JPH0142052Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is used to issue an alarm to prompt the battery to be replaced when the battery voltage drops in a device that uses a built-in battery as a power source, such as a simple fire detector for home use. This invention relates to a battery voltage drop alarm circuit.

Conventionally, this type of battery voltage drop alarm circuit generally issues an alarm by detecting the non-conducting state of the Zener diode when the battery voltage drops below the Zener voltage based on the Zener voltage of the Zener diode. There is.

However, when the battery voltage is low, for example 6 volts or less, as shown in Figure 1, the constant voltage characteristics of a Zener diode with a low Zener voltage are not good, making it difficult to accurately detect voltage using a Zener diode. It is.

Therefore, as shown in FIG. 2, conventional battery voltage drop alarm circuits with high detection accuracy rectify and boost the output of an oscillation circuit 1, which oscillates at several hundred Hz or more, in a boost circuit 2, and send it to a voltage detection circuit 3. A Zener diode ZD that has a high Zener voltage with good constant voltage characteristics is used when the boost voltage is higher than a predetermined value determined by the Zener diode ZD. While the output is kept at L level, when the boost voltage falls below a predetermined value as the battery voltage decreases, Zener diode ZD becomes non-conductive, turning off transistor Tr, and at this time, the output of inverter 4 goes to H level. The oscillation circuit 5
is activated to generate a pulse about once every 45 seconds or 10 seconds, and this pulse output activates the alarm circuit 6, which intermittently sounds a buzzer or the like to notify of a drop in battery voltage.

However, in the above circuit, even when the battery voltage is normal, the boost circuit 2 always generates a boost voltage, and the Zener diode ZD and transistor Tr are also on, so the current consumption is large and the battery There was a problem that the battery wears out quickly.

The present invention was developed in view of the above, and generates a boosted voltage by superimposing the battery voltage on the charging voltage of a capacitor that is charged to the battery voltage at every predetermined cycle using an oscillation pulse. A low battery voltage alarm circuit is designed to issue an alarm intermittently in synchronization with the above oscillation pulse when the voltage drops below the specified oscillation pulse, thereby significantly reducing the current consumption due to boosting and voltage detection, thereby extending the life of the battery. The purpose is to provide.

Hereinafter, the present invention will be explained based on the drawings.

FIG. 3 is a circuit block diagram showing an embodiment of the present invention. First, to explain the configuration, the oscillation circuit 7
outputs a rectangular pulse signal with a predetermined pulse width at predetermined intervals, and its oscillation cycle is set to match the intermittent battery voltage drop alarm cycle, for example, in the range of 10 to 45 seconds. ing. A resistor R ₁ , a capacitor C, and a forward diode D are connected in series between the positive and negative terminals 8 and 8' of the battery. transistor controlled off
A booster circuit 9 is formed by connecting Tr1 and these circuit parts.

In addition, the resistor _R1 and capacitor C of the booster circuit 9
Variable resistor VR and Zener diode ZD in parallel with
The output of the variable resistor VR is connected to the base of the transistor Tr2, and the voltage detection circuit 10 is formed by the variable resistor VR, the Zener diode ZD, and the transistor Tr2.

Further, the emitter terminal of the transistor Tr1 of the booster circuit 9 is connected to the collector terminal of the transistor Tr2 of the voltage detection circuit 10 via a resistor _R2 , and this collector terminal is connected to the alarm circuit 12 via an inverter 11.
The input is connected to the

Next, the operation of the above embodiment will be explained.

First, the operation when the battery voltage V _B is normal will be explained. As shown in FIG. 5, the oscillation circuit 7 outputs a rectangular pulse with a pulse width τ = 10 to 30 milliseconds at a constant period T, for example every 5 to 10 seconds, and this pulse signal causes the transistor of the booster circuit 9 to Tr1 is turned on and off at predetermined intervals. On the other hand, the booster circuit 9
The capacitor C is charged to a charging voltage V _C which is approximately equal to the battery voltage V _B . When transistor Tr1 is turned on in this state, the series circuit of resistor _R1 and capacitor _C1 , that is, the variable resistance of the voltage detection circuit
A boosted voltage of approximately 2V _B , which is obtained by superimposing the charging voltage of the capacitor C on the battery voltage V _B , is generated across the series circuit of VR and the Zener diode ZD.

The details of how this boosted voltage is generated are as shown in the equivalent circuit in Figure 4. When transistor Tr1 is turned on, capacitor C is connected in series with battery 13, and in this state Since a series circuit of a variable resistor VR and _a Zener diode ZD is connected in parallel with the _series circuit of
A boosted voltage equal to 2V _B will be applied.
Note that the diode D prevents the capacitor C from discharging when the transistor Tr1 is turned on.

Therefore, the Zener diode ZD of the voltage detection circuit 10 has a voltage approximately twice the normal battery voltage _VB .
By using a Zener diode with a predetermined value lower than 2V _B , when a boost voltage is applied by the operation of the booster circuit 9 when the battery voltage is normal, the Zener diode ZD becomes conductive, so that the transistor
Tr2 is turned on, the power supply voltage is applied to the input terminal of the inverter 11 via the transistor Tr2, and the output becomes an H level, and the output of the inverter 11 becomes an L level, so the alarm circuit 12 does not operate.

Next, during the rest period of the rectangular pulse of the oscillation circuit 7, the transistor Tr1 returns to off, the voltage applied to the voltage detection circuit 10 by the booster circuit 9 returns to the battery voltage _VB , and the Zener diode ZD and transistor Tr2 are turned off. , the battery voltage V _B is applied to the input of the inverter 11 via resistors R ₁ and R ₂ to maintain the H level, and similarly, the output of the inverter 11 remains at the L level and the alarm circuit 12 is not activated.

Next, the operation when the battery voltage drops and a battery voltage drop alarm is issued will be explained.

When the battery voltage V _B decreases, the boosted voltage generated by the booster circuit 9 at predetermined intervals also decreases, and when it falls below the Zener voltage of the Zener diode ZD, even if the booster circuit 9 generates a boosted voltage, ,
The Zener diode ZD of the voltage detection circuit 10 ceases to conduct. Therefore, the transistor Tr2 also remains off, and since the transistor Tr1 is on at this time, the inverter ₁ is connected via the resistor R2.
1 is pulled to the L level, and as shown in FIG. 5, the output of the inverter 11 becomes the H level and activates the alarm circuit 12. This inverter 1
The H level output of 1 is synchronized with the rectangular pulse output from the oscillation circuit 1, so the alarm circuit 13 intermittently sounds a buzzer or the like in response to the pulse output of the oscillation circuit 1 to notify of a drop in battery voltage.

What should be noted here is that, as is clear from the above operation, in the circuit of the present invention, current consumption flows only when the oscillation circuit 1 outputs a rectangular pulse. That is, when the battery voltage is normal, the transistors Tr1 and Tr2 and the Zener diode are activated by the pulse output of the oscillation circuit 1.
Current consumption occurs in ZD, but the time is 5~
The current consumption is only 10 milliseconds, and no current is consumed during the rest period of the rectangular pulse, so the current consumption is small, and the influence on battery consumption by the circuit of the present invention is minimized.

In addition, when the battery voltage drops, transistor Tr1 simply turns on and off and consumes current, and compared to when the voltage is normal, the battery voltage drop is detected with further suppressed current consumption. This has the advantage that even if the battery voltage drops, the time it takes for the voltage to drop until the circuit becomes inoperable can be extended.

FIG. 6 shows another embodiment of the present invention,
Boost control of the boost circuit 9 is performed by an inverter 15 that inverts the output of the oscillation circuit 1, and a resistor _R3 is connected to the collector terminal of the transistor Tr2 of the voltage detection circuit 10, so that the Zener diode ZD is made conductive by the boost voltage. H level output during normal operation,
Further, when the battery voltage drops, an L level output is generated, and the alarm circuit 12 is activated by taking out the inverted OR of the output of the inverter 15 and the voltage detection circuit 10 using a NOR gate 14.

Next, the operation will be explained with reference to the signal waveforms shown in FIG. If the battery voltage is normal, the output of the inverter 15 changes from H level to L level every time the oscillation circuit 1 outputs a rectangular pulse, and therefore the charging voltage V _C of the capacitor C is superimposed on the battery voltage V _B to boost the voltage. The voltage is generated by the booster circuit 9 and the voltage is detected by the voltage detection circuit 1.
0, turning on the Zener diode ZD and transistor Tr2. Therefore, the input terminal a of the NOR gate 14 becomes L level, the input terminal b becomes H level, and its output is L level, so the alarm circuit 1
2 does not work.

During the rest period of the rectangular pulse of the oscillation circuit 1, the output of the inverter 15 is at H level, and the voltage detection circuit 10
Since the output becomes L level and is applied to NOR gate 14, the output of NOR gate 14 is similarly maintained at L level and alarm circuit 12 is not activated.

On the other hand, when the battery voltage decreases, even if a boosted voltage is applied to the voltage detection circuit 10, the Zener diode ZD is non-conductive and the transistor Tr2 is not turned on, and the input terminal b of the NOR gate 14 remains at the L level. At this time, the input terminal a is set to L level by the inverter 15, so every time the oscillation circuit 1 outputs a rectangular pulse, the output of the NOR gate 14 becomes H level, activating the alarm circuit 12 and intermittently generating a buzzer etc. By sounding, a drop in battery voltage is notified, and as in the embodiment shown in FIG. 3, the current consumption is kept low.

The low battery voltage alarm circuit according to the present invention is used in simple fire detectors for home use that use a built-in battery as a power source. Since it is necessary to detect a drop in voltage and issue an alarm prompting battery replacement, the present invention is suitable as a means of notifying a drop in battery voltage in such a simple fire detector. It has the advantage of extending the exchange period.

In addition, among this type of fire detector, there is a photoelectric type smoke detector that detects the scattering or dimming of light due to incoming smoke and issues a fire alarm, and from the viewpoint of reducing current consumption, light emitting diodes are used. It is driven by pulses. Therefore, when the circuit of the present invention is used in such a photoelectric smoke detector, the output pulse of the oscillation circuit that operates the booster circuit can also be used to drive the light emitting diode.
It is possible to simplify the circuit configuration and reduce costs.

Of course, the application of the present invention is not limited to the above-mentioned fire detector, but can be used in various types of equipment that incorporate a battery as a power source.

As explained above, according to the present invention, the configuration is such that the charging voltage of the capacitor that charges the battery voltage is superimposed on the battery voltage at predetermined intervals to generate a boosted voltage. When the voltage drops below a predetermined value, an alarm is issued intermittently at the predetermined cycle, so boosting the battery voltage and determining the level of the boost voltage are performed at regular intervals, and the circuit is activated only at that time. operates and consumes current, so the current consumption can be kept low and battery consumption is prevented, and a drop in battery voltage is detected by applying a boosted voltage to the Zener diode. It is possible to use a Zener diode with a high Zener voltage and good characteristics, and a drop in battery voltage can be detected with high accuracy.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the voltage-current characteristics of a Zener diode used for voltage detection, Fig. 2 is a circuit block diagram showing an example of a conventional battery voltage drop alarm circuit, and Fig. 3 is an implementation of the present invention. A circuit block diagram showing an example, FIG. 4 is an equivalent circuit diagram formed during boosting in the embodiment of FIG. 3, and FIG. 5 is a time chart showing signal waveforms of various parts in the embodiment of FIG. 3. FIG. 6 is a circuit block diagram showing another embodiment of the present invention, and FIG. 7 is a time chart showing signal waveforms at various parts in the embodiment of FIG. 1, 5, 7... Oscillation circuit, 2, 9... Boost circuit, 3, 10... Voltage detection circuit, 4, 11, 13
...Inverter, 6,12...Alarm circuit, 8,
8'... Battery electrode, 13... Battery, 14... Noah gate, Tr, Tr1, Tr2... Transistor,
ZD...Zener diode, D...diode,
_R1 to _R3 ...Resistance, VR...Variable resistance, C...Capacitor.

Claims (1)

[Scope of utility model registration request] A battery as a power source, a capacitor that charges the battery voltage of the battery, an oscillation circuit that outputs a pulse signal at predetermined intervals, and an oscillation circuit that operates every time the oscillation circuit outputs a pulse signal to charge the capacitor. A booster circuit that generates a boosted voltage by superimposing a battery voltage on the voltage, a voltage detection circuit that detects when the boosted voltage generated by the booster circuit drops below a predetermined value and outputs it, and when the detection circuit outputs. and an alarm circuit that intermittently issues an alarm in synchronization with the output pulse of the oscillation circuit.