JPS6239829A - Battery checking circuit for camera - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a battery check circuit for a camera.

(Background of the Invention) To measure the brightness of a subject, a light receiving element such as a silicon photodiode or cadmium sulfide is generally used.

The output of these photodetectors is affected by the ambient temperature, so
Conventionally, temperature compensation for the output of a light receiving element has been performed in various forms.

As one type of temperature compensation, a voltage generating circuit that generates a voltage proportional to absolute temperature is provided. In cases where analog and digital systems are used for exposure control, etc., a voltage proportional to absolute temperature can be used as an analog voltage source, or as an analog-to-digital converter (A/D converter) or digital-to-analog converter (D/A converter). A converter) is used as a reference voltage.

By the way, if the voltage of the battery of the camera drops below a predetermined value, proper exposure control etc. cannot be performed, so cameras having an automatic fog control function etc. have conventionally been equipped with a battery check mechanism. A battery check is performed by comparing the battery voltage with a reference value, but since the battery voltage is usually not affected by the ambient temperature, it is necessary to check the battery voltage in cameras that have analog and digital systems that perform temperature compensation as described above. With reference voltage proportional to temperature, A/
When performing a battery check by performing D conversion and comparing the digital value with a reference value, the digital value changes depending on the temperature even if the battery voltage is at the same level, so the reference value itself cannot be changed in proportion to the temperature. Otherwise, the circuit becomes complicated and expensive.

(Objective of the Invention) An object of the present invention is to digitally convert battery voltage using an A/D converter that uses a voltage proportional to absolute temperature as a reference voltage, and convert the digital value into a digital value, in order to solve the problems of the conventional technology. To provide a battery check circuit for a camera that does not require changing a reference value according to ambient temperature when checking a battery by comparing it with a reference value.

(Summary of the Invention) The present invention includes voltage generation means that generates a voltage proportional to absolute temperature according to a first temperature coefficient, and the output voltage thereof is used as a reference voltage of the analog-to-digital conversion means. The present invention further includes temperature coefficient imparting means for imparting a second temperature coefficient smaller than the first temperature coefficient to the battery voltage, and the battery check voltage to which the second temperature coefficient has been imparted is based on the reference voltage. The analog-to-digital conversion means converts it into a digital value, the comparison and determination means compares the value with a predetermined reference value, and the quality of the battery voltage is determined from the comparison result.

, (Embodiment) FIG. 1 shows an example of a camera exposure control circuit including an embodiment of the battery check circuit of the present invention, where l represents a battery E and a voltage dividing resistor for extracting the battery voltage at a predetermined value. The battery E is connected to a voltage generation circuit 3, which will be described later, and the connection point between the resistors R1 and R2 is connected to the base of the transistor Ql. The emitter of transistor Q1 is connected to the 7 node of diode D1, and its cathode is grounded via resistor R3. Further, the cathode of the diode DI is connected to the channel CH2 of the A/D converter 4. Here, the transistor Ql and the diode DI constitute a temperature coefficient applying circuit 2, and the applying circuit 2 applies a predetermined temperature coefficient to the voltage Vx at the connection point between the resistors R1 and R2.

The voltage generating circuit 3 is configured to generate a voltage proportional to absolute temperature. That is, the resistor R4 and the diodes D2 and D3 are connected in series to the battery E, and the connection point between the constant current source C1 and the resistor R4 is connected to the inverting input terminal of the operational amplifier AI via the resistor R5.
The connection point of is connected to the non-inverting input terminal of operational amplifier Al. The output terminal of the operational amplifier At is connected to a reference voltage input terminal VR of the A/D converter 4 and a photometric circuit 5, which will be described later, and is grounded via resistors R6 and R7. Which connection point of resistors R6 and R7 and operational amplifier A
Diodes D4 and D5 are connected between the inverting input terminal of
is connected.

Reference numeral 5 indicates a photometric circuit, in which a photodiode FD is interposed between the two input terminals of the operational amplifier A2, and two diodes D6 and D7 are installed between the output terminal and the inverting input terminal of the operational amplifier A2. are connected in series. Furthermore, the output terminal of the operational amplifier A2 is connected to diodes D8 and D9 connected in series, and the cathode of the diode D9 is grounded via a constant current source C2.
It is connected to the input channel CH1 of the A/D converter 4.

The A/D converter 4 is followed by a microprocessor 6, and as is well known, the microprocessor 6 is connected to a C.
It consists of a PU, ROM, RAM, etc., and various programs such as a main routine and a battery check subroutine to be described later are stored in advance in the ROM, and various controls such as camera exposure control are executed based on the results calculated according to the programs. .

Checking the battery voltage in this example will be explained with reference to the para-terite cell lag subroutine in FIG.

This subroutine switches the camera's power switch (not shown)
It is started by jumping from the main routine which is always started while the A/D converter 4 is turned on. When jumping from the main routine to this routine at a predetermined timing, first, in step S1, the A/D converter 4
The input voltage of input channel CH2, that is, the battery check voltage V ch2 is quantized into digital data V
Read in. Next, in step S2, the digital data Vin is compared in magnitude with a battery check reference value RN stored in the ROM in advance. If the digital data Vin is larger, the process returns to the main routine without doing anything, and if the digital data Vin is smaller than the reference value RN, a negative determination is made and the process proceeds to step S3.
It prohibits the release, displays a message indicating that the battery needs to be replaced, or displays that the battery voltage is low, and then returns to the main routine.

Here, in determining the battery check reference value RN, it is necessary to take into account that a voltage proportional to the absolute temperature is used as the reference voltage of the A/D converter 4.

That is, the output voltage VAI of the voltage generating circuit 3 can be expressed as follows, and the photometric output VA2 of the photometric circuit 5 to which the voltage VAI is supplied is expressed as follows: q: electronic charge: Portzmann's constant T: absolute temperature can be expressed.

Therefore, the current 2 of resistors R4 to R7 and constant current source C2
If the temperature coefficients of the voltage generation circuit 3 and the photocurrent IL are the same, then the output voltages VAI and V of the voltage generation circuit 3 and the photometry circuit 5 are
It can be seen that A2 is proportional to the absolute temperature T.

Here, when the amount of light incident on the photodiode PD doubles, the photocurrent IL also doubles, and the photometric output due to the change in light amount, that is, the change in the output voltage of the operational amplifier A2 Δ
VA2 can be expressed as KT - one sentence n2 (3). That is, when the amount of incident light is doubled, the output voltage of the operational amplifier A2 increases by KT - n,2 (V). IE that the amount of light is doubled
This is nothing but an increase in the V-equivalent light quantity, so in this example, at an ambient temperature of 25°C, voltage changes due to fluctuations in factors related to IEV-equivalent exposure are expressed as KT -! ln2', 36 CmV/EV). Also, since a resolution of 1/6 of IEV is sufficient for camera exposure control, etc., the L of A/D converter 4 is
The voltage corresponding to SB is selected. And A/D
If the converter 4 is 8 bits, the reference voltage Vref (=VAl
), ≠1.52 (V)...
...(4), resistors R4 to R7 of the voltage generation circuit 3
The resistance value is determined to control each exposure factor with a desired resolution.

Now, in order to find the temperature coefficient of the reference voltage V ref supplied to the reference voltage input terminal VR of the A/D converter 4, by differentiating both sides of the fourth equation with respect to the absolute temperature T, the following is obtained. Therefore, the temperature of the reference voltage V ref is The coefficient is about 5.
1 (mV/deg').

On the other hand, in FIG. 1, if the voltage at the connection point of resistors R1 and R2 is Vx, the base-emitter junction voltage of transistor Ql is Ve, and the forward voltage of diode D1 is Vd, then
The battery check voltage Vcb2 supplied to channel CH2 of the A/D converter 4 is Vch2 = Vx-We-Vd - (El)
It can be expressed as Differentiating this sixth equation with respect to the absolute temperature T gives the following equation. The voltage Vx can be expressed as: where E: battery voltage, so if the temperature coefficients of the resistors R1 and R2 are made equal, then the following equation is obtained. In addition, the base-emitter junction voltage of a transistor and the forward voltage of a diode are -2 (mV/deg)
Since it has a temperature coefficient of approximately That is, in this example, the temperature coefficient of battery check voltage Vch2 supplied to input channel CH2 of A/D converter 4 for battery check is 4
/deg).

As mentioned above, in the camera of this embodiment, the ambient temperature is 25
℃, the reference voltage V of the A/D converter 4
Since ref must be at least 1.52 (V), the battery voltage at that time must also be at least a corresponding value.

Therefore, the battery check reference value RN is the reference voltage Vret and the battery check voltage V ch2 described above.
It is determined as follows, taking into account the temperature coefficient of In other words, the reference voltage Vref is 1.52 when the ambient temperature is 25°C.
(V), the battery check voltage Vch2 should be as follows due to the difference in temperature coefficient between the two. Here, the full scale (258: decimal number) of A/D converter 4 is 1.5
2 (V), so 1.1 is applied to channel CH2.
When 8 (V) is input, the A/D output is as follows. Therefore, in the case of this embodiment, the reference value RN is set to 2.
It is sufficient to set it as 01 (decimal number).

Of course, the values of the voltage dividing resistors R1 and R2 of the power supply 1 are as follows.

It is necessary to take into account the forward voltage of the diode DI and set the battery check voltage V ch2 to 1.1111 (V) (ambient temperature 25° C.).

In this way, in this embodiment, the battery voltage is set to 4(+IIV/d) using the transistor Ql and the diode Ill.
eg) as well as giving a positive temperature coefficient.

The temperature coefficient of the reference voltage of the A/D converter 4 is set to 5.1 [V/deg], and the temperature coefficient of the A/D converter 4 is
The resolution of is set to 2, and the reference value RN for battery check is set as . Therefore, since both the reference voltage V ref and the battery check voltage V ch2 have a temperature coefficient,
It is possible to accurately check the battery voltage without changing the reference value RN every time the temperature changes.

The first θ equation can be generally expressed as follows.

However, N is the number of bits of the A/D converter 4.

By the way, the temperature coefficient of the battery check voltage in Equation 11 is the temperature coefficient due to the junction of semiconductors of transistors and diodes in the temperature coefficient giving circuit 2, and in this embodiment, it is set smaller than the temperature coefficient of the reference voltage Vref. ing. Here, if the temperature coefficient given to the battery voltage V ch2 by the temperature coefficient giving circuit 2 is made larger than the temperature coefficient of the reference voltage VreF of the A/D converter 4, the temperature will rise to a certain temperature depending on the voltage division ratio of the discrete voltage. In this case, the battery check voltage Vch2 exceeds the reference voltage Vrer, and the A/D output from the A/D converter 4 is no longer reflected in the battery check voltage Vch2, making it impossible to perform an accurate battery check. The temperature coefficient given to the voltage V ch2 must be smaller than the temperature coefficient of the reference voltage Vref. Expressing this generally, m×α, ≦β ・・・・・・(1
2) However, m is the number of semiconductors used in the temperature coefficient imparting circuit 2, αj is the junction temperature coefficient of the semiconductors, and β is the reference voltage Vre.
It can be expressed as the temperature coefficient of f. If the temperature coefficients of the semiconductors used are different, (α1+αtsuji...α,,l)≦β・
...(13). On the other hand, normally the junction temperature coefficient of a transistor or diode is approximately 2 (mV/deg)
Since the number of semiconductors used in the 4-circuit with temperature coefficient 2 is an integer, the temperature coefficient of the temperature coefficient giving circuit 2 shown by equations 11 and 12 is a discontinuous value that cannot be arbitrarily selected. .

Note that two other examples of the temperature coefficient imparting circuit 2 are shown in FIGS. 3 and 4. In Figure 3, two transistors Ql, Q
In FIG. 4, two diodes D I ,
The case where DI' is used is shown.

(Effects of the Invention) According to the present invention, a battery check voltage having a second temperature coefficient smaller than the first temperature coefficient is A/D converted according to a reference voltage having a first temperature coefficient, and the first and second temperature coefficients are Since the battery voltage is checked by comparing the battery check reference value determined according to the second temperature coefficient and its A/D conversion value, the battery check reference value is changed according to the temperature. This simplifies the configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a flowchart showing an example of a battery check processing procedure, and FIG.
4 and 4 are circuit diagrams showing two embodiments of the temperature coefficient imparting circuit. ■=Main power source: Battery R1, R2: Resistor 2: Temperature coefficient imparting circuit Ql: ) Ransistor Dl: Diode R3: Resistor 3: Reference voltage generation circuit D2-D5: Diode R4-R7: Resistor C1: Constant current source 4: A/D converter 5: Photometric circuit D6 to D9: Diode PD: Photodiode C2: Constant current source 6: Microprocessor Applicant: Nippon Kogaku Kogyo Co., Ltd. Representative Patent Attorney Fuyuki Nagai Figure 5 Figure 4

Claims (1)

[Scope of Claims] Voltage generating means connected to a power supply and generating a voltage proportional to absolute temperature according to a first temperature coefficient; and a second temperature coefficient smaller than the first temperature coefficient applied to the voltage of the power supply. a temperature coefficient applying means for applying a temperature coefficient; an analog-to-digital converting means for converting the voltage from the temperature coefficient applying means into a digital value using the voltage from the voltage generating means as a reference voltage; and a digital value obtained by the converting means. A battery check circuit for a camera, comprising: comparison and determination means for determining the voltage of the power supply by comparing the voltage with a reference value determined based on the first and second temperature coefficients.