JPS61221732A - Power supply circuit for camera - Google Patents

Abstract

PURPOSE:To prevent malfunction of camera control and deterioration of function by supplying a specific source voltage to a camera control circuit even while a main capacitor as a strobe light emission source is charged. CONSTITUTION:When the main capacitor C5 is charged with the voltage of a high voltage line l, the voltage at the connection point between a low voltage coil T1L and the collector of a transistor (TR) Q3 becomes a pulse signal which is about 20V high on the basis of a potential nearly equal to the potential of a ground line l0. this voltage V1 is applied to a smoothing capacitor C2 through the anode and cathode of a diode D2 and a resistance R8, made constant through a TR Q5 which is turned on with a charge control signal S3 and a Zener diode ZD, and applied to a system controller 20 and the plus power source input terminal + of a control circuit 30. Consequently, a DC-DC converter 10 is put in operation to supply electric power to the system controller 20 and control circuit 30 without any voltage drop even while the main capacitor C5 is charged.

Description

Detailed Description of the Invention (Technical Field) The present invention provides a common power source for supplying power to a booster circuit that charges a main capacitor serving as a strobe light source and to a camera control circuit such as a system controller IC. This invention relates to a camera power supply circuit that is powered by batteries.

(Prior Art) In recent years, so-called fully automatic cameras, which automatically perform operations such as object distance adjustment, exposure control, film winding control, film rewinding control, and strobe light emission, have been put into practical use. In such cameras, the control of the strobe built into the camera body is also automated. In other words, automatic charging of the main capacitor that serves as the strobe light source, automatic flash firing under shooting conditions that require flash firing, monitoring of the charging voltage to the main capacitor, and stopping charging when the main capacitor is fully charged, etc. Control is automated.

Therefore, camera control circuits such as system controller circuits for controlling such automated camera systems are always kept in a standby state, even when the main capacitor is being charged. Charging is controlled based on a charging control signal sent from the camera control circuit.

The main capacitor is charged by operating a booster circuit that boosts the voltage of the shared power supply battery, which is about several volts, to a voltage of about 250 to 300 volts. The current consumption of this booster circuit is a large current of about several amperes at the beginning of charging the main capacitor, and then becomes smaller as the charging progresses. Therefore, due to the large current at the beginning of charging, the terminal voltage of the common power supply battery drops significantly, and the voltage supplied to the camera control circuit connected to this common power supply battery drops significantly. For example, if the common power battery has a nominal voltage of 6V
When a lithium battery is used, the voltage of the battery drops to 2 to 3 V at the initial stage of charging.

For this reason, there is a risk that a camera control circuit such as a system controller may cause program runaway or malfunction in the initial stage of charging.

To solve this problem, it has been proposed that the main capacitor, which is the strobe light source, should not be charged while the voltage of the shared power supply battery is being supplied to the camera control circuit (Unexamined Japanese Patent Publication No. (See Publication No. 52-127232).

In addition, for cameras that have the function of imprinting data such as date, time, etc. on film by firing a strobe, it has also been proposed that the operation of the booster circuit be stopped or nearly stopped during the data imprinting operation. (Refer to Japanese Unexamined Patent Publication No. 54-51822).

Furthermore, it has been proposed to prohibit charging of the main capacitor, which is the strobe light source, while the shutter blade is open (see Japanese Patent Publication No. 55-10051).
.

In such conventional camera power supply circuits, the main capacitor that serves as the strobe light source is charged at a time when the camera control circuit such as the system controller will not malfunction due to a drop in the power supply battery voltage due to charging. ing.

Therefore, the camera control circuit cannot be operated reliably during the charging operation of the main capacitor, resulting in a decline in functionality. For example, in a camera having an A1 function in the camera control circuit, the A1 function cannot be activated immediately after flash photography, and the AP function must wait until the main capacitor is fully charged, resulting in a decrease in photography efficiency.

(Objective) The object of the present invention is to be able to supply power at a predetermined voltage to the camera control circuit even when the main capacitor that serves as the strobe light source is being charged, thereby preventing camera control from malfunctioning or functional deterioration. It is an object of the present invention to provide a power supply circuit for a camera that does not cause any problem.

(Summary) The camera power supply circuit according to the present invention charges a main capacitor that serves as a strobe light source by increasing the voltage of a shared power supply battery. The present invention is characterized in that a voltage is applied to the power input terminal of the camera control circuit in parallel with the output of the shared power supply battery to prevent a drop in the power supply voltage of the camera control circuit.

(Example) First, a first example of the present invention will be described using FIGS. 1 to 3.

In Figure 1, the DC-DC converter O is a booster circuit for charging the strobe main capacitor C5.
A shared power supply battery E, which serves as a power supply for a camera control circuit comprising a system controller 20, a control circuit 30 for focus detection and automatic exposure, and the like, has its negative terminal grounded and connected to a ground line g. The positive electrode is connected to the low voltage line IIL. Both lines go, f
IL is connected to the power input terminal of the DC-DC converter O, and a series circuit of a capacitor C1 and a resistor R1 is connected between both inputs DL and 110.

In addition, a resistor R2 and a resistor R are connected between both IIL and flo.
3 and the collector-emitter series circuit of the NPN transistor Q2 are connected, and the emitter-collector of the PNP transistor Ql, the emitter-collector of the PNP transistor Q4, and the series circuit of the resistor R5 are connected. Low voltage coil of step-up transformer T “IL and NP”
A series circuit of collector and emitter of an N-type transistor Q3 is connected.

The connection point between the capacitor C and the resistor R1 is connected to the base of the transistor Q4, and the collector of the transistor Q is connected to the transistor Q through the resistor R6.
It is connected to the base of 3.

The connection point between the low voltage coil T1L of the step-up transformer T and the collector of the transistor Q3 is connected to the low voltage line p via the anode and cathode of the diode D and the resistor R9 in sequence.
Connected to L. One end of the high voltage coil Ti1l of the step-up transformer Tt is connected to the base of the transistor Q4, and the other end is connected to the high voltage line '11 as the output voltage line of the DC-DC converter O via the anode and cathode of the diode D1. It is connected.

The contact point between the cathode of the diode D and the resistor R9 is:
It is connected to the smoothing capacitor C2 via the resistor R8, and also to the positive voltage power input terminal of the system controller 20, and further connected to the positive voltage power input terminal + of the control circuit 30.

The other end of the capacitor C is connected to the ground line go and to the negative voltage power input terminals of the system controller 20 and the control circuit 30, respectively. This system controller 20 controls the shutter of the camera to perform exposure control and perform signal processing such as in-focus point detection, and is connected to the control circuit 30 via a path line.

Further, this system controller 20 is configured to receive a charging completion detection signal S, a light emission trigger signal S2, and a charging control signal S3.

The above high voltage line g and ground line g. A charging completion indicating circuit consisting of a neon lamp NE for indicating charging completion and a series circuit of a resistor R1° and a resistor R1□ is connected between and. The connection point O between this resistor R and resistor R1□ is connected to the base of the NPN transistor QB,
The collector of the transistor is supplied with the charging completion detection signal S1 from the system controller 20 described above, and the emitter is connected to the ground line go.

Also, the above-mentioned high voltage line g and ground line g. A series circuit consisting of a resistor R, a trigger capacitor C4, and a low-voltage coil "2L" of a trigger transformer T is connected between them, as well as a flash discharge tube XL.
One end of the high voltage coil T2H is the ground line g. The other end of the flash discharge tube XL is connected to the electrode. Further, between the high voltage line g and the ground line fIo, there is connected a main capacitor C5 which serves as a light source for the flash discharge tube XL.

The connection point between the resistor R and the trigger capacitor C4 is connected to the anode of the trigger thyristor SCR, and the cathode of the trigger thyristor SCR is connected to the ground line j! connected to o. The gate of this trigger signal SCR is connected to the ground line g through a parallel circuit of a capacitor C and a resistor R12.

It is connected to the system controller 20 as well as to the system controller 20, and the light emission trigger signal S2 sent from the system controller 20 is supplied thereto.

Further, the charging control signal S sent from the system controller 20 is supplied to the base of the transistor Q2 via the resistor R4, and is also supplied to the base of the transistor Q5 via the resistor R. It also looks like this.

Therefore, the negative electrode voltage of the shared power supply battery E is the ground line fI
It is applied to each negative power input terminal of the system control roller 20 and the control circuit 30 through the power supply terminal 0. On the other hand, common power supply battery E
The positive voltage is applied to the positive voltage power input of the system controller 29 through the path of the low voltage line fIL -> the low voltage coil TIL of the step-up transformer T -> the anode/cathode of the diode D2 -> the resistor R8, and the path of the low voltage line p - the resistor R9 - the resistor R8. Applied to each end. Therefore, the voltage of the shared power supply battery E is applied to both ends of the capacitor C2, and is applied to the respective power input terminals of the system controller 20 and the control circuit 30, and the voltage of the shared power supply battery E is applied to the power input terminals of the system controller 20 and the control circuit 30, respectively. Operating power is supplied to the control circuit 30.

When the charge control signal S3 sent from the system controller 20 goes to H level as shown in FIGS. 2 and 3 in order to charge the main capacitor C5 prior to flash photography, the transistor Q2 is turned on and the transistor Q5 turns on.

When transistor Q2 is turned on, the base potential of transistor Q2 is lowered and transistor Q1 is turned on. When the transistor Ql is turned on, the collector potential of the transistor Q4 rises, and a base current flows through the base of the transistor Q4 due to the resistor Rt, so that the transistor Q4 is turned on. Along with this, the base potential of transistor Q3 rises and transistor Q3 is turned on. Therefore, low pressure line gL→
A current ■ flows in the direction of arrow i in the low voltage coil TIL through the path of low voltage coil TIL→collector/emitter of transistor Q3→ground line go. This current 1 is the low voltage coil T
Since the IL impedance is very close, a large value (several A
2), and the voltage vDD of the shared power supply battery E rapidly drops as shown in FIGS. 2 and 3. Low voltage coil TIL
When the magnetic flux of the step-up transformer T1 is saturated due to the current flowing through the high-voltage coil T111, the current flowing through the high-voltage coil T111 rapidly decreases, and the current flowing through the high-voltage coil TIH becomes 0, which generates a back electromotive force in the high-voltage coil TIH and increases the voltage of the transistor Q4. Transistor Q is turned off to bring the base to a negative potential. When the transistor Q4 is turned off, the base potential of the transistor Q3 decreases and the transistor Q3 is turned off. Then, the current flowing in the direction of arrow i flowing through the low voltage coil TIL is abruptly cut off, so the low voltage coil TIL
A back electromotive force is generated in the direction of arrow i.

By repeating this operation, a voltage of about 250 to 300V is generated on the high voltage line 'I+,
This voltage charges the main capacitor C5.

At this time, the voltage V1 at the connection point between the low voltage coil TIL and the collector of the transistor Q3 is connected to the ground line g as shown in FIG. (a potential increased by the on-voltage of transistor Q3 from the potential of ground line J7o)
The pulse voltage signal is a pulse voltage signal with a pulse height of about 20V with reference to .

Such a voltage V1 is applied to the smoothing capacitor C2 via the anode/cathode of the diode D2 and the resistor R8, and is made constant by the transistor Q5, which is turned on by the charge control signal S3, and the Zener diode ZD. , system controller 20. Control circuit 3
0 is applied to the positive power input terminal. For this purpose, DC-
Even while operating the DC converter 10 and charging the main capacitor c5, the system controller 20
Power is supplied to the control circuit 30 without voltage drop.

After that, when the charging voltage of the main capacitor C5 reaches a predetermined value, the neon lamp NE lights up, indicating that charging is complete, and the base potential of the transistor Q6 rises, which turns on the transistor Q6 and outputs the charging completion detection signal S.
The line No. 1 connects to the ground line g via the collector and emitter of the same transistor Q6. The charging completion detection signal s1 becomes L level. Such a charging completion detection signal s
When a level change of 1 is detected by the system controller 2o, the high level is maintained. ti control signal S3 falls to L level. When the charge control signal S3 becomes L level, the transistor Q2. Both Q5 are turned off.

Accordingly, the operation of the DC-DC converter IO stops, and the constant voltage circuit by the Zener diode ZD stops working, so that no current flows through the Zener diode ZDJ when the DC-DC converter IO is not operating.

Therefore, the system controller 20. Power is supplied to the control circuit 30 only by the shared power supply battery E.

Therefore, regardless of whether or not the main capacitor C5 is charged, the system controller 20. Power is supplied to the control circuit 30.

Thereafter, when the release button (not shown) is pressed, the shutter opens according to a command from the system controller 20, and when the shutter is fully opened, a light emission trigger signal S2 is sent.
becomes H level. Then, high voltage line gH → resistance R13
→The charged charge of the trigger capacitor C4, which has already been fully charged, flows through the path from the trigger capacitor C4 to the low voltage coil of the trigger transformer T (2L-ground line g). →It is discharged in the path of the low voltage coil of the trigger transformer T2.At this time, the high voltage coil T2 of the trigger transformer T2
A high voltage of several kilovolts is generated at H, the flash discharge tube XL is excited by this high voltage, and the flash discharge tube XL emits a flash by the charge in the main capacitor C5.

Then, when the voltage of the main capacitor C5 decreases due to the flash emission of the flash discharge tube XL, the neon lamp NE goes out and the base potential of the transistor Q6 decreases.
The transistor Q6 is turned off, and the line of the charging completion detection signal S1 from the system controller 20 becomes H level. Then, the charging control signal S3 becomes H level due to the action of the system controller 20, and as described above, the main capacitor C5 is charged and the drop in the power supply voltage to the system controller 20 and the control circuit 30 is compensated for.

Next, a second embodiment of the present invention will be described using FIGS. 4 to 6. This embodiment is a partial modification of the circuit in the first embodiment.

That is, instead of the series circuit of diode D and resistor R8 (see Figure 1), a series circuit of resistor R20 and N-channel field effect transistor Q20 is connected, and resistor R9 (see FIG. 1) is connected.
(see FIG. 1), and the gate of the transistor Q20 is connected to the connection point between the resistors R2 and R3. Since the other circuit parts are the same as shown in FIG. 1 above, the corresponding parts are given the same reference numerals as shown in FIG. 1 above, and the explanation thereof will be omitted.

Therefore, the negative electrode voltage of the shared power supply battery E is connected to the ground line go
The voltage is applied to each negative power input terminal of the system controller 20 and the control circuit 30 through. At this time, the gate of transistor Q20 is at H level, so it is in an on state. Therefore, the positive electrode voltage of the shared power supply battery E is as follows: low voltage line gL → low voltage coil TIL of step-up transformer T → resistor R2
It is applied to the positive voltage power input terminal of the system controller 20 through the 0→transistor Q2op path. Therefore, the voltage of the shared power supply battery E is applied across the capacitor C2,
The power is applied to the power input terminals of each of the system controller 20 and the control circuit 30, and the operating power is supplied to the system controller 20° control circuit 30.

When the charging control signal S3 sent from the system controller 20 goes to H level as shown in FIGS. 5 and 6 in order to charge the main capacitor C5 prior to flash photography, the transistor Q is turned on and the transistor Q5 turns on.

When the transistor Q2 turns on, the base potential of the transistor Q1 decreases and the transistor Q1 turns on.

When the transistor Q1 is turned on, the collector potential of the transistor Q4 rises, and the base current of the resistor R1 flows through the base of the transistor Q4, so that the transistor Q4 is turned on. Along with this, the base potential of transistor Q3 rises and transistor Q3 is turned on. Therefore, low pressure line I
+.

→Low voltage coil TII, →Collector φ of transistor Q3
Low voltage coil "11" in the path of emitter → ground line 10,
A current 1 flows in the direction of arrow i. This current 1 has a large value (
(approximately several A), and the voltage vDD of the shared power supply battery E rapidly decreases as shown in FIGS. 5 and 6. Low voltage coil T
When the magnetic flux of the step-up transformer Tl is saturated due to current flowing through IL, the high-voltage coil T1! ! The current flowing through the high-voltage coil Ttu rapidly decreases and the current flowing through the high-voltage coil Ttu becomes zero, so that a back electromotive force is generated in the high-voltage coil TIH, and the transistor Q4 is turned off in order to set the base of the transistor Q4 to a negative potential. When transistor Q4 turns off,
The base potential of transistor Q3 decreases, turning off transistor Q3. Then, an arrow flows to the low voltage coil TIL! Since the current in the direction is abruptly cut off, a back electromotive force is generated in the low voltage coil TIL in the direction of arrow i.

By repeating such operations, a voltage of about 250 to 300 V is generated on the high voltage line gH, and the main capacitor C5 is charged with this voltage.

At this time, the voltage ■1 at the connection point between the low voltage coil T and the collector of the transistor Q3 is connected to the ground line j! as shown in FIG. A potential approximately equal to the potential of o (ground line g
The pulse voltage signal becomes a pulse voltage signal with a pulse height of about 20 V based on the potential increased by the on-voltage of the transistor Q3 from the potential.

When the transistor Q3 is off, the gate potential of the transistor Q2o is approximately the voltage vDD of the power supply battery E, so the potential difference between the gate and the cathode of the Zener diode ZD becomes a slight reverse bias, and the potential difference corresponds to this potential difference. Due to the series resistance of the on-resistance and the resistor R, the smoothing capacitor C2 is charged by the current in the direction of the arrow.

Furthermore, when the transistor Q3 is on, the potential that is the sum of the collector potential of the transistor Q3 and the voltage drop across the resistor R2o due to the discharge current in the direction of the arrow g is the potential of the transistor Q3.
and the resistor R2o, and at this time, since the transistor Q2 is on, the gate of the transistor Q2o is at the impo level, which is approximately grounded. In this case as well, the transistor Q2o is in a slightly reverse biased state, and the smoothing capacitor C2 is connected to the gate of the transistor Q at this time through the series resistance of the on-resistance corresponding to the potential difference between the resistor R12 and the transistor Q2o, and the resistor R2o. Charged charge is discharged.

Note that when the DC-DC converter IO is not operating, the transistor Q2o has a low on-resistance, so the capacitor C2 is charged with the voltage of the shared power supply battery E.

After that, when the charging voltage of the main capacitor C5 reaches a predetermined value, the neon lamp NE lights up, indicating that charging is complete, and the base of the transistor Q6 rises, turning on the transistor QB, which outputs the charging completion detection signal S1.
line is connected to the ground line p via the collector and emitter of the same transistor Q6. is connected to the charge completion detection signal S
1 becomes L level. Such a charging completion detection signal S1
When a change in level is detected by the system controller 20, the charging control signal S3, which is maintained at the H level, falls to the L level. When the charge control signal S3 becomes L level, the transistor Q2. Both Q5 are turned off. Therefore, the operation of the DC-DC converter 1G stops and the constant voltage circuit using the Zener diode 2D stops working.

Therefore, the system controller 20. Power is supplied to the control circuit 30 only by the shared power supply battery E.

Therefore, regardless of whether or not the main capacitor C5 is charged, the system controller 20. Power is supplied to the control circuit 30.

Thereafter, when a release button (not shown) is pressed, flash light is emitted by the flash discharge tube XL in the same manner as described above.

Then, as described above, the main capacitor C5 is charged in preparation for the next strobe light emission, and the system controller 20. Compensation for a drop in the power supply voltage to the control circuit 30 is performed.

In the first and second embodiments described above, the main capacitor C5 is always kept fully charged regardless of whether or not strobe photography is performed. Capacitor C
Of course, it is also possible to perform charging to 5.

(Effects of the Invention) As described above, according to the power supply circuit for a camera according to the present invention,
A power supply that smoothes part of the induced voltage generated in the booster circuit that charges the main capacitor that serves as the strobe light source when it is operating is connected to the common power supply battery at the power input terminal of the camera control circuit. Since they are connected in parallel, problems caused by a drop in the terminal voltage of the shared power supply battery while the main capacitor is being charged are eliminated.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram of a camera power supply circuit showing a first embodiment of the present invention; FIGS. 2 and 3 are waveform diagrams for explaining the operation of the power supply circuit of the first embodiment; FIG. 4 is an electric circuit diagram of a power supply circuit for a camera showing a second embodiment of the present invention, and FIGS. 5 and 6 are waveform diagrams for explaining the operation of the power supply circuit of the second embodiment. be. 10...... Boost circuit 20... System controller (camera control circuit) 30... Control circuit (camera control circuit) E... ... Common power supply battery R8 ... Resistor ZD ... Zener diode C2 ... Smoothing capacitor XL ... Flash discharge tube C5 ...・Main capacitor 42 wards Ishi 3 wards S+H O 5 wards Uma 6 wards Procedure amendment (voluntary) 1985 4
March 24, 3, Name of the person making the amendment (037) "Detailed description of the invention" column and drawings (1) of the Olympus Optical Industry Co., Ltd. specification.
) Delete the words after "gate" in line 9 of page 16 of the specification and before "and" in line 10, and substitute the following. " is connected to the line fIL through the resistor R, and N
It is connected to the collector of a PN type transistor Q7, its base is connected to the collector of the transistor Q4 through a resistor R, and its emitter is connected to the ground line 1o. ” (2) “Input terminal 1” written in the 3rd line of page 17 of the same
Correct it to "input end +". (3) Figures 3, 4, and 6 of the drawings attached to the application will be replaced with the attached drawings.

Claims (1)

[Scope of Claims] A camera in which a common power supply battery is connected to the respective power input terminals of a booster circuit that charges a main capacitor serving as a strobe light source and a camera control circuit such as a system controller through a direct power supply line. A power supply circuit for a camera, characterized in that a part of the induced voltage generated during operation of the booster circuit is applied in parallel to a power input terminal of the camera control circuit.