JPH0226066Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a battery check circuit for a camera or the like.

Conventionally, this type of battery check circuit includes:
A voltage detection circuit operated by a check switch detects whether the power supply voltage is higher than a predetermined check level voltage, and a display circuit displays the detection result.

However, in such a circuit, the voltage detection circuit generates an unstable detection output immediately after starting its operation due to check switch chattering, delay in operation of the elements that make up the circuit, etc., and the display circuit may display an incorrect display. There was a problem that it became unstable and difficult to see.

As a configuration for solving such problems, a method can be considered in which the display circuit is not activated for a certain period of time after the check switch is activated (for example, as disclosed in Japanese Patent Application No. 70161/1983 filed by the present applicant), but the voltage detection circuit When a hysteresis characteristic is imparted to the signal, the following problem occurs. In other words, if the power supply voltage is higher than the check voltage by a voltage that is less than the hysteresis voltage, if the voltage detection circuit determines that it is below the check level for some reason (described later), the voltage detection output will be lowered due to the above hysteresis characteristics. continues to indicate an insufficient power supply voltage condition. Therefore, the display of the voltage detection result remains erroneous.

This drawback will be explained in detail below with reference to FIG.

A power supply battery 1 applies voltage to the entire circuit via a check switch 2. Constant current source 3, transistors 4, 5, 6, 7, 8, constant current sources 9, 11, and resistors 10, 12, 13 are used for comparison to detect whether the voltage of power supply 1 is higher than a predetermined reference level. Configure the vessel. In this comparator, a reference voltage is input to input point A, and a voltage obtained by dividing the power supply voltage by resistors 12 and 13 is input to input point B, respectively. This input point A,
The voltage of B varies depending on the magnitude of the voltage of the power supply 1 (shown on the horizontal axis), as shown in FIG.
When the voltage of power supply 1 reaches a predetermined check level voltage Vch, the voltages at input points A and B become equal. Next, a diode 1 is connected to the output of this comparator.
4. Transistors 15, 16, 17, 18, 19
are connected, and the comparator drives a display circuit 20, such as an LED, through these circuits. The timer circuit 21 starts counting when the check switch 2 is turned on and the comparator is activated, and then turns on the transistor 22 for a predetermined period of time and turns off the transistor 19. As a result, the display operation of the display circuit 20 is forcibly stopped. Transistor 17 constitutes a positive feedback circuit for the comparator. As shown in Figure 3, once the check level voltage Vch is
When the voltage of power supply 1 drops below, transistor 8 turns OFF and transistors 15 and 17 turn ON.
Therefore, the voltage at the output point B is further increased via the transistor 17. Therefore, if the third
As shown in the figure, even if the power supply voltage increases by Vh, point A,
The magnitude relationship of the voltage of B will no longer be reversed.
In this way, once the check level voltage Vch
When the comparator detects that the power supply voltage has dropped below this level, the positive feedback circuit clamps the comparator output to prevent it from inverting again. That is, a hysteresis characteristic is given to the comparator.

Now, when switch 2 is turned on, the voltage from power supply 1 is applied to the circuit shown in Figure 1. Here, power supply 1
If the voltage is high enough, for example, if Vch is 2.1V,
When the power supply voltage is 2.15V or more, the potential at point A is higher than the potential at point B as shown in Figure 3, so transistor 8 is turned on and transistor 15 is turned on.
It becomes OFF. Therefore, transistors 16-18
Therefore, the display circuit 20 does not operate regardless of the operation of the timer circuit 21. In this way, it can be seen that the voltage of the power supply 1 is sufficiently high.

Next, the voltage of power supply 1 becomes check level voltage Vch
We will explain the case where it is lower than . In this case, as shown in FIG. 3, the voltage at input point A is sufficiently lower than the voltage at input point B, so transistor 8 of the comparator
It is turned OFF, transistor 15 is turned ON, and transistors 16 to 18 are turned ON. On the other hand, the timer circuit 21 generates an H level output for a predetermined period of time after the switch 2 is turned on, and the transistor 22
is turned on, so transistor 19 is still turned off. After the predetermined time has elapsed, the output of the timer circuit 21 becomes L, and the transistor 22
It becomes OFF. Therefore, the transistor 19 is also turned on, the display circuit 20 is activated, and it can be seen that the voltage of the power supply 1 is lower than the check level voltage Vch.

Next, the voltage of power supply 1 becomes check level voltage Vch
Although it is slightly higher, a case will be described in which an erroneous determination is made due to chattering of the switch 2 or a delay in the operation of elements constituting the circuit.

First, when switch 2 is turned on, the comparator is activated. In this case, since the voltage of the power supply 1 is slightly higher than Vch (for example, about 2.1V to 2.15V), the transistor 8 should originally be turned on. However, due to the chattering that occurs when switch 2 is turned on, transistor 8
Before turning on, transistors 15, 16, 1
7 and 18 may become ON. In that case, the potential at point B is raised via transistor 17, so transistor 8 eventually becomes
It does not turn ON, and the display circuit 20 displays that the power supply voltage is lower than the check level Vch as described above. In other words, the result is an erroneous determination. In this state, even after the voltage of the power supply 1 applied to the comparator reaches the actual voltage of the power supply 1, the voltage at point B is increased by the transistor 17, so the display circuit 20 is Maintain a false representation. still,
In order to reverse this display state, the voltage of the power supply 1 must rise from the check level Vch in FIG. 3 to a level higher by Vh.

In this way, once the comparator 1 determines that the voltage of the power supply 1 is below the check level Vch,
A problem arises in that the transistor 17 is activated and the check level voltage Vch appears to rise, making it impossible to easily return to the original correct display state.

Generally, the display circuit 21 itself operates so that it is not possible to continue taking pictures when the power supply voltage is lower than the check level voltage Vch, for example, the display circuit 21 is often configured to have a release lock. With such a configuration, there is a problem in that the shutter release is locked due to the above-mentioned erroneous determination.

In order to solve such problems, the battery check circuit according to the present invention aims to prevent misjudgment of the power supply voltage and maintenance of the misjudgment due to chattering, delay in operation of component elements, etc.

FIG. 2 is a diagram showing an embodiment of the present invention.

Transistor 23 constitutes an active element according to the present invention. The other configurations are the same as those shown in the first figure. When the switch 2 is turned on and the comparator starts operating, the timer circuit 21 is activated and the transistor 23 is turned on. Therefore, by turning on transistor 23, transistor 1 is forced to turn on.
5, 16, and 17 are turned off, the operation of the positive feedback circuit is stopped. That is, the voltage at point B does not rise.
After a predetermined period of time has elapsed, the timer circuit 21 turns off the transistor 23. Transistors 15, 16, 17, 18, 19 can then be activated in response to the output of the comparator.

In this way, since the operation of the positive feedback circuit is stopped for a predetermined period of time after the comparator starts operating, if the voltage of the power supply 1 is only slightly higher than the check level Vch, the noise generated when the switch 2 is turned on will cause the transistor 8 transistor 1 before
Even if transistor 5 is turned on, the voltage at point B is not increased by the positive feedback circuit, and when the positive feedback circuit operates after a predetermined period of time, transistor 8
is turned ON and transistors 15 to 19 are turned OFF, so that it is correctly displayed that the power supply voltage is higher than the check level Vch.

As described above, according to the present invention, even if the power supply voltage is close to the check level Vch, erroneous determination of the voltage level is prevented, so that the detection accuracy of the battery check circuit is significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the configuration of a battery check circuit, FIG. 2 is a diagram showing an embodiment of the battery check circuit according to the present invention, and FIG. 3 is a diagram showing the operation of the battery check circuit. FIG. Explanation of symbols of main parts, voltage detection circuit...3~
13, Timer circuit...21, Active element...23,
Check level...Vch.

Claims (1)

[Claims for Utility Model Registration] A check switch that is turned on when detecting the power supply voltage, and a hysteresis characteristic that determines whether the power supply voltage is below a predetermined check level by turning on the check switch. Voltage detection means; first switch means for prohibiting the discrimination operation of the voltage detection means having hysteresis characteristics; and a display that receives the discrimination output of the voltage detection means and lights up when the power supply voltage is below a predetermined check level. means, second switch means for prohibiting the display operation of the display means, and counting a predetermined time from when the check switch is turned on, and turning off the first and second switch means until the predetermined time elapses. 1. A battery check circuit comprising: one timer means which is activated to inhibit a discrimination operation having a hysteresis characteristic of the voltage detection means and a display operation of the display means.