JP5029337B2 - Power circuit - Google Patents

Description

  The present invention relates to a power supply circuit.

  A technique is known in which the booster circuit is stopped when the battery voltage is higher than the operating voltage of the load, and the battery power is efficiently extracted by operating the booster circuit when the battery voltage is lower than the operating voltage of the load. Reference 1).

Japanese Utility Model Publication No.7-11891

  In the prior art, there is a problem that a case where a plurality of loads having different operating voltages is provided is not considered.

(1) A power supply circuit according to the present invention includes a booster circuit that boosts a battery voltage, a first load and a load having a second load that requires a lower voltage than the first load, and a voltage that has been boosted via the booster circuit. A first path for supplying the battery voltage to the load side, a second path for supplying the battery voltage to the load side without going through the booster circuit, and a step-down means for stepping down the voltage supplied to the load side to a voltage required by the second load When the battery voltage is higher than the voltage required for the first load when the first load is in operation, the second path is switched, and when the battery voltage is lower than the voltage required for the first load, the first path is switched. Switching means.
(2) In the power supply circuit according to claim 1, the switching means switches to the second path when the first load is inactive and the battery voltage is higher than the voltage required by the second load and the step-down means. It is preferable to switch to the first path when the battery voltage is lower than the voltage required for the two loads and step-down means.
(3) In the power supply circuit according to claim 1 or 2, it is preferable that the booster circuit stops the boosting when the switching means is switched to the second path.
(4) In the power supply circuit according to claim 1, the booster circuit preferably boosts the battery voltage to a necessary voltage at the first load when the switching means is switched to the first path.
(5) In the power supply circuit according to claim 2, when the switching means is switched to the first path, the booster circuit preferably boosts the battery voltage to a necessary voltage by the second load and the step-down means.
(6) In the power supply circuit according to claim 1 or 4, the first load may include a motor. The switching means in this case is preferably switched to the first path when the rotation of the motor does not reach a predetermined speed after switching to the second path.
(7) In the power supply circuit according to claim 6, when the switching means is switched to the first path, the booster circuit preferably increases the boosted value so that the rotation of the motor reaches a predetermined speed.
(8) In the power supply circuit according to claim 7, the booster circuit preferably maintains the boost value when the battery voltage drops below a predetermined voltage while the boost value is being increased.

  According to the present invention, it is possible to drive a plurality of loads having different operating voltages depending on the battery with low loss.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a main part of a camera equipped with a power supply circuit according to an embodiment of the present invention. The camera includes a booster circuit 2, a motor drive circuit 3, a motor 4, a speed sensor 5, a main CPU 6, a switch 7, a step-down circuit 8, a sub CPU 9, and an operation member 10. Loaded.

  The booster circuit 2 boosts the input voltage from the battery 1 to a predetermined voltage. On / off of the boosting operation by the booster circuit 2 and the output voltage (boost target voltage) when the boosting is on are controlled by a control signal from the sub CPU 9. When the battery 1 is a lithium ion battery, the battery voltage is about 3.0V to 4.2V.

  The switch 7 is on / off controlled by a control signal from the sub CPU 9. The switch 7 is turned on when the booster circuit 2 stops boosting. The switch 7 is turned off at the time of boosting by the boosting circuit 2.

  The motor drive circuit 3 drives the motor 4 by a predetermined amount according to an instruction from the sub CPU 9. The rotational speed of the motor 4 is configured to change according to the voltage supplied to the motor drive circuit 3. The motor 4 rotates at a higher speed as the supply voltage to the motor drive circuit 3 is higher, and rotates at a lower speed as the supply voltage to the motor drive circuit 3 is lower. The motor 4 is used, for example, as a drive source for moving a zoom lens (not shown) forward and backward in the optical axis direction and changing the zoom magnification by the zoom lens.

  The speed sensor 5 detects the rotational speed of the motor 4 and sends a detection signal to the main CPU 6. The main CPU 6 communicates with the sub CPU 9 to send the rotational speed information of the motor 4 to the sub CPU 9. The main CPU 6 also performs various calculations and sequence control related to the shooting process performed by the imaging apparatus 11, but this description focuses on the power supply control process, and a description of the shooting process is omitted.

  The step-down circuit 8 steps down the input voltage to a predetermined voltage. The sub CPU 9 operates in response to the supply of the step-down voltage from the step-down circuit 8. The sub CPU 9 receives operation signals from operation members 10 such as a main switch, zoom switch, release button, aperture ring, and shutter dial. The sub CPU 9 communicates with the main CPU 6 and sends operation information of the operation member 10 to the main CPU 6. Further, the sub CPU 9 performs the voltage detection of the battery 1 without passing through the main CPU 6, instructs the booster circuit 2 to turn on / off the boost operation, instructs the boost target voltage when the booster is on, and instructs the switch 7 to turn on / off.

<Power control during motor drive>
FIG. 2 is a flowchart for explaining the flow of power control processing performed by the sub CPU 9. The process according to FIG. 2 is started when the motor 4 is driven. In step S101 in FIG. 2, the sub CPU 9 transmits an off control signal to the switch 7 and proceeds to step S102. In step S102, the sub CPU 9 determines whether or not the battery voltage is 3.8V or higher. The sub CPU 9 A / D converts the voltage signal for voltage detection from the battery 1 to check the voltage value. If the detected voltage is 3.8 V or higher, the sub CPU 9 makes an affirmative decision in step S102 and proceeds to step S108. If the detected voltage is less than 3.8 V, the sub CPU 9 makes a negative determination in step S102 and proceeds to step S103.

  In step S103, the sub CPU 9 sends an instruction to the booster circuit 2, starts the boosting operation with 3.8V as the boost target voltage, and proceeds to step S104. Thereby, the booster circuit 2 boosts the input voltage (battery voltage) to 3.8 V and maintains the boosted voltage. The step-up voltage (output voltage) from the step-up circuit 2 is supplied to the motor drive circuit 3 through the path 101 and also to the step-down circuit 8. In this case, the step-down circuit 8 steps down the voltage supplied from the step-up circuit 2 to a predetermined voltage (for example, 3.3 V).

  In step S108, which proceeds after making an affirmative decision in step S102, the sub CPU 9 transmits an ON control signal to the switch 7 and proceeds to step S109. In step S109, the sub CPU 9 sends an instruction to the booster circuit 2, stops the boost operation, and proceeds to step S104. As a result, the voltage of the battery 1 is supplied to the motor drive circuit 3 through the path 102 and also supplied to the step-down circuit 8. In this case, the step-down circuit 8 steps down the battery voltage to a predetermined voltage (for example, 3.3 V).

  In step S <b> 104, the sub CPU 9 sends an instruction to the motor drive circuit 3 and instructs the rotation amount (drive amount) of the motor 4 according to the zoom operation signal from the operation member 10. Thereby, the motor 4 starts driving.

  In step S105, the sub CPU 9 determines whether the rotation speed of the motor 4 has reached a predetermined speed or whether the battery voltage is 3.2 V or less. When the rotation speed reaches a predetermined speed, or when the detection voltage of the battery 1 is 3.2 V or less, the sub CPU 9 makes a positive determination in step S105 and proceeds to step S106. If the rotation speed is less than the predetermined speed and the detected voltage of the battery 1 exceeds 3.2 V, the sub CPU 9 makes a negative determination in step S105 and proceeds to step S110.

  In step S110, the sub CPU 9 increases the voltage supplied to the motor drive circuit 3 to increase the rotation speed of the motor 4. In step S110, the sub CPU 9 transmits an off control signal to the switch 7 and proceeds to step S111. If the switch 7 has already been turned off, step S110 may be skipped without transmitting the off signal again. In step S111, the sub CPU 9 sends an instruction to the booster circuit 2, starts a boost operation using a predetermined upper limit voltage (for example, 4.2V) as a boost target voltage, returns to step S105, and repeats the above processing. Thereby, the booster circuit 2 starts to increase the output voltage. The boosted voltage (output voltage) from the booster circuit 2 is supplied to the motor drive circuit 3 and also to the step-down circuit 8.

  The sub CPU 9 that proceeds to step S106 while increasing the output voltage of the booster circuit 2 sends an instruction to the booster circuit 2, stops the voltage increase, and maintains the boosted value (output voltage) at that time. Thereby, the rotational speed of the motor 4 maintains the above-mentioned specified speed. In step S106, the sub CPU 9 causes the motor 4 to drive a predetermined amount and proceeds to step S107. In step S107, when the driving amount of the motor 4 reaches a predetermined amount, the sub CPU 9 sends an instruction to the motor driving circuit 3, instructs the motor 4 to stop (stop driving), and ends the processing of FIG. Thereby, the motor 4 stops.

<Power control when the motor is not driven>
When the motor 4 is not driven (for example, in the playback mode when the camera is an electronic camera, in the standby mode of the camera, etc.), the power control process illustrated in FIG. 3 is used instead of the power control process illustrated in FIG. Is used. In step S201 in FIG. 3, the sub CPU 9 determines whether or not the battery voltage is, for example, 3.5 V or higher. The sub CPU 9 performs A / D conversion on the voltage signal for voltage detection from the battery 1 to check the voltage value. If the detected voltage is 3.5 V or more, the sub CPU 9 makes a positive determination in step S201 and proceeds to step S204. If the detected voltage is less than 3.5 V, the sub CPU 9 makes a negative determination in step S201 and proceeds to step S202.

  In step S202, the sub CPU 9 transmits an off control signal to the switch 7 and proceeds to step S203. In step S203, the sub CPU 9 sends an instruction to the booster circuit 2, starts a boost operation with 3.5V as a boost target voltage, and returns to step S201. Thereby, the booster circuit 2 boosts the input voltage (battery voltage) to 3.5 V and maintains the boosted voltage. The boosted voltage (output voltage) from the booster circuit 2 is supplied to the step-down circuit 8. In this case, the step-down circuit 8 steps down the voltage supplied from the step-up circuit 2 to a predetermined voltage (for example, 3.3 V).

  In step S204, which proceeds after making an affirmative decision in step S201, the sub CPU 9 transmits an ON control signal to the switch 7 and proceeds to step S205. In step S205, the sub CPU 9 sends an instruction to the booster circuit 2, stops the boost operation, and returns to step S201. As a result, the voltage of the battery 1 is supplied to the step-down circuit 8. In this case, the step-down circuit 8 steps down the battery voltage to a predetermined voltage (for example, 3.3 V).

According to the embodiment described above, the following operational effects can be obtained.
(1) Since the first path 101 that boosts the battery voltage by the booster circuit 2 and supplies the load to the load and the second path 102 that supplies the battery voltage to the load without going through the booster circuit 2 can be switched. When switching to the second path 102, loss due to the booster circuit 2 can be reduced compared to switching to the first path 101.

(2) When driving the motor 4 as a load with the battery 1, if the battery voltage is higher than the voltage necessary for driving the motor 4 (for example, 3.8V), the booster circuit 2 is stopped in the second path 102 (step S108). (Step S109) When the battery voltage is lower than the voltage required for driving the motor 4, the booster circuit 2 is boosted in the first path 101 (Step S103). ), The loss due to the booster circuit 2 can be reduced. This is because the booster circuit generally has a smaller loss when the input / output voltage difference is reduced.

(3) Since the initial target boost voltage of the booster circuit 2 in the first path 101 is set to 3.8 V (step S103), a voltage higher than 3.8 V (for example, 4.5 V) is set as the target boost voltage. Thus, loss due to the booster circuit 2 can be reduced.

(4) After the booster circuit 2 is stopped in the second path 102 (step S109), if the motor 4 cannot obtain a predetermined rotational speed, the motor 4 is switched to the first path 101 (step S110), and the output of the booster circuit 2 Since the voltage is increased from 3.8 V (step S111), the boost value by the booster circuit 2 can be increased so that the drive performance (for example, the rotation speed) of the motor 4 can be obtained. Since the upper limit of the boost target voltage is 4.2 V, the possibility of exceeding the input rated voltage of the motor drive circuit 3 can be eliminated.

(5) When the battery voltage decreases to 3.2 V or lower while the output voltage of the booster circuit 2 is increased according to the above (4), the increase of the output voltage by the booster circuit 2 is stopped and the output voltage at that time is maintained. As a result, the battery voltage can be prevented from further decreasing.

(6) Since the step-down circuit 8 is provided to supply a voltage to the circuit member (sub CPU 9) driven at a lower voltage than the motor 4, even when the battery voltage is raised by the step-up circuit 2 in the first path 101, A voltage suitable for the CPU 9 can be supplied.

(7) In addition to the above (6), since the voltage boosting by the booster circuit 2 is suppressed to the minimum necessary, the loss by the step-down circuit 8 can also be reduced. This is because, in general, the step-down circuit has a smaller loss when the input / output voltage difference is reduced.

(8) In the operation mode in which the motor 4 is not driven, if the battery voltage is higher than the voltage required for the step-down circuit 8 and the sub CPU 9 (for example, 3.5 V), the booster circuit 2 is stopped in the second path 102 (step S204) ( Step S205) When the battery voltage is lower than the voltage required for the step-down circuit 8 and the sub CPU 9, the step-up circuit 2 is stepped up in the first path 101 (Step S202) (Step S203). Loss due to the booster circuit 2 and the step-down circuit 8 can be reduced without sacrificing performance (for example, calculation speed).

(Modification 1)
In the description of the power supply circuit described above, the example in which the booster circuit 2 and the switch 7 are individually provided as surrounded by the one-dot chain line in FIG. 1 has been described. Instead of this, the booster circuit 2 may be configured to include the function of the switch 7. FIG. 4 is a diagram illustrating a booster circuit in this case. In FIG. 4, the booster circuit includes an input capacitor C1, an output capacitor C2, a DC / DC converter IC, a transistor Tr1, feedback resistors R1 and R2, a booster coil L1, and a diode D1.

  The input capacitor C1 and the output capacitor C2 are for smoothing. When a control signal instructing the start of boosting is input to the DC / DC converter IC, the DC / DC converter IC starts switching control of the transistor Tr1 at a predetermined frequency. Charge is accumulated in the booster coil L1 by switching of the transistor Tr1, and the accumulated charge is supplied to the capacitor C2 via the diode D1.

  The voltage on the capacitor C2 side is divided by resistors R1 and R2, and the DC / DC converter IC sets the transistor Tr1 in accordance with the comparison result between the divided voltage and the internal reference voltage (voltage corresponding to the boost target voltage). Controls the pulse width for switching.

  The DC / DC converter IC is configured to maintain the transistor Tr1 in an off state when a control signal for instructing boost stop is input. In this case, the direct current component (current from the battery 1) input to the input terminal can be made to flow to the output terminal via the boost coil L1 and the diode D1. That is, even if the switch 7 is not provided, the operation is the same as when the switch 7 is turned on.

  According to the modified example 1 described above, the switch 7 does not have to be provided independently of the booster circuit 2, which is effective in reducing the number of components and mounting space.

(Modification 2)
Although the power supply circuit has been described by taking the camera as an example, if the battery voltage is higher or lower than the voltage required by the load in the device, the power supply circuit according to the present invention should be mounted on devices other than the camera. Can do.

  The above description is merely an example, and is not limited to the configuration of the above embodiment.

It is a principal part block diagram of the camera carrying the power supply circuit by one embodiment of this invention. It is a flowchart explaining the flow of the power supply control processing which a sub CPU performs. It is a flowchart explaining the flow of the power supply control processing which a sub CPU performs. It is a figure which illustrates a power supply circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery 2 ... Booster circuit 3 ... Motor drive circuit 4 ... Motor 5 ... Speed sensor 6 ... Main CPU
7 ... Switch 8 ... Step-down circuit 9 ... Sub CPU
101 ... First route 102 ... Second route

Claims (8)

A booster circuit for boosting the battery voltage;
A load having a first load and a second load that requires a lower voltage than the first load;
A first path for supplying the boosted voltage to the load side via the boost circuit;
A second path for supplying the battery voltage to the load without passing through the booster circuit;
Step-down means for stepping down from a voltage supplied to the load side to a voltage necessary for the second load;
When the battery voltage is higher than the voltage required for the first load when the first load is in operation, the second path is switched to, and when the battery voltage is lower than the voltage required for the first load, A power supply circuit comprising switching means for switching to the first path. The power supply circuit according to claim 1,
The switching means switches to the second path when the battery voltage is higher than a voltage required for the second load and the step-down means when the first load is inactive, and the second load and the step-down means And switching to the first path when the battery voltage is lower than the required voltage. The power supply circuit according to claim 1 or 2,
The booster circuit stops the boosting when the switching means is switched to the second path. The power supply circuit according to claim 1,
The booster circuit boosts the battery voltage to a required voltage at the first load when the switching means switches to the first path. The power supply circuit according to claim 2,
The booster circuit boosts the battery voltage to a voltage required by the second load and the step-down unit when the switching unit switches to the first path. The power supply circuit according to claim 1 or 4,
The first load includes a motor;
The switching means switches to the first path when the rotation of the motor does not reach a predetermined speed after switching to the second path. The power supply circuit according to claim 6,
The booster circuit increases the boost value so that the rotation of the motor reaches a predetermined speed when the switching means switches to the first path. The power supply circuit according to claim 7,
The booster circuit maintains the boosted value when the battery voltage falls below a predetermined voltage while the boosted value is being increased.

Images