JP4502342B2 - Strobe device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a strobe device for photography or the like.
[0002]
[Prior art]
In a conventional strobe device, a battery voltage is boosted using a bipolar transistor as an oscillation transistor, and the boosted charge is accumulated in a main capacitor and discharged through a discharge tube, for example, to emit light to illuminate a subject. Things were common.
[0003]
Since the bipolar transistor has a low operating voltage and the current DC / DC converter is a current feedback type, the charging current to the main capacitor can be operated in a loop between the base and emitter of the oscillation transistor. However, there was an advantage that much less.
[0004]
However, as the size of cameras has been reduced, the number of batteries used has also been reduced due to the reduction in size, and the power supply voltage, which has been mainstream of 6V in the past, is increasingly used at 3V.
[0005]
Further, in recent compact cameras, a camera having a zoom function and a large guide number is required in order to expand a photographing area.
[0006]
Therefore, the performance of the bipolar transistor for oscillation is h_FEIs higher, and the emitter-collector saturation voltage V_CESince a transistor having a lower (sat) and a larger current capacity is required, usable bipolar transistors are currently limited.
[0007]
Compared to this bipolar transistor, FET, which is an insulated gate type transistor, has been improved remarkably recently, the gate drive voltage for conducting the FET has been lowered to 2.5-4V, and the operating resistance when conducting is about 20-30 mΩ. The element is coming out. Furthermore, there are many elements with a current capacity of 5A to 10A, which is sufficient as a strobe oscillation element.
[0008]
High h required for bipolar transistors_FESince the FET can be operated by guaranteeing the gate drive voltage, even if the power supply voltage of the battery or the like tends to become lower in the future, it is possible to cope with it.
[0009]
  A conventional example using this FET is shown in FIG. 1 is a battery as a power source, 60 is a capacitor for stabilizing the power source connected to both ends of the battery 1, 12 is a transformer for boosting the voltage of the battery 1, and a power source is connected to one terminal e of the primary winding. Battery 1 anodeConnectedThe other terminal f of the primary winding is connected to the drain of an N-channel field effect FET 13 (hereinafter abbreviated as FET), which will be described later, and one terminal g of the secondary winding is connected to a rectifier diode described later. 15 anodes are connected, and a base of a PNP transistor 81 (to be described later) is connected to the other terminal h of the secondary winding.
[0010]
Reference numeral 13 denotes an N-channel field effect transistor as a switch element. The drain is connected to the other terminal f of the primary winding of the transformer 12, the source is connected to the cathode of the battery 1, and the gate is an active element that is control means described later. Is connected to the output of the logic circuit 37.
[0011]
Reference numeral 37 denotes a logic circuit which is one of the active elements of the control means, and is composed of, for example, AND logic. This active element has an output V from a constant voltage circuit (power source) 120 described later._ccThe output depends on the power supply voltage. This is a driver circuit for driving the gate of the FET 13 described above, and has functions of stabilizing the gate voltage and improving the rise / fall characteristics of the on / off time control.
[0012]
One input of the active element 37 is an output of a current-voltage conversion means 48 described later, and the other is input from a signal terminal CGCOM from a control circuit 125 described later. The output of the active element 37 of the control means is connected to the gate of the FET 13.
[0013]
The active element 37 of this control means outputs HL only when both the output of the current-voltage conversion means 48 and the CGCOM signal are at a high level (hereinafter abbreviated as HL).
[0014]
When the CGCOM signal is at a low level (hereinafter abbreviated as LL), LL is output. Reference numeral 48 denotes current-voltage conversion means, which includes a transistor 81, a resistor 82, a capacitor 83, and a resistor 84.
[0015]
  The current-voltage conversion means 48 switches the current flowing from the secondary winding of the transformer 12 to the main capacitor 20 as a switching element.(FET13)The PNP transistor 81 has an emitter that outputs an output V of a constant voltage power source 120 to be described later._ccAnd the base is connected to the terminal h of the secondary winding of the transformer 12. The protective resistor 82 is connected between the emitter and base of the PNP transistor 81, and the capacitor 83 isOf the PNP transistor 81Connected between emitter and base. The resistor 84 has one end of the PNP transistor 81.collectorAnd the other end is connected to the cathode of the battery 1, and when the base current of the PNP transistor 81 is drawn during oscillation, a proportional current flows between the emitter and collector of the PNP transistor 81, and the electromotive force is generated in the resistor 84. Is converted from current to voltage. Resistor 61 is connected to the base of PNP transistor 81Of the control circuit 125Current limiting resistor connected between CGST pins.
[0016]
The resistor 47 has one end connected to the CGCOM terminal of the control circuit 125 and the other end connected to the input of the active element 37 of the control means.
[0017]
  41 is an output V of the constant voltage circuit 120 described later._ccAnd a capacitor for stabilizing the operation connected between the cathode of the battery 1 and a constant voltage circuit 93 that accompanies a drop in the battery voltage during charging.120Output voltage (V_ccWell-known output voltage maintaining circuit for maintaining the voltage)Is. If the input voltage (battery) suddenly drops as during charging, the output voltage cannot be maintained. Therefore, the power supply voltage cutoff level (hereinafter referred to as V) where the input voltage is set by the constant voltage circuit 120._refThe control signal CGCOM is set to be cut off when the voltage is abbreviated below.
[0018]
  2 is a resistor, one end is the anode of the battery 1 and the other end is a positive terminal of the comparator 4 described later.veryConnected to input terminal. 3 is a capacitor, one endButThe other end is connected to the positive input terminal of the comparator 4 described later.ButConnected to the cathode of battery 1. This capacitor 3 adds hysteresis to the input. Reference numeral 4 denotes a comparator. Here, the output is an open collector type comparator. The other end of the resistor 2 and one end of the capacitor 3 are connected to the positive input terminal of the comparator 4, and the power supply voltage cutoff level (V) that is the output of the constant voltage circuit 120 is connected to the negative input terminal._refVoltage) is input. The output is connected to one end of the resistor 47 and the input of the active element 37.
[0019]
  The specific operation isFirstPower supply voltage cutoff level set by constant voltage circuit 120(V_refVoltage)Is input to the negative input terminal of the comparator 4.
[0020]
  The positive input terminal of the comparator 4 detects the voltage of the battery 1 via the resistor 2. Start boosting operation in this stateDoIn this case, the oscillation start signal CGCOM signal is changed from “LL” to “HL” by the control circuit 125. The input of the active element 37 becomes HL.
[0021]
  After that, from the CGST terminal of the control circuit 125,From “OPEN” (open) to “LL” for a momentChangeOne-shot signal through resistor 61Then outputAnd oscillation starts. As a result, the base current of the PNP transistor 81 is drawn.
[0022]
  Base of PNP transistor 81 of current-voltage conversion means 48CurrentIs pulled, transistor81Is on and V_ccA current flows from the emitter connected to the voltage terminal to the collector, and a voltage is generated across the resistor 84.
[0023]
  Then, since the inputs of the active element 37 both become HL, the output of the active element 37 is determined to be HL. As a result, the FET 13 is turned on, and the current of the battery power source 1 is changed to the terminal e of the primary winding of the oscillation transformer 12.fPNP transistor connected to a terminal h of the secondary winding of the transformer 12 while a current corresponding to the primary side flows and a voltage corresponding to the winding ratio is generated on the secondary side. Subtract 81 base current.
[0024]
  V_ccTransformer from constant voltage source via emitter-base of PNP transistor 8112Then, a current is supplied to the main capacitor 20 through the high-voltage rectifier diode 15. As the current increases, the magnetic saturation of the transformer 12OccurThe current decays rapidly. As a result, the base current of the PNP transistor 81 is not drawn, and a current proportional thereto flows between the emitter and collector of the PNP transistor 81, and the voltage is lowered by the resistor 84 (voltage-current conversion), whereby the output of the active element 37 becomes LL. Thus, the FET 13 is turned off because the gate of the FET 13 becomes LL, and the power supply of the battery power supply 1 to the terminal e of the primary winding of the oscillation transformer 12 is cut off.
[0025]
  However, since the secondary current of the transformer 12 oscillates, the voltage across the resistor 84 in the current-voltage conversion means 48 rises again, and both the inputs of the active element 37 of the control means become HL.WhenThe output of the active element 37 of the control means is determined to be HLTheFET13Is turned on and the current of the battery power source 1 is changed to the terminal e of the primary winding of the oscillation transformer 12.fCurrent flows through the FET 13 to the drain-source of the FET 13 and the current again flows to the primary side, repeating the same oscillation as described above.The This, Main capacitor20As the charge accumulates, the voltage rises.
[0026]
  At this time, the voltage of the power supply 1 is suddenly lowered by turning on the FET 13, but the V of the input of the comparator 4_refUp to voltagePower supplyWhen the voltage of 1 drops, the comparator 4 is inverted from the open state to LL, the output of the charge control signal CGCOM of the control circuit 125 is lowered, and one of the inputs of the active element 37 becomes LL, so that the output becomes LL. The FET 13 is turned off and oscillation stops.
[0027]
  When the oscillation stops, the voltage drop of the power source 1 stops and the voltage is restored. The voltage of the power supply 1 is restored and the input V of the comparator 4_refWhen the voltage is exceeded, the output of the comparator 4 is inverted from LL to open, the input of the active element 37 becomes HL, the output becomes HL again, and the FET 13 is turned on to oscillate. By repeating this, the power supply voltage becomes a constant voltage.(V _ref Voltage)I try not to be below.
[0028]
[Problems to be solved by the invention]
However, in the conventional strobe device described above, the charging current flowing through the main capacitor 20 is such that the secondary winding terminal g of the oscillation transformer 12, the main capacitor 20, the constant voltage circuit 120, the emitter of the transistor 81 to the base, the oscillation transformer 12 It flows in the loop of the terminal h of the secondary winding.
[0029]
Since this current flows through the constant voltage circuit 120, the constant voltage circuit 120 needs a large current capability. In a general strobe, when the power supply voltage is 6 V, an average current of about 6 A is supplied from the battery. When there is no loss, a current 1 / (the secondary winding ratio of the transformer) of the transformer flows on the secondary side of the transformer.
[0030]
I b = Ic / n, I b is a secondary current, I c is a primary current, and n is a winding ratio.
[0031]
If the transformer turns ratio is 100 (n), the supply capability of about 60 mA can be explained roughly. Furthermore, when the current consumption of other control circuits is taken into account, there is a drawback that a larger current supply capability is required.
[0032]
An object of the invention according to the present application is to provide a strobe device capable of suppressing the current supply capability of an auxiliary power source.
[0033]
  The present inventionIs the strobe deviceIsonceA transformer having a winding and a secondary winding;Switch between conducting and non-conducting states, in conducting stateFor transformer primary windingFrom power batteryCurrentA transistor,Output from transformer secondary windingAtWith capacitor to be charged,Secondary winding of transformerandCapacitorA diode provided on the current path when charging the capacitor, and one end connected to the output side of the diode and the other endVoltageSuppliedWith circuit membersWhen the charging current of the capacitor flows, the output of the circuit member decreases by a value corresponding to the voltage drop due to the diode compared to when the charging current does not flow, and the transistor has a charging current flowing It becomes a conduction state by the output of the circuit member ofSaturation of transformer magnetic fluxAtWhen the charging current dropsA non-conducting state is established by the output of the circuit member.
[0040]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
1 to 4 show a first embodiment of the present invention.
[0041]
  FIG. 1 shows a circuit diagram of a strobe device.In this embodimentThe constant voltage circuit and the control circuit are the same as those shown in FIG. 6, and only the terminal names are given and the illustration is omitted.
[0042]
  In FIG. 1, 1 is a battery as a power source, and 30 is a power supply capacitor, which are connected to the battery 1 in parallel. 2 is a resistor, 3 is a capacitor, 4 is a comparison circuit, and a series circuit of a resistor 2 and a capacitor 3 is connected in parallel to the battery 1.Series circuitThe potential at the middle point is input to the (+) input of the comparison circuit 4 shown in the figure. The comparison circuit 4 is an open collector comparator.
[0043]
Reference numeral 5 denotes a resistor, 6 denotes a resistor, 8 denotes a transistor, the resistor 6 is connected between the base and the emitter of the transistor 8, and the resistor 5 is connected to limit the base current of the transistor 8. 7 and 9 are resistors, 10 is a NOR gate circuit, and resistors 7 and 9 are connected as pull-up resistors for NOR gate input.
[0044]
A resistor 11 is connected as an input protection resistor of the NOR gate circuit 10. Reference numeral 12 denotes an oscillation transformer, 13 denotes an FET, and 14 denotes a gate pull-down resistor of the FET 13.
[0045]
  Of the primary winding P of the oscillation transformer 12one endIs the positive electrode of battery 1 which is the power source,The other endIs connected to the drain of the FET 13, and the source of the FET 13 is connected to the negative electrode of the battery 1 as a power source.
[0046]
15 is a high voltage rectifier diode, 16 is a rectifier, 17 is a voltage detection circuit, 18 is a trigger circuit, 19 is a discharge tube, 20 is a main capacitor, and the secondary winding S of the oscillation transformer 12 is connected to the high voltage rectifier diode 15, A series circuit of the main capacitor 20 and the rectifying element 16 is connected.
[0047]
The voltage detection circuit 17 is connected in parallel to the main capacitor 20 so as to detect the voltage of the main capacitor 20. The trigger circuit 18 is connected in parallel to the main capacitor 20 and is configured to give a high-pressure trigger pulse to a discharge tube 19 connected in parallel to the main capacitor 20 by a light emission signal from a camera control circuit shown in FIG. Has been. Reference numerals 21 and 22 denote power supplies from the camera control circuit, and reference voltages V, respectively._ref Auxiliary power supply V_ccIs shown.
[0048]
  Figure 2 shows the strobecircuit1 shows a control circuit of a camera including a microcomputer for operating 100.
[0049]
In FIG. 2, reference numeral 120 denotes a constant voltage circuit shown as a block._ccControlled via the EN terminal, the reference voltage V_refAnd power supply V of each circuit block_ccSupply.
[0050]
121 is a photometric circuit shown as a block, 122 is a switch circuit shown as a block, and a power source V_ccAnd the change of each switch is transmitted to the control circuit 125. Reference numeral 123 denotes a shutter circuit shown as a block, and reference numeral 124 denotes a display circuit shown as a block, which displays necessary information on a display unit such as an LCD.
[0051]
  126 is a distance measuring circuit shown as a block, 127 is a temperature detection circuit shown as a block, and 128 is a film sensitivity shown as a block.DetectionThis is a circuit and transmits information necessary for photographing to the control circuit 125 via each terminal. Reference numeral 129 denotes a lens driving circuit shown as a block. Reference numeral 130 denotes a film driving circuit shown as a block, which feeds the film under the control of the control circuit 125.
[0052]
Next, the operation of the strobe device of FIG. 1 together with the operation of the control circuit will be described based on the flowchart of FIG. Here, it is assumed that the power supply on the camera control circuit side is already turned on, and in this state, the camera control circuit 125 is in the low consumption mode and the operation is stopped.
[0053]
When the power switch in the switch circuit 122 interlocked with a member such as a lens barrier of the camera is turned on, the control circuit 125 of the microcomputer starts to operate. The control circuit 125 supplies V to the constant voltage circuit 120._ccA signal is applied through the EN terminal, and the constant voltage circuit 120 is connected to the reference voltage V_refAnd power supply V to each circuit_ccSupply.
[0054]
  The subsequent operations are shown in the flowchart of FIG.TheThe description will be given with reference.
[0055]
First, initial setting necessary for the microcomputer is performed (S1). Next, the power supply V is supplied to the switch circuit 122._ccIs supplied (S2).
[0056]
In this state, when the first switch SW1 (not shown) is turned on by the first stroke operation (half-press operation) of the release button (S3), a predetermined counter is set to the initial state (S4), and further the battery check Is performed (S5), and it is determined whether or not a power supply state necessary for photographing by the camera is present (S6).
[0057]
  If the power is insufficient (NG), the process returns to S2. When the power supply is sufficient (OK), a signal is given to the terminal AFC, and the distance measuring circuit 126 is operated to shoot the subject.UntilIs measured (S7). The distance measurement information is given to the control circuit 125 from the AFD terminal.
[0058]
Subsequently, the luminance of the subject is measured, and this information is given to the control circuit 125 via the terminal SP (S8). Then, it is determined from this luminance data whether the subject luminance is brighter or darker than the predetermined luminance (S9), and if the luminance is low, the process proceeds to the flash mode (S10).
[0059]
Here, the operation of the strobe device will be described with reference to the flowchart shown in FIG. In this mode, a charge prohibition timer, which is a timer for terminating charging, is activated (S21). This timer is generally about 10 to 15 seconds.
[0060]
Next, in order to start oscillation, a high level signal is given from the camera control circuit via the terminal a (A / D COM), and a low level signal is given to the terminal b (CGST) for a predetermined time. This low level signal is a pulse signal of several + μsec. Since the high level signal applied to the terminal a becomes the base current of the transistor 8 through the resistor 5, the transistor 8 becomes conductive.
[0061]
For this reason, the auxiliary power supply V_ccFurther, one input terminal of the NOR circuit 10 that has been pulled up via the resistor 7 becomes low level. Further, since the other input also becomes low level due to the one-shot signal in which the terminal b becomes low level for a predetermined period, the output of the NOR circuit 10 becomes high level and gives a potential to the resistor 14.
[0062]
Since this potential is connected to the gate terminal of the FET 13, the FET 13, which is an oscillation transistor, receives the gate drive voltage and becomes conductive. Due to the conduction of the oscillation transistor FET 13, current flows from the battery 1 to the primary winding P of the oscillation transformer 12, so that inductive power is generated in the secondary winding S, and the high-voltage rectifying diode 15, the main capacitor 20, current flows through the loop of the rectifying element 16.
[0063]
  For this reason, since the cathode potential of the rectifying element 16 is about −0.7 V, a current flows from the auxiliary power source through the resistor 9 and the resistor 11, in other words, the rectifying element 16 flows from the anode toward the cathode. A part of the charging current of the capacitor 20 is V_ccThe current is shunted through the power source, the resistor 9 and the resistor 11. Here, the resistance values of the resistor 9 and the resistor 11 are set to R₉And R₁₁Then approximately
      (V_cc+0.7) × (R₁₁/ R₉+ R₁₁)~0.7
connection of(Relationship that generally matches the cathode potential of the rectifying element 16)It is desirable to select the resistance value with. That is, if the potential generated by the current shunting through the resistor 11 is equal to the operating potential during the operation of the rectifying element 16, the gate voltage connected to the resistor 11 of the NOR circuit 10 is canceled out. That is, when the resistor 11 is not provided, the input gate becomes negative due to the operating voltage of the rectifying element 16.Therefore, the resistor 11 isIt works as a protective element to prevent malfunctions.
[0064]
  It is also possible to replace the resistor 11 with a diode.ButThe cathode is connected to the cathode side of the diode 16 to the resistor 9. thisBySimilar to the case of using the resistor 11,It is also possible to cancel the operating voltage of the diode 16.
[0065]
Therefore, since the potential connected to the middle point of the resistors 9 and 11 becomes low level when the charging current flows, the low level can be maintained even when the low-level pulse for the predetermined period to the terminal b ends. I can do it.
[0066]
Here, as described above, the control circuit output of the camera connected to the terminal b is in the form of an open collector or an open drain. When conduction of the FET 13 which is an oscillation transistor continues and the magnetic flux of the core of the oscillation transformer 12 is saturated, a back electromotive force is generated, the charging current to the main capacitor 20 is lost, and the current merged with the resistors 9 and 11 is lost. Therefore, one of the inputs of the NOR circuit 10 becomes a high level, and the output of the NOR circuit 10 becomes a low level.
[0067]
  Noah circuit10When the output becomes low level, the gate charge of the FET 13 which is an oscillation transistor becomes low level, and the FET 13 becomes non-conductive instantly. At this time, the rectifying element 16 is reverse-biased by the back electromotive force and by the capacitance of the high-voltage rectifying diode 15, and the auxiliary power supply voltage is generated during the period in which the back electromotive force is generated.V _cc A higher potential is generated.
[0068]
  For this reason, a capacitor may be connected in parallel with the rectifying element 16, or the rectifying element.AsIt is also possible to protect the input terminal of the NOR circuit 10 by using a Zener diode having a slightly higher potential than the auxiliary power supply.
[0069]
  Of the oscillation transformer 12When the magnetic flux of the core decreases and the back electromotive force reverses to the forward oscillating voltage, the rectifier is again16As a result of the bias current being reduced and the cathode potential being lowered, a current flows through the resistors 9 and 11 as described above, the input of the NOR circuit 10 becomes low level, the FET 13 is turned on again, and this is repeated to oscillate and cause oscillation. The capacitor 20 stores the boosted charge.
[0070]
While charging is performed in this manner, in the sequence of FIG. 4, it is determined whether or not the charging voltage of the main capacitor 20 has increased and a charging completion signal has been input from the voltage detection circuit 17 via the terminal c (CGUP) (S23). ).
[0071]
  Here, when the charge completion signal is not input, it is confirmed whether it is within the charge prohibition timer period (S24), the charge completion signal is not input and the charge prohibition timer is counted as an end count value (charge prohibition timer count up). ) Is stopped, the signal supplied via the terminal a is stopped, the step-up operation of the strobe is stopped (S27), the charge NG flag that is not fully charged is set (S28), and then, as shown in FIG. FlowchartS11Return to. If the charge completion signal is not input and the charge prohibition timer has not reached the end count value, the process returns to S23.
[0072]
  On the other hand, when the charge completion signal is input in S23, the signal given to the terminal a is stopped (S25), and the charge completion flag is set and the flowchart of FIG.S11Return to (S26).
[0073]
  If it is determined in S9 of the flowchart of FIG. 3 that the subject brightness is brighter than the predetermined value, whether or not the second switch SW2 (not shown) that is turned on by the second stroke operation (full pressing operation) of the shutter button is turned on. Is determined (S12). When the second switch SW2 is on, focus adjustment is performed by controlling the lens driving circuit 129 based on the distance measurement data in S7 (S13).
[0074]
  Further, the shutter aperture is controlled via the shutter circuit 123 according to the brightness of the subject obtained in S8 and the condition based on the ISO sensitivity data.Light emissionIf it is necessary to perform shutter control using distance measurement data and ISO sensitivityWhileThe strobe is caused to emit light at a predetermined aperture value (S14).
[0075]
The strobe light is emitted by applying a high level signal to the terminal d (TRIG) in FIG. When a high level signal is applied to the terminal d, a high-voltage pulse voltage is generated at the output of the trigger circuit 18 and applied to the trigger electrode of the discharge tube 19, thereby exciting the discharge tube 19. Due to this excitation, the impedance of the discharge tube 19 is reduced at once, and the charging energy of the main capacitor 20 is discharged and converted into light energy to illuminate the subject. When a strobe is used, 1 is set in the flash flag (FAL).
[0076]
  ShuttercloseThen, the lens at the focal position is returned to the initial position (S15). And after the end of shooting,The film driving circuit 130 is controlled to wind up the film by one frame (S16).
[0077]
  Next, it is confirmed whether “1” is set in the flash flag indicating that the strobe is used (S17). When the flag “1” is set, the flash mode is set and S10 is set.(Subroutine shown in FIG. 4)In the same manner as described above, the main capacitor 20 is charged (S18), and a series of photographing sequences is completed. If the strobe is not used, the process returns to S2 without passing through S18, and a series of photographing sequences is completed.
[0078]
  Here, the comparison circuit 4, which is an open collector type comparator, detects the voltage of the battery 1 via the resistor 2, and the reference voltage V provided from the constant voltage circuit 120 of the camera._refCompared to the reference voltage V_refIn the following cases, since the output is set to the low level, the base current of the transistor 8 is bypassed and becomes non-conductive, the input of the NOR circuit 10 is pulled up by the resistor 7, and as a result, the output is inverted to the low level, and the gate of the FET 13 Stop supplying the potential. Due to this supply stop, the FET 13 becomes non-conductive. For this reason, the potential of the battery 1 rises again, and the comparison circuit4The (+) input rises and the output opens again, and the battery voltage is the reference voltage V_refThe following voltage is prevented. Here, the capacitor 3 gives some time hysteresis by the time constant of the resistor 2, and constitutes a time constant of about 1 to 2 μsec. Note that the comparison circuit 4 may be an element having voltage-like hysteresis.
[0079]
Where reference voltage V_refIs set to a level that can guarantee the auxiliary power supply capability. If the auxiliary power supply includes a switching regulator, the auxiliary power supply is set to a potential level that can guarantee the operation of the switching regulator.
[0080]
Second embodiment
FIG. 5 shows a second embodiment of the present invention.
[0081]
In FIG. 5, the same reference numerals are given to components having functions equivalent to those of the constituent elements shown in FIG. 1.
[0082]
This configuration is a push-pull type DC / DC converter, and additional components will be described below with respect to the first embodiment. In this embodiment, in addition to the NOR circuit (first NOR circuit) 10 shown in the first embodiment, a second NOR circuit 25 is provided, and in addition to the FET 13 (first FET 13), the second NOR circuit 25 is provided. An FET 27 or the like is provided.
[0083]
  23 is a resistor, 24 is a resistor, 25 is a NOR circuit, and one of the inputs of the NOR circuit 25 is connected to the auxiliary power source V by the resistor 23._ccHas been pulled up from. The resistor 24 is a NOR circuit similar to the resistor 11 described above.25This is the input protection resistance.
[0084]
Reference numeral 26 denotes a resistor, and reference numeral 27 denotes a second FET which is an oscillation transistor. The resistor 26 is connected as a pull-down resistor between the gate and source of the second FET 27.
[0085]
  The oscillation transformer 12 has a primary winding P connected to the oscillation transformer of FIG.₁, P₂Push-pull type transformer pulled out asIs.
[0086]
  28 and 31 are backflow prevention diodes, 29 and 32 (corresponding to the rectifying element 16 in FIG. 1) are rectifying elements, and a series circuit of the diode 28 and the rectifying element 29 is a secondary winding S of the oscillation transformer 12.One end ofIn addition, a series circuit of the diode 31 and the rectifying element 32 is formed of the secondary winding S.The other endConnected toThe diodes 28 and 31 and the rectifier elements 29 and 32Each midpoint is connected to one input of the second NOR circuit 25 via the resistor 24 and to one input of the first NOR circuit 10 via the resistor 11.
[0087]
  Reference numeral 30 denotes a second high-voltage rectifying diode, which is a secondary winding of the oscillation transformer 12.The other endIt is inserted between the main capacitors 20.
[0088]
Since the camera sequence is similar to the flowcharts shown in FIGS. 3 and 4, the description of the camera shooting sequence is omitted here and only the operation of the strobe device is described.
[0089]
When the camera control circuit determines that the strobe needs to be charged, a high level signal is applied to the terminal a (A / DCOM). As a result, a base current flows through the transistor 8 via the resistor 5 and the transistor 8 becomes conductive, and one of the input terminals of the first NOR circuit 10 and the second NOR circuit 25 becomes low level.
[0090]
  At the same time, a low level signal for a predetermined time is input to the terminal b (CGST). Accordingly, since the first NOR circuit 10 has both inputs at a low level, the output is at a high level, and a gate potential is applied to the first FET 13. As a result, the first FET 13 becomes conductive. By this conduction, the primary winding P of the oscillation transformer 12₂A current flows from the battery 1. This current causes the secondary winding S to have a first high-voltage rectifying diode 15, a main capacitor 20,Rectifier elementCurrent flows in a loop through 32 and the diode 31.
[0091]
  Due to this current, the cathode potential of the rectifying element 32 is reduced by the operating voltage, and a part of the charging current of the main capacitor 20 which is the output current of the oscillation transformer 12 is sub-power source V._ccFurther, the current flows through the resistor 9 and the resistor 11. This resistance value is assumed to be auxiliary power supply V_ccIs 5V and resistor 9 is 22KΩ, resistance11Is 3. About 3KΩ, auxiliary power supply V_ccThe current shunted through is about 230 μA.
[0092]
  With this current, the input connected to the midpoint of the resistors 9 and 11 of the first NOR circuit 10 maintains the low level. Here, the low level of the terminal b at the start of oscillationPredeterminedThe time is a time during which the secondary output of the oscillation transformer 12 is stably generated. A time of several tens of microseconds is sufficient, and the low level is maintained by the secondary output.
[0093]
When the conduction of the first FET 13 continues and the magnetic flux in the core of the oscillation transformer 12 is saturated, the charging current disappears and a back electromotive force is generated. When the charging current disappears, the forward bias current of the rectifying element 32 disappears, and the first NOR circuit 10 becomes high level because the input becomes high level, and the first FET 13 is stopped instantaneously.
[0094]
Here, the back electromotive force flows through a loop of the high voltage rectifier diode 30, the main capacitor 20, the rectifier element 29, and the diode 28, the potential of the anode of the rectifier element 29 is lowered by the operating voltage, and a part of the charging current is auxiliary power supply V._ccFrom the first through the resistors 23 and 24, one of the inputs of the second NOR circuit 25 becomes low level. Here, since the other input is connected to the collector of the transistor 8 and is already at the low level, both the inputs of the second NOR circuit 25 are at the low level and the output is at the high level. FET 27 is turned on. Since the current flowing through the rectifier 32 is stopped in the first FET 13, the output of the first NOR circuit 10 is at a low level.
[0095]
  Conduction of the second FET 27 is performed, and a current flows through the primary winding P 1 of the transformer 12, and this current causes a diode 30, a main capacitor 20,Rectifier element29And diodeCurrent flows in a loop through 28. Thereafter, when the magnetic flux of the core of the oscillation transformer 12 is saturated, the second NOR circuit 25 becomes a low level as in the case of the first NOR circuit 10, and the second FET 27 is stopped instantaneously. Here, the starting power is the diode 15,mainCapacitor 20,Rectifier element32,diodeThe output of the first NOR circuit 10 is shifted to a high level. By this operation, the second FET 27 and the first FET 13 are alternately turned on and off repeatedly to perform an oscillation operation, and the boosted charge is stored in the main capacitor 20. Since the subsequent operations are the same as those in the first embodiment, a description will be given.Omit.
[0096]
Third embodiment
FIG. 7 shows a third embodiment.
[0097]
  101 is a resistor, 102 is a diode, and the others are conventional examples.(Fig. 6)Is equivalent to
[0098]
In the operation of this embodiment, the charging loop to the main capacitor 20 is separated into a loop between the base and emitter of the transistor 81 and the resistor 101 and a loop bypassing to the diode 102, and the current through the constant voltage circuit 120 is supplied. It is greatly reduced.
[0099]
  For example, the voltage of the constant voltage circuit 120 is set to V_regThen, the current i flowing through the constant voltage circuit 120 is
  i = (V_reg+ V_F-V_BE) / R₁₀₁
    V_F Operating voltage of the diode 102
    R₁₀₁ ; Resistance value of the resistor 101
    V_BEThe gate drive voltage of the transistor 81
And R₁₀₁ 10KΩ, V_regIf the voltage is about 5V, the constant voltage circuit will be about 500μA.120Output ofsuppressIt becomes possible.
[0100]
【The invention's effect】
  As explained above, according to the present invention,,SimpleThe auxiliary power supply can be kept low with a simple configuration.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a strobe device showing a first embodiment of the present invention.
FIG. 2 is an electric circuit diagram of a camera connected to the strobe device of FIG.
FIG. 3 is a flowchart showing the operation of FIG. 2;
4 is a flowchart showing the operation of the strobe device of FIG. 1. FIG.
FIG. 5 is a circuit diagram of a strobe device showing a second embodiment of the present invention.
FIG. 6 is a circuit diagram of a conventional strobe device.
FIG. 7 is a circuit diagram of a strobe device showing a third embodiment of the present invention.
[Explanation of symbols]
1 battery
4 Comparison circuit
10, 23, 26 NOR circuit
13, 28, 13 FET
16, 29, 32, 102 Rectifier
15,30 High voltage rectifier diode
19 Discharge tube
20 Main capacitor

Claims (5)

A transformer having a primary winding and a secondary winding,
A transistor that switches between a conducting state and a non-conducting state, and causes a current from the power supply battery to flow through the primary winding of the transformer in the conducting state ;
A capacitor charged by the output from the secondary winding of the transformer,
A diode connected to the secondary winding of the transformer and the capacitor , and provided on a current path during charging of the capacitor;
One end connected to the output side of the diode, and a circuit member to which a predetermined voltage is supplied to the other end,
The output of the circuit member decreases by a value corresponding to a voltage drop by the diode as compared to when the charging current does not flow due to the charging current of the capacitor flowing,
The transistor includes: the rendered conductive by the output of the circuit member, thus non-conducting state to an output of said circuit member when said charging current drops in the transformer flux saturation when the charging current is flowing a flash device characterized by comprising. The strobe device according to claim 1, wherein the diode has an anode connected to the capacitor and a cathode connected to the secondary winding. The strobe device according to claim 1, wherein the circuit member is a voltage dividing resistor. The circuit member is a series circuit of a resistor to which the predetermined voltage is supplied and a diode having an anode connected to the resistor and a cathode connected to an output side of the diode. Or the strobe device described in 2. A logic circuit to which an output of the circuit member is input ;
The logic circuit receives the output of the circuit member when the charging current is flowing and outputs a first signal, and the circuit member when the charging current decreases due to saturation of the magnetic flux of the transformer To output a second signal,
5. The strobe device according to claim 1, wherein the transistor is turned on by the first signal and turned off by the second signal. 6.

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