JP2003052173A - Flyback-type voltage step-up circuit of capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a primary current to the predetermined current, which is equal to or lower than the saturation current with respect to saturation current which is different, depending on the oscillation transformer. SOLUTION: In a flyback-type voltage step-up circuit of capacitor, where the primary current of the oscillation transformer is detected and when the primary current becomes equal to a predetermined current (Ipmax) (S104), the primary current is cut off (S105), to generate a voltage stepped up to a secondary side of the oscillation transformer to charge the capacitor, and the predetermined current is changed (S100) by the data stored previously in a digital memory (S99).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a flyback type booster circuit of a capacitor suitable for an electronic flash device.

[0002]

2. Description of the Related Art As a booster circuit of a conventional electronic flash device, a forward type booster circuit has been mainly used. In particular, the forward type self-exciting booster circuit has a simple circuit configuration, stably oscillates regardless of the type and shape of the oscillating transformer, and is generally widely used. Recently, as the size of the camera has been reduced, a battery with a small capacity has been used, and the guide number has been increased to the contrary. For this reason, the adoption of a flyback type booster circuit, which is more efficient than the forward type, is increasing.

[0003]

However, when the main capacitor is charged by the flyback booster circuit, the efficiency can be improved by charging with a small current, but the charging is mainly performed with a small current. It takes a long time to charge the capacitor, which causes a release time lag at the time of shooting, and misses a photo opportunity. Therefore, in order to shorten the charging time as in the forward type booster circuit, it is necessary to flow a relatively large current.

The flyback type booster circuit must be used below the saturation current of the oscillating transformer, and when the oscillating transformer is saturated, the primary current rapidly increases and an excessive current flows through the switching element. A structure is provided to increase the saturation current.

In an oscillation transformer for flyback, an air gap called a gap is provided in the core, and this gap reduces variation in inductance, suppresses saturation of the core, and consequently increases the saturation current. ing. However, if the gap is made too large, the charging efficiency of the booster circuit also decreases. Therefore, the tolerance of the inductance, that is, the variation of the oscillation transformer is generally set to about ± 10% to ± 20% as a gap of about several tens of micrometers. I try to keep it down. Variation of inductance also affects saturation current,
If the gap is small, the inductance is large and the saturation current is small, and if the gap is large, the inductance is small and the saturation current is large. In order to flow a relatively large current close to the saturation current in a flyback booster circuit, it is necessary to accurately control the primary current to a predetermined current below the saturation current in consideration of such variations in the saturation current. Further, since the inductance and the saturation current naturally differ depending on the type and shape of the oscillation transformer, it is an important issue to control the primary current of the oscillation transformer to a predetermined current equal to or lower than the saturation current with high accuracy.

(Object of the Invention) A first object of the present invention is to accurately control a primary current to a predetermined current equal to or lower than the saturation current with respect to a saturation current which varies depending on variations, types and shapes of oscillation transformers. It is an object of the present invention to provide a flyback booster circuit for a capacitor.

A second object of the present invention is to achieve the above first object and to set the primary current with high accuracy even when the state of the battery changes, thereby shortening the charging time. It is an object of the present invention to provide a flyback type booster circuit of a capacitor capable of achieving the above.

[0008]

In order to achieve the first object, the present invention according to claim 1 detects the primary current of an oscillating transformer, and detects the primary current when the primary current reaches a predetermined current. In a flyback type booster circuit of a capacitor that cuts off and generates a boosted voltage on the secondary side of the oscillation transformer to charge the capacitor, the predetermined current is changed by data stored in advance in a digital memory. This is a flyback booster circuit with a characteristic capacitor.

Further, in order to achieve the first object,
According to a fifth aspect of the present invention, the primary current of the oscillating transformer is energized for a predetermined time set by a timer, the primary current is cut off after the predetermined time, and a boosted voltage is generated on the secondary side of the oscillating transformer. A flyback booster circuit of a capacitor for charging the capacitor, wherein the predetermined time is changed according to data stored in advance in a digital memory.

In order to achieve the above second object,
The present invention according to claim 9 is characterized in that the predetermined time is changed depending on a state of a battery as a power source.
The flyback type booster circuit of the described capacitor.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 shows a circuit diagram of an electronic flash device and a camera having a flyback booster circuit of a capacitor, which is a first embodiment of the present invention.

First, the circuit configuration of the electronic flash device will be described. 1 is a battery as a power source, 2 is a power capacitor, 3 is a switching element such as a field effect transistor, 4
Reference numerals 5 and 5 are resistors, and reference numeral 6 is a comparator. The negative input terminal is connected to the connection point between the switch element 3 and the resistor 5 so that the potential of the resistor 5 connected in series with the switch element 3 can be measured. The resistor 4 is a pull-down resistor connected to the control terminal of the switch element 3, and is connected between the control terminal and the negative electrode of the battery 1. Reference numeral 7 is a resistor for pulling up the output of the comparator 6 from the power supply Vcc from the constant voltage circuit described later. 8 is an oscillation transformer, 9 is a high-voltage rectifying diode, 10 is a voltage detection circuit, 11 is a trigger circuit,
12 is a flash discharge tube, and 13 is a main capacitor. The secondary winding S of the oscillation transformer 8 is connected between both electrodes of the main capacitor 13 via a high-voltage rectifying diode 9, and the negative electrode of the main capacitor 13 is connected to the negative electrode of the battery 1. A voltage detection circuit 10, a trigger circuit 11 and a flash discharge tube 12 are connected in parallel with the main capacitor 13.

Reference characters a to f are connection lines to a camera control unit 125, which will be described later, and a is connected to a control electrode of the switch element 3. Reference numeral b is a line which is connected to the positive input terminal of the comparator 6 and which transmits the output of the D / A converter in the camera control circuit 125 described later. c is the comparator 6
Is connected to the output terminal of. d is a line for supplying a drive signal for driving the voltage detection circuit 10, and e is a connection line for inputting the output signal of the voltage detection circuit 10 to the camera control circuit 125 and detecting the charging voltage of the main capacitor 13. . Reference numeral f is a connection line that gives a start signal for operating the trigger circuit 11 for causing the flash discharge tube 12 to emit light.

The camera control circuit 125 includes an A / D converter, a D / A converter, and a non-volatile memory EEPR.
The camera control circuit includes a microcomputer (hereinafter referred to as a microcomputer) including an OM and an interface circuit. A constant voltage circuit 120 is controlled by the camera control circuit 125 via the VCCEN terminal, and supplies Vcc, which is a power source, to each circuit.

Reference numeral 121 denotes a switch detection circuit, which is operated by a battery or a power source Vcc and transmits the state or change of each switch to the camera control circuit 125 by switch detection information SWD. 122 is a temperature detection circuit, which is a start signal THEN
The operation is started by the input of, and temperature information THD is given to the camera control circuit 125. Reference numeral 123 is a film sensitivity detection circuit for obtaining information such as film sensitivity and the number of frames.
The operation is started by inputting IMEN, and the film information FI
The MD is supplied to the camera control circuit 125. Reference numeral 124 denotes a battery check circuit, which starts its operation when an activation signal BATCK is input, and provides the camera control circuit 125 with battery information BATD necessary for checking whether or not the remaining battery level is sufficient for photographing. A shutter drive circuit 126 drives the shutter by a drive signal SHDRV. Reference numeral 127 denotes a distance measuring circuit, which detects a distance information AF to a subject by a start signal AFEN from the camera control circuit 125.
D is measured and given to the camera control circuit 125. Reference numeral 128 denotes a photometric circuit, which is a start signal A from the camera control circuit 125.
Upon receiving the EEN, the brightness information AED of the subject is given to the camera control circuit 125. Reference numeral 129 is a display circuit for displaying necessary information by a liquid crystal display LCD or the like. Reference numeral 130 denotes a lens drive circuit for driving the taking lens, which drives the taking lens by a drive signal LNZDRV. Reference numeral 131 denotes a film drive circuit for feeding the film, which is a drive signal FILMD from the camera control circuit 125.
The film is fed by RV.

Next, referring to the flow chart of FIG.
The operation of the circuit shown in FIG. When the power of the camera is turned on, the camera control circuit 125 makes necessary initial settings for the microcomputer (step S1), and confirms the information necessary for photographing by the switch detection information SWD of the switch detection circuit 121 (step S2).

Here, the generation of the first stroke signal, which is the half-depressed state (SW1 ON) of the release button (not shown) for the preparation for photographing, is waited (step S3), and when the first stroke signal is generated, the predetermined stroke signal is generated. The counter is reset to the initial state (step S4), the battery check circuit 124 is activated by the activation signal BATCK, and the necessary battery information BATD is taken into the camera control circuit 125 (step S5). Based on this information, it is determined whether or not the camera is in the power state necessary for shooting (step S
6) If not sufficient, the process returns to step S2, and if it is determined that the power supply is sufficient, the distance measuring circuit 1 is activated by the activation signal AFEN.
27 is operated to measure the distance to the subject (step S7). The distance information AFD is fetched by the camera control circuit 125. Subsequently, the activation signal AEEN is sent to measure the brightness of the subject, and the brightness information AED is taken into the camera control circuit 125 (step S8). It is determined from the brightness information AED whether the subject brightness is higher or lower than a predetermined brightness (step S9), and if the brightness is low, the process proceeds to the flash mode of step S10.

The operation of the flash mode in step S10 will be described below with reference to the flow chart shown in FIG. First, the contents of the EEPROM, which is a non-volatile memory of the camera control circuit 125, are confirmed (step S9).
9).

The operation of the flyback type booster circuit will be described here. The operation of the flyback type booster circuit is performed by controlling ON / OFF of the switch element 3. The saturation current varies depending on the variation, type and shape of the oscillation transformer 8. Although it is necessary to increase the primary peak current Ipmax (limit current) in order to accelerate the charging time of the main capacitor 13, when the oscillating transformer 8 reaches saturation, an overcurrent flows through the switch element 3 and there is a risk of damage. There is. Therefore, the primary peak current Ipmax of the oscillation transformer 8 needs to be set to be equal to or lower than the saturation current of the oscillation transformer 8.

The data obtained in step S99 corresponds to the primary peak current Ipmax equal to or lower than the saturation current of the oscillation transformer 8 used, and is set in advance depending on the variation of the oscillation transformer 8 and the type and shape thereof. It is a value. For example, if there is variation, it can be set by measuring the inductance. As described above, the inductance and the saturation current have an inverse relationship, and if the inductance is large, the primary peak current Ipm depends on the inductance.
If ax is set small, and the inductance is small, the primary peak current Ipmax may be set large according to the inductance. It is also possible to monitor the primary current of the oscillating transformer 8 directly as a voltage generated in the resistor 5 and set it to a value equal to or lower than the saturation current. Further, the variation of the inductance due to the type, the shape, etc. is different only in the value that is the center of the variation, and the similar setting can be made for these variations. Here, the reference voltage V (D / A) of a digital value corresponding to the primary peak current Ipmax is set by the D / A converter in the camera control circuit 125, and this reference voltage V (D / A) is applied to the connection line b. It is given to the positive input terminal of the comparator 6 via the (step S100).

By setting the reference voltage V (D / A), the primary peak current Ipmax is set as follows.

Ipmax = V (D / A) / R5 V (D / A): Reference voltage applied to the positive input terminal of the comparator 6 R5: Resistance value of the resistor 5 In this relationship, the resistance value of the resistor 5 is changed. It is also possible. However, in order to reduce the detection resistance loss,
The resistance value of the resistor 5 should be set to be as small as possible. Therefore, the resistance value series of low resistance has a wide stepwise width, and finer control becomes possible by setting the resistance value series by the D / A converter.

Next, a charging timer, which is a timer for stopping charging when the charging time of the main capacitor 13 becomes long, for example, a timer having a set time of about 10 to 15 seconds is started (step S101), Then, in order to detect the voltage of the main capacitor 13, a high-level drive signal is applied from the camera control circuit 125 to the voltage detection circuit 10 via the connection line d to operate (step S).
102). The voltage information of the main capacitor 13 is the connection line e
Is given to the A / D converter of the camera control circuit 125 via the, converted into a digital value, and taken into the microcomputer.

Next, in order to start charging, a high-level ON control signal is applied from the camera control circuit 125 shown in FIG. 1 to the control electrode of the switch element 3 through the connection line a (step S103).

The primary current I of the oscillation transformer 8 can be roughly calculated by the following calculation, where t is the energization time of the switching element 3.

I = (E / Rloop) * {1-exp (-R
loop * t / L)} Rloop: loop resistance on the primary side including internal resistance of battery 1, primary resistance component of oscillation transformer 8 and wiring resistance of pattern E: battery voltage L: primary inductance of oscillation transformer 8 When the resistance Rloop is small, it is shown as I = (E / L) * t.

Therefore, when the loop resistance Rloop is small, the primary current I of the oscillation transformer 8 is the switching element 3
Linearly increases with respect to the energization time t.

EEPROM confirmed in step S99
Is given as the reference voltage V (D / A) of the comparator 6 for detecting the above-mentioned primary peak current Ipmax. Regarding the data relating to the primary peak current Ipmax, since the resistance value of the detection resistor 5 is known, voltage data determined as V (D / A) = R5 * Ipmax may be used.

FIG. 4 shows the waveform of each part of the flyback type booster circuit of the present invention. 4, FIG. 4-A is a voltage waveform given to the control electrode of the switch element 3 from the camera control circuit 125, FIG. 4-B is a current waveform flowing in the primary winding P of the oscillation transformer 8, and FIG. 4-C is a comparator. 6 shows the output voltage waveform of FIG. 6, and FIG. 4-D shows the current waveform of the secondary winding S of the oscillation transformer 8.

First, the voltage waveform shown in FIG. 4A is given from the camera control circuit 125, and the switch element 3 is turned on by a high-level on control signal (step S1).
03). When the switching element 3 is turned on, the primary current of the oscillation transformer 8 linearly increases with time as shown in FIG. 4-B, and when this current reaches the primary peak current Ipmax, that is, the primary current of the oscillation transformer 8 is reached. As a result, the voltage drop across the resistor 5 is caused by the reference voltage V (D
/ A) (step S104), the output voltage of the comparator 6 changes from the high level to the low level as shown in FIG. 4-C. This low-level output voltage is applied to the camera control circuit 125 via the connection line c, and accordingly the high-level ON control signal applied from the camera control circuit 125 via the connection line a is shown in FIG. As shown in (4), the control signal changes to a low level off control signal (step S105). As a result, the switch element 3 is turned off, and the energy of the oscillation transformer 8 {(1
/ 2) * L * Ipmax * Ipmax} is discharged from the secondary winding S of the oscillation transformer 8 through the high voltage rectifying diode 9 and the main capacitor 13 as shown in FIG. 4-D, and the main capacitor 13 is charged. Then, the voltage of the main capacitor 13 rises. FIG. 4-D shows the secondary winding S of the oscillation transformer 8 at this time.
In step S106, a predetermined time is waited for the current discharge time of the secondary winding S. It should be noted that the charging voltage information of the main capacitor 13 is given to the camera control circuit 125 via the connection line e, converted into a digital value by the internal A / D converter, taken into the microcomputer, and the charging is completed. It is determined whether or not (step S107). Here, if the predetermined charge completion voltage is reached, the process proceeds to step S109, and if not, the process proceeds to step S108. In step S108, step S1
It is confirmed whether or not the charging timer started at 01 has counted up (step S108), and if counting, the process returns to step S103, and if counting, the process proceeds to step S110. Therefore, if the charging is not completed and the time of the charge cutoff is not reached, the loop from step S103 to step S108 is repeated,
The main capacitor 13 is charged.

When the charging is completed before the count-up of the charging timer, the OK flag indicating that the charging is completed is set (step S109), and step S111.
Proceed to. In step S111, the signal on the connection line d is switched from high level to low level in order to stop the detection of the charging voltage. Next, the charging timer is stopped (step S112). Further, if the charging timer counts up before the completion of charging of the main capacitor 13 in step S108, an NG flag indicating that charging is not completed is set (step S110), and the process proceeds to step S111 to stop the detection of the charging voltage. Then, the signal on the connection line d is switched from high level to low level. Next, the charging timer is stopped (step S112), and the process returns to the main routine (step S11 in FIG. 2).

After exiting the flash mode in step S10, in step S11, step S10 in FIG.
9 or it is confirmed whether the flag set in step S110 is OK or NG. If the NG flag is not charging, the process returns to step S2. If the flag is OK, the process proceeds to step S12. Next, the first release switch (not shown)
It waits for the second stroke of the release switch (full-press operation: SW2 ON) from the stroke state (steps S12 and S13). If the first stroke is released here, the process returns to step S2, and if the second stroke is input, the process proceeds to step S14 and step S7.
The lens drive circuit 130 is controlled on the basis of the distance information to adjust the focus. Further, in step S15, when the shutter opening is controlled through the shutter drive circuit 126 according to the condition based on the luminance information of the subject and the film sensitivity information obtained in step S8, the luminance is low, and the electronic flash device is required. The shutter control is performed based on the distance information and the film sensitivity information, and the electronic flash device is caused to emit light with an appropriate aperture value (step S15).

The light emission of the electronic flash device is the connection line f in FIG.
To the high level start signal. When a high level signal is applied to the connection line f, a high-voltage pulse voltage is generated at the output of the trigger circuit 11 and applied to the trigger electrode of the flash discharge tube 12, and the flash discharge tube 12 is excited.
Due to this excitation, the impedance of the flash discharge tube 12 is suddenly lowered, the charging energy of the main capacitor 13 is discharged and converted into light energy, and the subject is illuminated. If an electronic flash device is used, the flash flag F
AL is set to 1.

When the shutter is closed by the shutter drive circuit 126, the lens drive circuit 130 is controlled to return the photographing lens in the in-focus position to the initial position (step S16). Then, the film which has been photographed is wound by one frame under the control of the film drive circuit 131 (step S17).

Next, it is confirmed whether "1" is set in the flash flag FAL indicating that the electronic flash device is used (step S18). Flash flag FA
When "1" is set in L, the flash mode is set in step S19, the main capacitor 13 is charged in the same manner as in step S10, and the series of sequences is ended. Further, when "0" is confirmed in the flash flag FAL (step S18), the series of sequences is terminated without shifting to the flash mode.

(Second Embodiment) FIG. 5 shows a circuit diagram of an electronic flash device and a camera provided with a flyback type booster circuit of a capacitor, which is a second embodiment of the present invention.

In this embodiment, the first shown in FIG.
Elements and the like that perform the same operations as in the above embodiment are denoted by the same symbols.

The configuration different from the configuration shown in the first embodiment is that the detection resistor 5, the comparator 6, the pull-up resistor 7,
The connection line c to the camera control circuit 125 is deleted, and other configurations are the same as those in FIG. In the first embodiment, the current flowing when the switch element 3 is turned on is detected by the detection resistor 5 and the comparator 6, and the switch element 3 is turned off when the primary peak current Ipmax is reached. The change of the switching element 3 to the non-conducting state is controlled by the variable primary timer of the above.

The operations of the electronic flash device and the camera control circuit 125 are almost the same as those in the flow chart shown in FIG. 2, and the operation only in the flash mode will be described here.

The flash mode will be described with reference to the flowchart of FIG. 6. First, the camera control circuit 12 will be described.
The contents of the EEPROM, which is the non-volatile memory of No. 5, are confirmed (step S199).

The operation of the flyback booster circuit is performed by controlling the on / off of the switch element 3. In order to shorten the charging time, the primary peak current Ipmax of the oscillating transformer 8 must be set to a predetermined current that is close to the saturation current of the oscillating transformer 8 and does not exceed it. Since the saturation current of the oscillating transformer 8 varies depending on variations, types and shapes of the transformer, it is necessary to set the energization time of the switch element 3 for each.

The data obtained in step S199 includes the data corresponding to the predetermined current Ipmax equal to or less than the saturation current of the oscillation transformer to be used, and the type and shape of the oscillation transformer 8 including the inductance of the oscillation transformer 8 and variations in the inductance. It is the data set by.

The primary current I of the oscillating transformer 8 can be obtained by the following calculation as described above, where t is the energization time of the switching element 3.

I = (E / Rloop) * {1-exp (-R
loop * t / L)} Rloop: loop resistance on the primary side including internal resistance of battery 1, primary resistance component of oscillation transformer 8 and wiring resistance of pattern E: battery voltage L: primary inductance of oscillation transformer 8 When the resistance Rloop is small, it is shown as I = (E / L) * t.

From this equation, the primary peak current Ipmax changes depending on the primary inductance L of the oscillation transformer 8, and in order to keep it constant, the set time of the primary timer is varied so as to be inversely proportional to the primary inductance L, and the switch element 3 It is necessary to change the current-carrying time t of (1) at a predetermined current equal to or less than the saturation current. Therefore, the data obtained in step S199 corresponds to the time data corresponding to the primary peak current Ipmax below the saturation current value determined by the type and shape of the oscillation transformer 8 and the inductance due to the difference in the type and shape of the oscillation transformer 8. The data.

Furthermore, the standard primary inductance L (a
ve) may be set and the energization time t may be determined from the primary inductance L that differs depending on the type and shape used, and the primary peak current Ipm at the standard primary inductance L (ave)
Assuming that the energization time for obtaining ax is t0, the primary peak current I can be obtained by calculating t = t0 * L / L (ave).
It is possible to set pmax as an almost constant current. Further, here, L / L (ave) is externally applied to the power supply time t
It may be input as a correction coefficient of. Also in this case, it goes without saying that the energization time t is set such that the predetermined current is equal to or lower than the saturation current. The saturation current I (s
If the data of (at) is given, the saturation time t (sat) is calculated as t (sat) = I (sat) * L / E, where E is the battery voltage, and this saturation time t (sat) is exceeded. The energization time t may be set so that it does not occur.

The standard primary inductance L (ave)
The energization time t may be set by using both the data of the ratio of the primary inductance L and the data of the saturation current I (sat).

Thus, the energization time t by the primary timer is set by the data of the EEPROM (step S
200).

Next, when the charging time to the main capacitor 13 becomes long, a charging timer which is a timer for stopping charging, for example, a timer having a set time of about 10 to 15 seconds is started (step S201), and Camera control circuit 1 for detecting the voltage of the main capacitor 13
A drive signal of a higher level than 25 is applied to the voltage detection circuit 10 via the connection line d to operate (step S20).
2). The voltage information of the main capacitor 13 is given to the A / D converter input of the camera control circuit 125 via the connection line e.

Next, in order to start charging, a high level ON control signal is applied from the camera control circuit 125 shown in FIG. 5 to the control electrode of the switch element 3 through the connection line a, and at the same time the primary timer is started ( Step S2
03).

Therefore, the switch element 3 is turned on, the primary current of the oscillation transformer 8 flows, and increases with time.
When the preset time of the primary timer that regulates the primary current is reached, that is, when the primary current I reaches the primary peak current Ipmax (step S203), the camera control circuit 125.
The high-level ON control signal given from the above through the connection line a is switched to the low-level OFF control signal, whereby the switch element 3 is turned off (step S205). When the switch element 3 is turned off, the energy of the oscillation transformer 8 {(1/2) * L * Ipmax * Ipma
x} is discharged from the secondary winding S of the oscillation transformer 8 via the high-voltage rectifying diode 9 and the main capacitor 13, the main capacitor 13 is charged, and the voltage of the main capacitor 13 rises. The current discharge time of the secondary winding S waits until a predetermined time elapses (step S206). It should be noted that the charging voltage information of the main capacitor 13 is given to the camera control circuit 125 via the connection line e, converted into a digital value by the internal A / D converter, taken into the microcomputer, and the charging is completed. It is determined whether (step S
207). If the predetermined charging completion voltage has been reached, the process proceeds to step S209, and if not, the step S2.
Go to 08. In step S208, it is confirmed whether or not the charging timer started in step S201 is counting up (step S208). If counting is in progress, the process returns to step S203, and if counting up, the process proceeds to step S210. Therefore, if the charging is not completed and the time of the charge termination is not reached, the step S
The main capacitor 13 is charged by repeating the loop from 203 to step S208.

When the charging is completed before the count-up of the charging timer, the OK flag indicating that the charging is completed is set (step S209) and step S211 is executed.
Proceed to. In step S211, the signal on the connection line d is switched from high level to low level in order to stop the detection of the charging voltage. Next, the charging timer is stopped (step S212). If the charging timer counts up before the completion of charging of the main capacitor 13 in step S208, an NG flag indicating that charging is not completed is set (step S210), the process proceeds to step S211, and the detection of the charging voltage is stopped. Therefore, the signal on the connection line d is switched from high level to low level. Next, the charging timer is stopped (step S212), and the process returns to the main routine (step S11 in FIG. 2).

(Third Embodiment) FIG. 8 shows a flow chart of the flash mode in the third embodiment of the present invention. The circuit configuration of the third embodiment is almost the same as that of the second embodiment shown in FIG. In the present embodiment as well as in the second embodiment, the transition of the switch element 3 to the off state is controlled by the primary timer having a variable set time. In this embodiment, it has a circuit for determining the state of the battery. For example, a circuit such as the battery check circuit 124 in FIG. 5 is activated to confirm this state.

FIG. 7 shows an example of the battery check circuit 124. The configuration of this circuit includes a comparator 15, a transistor 16 and a resistor 17, and a series circuit of the transistor 16 and the resistor 17 is connected in parallel to the battery 1 and the power supply capacitor 2. The output terminal of the comparator 15 is connected to the base of the transistor 16, the positive input terminal is connected to the camera control circuit 125 of FIG. 5 through the connection line g that transmits the battery check activation signal BATCK, and the negative input terminal is current detection. Is connected to the resistor 17. Further, the battery information BATD is supplied from the collector of the transistor 16 to the A / D converter in the camera control circuit 125 as battery voltage data via the connection line h.

Next, the operation in the flash mode will be described with reference to FIG.

First, the battery voltage data in the open state is detected from the battery check circuit 124 via the connection line h. Next, a reference voltage is applied to the connection line g, and a constant current determined by the reference voltage and the resistor 17 is made to flow, and the voltage at this time is also A / D of the camera control circuit 125 via the connection line h.
The state of the battery 1 is confirmed by being supplied to the converter. Therefore, here, the loop resistance Rloop including the internal resistance of the battery 1 and the resistance of the battery segment and the pattern is obtained.

Assuming that the reference voltage applied is Ei and the resistance value of the resistor 17 is R17, a constant collector current determined by I0 = Ei / R17 flows through the collector of the transistor 16. The loop resistance Rloop including the internal resistance of the battery 1 at this time is calculated as Rloop = (E0-Ei) / I0, where E0 is the open circuit voltage of the battery 1 before the constant current flows.

In this way, the battery check circuit 124
Thus, the battery information is obtained from the loop resistance Rloop including the internal resistance of the battery 1 and the contact resistance of other battery sections (step S298). Next, the content of the EEPROM, which is a non-volatile memory of the camera control circuit 125, is confirmed (step S
299).

The contents of the EEPROM here are data of the energization time t of the switch element 3 for obtaining the primary peak current Ipmax of the oscillation transformer 8 and a coefficient value K described later.
In this embodiment, the energization time t is set in consideration of the state of the battery 1.

The relationship between the primary peak current Ipmax, the energization time t of the switch element 3 and the primary current I of the oscillation transformer 8 is Ipmax = (E0 / Rloop) * {1-exp (-Rloop *
t / L)} L: Primary inductance of the oscillation transformer 8 Therefore, the energization time t of the switch element 3 is t =-(L / Rloop) * Ln (1-Rloop * Ipmax / E
0) is required.

FIG. 9 shows the relationship between the energization time t and the primary current I. 9-a shows the primary current when the battery as the power source is new, and 9-b shows the primary current when the battery is exhausted. KI
1max is obtained by multiplying the maximum current value I1max that can flow from the battery by the loop resistance Rloop1 when the battery is new, by a coefficient K smaller than 1, and is shown as KI1max = (E0 / Rloop1) * K.

I1 (sat) indicates a saturation current at which current saturation occurs in the oscillation transformer 8 due to the primary current I, and I1 (sa)
Above t), the primary current I rises sharply.

The primary peak current Ipmax is the primary current value at the time of the energization time t2, and corresponds to the data of the energization time t2 previously input to the EEPROM.

KI2max is obtained by multiplying the maximum current value I2max which can be flown from the battery by the loop resistance Rloop2 when the internal resistance of the battery becomes large in a consumable battery or a low temperature condition by a coefficient K similar to the above, which is smaller than 1, and KI2max = Shown as (E0 / Rloop2) * K. Here, K takes a value of about 0.9 to 0.7 and is expressed as a coefficient in order to simplify the logarithmic term when calculating the energization time t, and L = Ln (1-Rloop * Ipmax / E0).

As shown in FIG. 9, when the battery 1 is relatively new, the current value KI1max, which is close to the maximum primary current that can be flowed as in 9-a, is larger than the primary peak current Ipmax.
The energization time t2 corresponding to the primary peak current Ipmax is set as the setting time of the primary timer. Further, when the resistance component of the battery 1 is large, the current value KI2max close to the maximum flowable current as in 9-b becomes smaller than the primary peak current Ipmax, and it takes time to reach the primary peak current Ipmax, or when the primary peak current Ipmax is not reached. Therefore, when the resistance component of the battery 1 is large, a current value KI2max close to the maximum current that can flow is set as the set time of the primary timer. Therefore,
The setting time of the primary timer is the primary peak current Ipmax or K
As indicated by I2max, the maximum current value is multiplied by the coefficient K to control the current value corresponding to the current value, whichever is shorter.

By setting the setting time of the primary timer in this way, it is possible to shorten the charging time even for a consumable battery or a battery having a high internal resistance at low temperature.

In this way, this calculation is performed and the energization time t is set by the primary timer (step S30).
0). Next, a charging timer, which is a timer for stopping the charging when the charging time of the main capacitor 13 becomes long, for example, a timer having a set time of about 10 to 15 seconds is started (step S301), and the main capacitor In order to detect the voltage of 13, the high-level drive signal is applied from the camera control circuit 125 to the voltage detection circuit 10 via the connection line d to operate (step S302).
The voltage information of the main capacitor 13 is given to the A / D converter input of the camera control circuit 125 via the connection line e.

Next, in order to start charging, a high level ON control signal is applied from the camera control circuit 125 shown in FIG. 5 to the control electrode of the switch element 3 through the connection line a, and at the same time the primary timer is started ( Step S3
03).

Therefore, the switch element 3 is turned on, the primary current of the oscillation transformer 8 flows, and increases with time.
When the preset time of the primary timer that regulates the primary current is reached, that is, when the primary current I reaches the primary peak current Ipmax or the current value KI2max (step S303).
The high level ON control signal given from the camera control circuit 125 via the connection line a is switched to the low level OFF control signal, and the switch element 3 is turned off (step S305). When the switch element 3 is turned off, the energy of the oscillation transformer 8 {(1/2) *
L * Ipmax * Ipmax} is discharged from the secondary winding S of the oscillation transformer 8 via the high-voltage rectifying diode 9 and the main capacitor 13, the main capacitor 13 is charged, and the voltage of the main capacitor 13 rises. The current discharge time of the secondary winding S waits for a predetermined time to elapse (step S306).
The charging voltage information of the main capacitor 13 is the connection line e.
It is given to the camera control circuit 125 via the, is converted into a digital value by the internal A / D converter, is taken into the microcomputer, and it is determined whether charging is completed (step S307). If the predetermined charge completion voltage has been reached, the process proceeds to step S309, and if not, the process proceeds to step S308. In step S308, it is confirmed whether the charging timer started in step S301 has counted up (step S308),
If it is counting, the process returns to step S303, and if it is counting up, the process proceeds to step S310. Therefore, if the charging is not completed and the time of the charge termination is not reached, the loop of steps S303 to S308 is repeated and the main capacitor 13 is charged.

When the charging is completed before the charging timer is counted up, an OK flag indicating that the charging is completed is set (step S309), and step S311 is performed.
Proceed to. In step S311, the signal on the connection line d is switched from high level to low level in order to stop the detection of the charging voltage. Next, the charging timer is stopped (step S312). If the charging timer counts up before the charging of the main capacitor 13 is completed in step S308, an NG flag indicating that charging is not completed is set (step S310), the process proceeds to step S311, and the detection of the charging voltage is stopped. Therefore, the signal on the connection line d is switched from high level to low level. Next, the charging timer is stopped (step S312), and the process returns to the main routine (step S11 in FIG. 2).

Here, the time data corresponding to the primary peak current Ipmax which differs depending on the type and shape of the oscillation transformer 8 may be time data including variation data of the primary peak current Ipmax of the same type of transformer.

Furthermore, the nonvolatile memory is an EEPROM.
Any form of digital memory such as a flash memory or a flash memory may be used.

Further, even in the mode in which the current is monitored and the primary peak current is set as in the first embodiment, the state of the battery is detected and the coefficient K is used in the same manner for D / A.
It goes without saying that the reference voltage may be controlled by the converter.

[0074]

As described above, according to claim 1 or 5,
According to the present invention described in (1), it is possible to accurately control the primary current to a predetermined current equal to or lower than the saturation current with respect to the saturation current that differs depending on the oscillation transformer.

Further, according to the present invention as set forth in claim 9, the primary current can be accurately set even when the state of the battery changes, and the charging time can be shortened.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an electronic flash device and a camera including a flyback booster circuit for a capacitor, which is a first embodiment of the present invention.

FIG. 2 is a flowchart showing the operation of the electronic flash device and camera of FIG.

FIG. 3 is a flowchart showing a flash mode of FIG.

FIG. 4 is a diagram showing waveforms at various parts of the flyback booster circuit shown in FIG.

FIG. 5 is a circuit diagram of an electronic flash device and a camera including a flyback booster circuit of a capacitor, which is a second embodiment of the present invention.

6 is a flowchart showing the operation of the electronic flash device and the camera of FIG.

FIG. 7 is a circuit diagram showing an example of the battery check circuit of FIG.

FIG. 8 is a flowchart showing the operations of the electronic flash device and the camera according to the third embodiment of the present invention.

FIG. 9 is a diagram showing a relationship between a primary current of an oscillating transformer and its energization time in a third embodiment of the present invention.

[Explanation of symbols]

1 battery 2 power capacitors 3 switch elements 5 Current detection resistor 6 comparator 8 oscillation transformer 10 Voltage detection circuit 12 Flash discharge tube 13 Main capacitor 124 Battery check circuit 125 camera control circuit

Claims (10)

[Claims] 1. A primary current of an oscillating transformer is detected, the primary current is cut off when the primary current reaches a predetermined current, a boosted voltage is generated on the secondary side of the oscillating transformer, and a capacitor is charged. A flyback booster circuit for a capacitor, wherein the predetermined current is changed according to data stored in advance in a digital memory. 2. The flyback booster circuit for a capacitor according to claim 1, wherein the data stored in the digital memory is data relating to a saturation current determined by the shape and type of the oscillation transformer. 3. The capacitor flyback booster circuit according to claim 1, wherein the data stored in the digital memory is data related to a saturation current determined by variations in the oscillation transformer. 4. The predetermined current is a predetermined current equal to or lower than a saturation current of the oscillation transformer.
Flyback type booster circuit of the described capacitor. 5. The primary current of the oscillating transformer is energized for a predetermined time set by a timer, the primary current is cut off after the predetermined time, a boosted voltage is generated on the secondary side of the oscillating transformer, and a capacitor is connected. A flyback booster circuit for charging a capacitor, wherein the predetermined time is changed according to data stored in advance in a digital memory. 6. The flyback booster circuit for a capacitor according to claim 5, wherein the data stored in the digital memory is time data relating to a saturation current determined by the shape and type of the oscillation transformer. . 7. The data stored in the digital memory is either time data related to a saturation current determined by variations in the oscillation transformer or both data related to the inductance of the oscillation transformer. The flyback type booster circuit of the capacitor according to claim 5. 8. The capacitor flyback booster circuit according to claim 5, wherein the predetermined time is within a range in which the primary current does not exceed a saturation current. 9. The flyback type booster circuit for a capacitor according to claim 5, wherein the predetermined time is changed depending on a state of a battery as a power source. 10. The flyback type booster circuit for a capacitor according to claim 7, wherein the data relating to the inductance of the oscillation transformer is data representing a variation of the oscillation transformer by a coefficient.