JP4820852B2 - Constant current drive control circuit - Google Patents

Description

  The present invention relates to a constant current drive control circuit suitable for a voice coil type shutter such as a digital camera.

  As a shutter for a digital camera or the like, a so-called voice coil type shutter is widely used. High-speed shutters have become indispensable with the recent improvement in image quality of digital cameras, and constant current driving is becoming common as a shutter driving method for that purpose.

  FIG. 2 shows a conventional constant current drive control circuit, where 1 is a power supply, 2 is a constant current control amplifier, a reference power supply is connected to the + input terminal, and a phase compensation capacitor C is connected to the output terminal. 4, 5, 6, and 7 are transistors constituting a current mirror circuit, 8 is a first transistor, a collector is connected to a collector of the transistor 4 constituting the current mirror circuit, and a base is controlled by the constant current through a resistor 10. It is connected to a connection point FC between the output terminal of the amplifier 2 and the phase compensation capacitor C.

  Reference numeral 11 denotes a second transistor, and a collector is connected to the emitter of the first transistor 8 via a resistor 12, and an ON / OFF signal is applied to the base in conjunction with a shutter button (not shown) of the camera. A third transistor 14 has a base connected to the collector of the transistor 7 constituting the current mirror circuit.

  Reference numerals 15 and 16 denote driving transistors controlled by the third transistor 14. A voice coil type shutter is connected between the collectors of the driving transistor 15 and the driving transistor 16, and the emitter of the driving transistor 15 is Connected to the power supply 1, the emitter of the driving transistor 16 is grounded via a current detection resistor 18. A connection point RFG between the driving transistor 16 and the current detection resistor 18 is connected to a negative input terminal of the constant current control amplifier 2.

  When a shutter button (not shown) is turned on now, an ON signal is generated in which the ON / OFF signal is kept at a high level for a certain period, and the base of the second transistor 11 is set to a high level so that it can be turned on. On the other hand, when the shutter button is turned on, the switch 20 is turned on and the power source voltage VCC from the power source 1 is applied to the constant current control amplifier 2 to start the operation and generate an output signal to start charging the phase compensation capacitor C. .

  When the phase control capacitor C is charged to the threshold level, when the first transistor 8 is turned on, the second transistor 11 that has been turned on is also turned on, so that the transistor 4, the first transistor 8 and the second transistor 11 are turned on. Current flows through the transistor 5 and the transistor 6, thereby turning on the transistor 7 and the third transistor 14 one after another, and turning on the driving transistors 15 and 16.

  When the driving transistors 15 and 16 are turned on, a current from the power source 1 flows through the voice coil type shutter 17 to open the shutter. When the driving transistors 15 and 16 are also turned on, the potential at the RFG point on the non-ground side of the current detection resistor 18 is applied to the negative input terminal of the constant current control amplifier 2 and compared with the reference voltage E1 of the reference power source 3. The output signal of the constant current control amplifier 2 is limited. Accordingly, since the base voltage of the first transistor 8 is controlled, the current flowing through each of the transistors 4, 5, 6 and 7 of the current mirror circuit is limited, and the drive current flowing through the voice coil type shutter 17 which is a load is also limited.

  Since the ON / OFF signal becomes a low level OFF signal after a predetermined period of time has elapsed, the second transistor 11 is turned off, the transistors 4, 5, 6, and 7 are turned off, and the driving transistors 15 and 16 are turned off. Is also turned off.

  In the above, when the shutter button of the camera is turned on, charging of the phase compensation capacitor is started with the output signal of the constant current control amplifier, and when charged to the threshold level, the first transistor is turned on and the driving transistor is turned on. The load is driven at a constant current.

  However, when the shutter button is operated continuously, the initial state of the charge of the phase compensation capacitor differs between the nth time and the (n + 1) th time, so that the potential rises to the threshold level at which the first transistor starts to operate. There was a difference in the time until.

  For this reason, the delay time from when the shutter button is turned on and the shutter drive signal is input to when the drive current for actually driving the shutter is output differs between the nth time and the (n + 1) th and subsequent times, so that a stable shutter is always obtained. Could not get the action.

  FIG. 3 shows a constant current drive control circuit for solving the above-mentioned problem. A discharge bias circuit 21 having a discharge transistor 22 is added, and the ON / OFF signal is turned on at the base of the discharge transistor 22. Then, the constant current circuit 23 that starts the operation and the bias diodes 24 and 25 are connected, and the emitter is connected to the connection point FC between the constant current control amplifier 2 and the phase compensation capacitor C via the resistor 26. The collector is grounded.

  When the nth shutter button (not shown), for example, is turned on now, an ON signal is generated in which the ON / OFF signal is kept at a high level for a certain period of time, and the base of the second transistor 11 is set to a high level and can be turned on. To do. On the other hand, when the shutter button is turned on, the switch 20 is turned on, the power supply voltage VCC from the power supply 1 is applied to the constant current control amplifier 2 and the comparator 32, and the operation is started to generate an output signal. At this time, since the constant current circuit 23 is operated, the discharging transistor 22 is in an inoperative state, so that the phase compensation capacitor C starts to be charged.

  When the phase control capacitor C is charged to the threshold level, the first transistor 8 and the second transistor 11 are turned on. As a result, a current flows through the transistor 4, the first transistor 8 and the second transistor 11 constituting the current mirror circuit, so that a current also flows through the transistor 5 and the transistor 6, thereby causing the transistor 7 and the transistor 14 to successively pass. A current flows, the third transistor 14 is turned on, and the driving transistors 15 and 16 are also turned on.

  When the driving transistors 15 and 16 are turned on, a current from the power source 1 flows through the voice coil type shutter 17 to drive the shutter mechanism and close the shutter. When the driving transistors 15 and 16 are also turned on, the potential at the RFG point on the non-ground side of the current detection resistor 18 is applied to the negative input terminal of the constant current control amplifier 2 and compared with the reference voltage E1 of the reference power source 3. The drive current of the constant current control amplifier 2 is limited. Accordingly, since the base voltage of the first transistor 8 is controlled, the current flowing through each of the transistors 4, 5, 6 and 7 of the current mirror circuit is limited, and the drive current flowing through the voice coil type shutter 17 which is a load is also limited.

  Since the ON / OFF signal becomes a low level OFF signal after a predetermined period, the second transistor 11 is turned off, the transistors 4, 5, 6, and 7 are also turned off, and the driving transistors 15, 16 are turned off. Is turned off.

  When the ON / OFF signal is turned off, the constant current circuit 23 is inactivated and the discharge transistor 22 is turned on, so that the charge of the phase compensation capacitor C passes through the resistor 26 and the emitter / collector of the discharge transistor 22. Then, the discharge is started and the constant current control amplifier 2 before the nth shutter button is turned on is discharged to the potential VA where it is not operating.

  Therefore, immediately after the second (ie, (n + 1)) shutter button is turned on, the ON / OFF signal generates an ON signal for a certain period of time, and the base of the second transistor 11 is set to the high level and turned on. On the other hand, when the shutter button is turned on, the switch 20 is turned on and the power source voltage VCC from the power source 1 is applied to the constant current control amplifier 2 to start operation and generate an output signal, and start charging the phase compensation capacitor C. To do.

  At this time, since the phase control capacitor C is discharged to the potential VA before the nth shutter button is turned on, it is charged to the threshold level after the same time as the previous time, and the first transistor 8 is turned on. Accordingly, the second transistor 11 is also turned on. As a result, a current flows through the transistor 4, the first transistor 8 and the second transistor 11 constituting the current mirror circuit, so that a current also flows through the transistor 5 and the transistor 6, thereby causing the transistor 7 and the transistor 14 to successively pass. A current flows, the third transistor 14 is turned on, and the driving transistors 15 and 16 are also turned on. As a result, a current from the power source 1 flows through the voice coil type shutter 17, and the shutter is closed.

  However, in the above method, when the time interval of load driving such as the (n-1) th and nth shutters is very long and the potential of the phase compensation capacitor has dropped to nearly zero, Since it took time to raise the potential of the phase compensation capacitor to the potential VA before the start of the nth time, the shutter or the like compared with the case where the potential of the phase compensation capacitor was near VA at the start of load driving of the shutter or the like. There was a problem that the response of the load operation became slow.

  There is also a problem that the delay time increases in proportion to an increase in the capacitance value of the phase compensation capacitor.

In order to solve the above problems, the present invention is a constant current drive control circuit for supplying a drive current to a load when a charge potential of a phase compensation capacitor is equal to or higher than a first predetermined potential, and is input to one input terminal. A first output signal is output in response to a first reference voltage and a feedback signal from a load input to the other input terminal, and the phase compensation capacitor is set at least until the charging potential becomes the first predetermined potential. The second output signal according to the constant current control amplifier to be charged, the second reference voltage input to one input terminal, and the potential corresponding to the charging potential of the phase compensation capacitor input to the other input terminal outputs, a charging circuit for charging the phase compensation capacitor to said charging potential is lower second predetermined potential than the first predetermined potential, and a discharge circuit for discharging the phase compensation capacitor, the Nde configured, the constant current control amplifier, the first signal to supply the drive current to the load is input to charge the phase compensation capacitor, stopping the supply of the drive current to the load When the second signal is input, the charging of the phase compensation capacitor is stopped, and when the first signal is input, the discharging circuit stops discharging the phase compensation capacitor, When the second signal is inputted, characterized Rukoto, a to discharge the phase compensation capacitor.

  In addition, a current detection resistor that converts a current flowing through the load into a voltage is included, and the feedback signal corresponds to a potential converted by the current detection resistor.

The constant current drive control circuit is used to drive the shutter of the camera, and the first signal is supplied to the constant current control amplifier and the charging circuit for a predetermined period when the shutter button of the camera is turned on. The second signal is a signal that is input to the constant current control amplifier and the charging circuit after the first signal is input for the predetermined period .

  As described above, the constant current drive control circuit of the present invention is provided with a quick charge circuit in the phase compensation capacitor, and when the switch is operated, the phase compensation capacitor is quickly charged through the quick charge circuit to determine a predetermined potential. Since the output signal of the constant current control amplifier is used to charge the battery, it is turned on in a predetermined time after the driving transistor operates the switch, and the load can be driven.

  The constant current drive control circuit of the present invention will be described with reference to FIG. The same components as those in the prior art are given the same numbers.

  Reference numeral 1 is a power source, 2 is a constant current control amplifier, a reference power source is connected to the + input terminal, and a phase compensation capacitor C is connected to the output terminal. 4, 5, 6, and 7 are transistors constituting a current mirror circuit, 8 is a first transistor, a collector is connected to a collector of the transistor 4 constituting the current mirror circuit, and a base is controlled by the constant current through a resistor 10. It is connected to a connection point FC between the output terminal of the amplifier 2 and the phase compensation capacitor 3.

  A discharge bias circuit 21 having a discharge transistor 22 is connected to a base of the discharge transistor 22 with a constant current circuit 23 that starts operation when the ON / OFF signal is turned ON and bias diodes 24 and 25. The emitter is connected to a connection point FC between the constant current control amplifier 2 and the phase compensation capacitor C via a resistor 26, and the collector is grounded.

  Reference numeral 30 denotes a quick charging circuit, which compares the reference voltage of the reference power supply 31 with the potential at the connection point FC between the output terminal of the constant current control amplifier 2 and the phase compensation capacitor C, and the emitter / collector path is the power supply 1. And a charging transistor 33 connected to the connection point FC and controlled by the output signal of the comparator 32.

  Reference numeral 11 denotes a second transistor, the collector of which is connected to the emitter of the first transistor 8 through a resistor 12, and an ON / OFF signal generated when a shutter button (not shown) of the camera is pressed is applied to the base. A third transistor 14 has a base connected to the collector of the transistor 7 constituting the current mirror circuit.

  Reference numerals 15 and 16 denote driving transistors controlled by the third transistor 14. A voice coil type shutter is connected between the collectors of the driving transistor 15 and the driving transistor 16, and the emitter of the driving transistor 15 is Connected to the power supply 1, the emitter of the driving transistor 16 is grounded via a current detection resistor 18. A connection point RFG between the driving transistor 16 and the current detection resistor 18 is connected to a negative input terminal of the constant current control amplifier 2.

  When a shutter button (not shown) is turned on now, an ON signal is generated in which the ON / OFF signal is kept at a high level for a certain period, and the base of the second transistor 11 is set to a high level so that it can be turned on. On the other hand, when the shutter button is turned on, the switch 20 is turned on and the power source voltage VCC from the power source 1 is applied to the constant current control amplifier 2 to start the operation and generate an output signal. At this time, since the constant current circuit 23 is operated, the discharging transistor 22 is in an inoperative state, so that the phase compensation capacitor C starts to be charged.

  When the phase control capacitor C is charged to the threshold level, the first transistor 8 and the second transistor 6 are turned on. As a result, a current flows through the transistor 4, the first transistor 8 and the second transistor 11 constituting the current mirror circuit, so that a current also flows through the transistor 5 and the transistor 6, thereby causing the transistor 7 and the transistor 14 to successively pass. A current flows, the third transistor 14 is turned on, and the driving transistors 15 and 16 are also turned on.

  When the driving transistors 15 and 16 are turned on, a current from the power source 1 flows through the voice coil type shutter 17 to drive the shutter mechanism and close the shutter. When the driving transistors 15 and 16 are also turned on, the potential at the RFG point on the non-ground side of the current detection resistor 18 is applied to the negative input terminal of the constant current control amplifier 2 and compared with the reference voltage E1 of the reference power source 3. The drive current of the constant current control amplifier 2 is limited. Therefore, since the base voltage of the first transistor 8 is controlled, the current flowing through each of the transistors 4, 5, 6 and 7 of the current mirror circuit is also limited, and the drive current flowing through the voice coil type shutter 17 which is a load is controlled and stabilized. The shutter is closed by the torque applied.

  Since the ON / OFF signal becomes a low level OFF signal after a predetermined period, the second transistor 11 is turned off, the transistors 4, 5, 6, and 7 are also turned off, and the driving transistors 15, 16 are turned off. Is turned off.

  When the ON / OFF signal is turned off, the constant current circuit 23 is inactivated and the discharge transistor 22 is turned on, so that the charge of the phase compensation capacitor C passes through the resistor 26 and the emitter / collector of the discharge transistor 22. Then, the discharge is started, and the constant current control amplifier 2 before the shutter button is turned on is discharged to the potential VA that is not operating.

  By the way, since time has elapsed since the last time the shutter button was operated, when the potential of the phase compensation capacitor C is discharged to VA or less, when the shutter button is operated, the reference voltage E2 of the reference power supply 31 is changed to the phase compensation capacitor. Therefore, the output terminal of the comparator 32 is at a low level, the charging transistor 33 is turned on, and the phase compensation capacitor C is connected via the emitter / collector of the charging transistor 33. The voltage from the power supply 1 is directly applied and quick charging is performed.

  When the phase compensation capacitor C is rapidly charged to VA, the potential at the connection point FC becomes larger than the reference voltage E2, so that the output terminal of the comparator 32 is set to the high level and the charging transistor 33 is turned off. Therefore, after the phase compensation capacitor C is rapidly charged to VA, it is charged with the output signal from the constant current control amplifier 2 as described above.

  When the phase compensation capacitor C is charged to the threshold level, the first transistor 8 is turned on and the second transistor 11 is also turned on accordingly. As a result, a current flows through the transistor 4, the first transistor 8 and the second transistor 11 constituting the current mirror circuit, so that a current also flows through the transistor 5 and the transistor 6, thereby a current also flows through the transistor 7. The third transistor 14 is turned on, the driving transistors 15 and 16 are also turned on, the current from the power source 1 flows through the voice coil type shutter 17, and the shutter is closed.

  If charging is performed only with the output signal from the constant current control amplifier 2, it takes time to charge to the threshold level, so the above problem becomes significant when the capacitance value of the phase compensation capacitor is large. Therefore, the driving transistors 15 and 16 can be quickly charged by rapidly charging through the charging transistor 33 to the potential determined in the phase compensation capacitor by the above-described means, and thereafter charging with the output signal of the constant current control amplifier 2. Can be turned on.

  It should be noted that when the shutter button is not turned on, the switch 20 is turned off and the circuit current consumption is designed to be zero.

  Although the case where the shutter is driven by the constant current drive control circuit of the present invention has been described above, when applied to a stepping motor or the like driven by a constant current, stable drive characteristics can be obtained from the start of motor drive.

It is a circuit diagram of the constant current drive control circuit of the present invention. It is a circuit diagram of the conventional constant current drive control circuit. FIG. 3 is a conventional circuit diagram obtained by improving the constant current drive control circuit of FIG. 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power supply 2 Constant current control amplifier 3 Reference power supply 8 1st transistor C Phase compensation capacitor | condenser 11 2nd transistor 14 3rd transistors 15 and 16 Driving transistor 17 Voice coil type shutter 18 Current detection resistor 21 Discharge bias circuit 22 Discharge Transistor 23 constant current circuit 30 charging circuit 32 comparator 33 charging transistor

Claims (3)

A constant current drive control circuit for supplying a drive current to a load when a charging potential of a phase compensation capacitor is equal to or higher than a first predetermined potential;
A first output signal is output in response to a first reference voltage input to one input terminal and a feedback signal from a load input to the other input terminal, and at least the charging potential is set to the first predetermined potential. A constant current control amplifier that charges the phase compensation capacitor until
A second output signal is output according to the second reference voltage input to one input terminal and the potential corresponding to the charging potential of the phase compensation capacitor input to the other input terminal, and the charging potential is A charging circuit for charging the phase compensation capacitor until a second predetermined potential lower than the first predetermined potential ;
A discharge circuit for discharging the phase compensation capacitor, and
The constant current control amplifier is:
When the first signal for supplying the drive current to the load is input, the phase compensation capacitor is charged and the second signal for stopping the supply of the drive current is input to the load. , Stop charging the phase compensation capacitor,
The discharge circuit is:
When the first signal is inputted, stops discharging the phase compensation capacitor, the second signal is input, Rukoto to discharge the phase compensation capacitor,
A constant current drive control circuit. The constant current drive control circuit according to claim 1,
A current detection resistor for converting a current flowing through the load into a voltage;
The constant current drive control circuit according to claim 1, wherein the feedback signal corresponds to a potential converted by the current detecting resistor . The constant current drive control circuit according to claim 1 is used to drive a shutter of a camera,
The first signal is:
When the shutter button of the camera is turned on, the constant current control amplifier and the charging circuit
Is a signal input for a predetermined period of time,
The second signal is:
A constant current drive control circuit, wherein the first signal is a signal input to the constant current control amplifier and the charging circuit after being input for the predetermined period .

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