JPH11266148A - Voltage detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly detect the consumption of a battery by holding the output of a comparator, while waiting the input of a voltage detection start signal when a detection object voltage becomes higher than a reference voltage. SOLUTION: Resistors R101 and R102 for battery division for dividing a battery voltage are connected serially, the side of the resistor R101 is connected to a battery 100, and the side of the resistor R102 is connected to a GND. For example, a latch circuit 104 such as an R-S latch using a NAND circuit holds the detected result of a low voltage, and its output (e) becomes a voltage detecting signal. In addition, a pulse generating circuit 105 generates a LOW active pulse, having the cycle of 1 ms and the width of 2 μs and this pulse becomes a voltage detection start signal. Thus, when the detection object voltage becomes lower than the reference voltage and when the detection object voltage gets higher than the reference voltage in the state of inputting the voltage detection start signal, the output of a comparator 103 is respectively held by the latch circuit 104.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a detection target voltage,
For example, it relates to a device driven by a battery and relates to a voltage detection circuit for detecting that the battery has been consumed and its voltage has dropped.

[0002]

2. Description of the Related Art A conventional voltage detection circuit will be described below. FIG. 8 shows a circuit configuration of the voltage detection circuit. In FIG. 8, reference numeral 800 denotes a battery, which includes resistors R801 and R8.
The reference voltage VREF is compared by the comparator 803 with the voltage divided by the resistor 02, and the comparison result is output as a voltage detection signal.

The battery 800 is gradually consumed from a fully charged state, and the battery voltage becomes (R801 / R80).
2 + 1) × VREF, the comparator 8
The output of 03 changes from "HI" to "LOW" to notify that the voltage has dropped.

[0004]

The conventional voltage detection circuit is configured as described above. When the battery voltage falls below the set value, the output is set to "LOW" and the low voltage detection is notified. Here, when the system that has received the notification stops supplying power to unnecessary parts in order to suppress the consumption of the battery 800, the voltage of the battery 800 temporarily increases.

However, in the conventional circuit, the increase in the resistance causes the voltage divided by the resistance to increase, and the output of the comparator becomes "HI" again. Thus, the battery 800
Has a problem in that the battery state cannot be accurately detected even though the battery is actually worn. Further, even after detecting the low voltage, there is a problem in that the divided resistors R801 and R802 and the comparator 803 consume more power from the consumed battery 800 because they are operating.

SUMMARY OF THE INVENTION The present invention solves the above-described problem. After the battery voltage has fallen below a set value, the detection result is retained even if the battery voltage fluctuates, and a voltage at which the consumption of the battery can be correctly detected. The object of the present invention is to provide a detection circuit.
An object of the present invention is to provide a voltage detection circuit capable of suppressing power consumption in the voltage detection circuit by disconnecting the ND and keeping the output of the comparator in the “LOW” state and in a stop state.

[0007]

According to a first aspect of the present invention, there is provided a voltage detection circuit comprising: a comparator for comparing a detection target voltage with a reference voltage; a voltage start signal generation circuit for outputting a voltage detection start signal; And a latch circuit for holding the output of the comparator when the voltage to be detected becomes higher than the reference voltage when the voltage becomes lower than the reference voltage and when the voltage detection start signal is input.

According to the first aspect of the present invention, the voltage detection circuit has a latch circuit and a voltage start signal generation circuit such as a pulse generation circuit, and when the comparator detects a low voltage due to a decrease in a detection target voltage such as a battery voltage. , The detection signal is set to, for example, “LOW”, and the state is maintained. When returning from the low voltage detection state, if the voltage detection start signal is input and the battery voltage is equal to or higher than the predetermined reference voltage of the comparator, the detection signal is returned to "HI".
For this reason, after the detection target voltage falls below the set value, the detection result is held even if the voltage fluctuates, and is held until the detection target voltage rises above the reference voltage again, such as when the battery is charged. Exhaustion can be correctly detected.

According to a second aspect of the present invention, there is provided a voltage detection circuit.
In the above, the detection target voltage is a voltage by a dividing resistor whose end is connected to GND, and has a switch for disconnecting the dividing resistor and GND when the detection target voltage becomes lower than the reference voltage. This is a comparator with a terminal for operation stop which stops operation when the target voltage becomes lower than the reference voltage.

According to the voltage detecting circuit of the second aspect, in addition to the same effects as those of the first aspect, the power consumption is reduced by stopping the current flowing through the dividing resistor and the operation of the comparator after detecting the low voltage of the battery. It is possible to suppress the power consumption of the used battery and the like.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 shows a block diagram of a voltage detection circuit according to a first embodiment of the present invention. In FIG. 1, reference numeral 100 denotes a battery, and R101 and R102 are battery dividing resistors for dividing the battery voltage.
1, R102 is connected in series, the resistor R101 side is connected to the battery 100, and the resistor R102 side is connected to GND. Further, a division point b by the resistors R101 and R102 is input to a non-inverting input of the comparator 103. VREF is a reference voltage connected to the inverting input of the comparator 103, and the battery voltage is (R10
When the voltage drops below the set voltage represented by (1 / R102 + 1) × VREF, the voltage drop is detected and the comparator 10
3 is inverted from "HI" to "LOW". 10
Reference numeral 4 denotes a latch circuit such as an RS latch using a NAND circuit, for example, which holds a result of detecting a low voltage. The output e of the latch circuit 104 becomes a voltage detection signal. A pulse generation circuit 105 is an example of a voltage detection start signal generation circuit, and generates a LOW active pulse having a width of 2 μs at a period of 1 ms. This pulse becomes a voltage detection start signal.

FIG. 2 is a flowchart showing the processing of the voltage detection circuit. Step 50 is a state in which a low voltage has not been detected. Step 51 compares the battery voltage with a reference voltage. Step 52 sets the comparator output to LOW when the battery voltage is low. Step 53 holds the low voltage detection state. Step 54 is a state of waiting for start pulse input. If no start pulse is received, the process returns to step 53, and if a start pulse is received, the process returns to step 51. Step 55 sets the comparator output to HI when the battery voltage is high.

FIG. 3 is a timing chart when a low voltage is detected.
FIG. 7 is a timing chart at the time of return from the low voltage detection state.
The operation of the first embodiment will be described with reference to FIGS. First, the battery 100 is currently fully charged, and (R101 / R102 + 1) × VR
It is assumed that the voltage is higher than the voltage set by EF. The operation in the case where the battery 100 is gradually consumed from this state and becomes lower than the set voltage will be described with reference to FIG. Hereinafter, reference numerals to indicate the operation in the range of the corresponding reference numerals in FIGS.

As the battery voltage decreases, the potential at point b decreases as shown in FIG. From the set reference voltage b
If the potential of the point is high, the output c of the comparator 103
Remains at "HI", no low voltage is detected, and the comparator 103 continues the comparison. Note that the output of the pulse generation circuit 105 is in a Hi state in which no pulse is generated. When the potential at the point b falls below the reference voltage, the point c becomes “L”.
OW ", and the internal signal d of the latch circuit 104 becomes" L ".
OW "changes to" HI. "At the time of voltage comparison, point a is" HI ", and point e is" HI "to" LOW ".
To notify that a low voltage has been detected.

[0015] Immediately after the detection of the low voltage, the battery voltage fluctuates and becomes higher than the reference voltage.
Is changed to "HI", the point d does not change to "HI" because the point e is "LOW". Therefore, the point e does not change to "LOW". The detection result is retained. Next, an operation in a case where the voltage of the battery 100 recovers and the battery 100 returns from the low voltage detection state will be described.
When the battery voltage rises above the set voltage while the voltage detection start signal (output a of the pulse generation circuit 105) outputs "LOW", it is possible to return from the low voltage detection state. This will be described with reference to FIG.

When the battery voltage has not risen sufficiently, the output e of the latch circuit 104 outputs "HI" while the voltage detection start signal "a" outputs "LOW". However, since d is "HI", the output a return to "HI" (time t _1), again e becomes "LOW", the low voltage detection state. When the voltage detection start signal “a” becomes “LOW” after the battery voltage has risen above the set voltage, the comparator output “c” becomes “HI”, so the latch circuit 104
Becomes “LOW”, and the voltage detection signal e becomes “H”.
"A. Signal d is" I "to become the voltage detection signal e, a is" LOW even back to HI "(time t ₂₎
"HI" will be maintained. This state will continue until the battery voltage falls below the set voltage.

As described above, the comparison result of the comparator 103 is held in the latch circuit 104, and the pulse generation circuit 105
By generating the voltage detection start signal in step (1), even if the battery voltage fluctuates after the detection of the low voltage, the consumption of the battery can be correctly detected. Second Embodiment FIG. 5 shows a block diagram of a voltage detection circuit according to a second embodiment of the present invention. FIG. 5 is different from FIG. 1 in that a comparator 503 with an operation stop terminal controlled by a voltage detection signal and a switch 506 are used.
By disconnecting between the voltage detection circuit 2 and GND, the power consumption of the voltage detection circuit itself can be suppressed.

In FIG. 5, reference numeral 500 denotes a battery, and R501 and R502 are battery voltage dividing resistors for dividing the battery voltage. The division point g by these resistors is input to the non-inverting input of the comparator 503. VREF is a reference voltage connected to the inverting input of the comparator 503, and the battery voltage is (R501)
/ R502 + 1) × VREF, the voltage drop is detected and the comparator 503
Is inverted from "HI" to "LOW". 504
Is a latch circuit which holds the result of detecting a low voltage.
The output j of the latch circuit 504 becomes a voltage detection signal. 50
Reference numeral 5 denotes a pulse generating circuit which has a 1 ms cycle and a 2 μs width LO.
This circuit generates a W active pulse. This pulse becomes a voltage detection start signal. Reference numeral 506 denotes a switch composed of an N-channel transistor.

FIG. 6 is a timing chart at the time of low voltage detection using the circuit of FIG. 5, and FIG. 7 is a timing chart at the time of return from the low voltage detection state using the circuit of FIG. The operation of the second embodiment will be described with reference to FIGS. By using a switch 506 that cuts off the current path to the divided resistor as shown in FIG. 5 and a comparator with an operation stop terminal as the comparator 503, the power consumption of the detection circuit itself can be reduced after detecting a low voltage. Can be. When the comparator is stopped, it uses a comparator that consumes no power and outputs "LOW". With this configuration, the power consumption of the battery in the voltage detection circuit after the detection of the low voltage can be suppressed without changing the sequence relating to the voltage detection.

The operation when the low voltage is detected in the circuit shown in FIG. 5 will be described with reference to FIG. As the battery voltage decreases, the potential at point g decreases as shown in FIG. If the potential at point g is higher than the reference voltage,
The output h of the comparator 503 remains "HI", no low voltage is detected, and the comparator 503 continues the comparison.
At this time, the point f of the pulse generation circuit 505 is Hi, the point i is LOW, and the voltage detection signal j is HI.

When the potential at point g becomes lower than the reference voltage, h is inverted to "LOW", and the internal signal i of the latch circuit 504 changes from "LOW" to "HI". The point f at the time of voltage comparison is “HI”, and the point j is inverted from “HI” to “LOW” to notify that a low voltage has been detected (time t ₃ ). Further, the switch 506 is turned off with the inversion of the point j, and the point g rises from the divided potential to the battery potential. In addition, the comparator 503 stops, and the output point h is fixed at “LOW”.

Even if the battery voltage fluctuates immediately after the detection of the low voltage, the output h of the comparator 503 remains "LOW" and does not change. Both the i-point and the j-point do not change, and the detection result is held. Next, an operation in a case where the voltage of the battery recovers and returns from the low voltage detection state will be described with reference to FIG.

When the battery voltage has not risen sufficiently, the output j of the latch circuit 504 outputs "HI" while the voltage detection start signal f outputs "LOW". Here, the switch 506 and the comparator 503 start operating, but since the battery voltage is lower than the set voltage, the comparator output h remains “LOW” and i remains “HI”, so that the output f changes to “HI”. When returning (time point t ₄ ), j again becomes “LOW”, and the state becomes the low voltage detection state.

When the voltage detection start signal f becomes "LOW" after the battery voltage rises above the set voltage, the comparator output h becomes "HI", so that the signal i of the latch circuit 504 becomes "HI". It becomes “LOW”, and the voltage detection signal j becomes “HI”. Signal i is "LOW"
To become, the voltage detection signal j is, f is to keep even go back to "HI" (time t ₅₎ "HI". This state will continue until the battery voltage falls below the set voltage.

As described above, by using the switch 506 for disconnecting the current path to the divided resistor and the comparator 503 having a terminal for stopping the operation, the sequence relating to the voltage detection shown in the first embodiment can be changed. Instead, the power consumption of the battery in the voltage detection circuit after the detection of the low voltage can be suppressed. In each of the embodiments described above,
The voltage detection start signal has been described using a pulse having a width of 2 μs and a period of 1 ms, but both the period and the pulse width may be freely set.

In the above embodiment, the latch circuit 1
Although an RS latch composed of two NAND gates is illustrated as 04 and 504, any configuration may be used as long as it has a function similar to this and can hold data. In the above embodiment, the reference voltage is connected to the inverting input of the comparator, and the output of the comparator is set to “LOW” when a low voltage is detected. However, the reference voltage is connected to the non-inverting input.
A configuration may be adopted in which the output of the comparator becomes “HI” when a low voltage is detected.

In the second embodiment, an N-channel transistor is used as the switch 506 for cutting off the current path to the divided resistor, but a CMOS switch may be used. As a detection start signal, a method of using an operation start signal of a circuit using this voltage detection signal is considered, but a more general-purpose voltage detection circuit can be realized by inputting a periodic short pulse. realizable.

[0028]

According to the voltage detection circuit of the first aspect,
It has a latch circuit and a voltage start signal generation circuit such as a pulse generation circuit. When the comparator detects a low voltage due to a decrease in a detection target voltage such as a battery voltage, the detection signal is set to "LOW" and the state is held. to continue. When returning from the low voltage detection state, if the voltage detection start signal is input and the battery voltage is equal to or higher than the predetermined reference voltage of the comparator, the detection signal is returned to "HI". For this reason, after the detection target voltage falls below the set value,
Even if the voltage fluctuates, the detection result is held and held until the detection target voltage rises again above the reference voltage, such as when the battery is charged, so that the consumption of the battery can be correctly detected.

According to the voltage detecting circuit of the second aspect, the same effects as those of the first aspect are obtained. In addition, after detecting the low voltage of the battery, the current flowing through the dividing resistor and the operation of the comparator are stopped to thereby reduce the consumption. It is possible to suppress the power consumption of the used battery and the like.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing a voltage detection circuit according to a first embodiment of the present invention.

FIG. 2 is a flowchart illustrating an operation at the time of voltage detection in the voltage detection circuit according to the first embodiment;

FIG. 3 is a timing chart showing an example of an operation when detecting a low voltage in the voltage detection circuit according to the first embodiment;

FIG. 4 is a timing chart showing an example of a return operation from low voltage detection in the voltage detection circuit according to the second embodiment.

FIG. 5 is a block diagram showing a voltage detection circuit according to a second embodiment of the present invention.

FIG. 6 is a timing chart showing an example of an operation when detecting a low voltage in the voltage detection circuit according to the second embodiment;

FIG. 7 is a timing chart showing an example of a return operation from low voltage detection in the voltage detection circuit according to the second embodiment.

FIG. 8 is a circuit block diagram of a voltage detection circuit having a conventional configuration.

[Explanation of symbols]

 100, 500, 800 Battery R101, R102 Battery voltage dividing resistor R501, R502 Battery voltage dividing resistor R801, R802 Battery voltage dividing resistor 103, 503, 803 Comparator, 104, 504 Latch circuit, 105, 505 pulse generation circuit, 506 switch

Claims (2)

[Claims] 1. A comparator for comparing a detection target voltage with a reference voltage, a voltage start signal generation circuit for outputting a voltage detection start signal, and an output of the comparator when the detection target voltage becomes lower than the reference voltage. And a latch circuit that waits for the input of the voltage detection start signal and holds the output of the comparator when the voltage to be detected becomes higher than the reference voltage. 2. The detection target voltage is a voltage generated by a divided resistor whose end is connected to GND. When the detection target voltage becomes lower than a reference voltage, the detection target voltage and the GND are output.
2. The voltage detection circuit according to claim 1, further comprising a switch for disconnecting the first and second comparators, and wherein the comparator is a comparator with an operation stop terminal that stops operation when the voltage to be detected becomes lower than the reference voltage.