JPH07104015A - Voltage detecting circuit - Google Patents

Abstract

PURPOSE:To detect a constant voltage even in the case where an external power source at 5V or 3.3V is used. CONSTITUTION:In the case where an external power source 1 at 3.3V is used, the voltage at 5V to be given to a power source of a constant voltage generating circuit for generating the voltage at 2.6V to be compared with the voltage of a battery 12 is obtained by using a booster circuit 20, and in the case where the external power source at 5V is used, the external power source 1 is given as it is to obtain the voltage at 5V, and the constant voltage is always given to the constant voltage generating circuit 13. With this structure, constant voltage is thereby generated by the constant voltage generating circuit 13 independently of the voltage of the external power source 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage detection circuit for detecting a low voltage battery voltage.

[0002]

2. Description of the Related Art The structure of a conventional voltage detection circuit is shown in FIG.
Will be described with reference to. FIG. 4 is a diagram showing a configuration of a conventional voltage detection circuit.

In FIG. 4, 1 is an external power source (terminal), 2
Is an internal power supply (terminal) that can be backed up with batteries,
3 is a GND (terminal) and 4 is a battery voltage detection signal (output terminal). Further, 5 and 6 are resistors for dividing the voltage of the external power source 1, 7 is a comparator, 8 is a reference voltage generating circuit using a band gap, 9 is a power source switching circuit for generating a signal for switching the external power source 1 and the battery, 10 Is a P-channel MOSFET, 11 is a diode for preventing reverse current, 1
2 is a battery, 13 is a reference voltage (about 2.
6 V) is a constant voltage generating circuit, 14 is a comparator, and 15 is a buffer which outputs a battery voltage detection signal. The above-mentioned components are inside the IC card, and the values of the resistors 5 and 6 are 70 kΩ and 50 kΩ, respectively.

Next, the operation of the above-mentioned conventional voltage detection circuit will be described. External power supply 1 is 0V to 3.3V,
Alternatively, when the voltage is changed from 0V to 5V, the non-inverting (+) input of the comparator 7 is changed from 0V to about 2.08V by the voltage dividing resistors 5 and 6.

In the reference voltage generating circuit 8, the external power source 1 has about 2
A reference potential of 1.25 V is generated at V or higher. Therefore, when the external power supply 1 is 3V, the non-inverting input is 1.25V, and the output of the comparator 7 is inverted before and after that. This output is received by the power supply switching circuit 9 to output the “H” level when the external power supply 1 is 0V to 3V, and outputs the “L” level when the external power supply 1 is 3V or more to output the P-channel MOSFET 10.
Turns off / on.

Next, the battery 12 supplies a voltage to the internal power supply 2 through the diode 11 when the external power supply 1 is 3 V or less. When the external power supply 1 is 3 V or higher, the external power supply 1 supplies a voltage to the internal power supply 2 through the MOSFET 10. At that time, a diode 11 is inserted in the power supply line of the battery 12 in order to prevent a reverse current from the internal power supply 2. Regarding the voltage of the battery 12, the constant voltage generating circuit 13 supplied with power from the external power supply 1 generates a voltage of about 2.6 V, and the comparator 14 compares the generated voltage with the battery voltage to detect the battery voltage via the buffer 15. It is output as signal 4.

[0007]

In the conventional voltage detecting circuit described above, when the external power supply 1 is 3.3V, the constant voltage generating circuit 13 does not operate normally and the desired voltage is 2.6V.
There was a problem of not outputting. This is because the constant voltage generating circuit 13 is configured to operate normally only when the external power supply 1 is at 5V.

The present invention has been made to solve the above-mentioned problems, and an object of the invention is to obtain a voltage detection circuit capable of correctly detecting a battery voltage even when the external power supply is 5V or 3.3V. And

[0009]

A voltage detecting circuit according to claim 1 of the present invention comprises the following means. [1] Detection means for detecting the voltage of the external power supply. [2] Switching signal generating means for generating a switching signal when the voltage of the external power source is lower than a predetermined value. [3] Boosting means for boosting the voltage of the external power supply based on the switching signal. [4] Constant voltage generating means for outputting a constant voltage based on the boosted external power source. [5] Comparison means for comparing the constant voltage and the battery voltage.

The voltage detecting circuit according to claim 2 of the present invention comprises the following means. [1] Reference voltage generating means for generating a reference voltage regardless of the voltage of the external power supply. [2] A step-down means for stepping down the battery voltage by a constant voltage. [3] Comparison means for comparing the reference voltage and the battery voltage reduced by the constant voltage.

The voltage detecting circuit according to claim 3 of the present invention comprises the following means. [1] A reference voltage generation circuit that generates a reference voltage regardless of the voltage of an external power supply. [2] A step-down circuit configured by a plurality of diodes to step down the battery voltage by a constant voltage. [3] A comparator that compares the reference voltage with the battery voltage reduced by the constant voltage.

A voltage detecting circuit according to a fourth aspect of the present invention comprises the following means. [1] A reference voltage generation circuit that generates a reference voltage regardless of the voltage of an external power supply. [2] A resistance voltage dividing circuit that divides the battery voltage into a constant voltage. [3] A comparator that compares the reference voltage and the battery voltage divided into the constant voltage.

[0013]

In the voltage detecting circuit according to the first aspect of the present invention, the voltage of the external power supply is detected by the detecting means. Further, the switching signal generating means generates a switching signal when the voltage of the external power supply is lower than a predetermined value.
Moreover, the voltage of the external power supply is boosted by the boosting means based on the switching signal. Further, the constant voltage generating means outputs a constant voltage based on the boosted external power source. Then, the comparison means compares the constant voltage with the battery voltage.

In the voltage detecting circuit according to the second aspect of the present invention, the reference voltage generating means generates the reference voltage regardless of the voltage of the external power source. Further, the voltage reducing means reduces the battery voltage by a constant voltage. Then, the comparing means compares the reference voltage with the battery voltage reduced by the constant voltage.

In the voltage detecting circuit according to the third aspect of the present invention, the reference voltage generating circuit generates the reference voltage regardless of the voltage of the external power source. Further, the voltage of the battery is stepped down by a constant voltage by the step-down circuit composed of a plurality of diodes. And by the comparator,
The reference voltage and the battery voltage reduced by the constant voltage are compared.

In the voltage detecting circuit according to the fourth aspect of the present invention, the reference voltage generating circuit generates the reference voltage regardless of the voltage of the external power supply. Moreover, the battery voltage is divided into a constant voltage by the resistance voltage dividing circuit. And
The comparator compares the reference voltage with the battery voltage divided into the constant voltage.

[0017]

【Example】

Example 1. The configuration of the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a configuration of a first embodiment of the present invention, and the external power supply 1 to the buffer 15 are similar to those of the conventional circuit described above. In each figure, the same reference numerals indicate the same or corresponding parts.

In FIG. 1, 16 and 17 are resistors for dividing the voltage of the external power source 1, 18 is a comparator, and 19 is 5V.
And a switching signal generating circuit for generating switching signals of 3.3V, 20 is a boosting circuit, and 21 is a switch. In addition,
The values of the voltage dividing resistors 16 and 17 are 110 kΩ and 50, respectively.
It is kΩ.

By the way, the detecting means according to claim 1 of the present invention is the same as the detecting means according to the first embodiment.
6 and 17 and a comparator 18, and the switching signal generating means according to claim 1 of the present invention is the switching signal generating means according to the first embodiment.
Corresponds to the switching signal generating circuit 19, and the boosting means according to claim 1 of the present invention comprises the boosting circuit 20 and the switch 21 in the first embodiment. The constant voltage generating means according to claim 1 of the present invention is The first embodiment corresponds to the constant voltage generating circuit 13, and the comparison means according to claim 1 of the present invention is
The first embodiment corresponds to the comparator 14.

Next, the operation of the above-described first embodiment will be described. When the external power supply 1 changes from 0V to 5V, the non-inverting (+) input of the comparator 18 changes from 0V to about 1.56V by the voltage dividing resistors 16 and 17.

In the reference power source generation circuit 8, the external power source 1 has about 2
A reference voltage of 1.25V is generated at V or higher. Therefore, when the external power supply 1 is 4V, the non-inverting input becomes 1.25V, and the output of the comparator 18 is inverted before and after that. This output is received by the switching signal generating circuit 19 of 5V and 3.3V and outputs "L" level when the external power source 1 is 0 to 4V and "H" level when it is 4V or more. This signal is sent to the booster circuit 2
When 0 is received, the voltage of the external power supply 1 is boosted to 5 V when it is at “L” level, and the voltage of the external power supply 1 is directly supplied by the switch 21 when it is at “H” level.
0 is inactive.

The first embodiment of the present invention, as described above,
A constant voltage generating circuit 13 that outputs a certain constant voltage (2.6 V) to be compared with the battery voltage in a voltage detection circuit that switches the external power supply and the battery power supply and further detects the battery voltage.
And a comparator 1 that compares the constant voltage with the battery voltage
4, a booster circuit 20 that boosts the power supply input to the constant voltage generation circuit 13, voltage dividing resistors 16 and 17 that detect the voltage of the external power supply 1, a comparator 18, and the external power supply 1
And a switching signal generating circuit 19 that determines whether the booster circuit 20 operates or not depending on the voltage.

The power supply voltage input to the constant voltage generating circuit 13 when the external power supply 1 is 3.3V is boosted to 5V by the boosting circuit 20. That is, the booster circuit 20 boosts the voltage to 5V when the external power supply 1 is 3.3V, supplies 5V only to the constant voltage generation circuit 13, and outputs the desired voltage (2.6V) from the constant voltage generation circuit 13. Output.

That is, the first embodiment is intended to detect with the same constant voltage even when the external power supply 1 is 5V or 3.3V. Therefore, the external power supply 1 supplies 3.3 V to the power supply of the constant voltage generation circuit 13 that generates 2.6 V which is a voltage to be compared with the battery voltage.
When the voltage is V, the booster circuit 20 is used to bring the voltage to 5 V, and the external power source 1
Is 5 V, the external power supply 1 is applied as it is to 5 V so that a constant voltage is always applied so that the voltage generated by the constant voltage generation circuit 13 is always constant regardless of the voltage of the external power supply 1. It is a thing. As a result, it is possible to correctly detect the battery voltage with the same value whether the external power supply 1 is 5V or 3.3V.

Example 2. The configuration of the second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a diagram showing the configuration of the second embodiment of the present invention, in which the power supply voltage 1 to the battery 1
2, the comparator 14 and the buffer 15 are the same as those of the conventional circuit described above.

In FIG. 2, reference numeral 22 is a step-down circuit for dropping the battery voltage to a certain voltage. In the second embodiment, the voltage is lowered to 1.35V for comparison with the reference voltage which is the reference voltage.

The reference voltage generating means according to claim 2 of the present invention is the reference voltage generating circuit 8 in the second embodiment.
The step-down means according to claim 2 of the present invention corresponds to the step-down circuit 22 in the second embodiment, and the comparison means according to claim 2 of the present invention corresponds to the comparator 1 in the second embodiment.
Equivalent to 4.

The reference voltage generating circuit according to claim 3 of the present invention corresponds to the reference voltage generating circuit 8 in the second embodiment, and the step-down circuit according to claim 3 of the present invention in the second embodiment. The comparator according to claim 3 of the present invention corresponds to the step-down circuit 22.
Equivalent to 4.

Next, the operation of the above-described second embodiment will be described. Whether the external power supply 1 is 3.3V or 5.0V, the reference voltage generation circuit 8 normally generates the reference voltage of 1.25V. When the battery voltage is lowered to 1.35V by the step-down circuit 22, when the battery voltage drops by about 2.6V, the non-inverting (+) input of the comparator 14 becomes 1.25V.
The battery voltage can be detected by inverting the output of the comparator 14 before and after. That is, the output of the comparator 14 changes when the voltage of the battery 12 is 2.6 V or more and when it is below, and the voltage of the battery 12 can be detected.

The second embodiment of the present invention, as described above,
In a voltage detection circuit that switches between an external power supply and a battery power supply, and further detects the battery voltage, a step-down circuit 22 that steps down the battery voltage by a certain constant voltage, and a reference voltage generation circuit 8 that generates a voltage for comparison therewith. , And a comparator 14 for comparing these voltages. That is, the reference voltage generation circuit 8 which operates from about 2V is used as the reference voltage, and the battery voltage is stepped down by a certain constant voltage for comparison. The step-down circuit 22 detects the battery voltage by stepping down the battery voltage and comparing it with the reference voltage generating circuit 8 that operates even when the external power supply 1 is at a low voltage. As a result, 3.3V even if the external power supply 1 is 5V
However, there is an effect that the battery voltage can be correctly detected with the same value.

Example 3. In the second embodiment described above, the diode drop voltage is used for the step-down circuit 22 that steps down a certain voltage, but in the third embodiment, the divided voltage of the resistors 23 and 24 is used as shown in FIG. It is a thing. Other configurations and operations are the same as those in the second embodiment. The value of the resistors 23 and 24 at this time is exactly 2.6 when the voltage of the battery 12 is 2.6.
1.25V to the non-inverting input of comparator 14 when V
Decide each value so that there is. Also, the battery 12
In order to suppress the arc extinction, it is necessary to make the resistance value as large as possible. For example, the resistance values of the resistors 23 and 24 are 27 MΩ and 25 MΩ, respectively.

The reference voltage generating means according to claim 2 of the present invention is the reference voltage generating circuit 8 in the third embodiment.
The step-down means according to claim 2 of the present invention is composed of resistors 23 and 24 in the third embodiment, and the comparison means according to claim 2 of the present invention corresponds to the comparator 14 in the third embodiment. To do.

Further, the reference voltage generating circuit according to claim 4 of the present invention corresponds to the reference voltage generating circuit 8 in the third embodiment, and the resistance voltage dividing circuit according to claim 4 of the present invention corresponds to the present embodiment. 3 comprises resistors 23 and 24, and the comparator according to claim 4 of the present invention corresponds to the comparator 14 in the third embodiment.

[0034]

As described above, the voltage detecting circuit according to the first aspect of the present invention generates the switching signal when the voltage of the external power supply is lower than the predetermined value and the detecting means for detecting the voltage of the external power supply. Switching signal generating means, boosting means for boosting the voltage of the external power supply based on the switching signal, constant voltage generating means for outputting a constant voltage based on the boosted external power supply, the constant voltage and battery voltage Since it has a comparison means for comparing, even if the external power supply is 5V,
Even at 3.3V, the battery voltage can be correctly detected with the same value.

As described above, the voltage detecting circuit according to the second aspect of the present invention includes the reference voltage generating means for generating the reference voltage regardless of the voltage of the external power source and the step-down means for stepping down the battery voltage by a constant voltage. And the comparison means for comparing the reference voltage with the battery voltage reduced by the constant voltage, it is possible to correctly detect the battery voltage with the same value regardless of whether the external power supply is 5V or 3.3V. Play.

As described above, the voltage detection circuit according to the third aspect of the present invention comprises a reference voltage generation circuit for generating a reference voltage regardless of the voltage of the external power supply, and a plurality of diodes to keep the battery voltage constant. Since the step-down circuit for stepping down the voltage and the comparator for comparing the reference voltage and the battery voltage stepped down by the constant voltage are provided, the battery voltage is correctly detected with the same value regardless of whether the external power source is 5V or 3.3V. There is an effect that can be.

As described above, the voltage detecting circuit according to claim 4 of the present invention includes a reference voltage generating circuit for generating a reference voltage regardless of the voltage of the external power source, and a resistor component for dividing the battery voltage into a constant voltage. Since the voltage circuit and the comparator that compares the reference voltage with the battery voltage divided into the constant voltage are provided, the battery voltage can be correctly detected with the same value regardless of whether the external power supply is 5V or 3.3V. Has the effect.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of the present invention.

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

FIG. 3 is a diagram showing a configuration of a third embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a conventional voltage detection circuit.

[Explanation of symbols]

 1 External power supply 2 Internal power supply 3 GND 4 Battery voltage detection signal 5 Resistance 6 Resistance 7 Comparator 8 Reference voltage generation circuit 9 Power supply switching circuit 10 MOSFET 11 Diode 12 Battery 13 Constant voltage generation circuit 14 Comparator 15 Buffer 16 Resistance 17 Resistance 18 Comparator 19 Switching signal generation circuit 20 Booster circuit 21 Switch 22 Step-down circuit 23 Resistor 24 Resistor

Claims (4)

[Claims] 1. A detecting means for detecting a voltage of an external power supply, a switching signal generating means for generating a switching signal when the voltage of the external power supply is lower than a predetermined value, and a voltage of the external power supply is boosted based on the switching signal. A voltage detection circuit comprising: boosting means, constant voltage generating means for outputting a constant voltage based on the boosted external power source, and comparing means for comparing the constant voltage with a battery voltage. 2. A reference voltage generating means for generating a reference voltage regardless of the voltage of an external power source, a step-down means for stepping down the battery voltage by a constant voltage, and a comparison between the reference voltage and the battery voltage stepped down by the constant voltage. A voltage detecting circuit comprising: 3. A reference voltage generation circuit for generating a reference voltage regardless of the voltage of an external power supply, a step-down circuit configured by a plurality of diodes for stepping down a battery voltage by a constant voltage, and the reference voltage and the constant voltage. A voltage detection circuit comprising a comparator for comparing stored battery voltages. 4. A reference voltage generating circuit for generating a reference voltage regardless of the voltage of an external power source, a resistance voltage dividing circuit for dividing a battery voltage into a constant voltage, and a battery divided into the reference voltage and the constant voltage. A voltage detection circuit comprising a comparator for comparing voltages.