camera is provided with a flash light emission circuit for emitting flash light. The flashlight circuit is applied to a booster circuit, a main capacitor that stores power boosted by the booster circuit, a light-emitting tube that emits flashlight by the power emitted from the main capacitor, and a trigger electrode of the light-emitting tube It has a trigger coil for generating a trigger voltage and a switch element for controlling the current flowing through the arc tube. As the switch element, an IGBT (Insulated Gate Bipolar Transistor) element is generally used. Here, since a relatively large peak current (for example, about 250 A in an arc tube for a compact camera) flows through the arc tube, an expensive IGBT element having a relatively large size is necessary to control the large peak current. Therefore, there is a problem that the cost increases.
[0003]
In view of this, a technique has been proposed in which a resistance element is inserted into a discharge loop that discharges power from the main capacitor to perform current detection, thereby reducing the peak current. According to this technique, since an inexpensive IGBT element can be employed, the cost can be reduced.
[0004]
[Problems to be solved by the invention]
However, the technique described above has a problem that power loss is large because a current is detected by inserting a resistance element in the discharge loop.
[0005]
SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a flash light emitting circuit in which power loss is kept small and cost is reduced.
[0006]
[Means for Solving the Problems]
The flash light emitting circuit of the present invention that achieves the above object charges a capacitor, and discharges the electric power charged in the capacitor through a discharge loop in which the arc tube is arranged midway, from the arc tube. In a flash light emitting circuit that emits a flash,
A switching element that is arranged in the discharge loop and opens and closes the discharge loop according to control;
A voltage detector for detecting the voltage of the capacitor;
A control unit for controlling the opening and closing of the discharge loop by the switch element,
The switch element has an allowable value lower than the peak value of the discharge current flowing in the discharge loop when the capacitor is discharged while the discharge loop is formed after the capacitor has been charged. Having a current,
The control unit refers to a detection result of the voltage by the voltage detection unit, and drives the switch element to pulse so that a discharge current flowing through the switch element is always equal to or less than an allowable current of the switch element. It is characterized by that.
[0007]
Since the flash light emitting circuit of the present invention refers to the detection result of the voltage of the capacitor, the switch element is pulse-driven so that the discharge current flowing through the switch element is always less than or equal to the allowable current of the switch element. An inexpensive switch element having a relatively small allowable current can be employed for emitting a flash from the arc tube. Therefore, compared with the conventional technique in which a resistance element is inserted in the discharge loop to reduce the peak current, the power loss in the discharge loop can be suppressed to be small and the cost can be reduced.
[0008]
Here, the control unit is programmed with a preceding sequence executed in advance and a final sequence executed after the preceding sequence, in which the pulse train sequences for driving the switching element are different from each other. And
The voltage detection unit detects the voltage of the capacitor at least once after the execution of the preceding sequence by the control unit,
The control unit, after starting the execution of the preceding sequence, is determined by the voltage of the capacitor detected by the voltage detection unit or by estimation based on the voltage, the timing when the voltage falls below a predetermined voltage It is preferable that the process proceeds to the final sequence.
[0009]
If the on-time of the pulse is made relatively short, it is possible not to exceed the allowable current of the switch element, but this may cause the total light emission time to exceed the camera exposure time. The charge charged in the capacitor is wasted. Therefore, the capacitor voltage is detected at least once after the start of the execution of the preceding sequence, the timing is shifted to the final sequence when the voltage falls below a predetermined voltage, and DC light emission (normal single light emission) is performed in the final sequence. By doing so, the charge charged in the capacitor can be used up for flash emission without exceeding the allowable current of the switch element. Therefore, in photographing, a flash can be emitted toward the subject with a sufficient exposure amount and a sufficient reach from the arc tube.
[0010]
In addition, the control unit is preferably programmed with an initial sequence executed earlier and an intermediate sequence executed after the initial sequence, in which the sequence of pulse trains is different from each other as the preceding sequence. .
[0011]
The arc tube is excited by receiving a trigger voltage of about 4 KV, for example, and shifts to arc discharge. However, due to variations in individual arc tubes and circuit elements, there is a variation in the time to shift to arc discharge (for example, 5 μS). Arise. Also, the transition time varies even under environmental conditions such as a bright room / dark room. Therefore, by dividing the preceding sequence into an initial sequence and an intermediate sequence, stabilizing the pulse emission in the initial sequence, and making the pulse emission for controlling the light quantity in the intermediate sequence, the unstable due to the above variations Light emission can be eliminated.
[0012]
Furthermore, it is also a preferable aspect that the voltage detection unit detects the voltage of the capacitor when the switch element is in a state where the discharge loop is opened.
[0013]
When the switch element is turned on and the discharge loop is closed, a discharge current flows around, for example, 100 A in the discharge loop. When such a large discharge current flows, the voltage at the voltage detection measurement point drops during the voltage measurement, and it is difficult to accurately measure the voltage of the capacitor. Therefore, when the voltage of the capacitor is detected when the switch element is in a state where the discharge loop is opened, that is, when the switch element is in the OFF state, the above voltage does not decrease, and therefore the voltage of the capacitor is accurately measured. Can do.
[0014]
The initial sequence is preferably composed of one pulse or a plurality of pulses.
[0015]
When there is a margin in the allowable current of the switch element, it is possible to shift to stable light emission with one pulse having a long ON time in the initial sequence. However, when there is no allowance for the allowable current of the switch element, it is necessary to repeat the fine on / off times. Therefore, the initial sequence is composed of a plurality of pulses, and by using a microcomputer with a relatively fast clock speed to detect and determine the voltage of the capacitor, the arc tube is surely stabilized at an early point in the initial sequence. can do. As a result, the power for the stable light emission of the capacitor can be small, and the continuous light emission for the light amount control performed thereafter can be stably performed.
[0016]
Furthermore, it is preferable that the intermediate sequence is composed of a plurality of blocks including pulses having the same width and the same period in each block.
[0017]
If light is emitted with the same on / off pulse in the intermediate sequence, the voltage of the capacitor gradually decreases for each light emission amount of one pulse, and the current decreases as the voltage decreases. It is desirable to gradually increase the on-time or gradually shorten the off-time, but this has the disadvantage of increasing the burden of control, for example, the burden of software when controlling using a microcomputer. Therefore, when the intermediate sequence is composed of a plurality of blocks consisting of pulses having the same width and the same period in each block, and processing such as increasing the ON time for each block, the above-mentioned control is performed finely. The same effect as can be obtained while suppressing the control burden. For example, the intermediate sequence is divided into 3 blocks, the first block is repeated 10 times with 4 μS / 10 μS on / off pulse, the next block is repeated 10 times with 5 μS / 9 μS on / off pulse, and the last block is 7 μS / 7 μS. The arc tube may emit light by repeating the ON / OFF pulse 10 times.
[0018]
The final sequence is preferably composed of one pulse or a plurality of pulses.
[0019]
Basically, one-pulse light emission (single DC light emission) is adopted in the final sequence, but the arc tube in the excited state is more current than the first light emission that is not in the excited state even if the voltage of the capacitor is low. Is easy to flow. For this reason, the final sequence is composed of a plurality of pulses. For example, it is safer to suppress the current flowing in the switching element more effectively by emitting one pulse first and then emitting one pulse next.
[0020]
Furthermore, the voltage detection unit detects the voltage of the capacitor after execution of one block constituting the intermediate sequence by the control unit,
It is also preferable that the control unit selects the next block based on the voltage detected at the timing after execution of one block constituting the intermediate sequence, and executes the selected block next. .
[0021]
The degree of decrease in the voltage of the capacitor due to pulse light emission varies depending on environmental conditions and the like. Therefore, when the block selected based on the voltage of the capacitor detected at the timing after execution of one block constituting the intermediate sequence is executed, the block corresponding to the voltage of the capacitor that changes depending on the environmental conditions is selected. can do. Therefore, light can be emitted with a high discharge current, and the total light emission time can be shortened.
[0022]
The voltage detector detects the voltage of the capacitor after the initial sequence is executed by the controller.
The control unit selects one of the blocks constituting the intermediate sequence or the final sequence based on the voltage detected at the timing after execution of the initial sequence, and then selects the selected block or final sequence. It is preferable to execute the above.
[0023]
When the environmental temperature is high, the equivalent resistance of the capacitor decreases and the discharge current tends to increase. In that case, the voltage of the capacitor after execution of the initial sequence reaches the voltage determined to shift to the final block. Therefore, if the intermediate sequence is skipped and the sequence is shifted to the final sequence, the total light emission time can be shortened. On the other hand, since the discharge current is small at a low temperature or the like, the capacitor charge after the execution of the initial sequence is not sufficiently discharged. Therefore, when the transition is made to any block constituting an intermediate sequence in which the discharge current becomes larger, the voltage of the capacitor can be lowered quickly, and therefore the total light emission time can be shortened.
[0024]
Further, the control unit is programmed with a plurality of different intermediate sequences as the intermediate sequence,
The voltage detection unit detects the voltage of the capacitor after execution of the initial sequence by the control unit,
The control unit selects one of the plurality of intermediate sequences based on the voltage detected at a timing after execution of the initial sequence, and then executes the selected intermediate sequence It is also preferable.
[0025]
In a plurality of intermediate sequences that are different from each other as the intermediate sequence, the on / off pulses constituting the pulse train often have a certain correlation. For example, it is assumed that the intermediate sequence is composed of three blocks whose frequency is the same as 33 KHz and whose duty is changed to 10%, 20%, and 30% (this is an intermediate block A group). Further, assuming that the initial sequence is a fixed pulse, the voltage drop amount (ΔV) of the capacitor is, for example, 5 V (Δ5 V) or 10 V (Δ10 V) due to environmental conditions or the like. In terms of the amount of light, the case of Δ5V is smaller than the case of Δ10V, and naturally the discharge current is also small. Therefore, when the intermediate block group A is selected under the condition of Δ10V, the discharge current is too large under the condition of Δ5V. Therefore, an intermediate block group B having a duty of 10, 20, 30% and a frequency of 60 KHz is selected. By doing in this way, discharge current can be made constant by simple control.
[0026]
Further, the control unit is a plurality of intermediate sequences different from each other as the intermediate sequence, and is executed first, a common initial block common to the plurality of intermediate sequences, and each intermediate sequence following the common initial block A plurality of intermediate sequences composed of one or more blocks for each intermediate sequence are programmed for each sequence,
The voltage detection unit detects the voltage of the capacitor both after execution of the initial sequence and after execution of the common initial block of the intermediate sequence,
The control unit executes the initial sequence and further executes the common initial block, and then selects one of the plurality of intermediate sequences based on both the voltages from the voltage detection unit. Preferably, the intermediate sequence block of the selected intermediate sequence is executed next.
[0027]
After executing the initial sequence, the transition to the intermediate sequence is performed, but it is often unpredictable how much current is flowing in the first pulse train, so the voltage of the capacitor after executing the first pulse train (first block of the intermediate sequence) By detecting this, the level of the discharge current can be estimated from the charge of the capacitor used in the first block. If the voltage drop is unexpectedly small, the total light emission time can be shortened by shifting to a completely different type of intermediate block.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described. Here, a flash light emitting circuit mounted on the camera will be described.
[0029]
FIG. 1 is a diagram showing a flash light emitting circuit according to an embodiment of the present invention.
[0030]
The flash light emitting circuit 10 shown in FIG. 1 includes a booster circuit 11 connected to a built-in battery 1 for controlling the entire camera. The booster circuit 11 boosts the voltage from the internal battery 1 to a predetermined voltage.
[0031]
Further, the flash light emitting circuit 10 is provided with a main capacitor 13_1 that accumulates the electric power boosted by the booster circuit 11 via the diode 12_1. A resistance element 14_1 and a trigger capacitor 13_2 are connected in series to both ends of the main capacitor 13_1. In addition, a resistance element 14_2 and a resistance element 14_3 are connected in series to both ends of the main capacitor 13_1.
[0032]
Further, the flash light emitting circuit 10 includes an arc tube 15, a trigger coil 16, an IGBT element 17 (an example of a switch element according to the present invention), a diode 12_2, and resistance elements 14_4 and 14_5.
[0033]
The arc tube 15 includes an anode 15a, a cathode 15b, and a side electrode 15c, and xenon (XE) gas is sealed inside. The arc tube 15 emits light by the electric power emitted from the main capacitor 13_1. The trigger coil 16 includes a primary winding 16a having a predetermined number of turns and a secondary winding 16b having a number of turns larger than the number of turns. One end of the primary winding 16a is connected to the cathode 15b of the arc tube 15 and the connection point of the resistance element 14_1 and the trigger capacitor 13_2. On the other hand, one end of the secondary winding 16 b is connected to the side electrode 15 c of the arc tube 15. The other ends of the primary winding 16a and the secondary winding 16b are connected to the collector of the IGBT element 17 and the anode of the bypass diode 12_2. The base of the IGBT element 17 is connected to the ground GND (the negative terminal of the built-in battery 1) via the resistance element 14_4, and is connected to the control circuit 19 described later via the resistance element 14_5. The emitter of the IGBT element 17 is connected to the ground GND. Further, the cathode of the bypass diode 12_2 is connected to the anode 15a of the arc tube 15. The anode 15a of the arc tube 15 is connected to the + side of the main capacitor 13_1.
[0034]
The trigger coil 16 transmits electric power flowing through the trigger capacitor 13_2 to the secondary winding 16b to give a trigger voltage to the arc tube 15. The primary coil 16a of the trigger coil 16 includes the arc tube 15 and the trigger coil 16_2. Together with the IGBT element 17, it is arranged in a discharge loop through which the electric power discharged from the main capacitor 13_1 flows. Further, when the IGBT element 17 is turned off, the bypass diode 12_2 has a large counter electromotive force generated in the primary side winding 16a because the current flowing in the primary side winding 16a immediately before that is suddenly cut off. The current is caused to flow, so that a large voltage due to the back electromotive force is prevented from being applied to the IGBT element 17, and the destruction of the IGBT element 17 is prevented.
[0035]
The IGBT element 17 is a switch element that is arranged in a discharge loop in which the power charged in the main capacitor 13_1 is discharged and opens and closes the discharge loop according to control, and in the state where the charging of the main capacitor 13_1 is completed. When the electric power of the main capacitor 13_1 is discharged while forming the discharge loop, the allowable current is lower than the peak value of the discharge current flowing through the discharge loop.
[0036]
The flash light emitting circuit 10 includes a voltage detection circuit 18 and a control circuit 19. The voltage detection circuit 18 detects the voltage of the main capacitor 13_1 based on the voltage at the connection point of the resistance elements 14_2 and 14_3 connected to both ends of the main capacitor 13_1. The control circuit 19 controls the opening and closing of the discharge loop by the IGBT element 17 based on the voltage detected by the voltage detection circuit 18. Refer to the detection result of the voltage by the voltage detection circuit 18 for details. Thus, the IGBT element 17 is pulse-driven so that the discharge current flowing through the IGBT element 17 is always less than or equal to the allowable current of the IGBT element 17.
[0037]
FIG. 2 is a diagram showing a part of the control circuit shown in FIG. 1 together with the main capacitor, arc tube, trigger coil, IGBT element, and the like.
[0038]
As shown in FIG. 2, the control circuit 19 includes a resistance element 19a. ₁ , 19a ₂ Are connected to each other, a P-channel transistor 19a, an N-channel MOSFET 19b, and a resistance element 19c disposed between the P-channel transistor 19a and the N-channel MOSFET 19b. The gate of the N-channel MOSFET 19b is connected to the resistance element 19a. ₂ Is connected to the base of the P-channel transistor 19a and receives the pulse bar signal FT_. The voltage VCC obtained by stabilizing the voltage of the built-in battery 1 by a regulator (not shown) is input to the emitter of the P-channel transistor 19a. Further, the voltage HV boosted by the booster circuit 11 (see FIG. 1) is applied to the main capacitor 13_1.
[0039]
FIG. 3 is a diagram showing waveforms in the flash light emitting circuit shown in FIG.
[0040]
In the present embodiment, a relatively inexpensive IGBT element 17 having an allowable current with a peak value of about 130 A is used. The control circuit 19 is executed after the preceding stage sequence and the preceding stage sequence, which are different from each other in the sequence of pulse trains for pulse driving the IGBT element 17 so as not to exceed the allowable current. A pulse signal FT programmed with a final sequence is output. The voltage detection circuit 18 detects the voltage MC of the main capacitor 13_1 at least once after the control circuit 19 starts executing the previous sequence. Further, after starting the execution of the preceding sequence, the control circuit 19 determines based on the voltage MC of the main capacitor 13_1 detected by the voltage detection circuit 18, and at the timing when the voltage MC falls below a predetermined voltage. It controls to shift to.
[0041]
If the ON time of the pulses constituting the pulse signal FT is made relatively short, it is possible not to exceed the allowable current of the IGBT element 17, but this may cause the total light emission time to exceed the exposure time of the camera. In addition, the charge charged in the main capacitor 13_1 for flash emission is wasted. Therefore, the voltage MC of the main capacitor 13_1 is detected at least once after the start of the execution of the preceding sequence, and when the voltage MC falls below a predetermined voltage, the final sequence is shifted to DC light emission (normal single light emission). ) By doing so, the charge charged in the main capacitor 13_1 can be completely used for flash emission without exceeding the allowable current of the IGBT element 17. Accordingly, in photographing, a flash having a sufficient exposure amount and a sufficient reach distance can be emitted from the arc tube 15 toward the subject.
[0042]
Further, the control circuit 19 outputs a pulse signal FT in which the initial sequence executed earlier and the intermediate sequence executed after the initial sequence, in which the pulse train sequences are different from each other, are programmed as the preceding sequence. It is. The arc tube 15 is excited by receiving a trigger voltage of about 4 KV and shifts to arc discharge. However, the arc tube 15 varies due to variations in individual arc tubes 15 and circuit elements, and varies in time to shift to arc discharge (for example, 5 μS). Occurs. Also, the transition time varies even under environmental conditions such as a bright room / dark room. Therefore, by dividing the preceding sequence into an initial sequence and an intermediate sequence, stabilizing the pulse emission in the initial sequence, and making the pulse emission for controlling the light quantity in the intermediate sequence, the unstable due to the above variations Light emission can be eliminated.
[0043]
Further, the voltage detection circuit 18 detects the voltage MC of the main capacitor 13_1 with the voltage determination pulse shown in FIG. 3 when the IGBT element 17 is in a state of opening the discharge loop. When the IGBT element 17 is turned on and the discharge loop is closed, a discharge current IC flows in the discharge loop, for example, around 100 A. When such a large discharge current IC flows, the voltage at the voltage detection measurement point (the connection point of the resistance elements 14_2 and 14_3 shown in FIG. 2) decreases, and the voltage MC of the main capacitor 13_1 is accurately measured. Is difficult. Therefore, when the IGBT element 17 is in a state where the discharge loop is opened, that is, when the IGBT element 17 is in the OFF state, the voltage MC of the main capacitor 13_1 is detected. Thereby, the voltage drop at the connection point is small, and therefore the voltage MC of the main capacitor 13_1 can be accurately measured.
[0044]
Next, the operation of the flash light emitting circuit 10 will be described with reference to FIG. 1, FIG. 2, and FIG. In the first initial sequence, the power from the internal battery 1 is boosted by the booster circuit 11, and the voltage MC of the main capacitor 13_1 is 320V. Further, the pulse bar signal FT_ shown in FIG. 2 is at the “H” level. Therefore, the P-channel transistor 19a and the N-channel MOSFET 19b are in an off state and an on state, respectively. Therefore, 'L' level is input to the base of the IGBT element 17 as the pulse signal FT via the resistance element 14_5, and the IGBT element 17 is in the OFF state. In addition, power is stored in the trigger capacitor 13_2 through the resistance element 14_1.
[0045]
Next, a 15 μS pulse ('L' level pulse) is input as the pulse bar signal FT_. Then, the P-channel transistor 19a and the N-channel MOSFET 19b are turned on and off, whereby a pulse of 15 μS ('H' level pulse) as the pulse signal FT passes through the resistance element 14_5 and the IGBT element 17 Entered into the base. Then, the IGBT element 17 is turned on, and the electric charge accumulated in the trigger capacitor 13_2 is discharged through the path of the primary coil 16a → IGBT element 17 → ground GND of the trigger coil 16. As a result, a current flows through the primary winding 16a, and an electromotive force is induced in the secondary winding 16b. Here, since the number of turns of the secondary winding 16b is larger than the number of turns of the primary winding 16a, the electromotive force induced in the secondary winding 16b is amplified and increased. Since such a large electromotive force is applied to the side electrode 15c of the arc tube 15 as a trigger voltage, the xenon gas sealed in the arc tube 15 is excited and the (+) side of the main capacitor 13_1 → the arc tube 15 A current IC flows through the path of the anode 15 a → the cathode 15 b of the arc tube 15 → the primary winding 16 a of the trigger coil 16 → the IGBT element 17 → the ground GND, and flash light is generated from the arc tube 15. In this manner, flash light is emitted in the initial sequence. In this initial sequence, a relatively large 15 μS pulse is output as the pulse signal FT in order to stabilize the excited state of the arc tube 15 and to reliably emit the flash light. Note that noise is generated when the IGBT element 17 is first turned on. Accordingly, a noise current IC as shown in FIG. 3 appears.
[0046]
Next, in the intermediate sequence, the first and second pulses having a relatively small pulse width are input as the pulse signal FT, and the arc tube 15 corresponds to the first and second pulses as described above. Two pulse currents IC (approximately 60 A) flow, and flash light is generated from the arc tube 15 in response to the two pulse currents IC. At this point, the voltage MC drops to about 300V. Further, when the third pulse is input, a pulse current IC flows through the arc tube 15, and flash light is generated from the arc tube 15. At this time, the voltage MC drops to about 280 V, that is, the voltage VS that falls within the allowable current of the IGBT element 17. Although the widths of the first, second, and third pulses are the same, since the excited states are different, the magnitude of light emission is different as shown in FIG.
[0047]
After the end of the third pulse, the voltage detection circuit 18 detects the voltage MC based on the voltage at the connection point of the resistance elements 14_2 and 14_3 connected to both ends of the main capacitor 13_1. In the present embodiment, as described above, the voltage MC is detected when the IGBT element 17 is off, so that the voltage MC can be accurately measured.
[0048]
As a result of the detection, if it is determined that the threshold value is higher than a preset threshold value (here, 280 V), the intermediate sequence is repeatedly executed. On the other hand, if it is determined that the threshold value is lower than the preset threshold value, the process proceeds to the final sequence. To do. Here, since the voltage MC is 280 V or less, the process proceeds to the final sequence.
[0049]
In the final sequence, a pulse having a relatively large pulse width is input as the pulse signal FT, whereby all charges accumulated in the main capacitor 13_1 are released, and so-called DC light emission (normal single light emission) is performed. Here, since the voltage MC is 280 V or less, the allowable current of the IGBT element 17 is not exceeded. Therefore, compared with the conventional technique of suppressing the peak current of the IGBT element by inserting a resistance element in the discharge loop, the flash light emitting circuit 10 in which the power loss is suppressed and the cost is reduced is realized. Is done.
[0050]
FIG. 4 is a diagram illustrating examples of the pulse signal FT.
[0051]
Example 1 shown in FIG. 4 is the pulse signal FT shown in FIG. 3 described above. In the present embodiment, the example in which the pulse signal FT shown in the first example is output from the control circuit 19 shown in FIG. 1 and the flash light is emitted from the arc tube 15 has been described. A flash light may be emitted from the arc tube 15 by the pulse signal FT shown in FIG.
[0052]
The initial sequence in the pulse signal FT shown in Example 2 includes a plurality of pulses (two pulses). When the allowable current of the IGBT element 17 has a margin, it is possible to shift to stable light emission with one pulse having a long on-time in the initial sequence. However, when there is no allowance for the allowable current of the IGBT element 17, it is necessary to repeat the fine on / off times. Therefore, the initial sequence is composed of a plurality of pulses to achieve stable light emission in the initial sequence.
[0053]
Furthermore, in the pulse signal FT shown in Example 2, the intermediate sequence is composed of a plurality of blocks including pulses having the same width and the same period in each block. If light is emitted with the same on / off pulse in the intermediate sequence, the voltage MC of the main capacitor 13_1 gradually decreases for each light emission amount of one pulse, and the current decreases as the voltage MC decreases. It is desirable to gradually increase the on time or gradually decrease the off time in order to approach a constant value, but this has the disadvantage of increasing the control burden. Therefore, as in Example 2 shown in FIG. 4, the intermediate sequence is composed of a plurality of blocks having pulses of the same width and the same period in each block, and processing such as increasing the ON time for each block is performed. And the same effect as the case where it controls finely as mentioned above is acquired, suppressing the burden of control. For example, the intermediate sequence is divided into 3 blocks, the first block is repeated 3 times with 4 μS / 10 μS on / off pulse, the next block is repeated 4 times with 5 μS / 9 μS on / off pulse, and the last block is 7 μS / 7 μS. The arc tube 15 may emit light as one on / off pulse.
[0054]
The initial sequence in the pulse signal FT shown in Example 3 is composed of one pulse as in Example 1, and the intermediate sequence is composed of a plurality of blocks as in Example 2. In this way, the arc tube 15 may emit light.
[0055]
The final sequence in the pulse signal FT shown in Example 4 is composed of a plurality of pulses (two pulses). Basically, one pulse light emission (single DC light emission) is adopted in the final sequence, but the arc tube 15 in the excited state is the first light emission that is not in the excited state even when the voltage MC of the main capacitor 13_1 is low. Current is easier to flow than time. For this reason, the final sequence is composed of a plurality of pulses. For example, it is safer to suppress the current flowing through the IGBT element 17 by emitting one pulse first and then emitting one pulse next.
[0056]
FIG. 5 is a diagram showing each form in which the voltage of the main capacitor is detected by the voltage detection circuit in each pulse signal FT shown in FIG.
[0057]
The voltage detection circuit 18 and the control circuit 19 may operate as follows. That is, as shown in Example 1 and Example 2, the voltage detection circuit 18 detects the voltage MC of the main capacitor 13_1 after execution of the initial sequence by the control circuit 19, and the control circuit 19 executes the initial sequence. Based on the voltage MC detected at a later timing, the blocks constituting the intermediate sequence are next executed.
[0058]
Further, as shown in Example 2, Example 3 and Example 4, the voltage detection circuit 18 detects the voltage MC of the main capacitor 13_1 after execution of one block constituting the intermediate sequence by the control circuit 19, The control circuit 19 selects the next block based on the voltage MC detected at the timing after execution of one block constituting the intermediate sequence, and executes the selected block next. The degree of decrease in the voltage MC of the main capacitor 13_1 due to pulse light emission varies depending on environmental conditions and the like. Therefore, when the block selected based on the voltage MC of the main capacitor 13_1 detected at the timing after execution of one block constituting the intermediate sequence is executed, the voltage MC of the main capacitor 13_1 that changes depending on the environmental conditions and the like. The block corresponding to the can be selected. Therefore, light can be emitted with a high discharge current, and the total light emission time can be shortened.
[0059]
FIG. 6 is a diagram showing a configuration different from the configuration shown in FIG. 5 in which the voltage of the main capacitor is detected by the voltage detection circuit.
[0060]
The voltage detection circuit 18 detects the voltage MC of the main capacitor 13_1 after execution of the initial sequence by the control circuit 19, and the control circuit 19 is based on the voltage MC detected at the timing after execution of the initial sequence. Then, any block (example 1) constituting the intermediate sequence or the final sequence (example 2 or example 3) is selected, and the selected block or final sequence is executed next. When the environmental temperature is high, the equivalent resistance of the main capacitor 13_1 decreases and the discharge current tends to increase. In that case, the voltage MC of the main capacitor 13_1 after execution of the initial sequence reaches the voltage determined to shift to the final block. Therefore, as shown in Example 2 and Example 3, when the intermediate sequence is skipped and the process proceeds to the final sequence, the total light emission time can be shortened. On the other hand, since the discharge current is small when the temperature is low, the charge of the main capacitor 13_1 after the execution of the initial sequence is not sufficiently discharged. Therefore, as shown in Example 1, when the transition is made to any block constituting an intermediate sequence in which the discharge current becomes larger, the voltage MC of the main capacitor 13_1 can be lowered quickly, and therefore the total light emission time can be shortened. it can.
[0061]
The control circuit 19 is programmed with a plurality of different intermediate sequences as an intermediate sequence, and the voltage detection circuit 18 detects the voltage MC of the main capacitor 13_1 after the initial sequence is executed by the control circuit 19. The control circuit 19 selects one of the plurality of intermediate sequences based on the voltage MC detected at the timing after execution of the initial sequence, and then selects the selected intermediate sequence. It may be executed. In a plurality of intermediate sequences that are different from each other as the intermediate sequence, the on / off pulses constituting the pulse train often have a certain correlation. For example, it is assumed that the intermediate sequence is composed of three blocks whose frequency is the same as 33 KHz and whose duty is changed to 10%, 20%, and 30% (this is an intermediate block A group). Further, assuming that the initial sequence is a fixed pulse, the voltage drop amount (ΔV) of the capacitor is, for example, 5 V (Δ5 V) or 10 V (Δ10 V) due to environmental conditions or the like. In terms of the amount of light, the case of Δ5V is smaller than the case of Δ10V, and naturally the discharge current is also small. Therefore, when the intermediate block group A is selected under the condition of Δ10V, the discharge current is too large under the condition of Δ5V. Therefore, an intermediate block group B having a duty of 10, 20, 30% and a frequency of 60 KHz is selected. By doing in this way, discharge current can be made constant by simple control. Hereinafter, a description will be given with reference to FIG.
[0062]
FIG. 7 is a flowchart of a routine for selecting one of the plurality of intermediate sequences based on the voltage MC detected at the timing after execution of the initial sequence and executing the selected intermediate sequence.
[0063]
This routine is started after execution of the initial sequence, and in step S11, the intermediate sequence is entered. Next, the process proceeds to step S12. Here, the above-described intermediate block A group (described as block A) is executed, and the process proceeds to step S13. In step S13, the voltage detection circuit 18 detects the voltage MC of the main capacitor 13_1. When the detected decrease amount (ΔV) of the voltage MC is smaller than the predetermined value, the process returns to step S12. On the other hand, when the detected decrease amount (ΔV) of the voltage MC is larger than a predetermined value, the process proceeds to step S14. In step S14, the intermediate block B group (described as block B) described above is executed, and the process proceeds to step S15. In step S15, the voltage MC of the main capacitor 13_1 is detected again by the voltage detection circuit 18, and when the detected decrease amount (ΔV) of the voltage MC is smaller than a predetermined value, the process returns to step S14, and the detected voltage MC If the decrease amount (ΔV) is larger than the predetermined value, the process proceeds to step S16. In step S16, the block C having a higher frequency than the block B is selected and executed to increase the discharge current, and this routine is terminated.
[0064]
The control circuit 19, the voltage detection circuit 18, and the control circuit 19 may each be configured as follows. That is, the control circuit 19 includes a plurality of intermediate sequences that are different from each other as an intermediate sequence, the common initial block (first block of the intermediate sequence) common to the plurality of intermediate sequences that is executed first, and the common A plurality of intermediate sequences including one or more blocks for each intermediate sequence following the initial block are programmed, and the voltage detection circuit 18 performs the main capacitor 13_1 after executing the initial sequence. And after the execution of the common initial block of the intermediate sequence. Further, after executing the initial sequence and further executing the common initial block, the control circuit 19 selects one of the plurality of intermediate sequences based on both the voltages from the voltage detection circuit 18. Next, the block by intermediate sequence of the selected intermediate sequence is executed next. After executing the initial sequence, the process proceeds to the intermediate sequence, but it is often impossible to predict how much current is flowing in the first pulse train in the intermediate sequence, so the first pulse train (first block of the intermediate sequence) was executed. By detecting the voltage MC of the main capacitor 13_1 later by the voltage detection circuit 18, the level of the discharge current can be estimated from the charge of the main capacitor 13_1 used in the first block. If the voltage drop is unexpectedly small, the total light emission time can be shortened if the control circuit 19 shifts to a completely different kind of intermediate block.
[0065]
【The invention's effect】
As described above, according to the present invention, power loss can be suppressed and cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a flash light emitting circuit according to an embodiment of the present invention.
FIG. 2 is a diagram showing a part of the control circuit shown in FIG. 1 together with a main capacitor, an arc tube, a trigger coil, an IGBT element, and the like.
FIG. 3 is a diagram showing waveforms in the flash light emitting circuit shown in FIG. 1;
FIG. 4 is a diagram illustrating examples of a pulse signal FT.
FIG. 5 is a diagram showing each form in which the voltage of the main capacitor is detected by a voltage detection circuit in each pulse signal FT shown in FIG. 4;
6 is a diagram showing a form different from the form shown in FIG. 5, in which the voltage of the main capacitor is detected by the voltage detection circuit.
FIG. 7 is a flowchart of a routine for selecting any one of a plurality of intermediate sequences based on a voltage MC detected at a timing after execution of the initial sequence, and executing the selected intermediate sequence.
[Explanation of symbols]
1 Built-in battery
10 Flash light emitting circuit
11 Booster circuit
12_1, 12_2 diode
13_1 Main capacitor
13_2 Trigger capacitor
14_1, 14_2, 14_3, 14_4, 14_5, 19a ₁ , 19a ₂ 19c Resistive element
15 arc tube
15a anode
15b cathode
15c Side electrode
16 Trigger coil
16a Primary winding
16b Secondary winding
17 IGBT element
18 Voltage detection circuit
19 Control circuit
19a P-channel transistor
19b N-channel MOSFET

Claims (3)

In a flash light emitting circuit that emits flash light from the arc tube by charging the capacitor and discharging the electric power charged in the capacitor via a discharge loop in which the arc tube is arranged in the middle,
A switching element disposed in the discharge loop and opening and closing the discharge loop according to control;
A voltage detector for detecting the voltage of the capacitor;
A control unit for controlling the opening and closing of the discharge loop by the switch element,
The switch element has an allowable value lower than the peak value compared to the peak value of the discharge current flowing in the discharge loop when the capacitor power is discharged while the discharge loop is formed after the capacitor is completely charged. Having a current,
The control unit refers to the detection result of the voltage by the voltage detection unit, and drives the switch element to pulse so that a discharge current flowing through the switch element is always equal to or less than an allowable current of the switch element. Thus, a preceding sequence executed in advance and a final sequence executed after the preceding sequence, in which pulse train sequences for driving the switching element are different from each other, are programmed, and further, the preceding stage is programmed. As a sequence, a sequence of pulse trains different from each other is programmed with an initial sequence executed earlier and an intermediate sequence executed after the initial sequence,
The voltage detection unit detects the voltage of the capacitor at least once after the execution of the preceding sequence by the control unit,
The control unit further starts the execution of the preceding sequence, and then shifts to the final sequence at a timing when the voltage of the capacitor detected by the voltage detection unit falls below a predetermined voltage,
The flash light emitting circuit according to claim 1, wherein the intermediate sequence is composed of a plurality of blocks including pulses having the same width and the same period in each block . The voltage detection unit detects the voltage of the capacitor after the execution of one block constituting the intermediate sequence by the control unit,
The control unit selects a next block based on the voltage detected at a timing after execution of one block constituting the intermediate sequence, and executes the selected block next. The flash light emitting circuit according to claim 1. The voltage detection unit detects the voltage of the capacitor after the execution of the initial sequence by the control unit,
The control unit selects one of the blocks constituting the intermediate sequence or the final sequence based on the voltage detected at a timing after execution of the initial sequence, and then selects the selected block or final sequence. The flash light emitting circuit according to claim 1 , wherein the flash light emitting circuit is executed .

Images