JPH0898418A - Over-discharge prevention unit - Google Patents

Abstract

PURPOSE: To obtain an over-discharge prevention circuit which is disabled during a predetermined time when an electronic apparatus undergoes heavy load current drive control. CONSTITUTION: The over-discharge prevention unit comprises a secondary battery 1, an electronic apparatus 4 being fed with power from the secondary battery 1, means 2, 3, 13, 14 for preventing over-discharge of the secondary battery 1, a controller 4 for the electronic apparatus 4, and means 3 for prohibiting the operation of the over-discharge prevention means 2, 3, 13, 14 during operation of the controller 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit structure for preventing overdischarge of a secondary battery and a system using the secondary battery as a main power source.

[0002]

2. Description of the Related Art Conventionally, an overdischarge prevention device for a secondary battery is shown in FIG.
Shown in. In FIG. 7, 1 is a secondary battery, 2 is a voltage detection device that directly detects the voltage of the secondary battery, 3 is a switching element that switches according to the signal obtained from the voltage detection means of 2, 4 is a CPU, 5 Is a load circuit driven according to the signal from the CPU 4, and 6 is an internal resistance of each secondary battery.

In FIG. 7, conventionally, when the voltage of the secondary battery 1 is equal to or higher than a predetermined voltage by the voltage detecting means 2, the switching element 3 is turned on to supply power to the CPU 4 and the load circuit 5 to operate the equipment. On the contrary, when the voltage detecting means 2 determines that the voltage of the secondary battery 1 is less than or equal to the predetermined voltage, the switching element 3 is turned off, the power supply to the CPU 4 and the load circuit 5 is stopped, and the secondary battery 1 is overloaded. It is configured to prevent discharge.

Here, the reason why the secondary battery over-discharge prevention circuit is necessary will be described. In recent years, lithium ion batteries have come into the market as secondary batteries. Unlike Ni-Cad (Nickel-Cadmium) batteries, it does not contain substances that destroy the environment such as cadmium, has little memory effect in terms of electrical characteristics, and has twice the cycle of charging and discharging as Ni-Cad batteries. Can be used. Further, it is a battery which will be the main force in future electronic devices using a secondary battery, having the same charge capacity and having about twice the charge capacity.

On the other hand, however, the battery has the following electrical characteristics. Overcharge is absolutely prohibited, and it deteriorates when overdischarged. This time, in particular, we will explain the characteristics when the lithium-ion battery is over-discharged and show the necessity of an over-discharge prevention circuit.

A typical operating voltage range for a single cell of a lithium ion battery is 2.7V to 4.2V (4.1V). Here, when used at 2.7 V or less, it is called over-discharge. If left below this voltage for a long time, the internal impedance becomes large due to its characteristics. By the way, if an unused battery is normally over-discharged with a value of 200 mΩ to 400 mΩ and the battery is left at the over-discharge voltage, 800 mΩ-
It increases to about 1.5Ω. Further, if the battery is left at 1.0 V or less for a long time, even if it is recharged, energy is not accumulated in the battery and the battery cannot be used. Therefore, a circuit for preventing overdischarge is required. . However, this voltage does not cause over-discharge deterioration when a load is applied for about several seconds.

As a reason, first, the relationship between the voltage across the secondary battery and the electromotive voltage of the secondary battery Eo (voltage across the secondary battery) = Ei (electromotive voltage of the secondary battery) -load current × Ri (2 The internal resistance of the secondary battery). Substituting the approximate voltage relationship into this equation, for example,
When the load current is 0 A, Eo = Ei. here,
Ei = 3.6 in the middle of the open circuit voltage of 2.7V to 4.2V.
V, Ri = 300 mΩ. The voltage across the battery when a load current of 5 A is applied is calculated.

Eo = Ei-Ri load current Eo = 3.6V-0.3Ω × 5A Eo = 2.1V The voltage across the battery is 2.1V, which seems to be over-discharged, but the battery is actually Since the electromotive voltage of 3 is 3.6 V, over-discharge does not occur. Therefore, over discharge deterioration does not occur in about several seconds. The reason why overdischarge occurs is that this electromotive voltage indicates when the electromotive voltage drops below the overdischarge voltage. By the way, to show how long the over-discharge voltage occurs, it is roughly represented by the formula of discharge time (h) ≈remaining battery capacity (mAh) / load current (A).

From the above, in particular, the lithium ion battery among the secondary batteries is prevented from being over-discharged for a long period of time by the construction of the above-mentioned over-discharge preventing circuit.

[0010]

However, in the above-mentioned conventional example, since the voltage of the secondary battery is directly detected and the voltage detecting means is always operated during the operation of the equipment, the following drawbacks are caused. was there. 2 depending on the load current of the device
The voltage across the secondary battery is expressed by the following equation.

Eo (voltage across the secondary battery) = Ei (2
Electromotive voltage of secondary battery) -load current x Ri (internal resistance of secondary battery) Therefore, for an electronic device or the like in which the load current becomes large even for a moment, the over-discharge prevention circuit immediately operates to operate the electronic device. Can't do it. Further, when the load is large, the switching element has a large power rating, which is disadvantageous in space for a small electronic device such as a camera.

The present application has been made in order to solve such a conventional problem. An over-discharge prevention circuit is provided which prevents the over-discharge prevention circuit from operating during heavy load current drive control of an electronic device within a predetermined time. The purpose is to provide.

[0013]

In order to achieve the above-mentioned object, the over-discharge prevention device of the present application is the same as that of claim 1
A secondary battery, an electronic device using the secondary battery as a power source, and
An over-discharge preventing means for preventing over-discharge of the secondary battery and a control device for controlling the operation of the electronic device, and a prohibiting means for prohibiting the operation of the over-discharge preventing means during the control operation of the control device. Is provided, and in Claim 2,
The electronic device has a secondary battery built-in or replaceable, an over-discharge prevention unit for preventing over-discharge of the secondary battery, and a secondary battery voltage detection unit for controlling the over-discharge prevention unit. A holding circuit for holding the voltage of the secondary battery is provided, the secondary battery voltage detecting means detects the output voltage of the holding circuit, and the holding circuit for holding the voltage of the secondary battery has a reverse voltage flow. It is composed of a prevention element and a capacitor.
An electronic device having a built-in or replaceable secondary battery, and the above 2
An overdischarge prevention unit for preventing overdischarge of the secondary battery; and a secondary battery voltage detection unit for controlling the overdischarge prevention unit,
Further, during operation of the electronic device, there is a boosting means for boosting the voltage of the secondary battery in response to a signal from the control circuit, and the voltage detecting means detects the voltage of the boosting means, and 6. The rechargeable battery according to claim 5, an electronic device capable of incorporating or replacing the rechargeable battery, an over-discharge prevention unit for preventing over-discharge of the rechargeable battery, and a control unit for controlling the over-discharge prevention unit. Secondary battery voltage detection means, and further has means for prohibiting the detection operation of the secondary battery voltage detection means in response to a signal from the control circuit during the operation of the electronic device. The electronic device described in the section may be a camera or other device.

[0014]

In the structure of claim 1 of the present invention, when the electronic equipment such as the camera is operated, the over-discharge preventing circuit is not operated during the energization time, and in the structure of claim 2, The voltage holding means backs up the operation of the control circuit even during the control operation of the electronic device, and operates so as to supply power to the control circuit. Further, in the structure according to the fourth aspect, the voltage boosting means of the secondary battery operates so as to increase the input voltage of the voltage detecting means so as to supply the power of the control circuit during the control operation of the electronic device. Further, in the structure of the fifth aspect, the operation of the secondary battery voltage detection means is prohibited by the signal from the control means during the operation of the electronic device such as the camera.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram best showing the features of the present invention, and is a circuit diagram showing a circuit of a camera as an example of electronic equipment, which will be described with reference to FIG.

Reference numeral 1 is a secondary battery, 2 is a voltage detecting means for indirectly detecting the voltage of the secondary battery 1, and 3 is an ON / OFF switch for supplying power to a load based on an output from the voltage detecting means 2. A switching element, 4 is a CPU of a camera which is an electronic device, 6 is an internal resistance existing inside due to the characteristics of the secondary battery,
7 is a data imprinting device including a clock function of a camera which is an electronic device, 8 is a strobe circuit of the camera, 9 is a motor drive circuit of the camera, 10 is a distance measuring circuit, 11 is a photometric circuit, 12
Is a motor operated by the motor drive circuit 9, 13 is a capacitor which is a voltage holding means for indirectly holding the voltage of the secondary battery 1, 14 is a diode which is a backflow preventing means, 20
1 is a CMOS comparator of the voltage detecting means 2;
Reference numerals 02 and 203 denote dividing resistors for detecting the voltage of the voltage detecting means 2, and reference numeral 204 denotes a reference voltage circuit for generating the reference voltage of the voltage detecting means 2. Reference numerals 15 and 16 are switches for operating a camera which is an electronic device, 17 is a camera shutter drive coil, and 18 is a camera shutter drive circuit.

Next, in the above configuration, the camera operation will be briefly described in the order of the flowchart of FIG. In the following flowchart, each step is abbreviated as S.

Starting from S101, first, it is determined whether or not the switch 15 which is a switch for obtaining subject information when the user uses the camera is turned on (S10).
102), if turned on, the process from S103 onward is performed, and if not turned on, S102 is repeated again. Then, the camera performs a distance measuring operation to obtain the distance information of the main subject (S103). Next, in S104, the photometric circuit 11 of FIG. 1 is operated to obtain the brightness information of the main subject. Next, according to the brightness information obtained in S104, the strobe circuit 8 in FIG. 1 charges the strobe (S105). In the flowchart of FIG. 2, the operation only when the strobe is charged will be described.

Next, when the charging of the strobe is completed, S1
In step S06, it is determined whether the switch 16 shown in FIG. 1, which is a switch for performing the main release operation of the camera, has been turned on (S106). When turned on, S108
Go to. When it is OFF, the switch 15 of FIG.
After confirming N-OFF (S107), if ON, the state is maintained as it is. If it is OFF, the process returns to the initial step S101 and waits for the switch 15 to be turned ON again. Next, in S108, according to the distance information of the main subject, the motor drive circuit 9 of FIG.
Use and drive. Next, in S109, the shutter drive circuit 18 of FIG. 1 drives the shutter. Next, in S110, the strobe light is emitted. Then, data such as date and time is imprinted on the film by the circuit of the data imprinting device 7 of FIG. 1 (S111), and when the photographing by the camera is completed, the film is advanced to the next frame. The motor drive circuit 9 drives the motor. This is the operation of the camera, especially during flash photography.

In the circuit diagram of FIG. 1, when a secondary battery (particularly, a lithium ion battery) 1 is used and the battery is left in the built-in battery, the CPU 4 and the data imprinting device (QD circuit 7) are used. Is operating continuously, so current is generated. At this time, the energy of the secondary battery (lithium ion battery) is gradually lost, and the secondary battery is over-discharged. In this case, if the battery is over-discharged due to the characteristics of the battery, it cannot be used even if it is recharged. In order to prevent over-discharge, the secondary battery 1 is passed through the diode 14 which is a backflow prevention element, and the capacitor 1 which is a voltage holding means.
3 is connected. The voltage detecting means 2 for detecting this voltage is connected to the capacitor 1 which is a voltage holding means.
When the voltage of 3 is higher than the predetermined V _REF voltage value of the reference voltage circuit 204, the switching element 3 is turned on to supply power to the CPU 4 and the QD device 7 having a clock function to operate the camera. Further, when the voltage of the capacitor 13 which is the voltage holding means is lower than the predetermined V _REF voltage value of the reference voltage circuit 204, the switching element 3 is turned off. As a result, the power supply to the CPU 4 and the QD device 7 having the clock function is stopped, and no operation is performed. Incidentally, the V _REF voltage value is set to a value of a few μA or less, which consumes a small amount of current in the voltage detecting means 2. Each of the other strobe circuit 8, motor drive circuit 9, distance measuring circuit 10, photometric circuit 11, and shutter drive circuit 18 is set to supply power in accordance with a signal from the CPU 4,
The current is not generated in the normal holding state.

Next, the over-discharge prevention circuit in the camera operating state will be described. . A description will be given while the camera is operating (especially when a heavy load such as a strobe). When charging a normal strobe,
In order to shorten the strobe charge, the primary side is shown in Figs.
A few amperes of pulse current as described above are applied to charge the battery. With such electronic devices and cameras that perform heavy load operation,
The voltage is held in the capacitor 13 which is the voltage holding means of FIG. 1 for the time corresponding to the pulse, and the over-discharge prevention circuit is not activated during that time. Therefore, a circuit that causes a heavy load on the secondary battery is a position that is not related to the overdischarge prevention circuit (a position that can be directly driven by the secondary battery).
Connect to.

The advantages of the first embodiment are: (1) The number of parts when holding the voltage is small. (2)
An electronic device or the like having a short operating time of a large current load is easy to design.

[Second Embodiment] FIG. 5 is a diagram showing a second embodiment of the present invention, and a circuit of a camera will be described as an example of an electronic apparatus. The configurations 1 to 18 are the same as those of the first embodiment shown in FIG. The point is that points 19, 20, and 23 are added to the configuration of the second embodiment.
Is CPU and data rewritable element EEPRO
DC / DC converter circuit for supplying power to M, 20
Is a diode which is a backflow prevention element, and 23 is an EEPROM
Is. In the above configuration, the sequence of the camera is the same as that in the flowchart (FIG. 2) shown in the first embodiment, and therefore its description is omitted.

In the second embodiment shown in FIG. 5, a DC / DC converter circuit 1 for boosting power supply during camera operation is provided.
9 to supply power to the EEPROM 23. This is necessary when the operating voltage of the EEPROM is higher than the secondary battery voltage. At the same time, by inputting the step-up power supply of the DC / DC converter circuit 19 to the input of the voltage detection device 2 of FIG. 5 through the diode 20, the camera, which is an electronic device, is operating (at a predetermined current or more with respect to the battery). When it operates), it works so as not to operate the over-discharge prevention circuit. And, as the effect of the second embodiment, (1) the capacity of the battery voltage holding capacitor can be reduced. Alternatively, the capacitor can be omitted. (2) While the electronic device is operating, the control circuit and the light load power supply can be backed up without operating the overdischarge prevention circuit.

[Third Embodiment] FIG. 6 is a diagram showing a third embodiment of the present invention, and a circuit of a camera will be described as an example of an electronic apparatus. The configurations 1 to 18 are the same as those of the first embodiment shown in FIG. 21 and 22 are added to the structure of this embodiment, and 21 is a switching element for switching the input of the comparator 201.
Reference numeral 2 is a resistor that pulls up the switching element 21. In the above configuration, regarding normal camera operation,
Since the same operation as that of the first embodiment is performed, the description is omitted.

Here, during operation of the camera (for the battery,
Over current corresponding to heavy load), over discharge prevention circuit 2
In order not to operate (FIG. 6), a signal is sent from the CPU 4 to the switching element 21 so as to short-circuit the resistor 203. When the resistor 203 is short-circuited, the comparator input level becomes the same as the power source level of the comparator 201,
The output of the comparator 201 becomes the power supply level. When this happens, the switching element 3 remains ON, and CP
It operates so as to supply power to the data imprinting device 7 including U4 and the clock function. Only when the camera is not operating normally, the over-discharge prevention circuit 2 of FIG. 6 operates, and the power of the CPU 4 and the data imprinting means 7 including the clock function is turned off.

The advantage of this third embodiment is that the CPU
4 and the data imprinting device 7 including the clock function, when the driving voltage is lower than the battery voltage during heavy load operation of the camera, the diode 14 as the current backflow prevention element and the capacitor 13 as the voltage holding means are unnecessary. Become. By the way, the power supply voltage is shown below.

Eo (voltage across the secondary battery) = Ei (2
Secondary battery electromotive force) -Load current x Ri (internal resistance of secondary battery 6 in Fig. 6) Indicates that the driving voltage is lower than this.

Further, as an effect of the third embodiment, even in an electronic device having no boosting means, the control circuit and the light load power supply are backed up without operating the over-discharge prevention circuit during the operation of the device. .

[Correspondence between Invention and Embodiment] In each of the above embodiments, the comparator 201 and the dividing resistors 202, 20 are provided.
3, the configuration including the voltage detection device 2 including the reference voltage circuit 204, the switching element 3, the capacitor 13, and the diode 14 corresponds to an overdischarge prevention unit that prevents overdischarge of the secondary battery according to the present invention. CPU 4 in the embodiment
Corresponds to a control device for controlling the electronic device (including the camera) of the present invention, and further holds the voltage in the capacitor 13 of the embodiment so that the electronic device (including the camera) in operation is energized, The fact that the overdischarge prevention circuit does not operate corresponds to prohibition means for prohibiting the operation of the overdischarge prevention means of the present invention, and the voltage detection device 2 of the embodiment is the overdischarge prevention means of the present invention. Corresponding to a secondary battery voltage detecting means for controlling the DC / DC converter circuit 19 (FIG. 5).
Corresponds to boosting means for boosting the voltage of the secondary battery of the present invention, and sends a signal from the CPU 4 to the switching element 21 in the embodiment to short-circuit the resistor 203 and set the output of the comparator 201 to the power supply level for power supply. The point of supplying the power corresponds to means for prohibiting the detection operation of the secondary battery voltage detection means of the present invention.

[0031]

As described above, claims 1 to 1 of the present application
According to 5, in the normal operation of the electronic device (especially during heavy load operation), by preventing the over-discharge prevention circuit from operating, the electronic device operates normally, and in the normal neglected state, The discharge prevention circuit operates to prevent over-discharge deterioration of the secondary battery. Further, according to claim 6, it is possible to prevent the secondary battery of the camera from being over-discharged.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a camera that is an electronic device according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a general operation of the camera of the first, second, and third embodiments of the present invention.

FIG. 3 is a flowchart showing a current waveform operation according to the first, second and third embodiments of the present invention.

FIG. 4 is a flowchart showing a current waveform operation according to the first, second, and third embodiments of the present invention.

FIG. 5 is a diagram illustrating a configuration of a camera that is an electronic device according to a second exemplary embodiment of the present invention.

FIG. 6 is a diagram illustrating a configuration of a camera that is an electronic device according to a third exemplary embodiment of the present invention.

FIG. 7 is a diagram illustrating a conventional example.

[Explanation of symbols]

 1 Secondary Battery 2 Voltage Detection Device 3 Switching Element 4 CPU 5 Load Circuit 6 Internal Resistance of Secondary Battery 7 Data Transfer Device 8 Strobe Circuit 9 Motor Drive Circuit 10 AF Circuit 11 AE Circuit 12 Motor 13 Capacitor 14 Diode 15, 16 Switch 17 Shutter coil 18 Shutter drive circuit 19 Booster circuit 20 Diode 21 Switching element 22 Resistor 23 EEPROM 201 Comparator 202, 203 Resistor 204 Reference voltage circuit

Claims (6)

[Claims] 1. A secondary battery, an electronic device using the secondary battery as a power source, an over-discharge prevention unit for preventing over-discharge of the secondary battery, and a control device for controlling the operation of the electronic device. An over-discharging prevention device having a prohibiting unit that prohibits the operation of the over-discharging preventing unit while the control device is in control operation. 2. An electronic device having a built-in or replaceable secondary battery, an over-discharge prevention unit for preventing over-discharge of the secondary battery, and a secondary battery voltage detection unit for controlling the over-discharge prevention unit. An over-discharge prevention device comprising: a holding circuit for holding the voltage of the secondary battery, wherein the secondary battery voltage detecting means detects the output voltage of the holding circuit. 3. The over-discharge prevention device according to claim 2, wherein the holding circuit that holds the voltage of the secondary battery includes a voltage backflow prevention element and a capacitor. 4. An electronic device having a built-in or replaceable secondary battery, an over-discharge prevention unit for preventing over-discharge of the secondary battery, and a secondary battery voltage detection unit for controlling the over-discharge prevention unit. Further, it is provided with boosting means for boosting the voltage of the secondary battery in response to a signal from the control circuit during operation of the electronic device, and the voltage detecting means detects the voltage of the boosting means. Over discharge prevention device. 5. A secondary battery, an electronic device capable of incorporating or replacing the secondary battery, an over-discharge preventing unit for preventing over-discharging of the secondary battery, and a secondary controlling the over-discharge preventing unit. An over-discharge prevention device, comprising: a battery voltage detecting means, and further having means for prohibiting the detecting operation of the secondary battery voltage detecting means in response to a signal from a control circuit during operation of the electronic device. . 6. The over-discharge prevention device according to claim 1, wherein the electronic device is a camera or other device.