JP2006177724A - Voltage detection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage detection circuit for reducing the current consumed in a reduced voltage state. <P>SOLUTION: The voltage detecting circuit 1000 detects the reduced voltage state of a battery voltage to be monitored. A first voltage detecting section 100 compares the battery voltage Vbat with a first threshold voltage Vth1. A second voltage detecting section 200 compares the battery voltage Vbat with a second threshold voltage Vth2, until the battery voltage Vbat reaches the second threshold voltage Vth2 that is higher than the first threshold voltage Vth1, after the battery voltage Vbat becomes lower than the first threshold voltage Vth1. An output section 300 is set in the reduced voltage state, until the battery voltage Vbat reaches the second threshold voltage Vth2, after the battery voltage Vbat becomes lower than the first threshold voltage Vth1. The first voltage detecting section 100 is turned off during this duration. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a voltage detection circuit that detects a reduced voltage state in which a voltage to be monitored is lower than a predetermined threshold voltage, and more particularly to a technique for reducing the current consumption.

  Many small information devices such as mobile phones and PDAs (Personal Digital Assistants) are equipped with a battery, and an internal electronic circuit is driven by a battery voltage output from the battery.

  Here, for example, in the case of a lithium ion battery, the output voltage of the battery is about 4.2 V at the time of full charge, and thereafter, the output voltage decreases with power consumption. Here, in order to stably operate the electronic circuit inside the small information device, each electronic circuit needs to be supplied with a predetermined voltage or more. Therefore, in many small information devices, a voltage detection circuit for detecting a reduced voltage state of the battery is provided.

  Here, the voltage detection circuit generally compares the battery voltage with a predetermined threshold value. For example, in Patent Document 1, a battery voltage is applied to the base of a bipolar transistor whose emitter is grounded, a forward voltage Vbe between the base and emitter is used as a threshold value, and a reduced voltage state is detected corresponding to the on / off state of the transistor.

Further, as a method of detecting the reduced voltage state more accurately, a method of detecting the reduced voltage state by comparing the battery voltage with the threshold voltage generated by the reference voltage source using a voltage comparator is also conceivable. .
JP 2001-258169 A

  Here, the case where the battery mounted in a small information device is a rechargeable battery is considered. When detecting a reduced voltage state for such a rechargeable battery, if the battery voltage rises due to charging in a reduced voltage state where the battery voltage has dropped due to power consumption, the normal state is restored again. Therefore, it is necessary to monitor the battery voltage even in a reduced voltage state where the battery voltage is lower than the threshold voltage. Here, in order to monitor the battery voltage in the reduced voltage state, it is desirable that the current consumption of the voltage detection circuit is as low as possible.

  The present invention has been made in view of these problems, and an object of the present invention is to provide a voltage detection circuit with reduced current consumption in a reduced voltage state.

  One embodiment of the present invention relates to a voltage detection circuit. The voltage detection circuit is a voltage detection circuit that detects a reduced voltage state in which a voltage to be monitored is lower than a predetermined threshold voltage, and a first voltage that compares the voltage to be monitored with a first threshold voltage. The detection unit and a period of time from when the monitored voltage becomes lower than the first threshold voltage until reaching the second threshold voltage set higher than the first threshold voltage, A second voltage detector for comparing the two threshold voltages and a period from when the monitored voltage becomes lower than the first threshold voltage to the second threshold voltage being output as a reduced voltage state And an output unit for turning off the first voltage detection unit in the reduced voltage state.

  According to this aspect, by providing the first voltage detection unit operating in the normal voltage state and the second voltage detection unit operating in the reduced voltage state, the current consumption and detection accuracy required in each state are individually set. be able to.

  The output unit includes a flip-flop that is set and reset by the outputs of the first voltage detection unit and the second voltage detection unit, and based on the output of the flip-flop, either the first voltage detection unit or the second voltage detection unit Either one may be turned on.

  Another embodiment of the present invention is also a voltage detection circuit. This voltage detection circuit is a voltage detection circuit for detecting a voltage to be monitored input to a detection terminal, and the first and second resistors connected to the detection terminal and the base terminal are connected in common, and the first The first and second transistors constituting the current mirror pair with the second resistor as the collector load, the third resistor connected to the emitter terminal of the second transistor, and the emitter terminal and the third resistor of the first transistor are connected. A fixed voltage terminal for supplying a fixed voltage, a base terminal connected to the collector terminal of the second transistor, an emitter terminal connected to the fixed voltage terminal, and a collector terminal of the third transistor and the detection terminal A fourth resistor connected thereto, and performs voltage detection based on a voltage appearing at a collector terminal of the third transistor.

According to this aspect, when the voltage to be monitored is low, the voltage between the emitter and collector of the first to fourth transistors is low, so that each transistor is turned off. When the voltage to be monitored rises and exceeds a certain threshold voltage, each transistor is turned on and current flows. Therefore, current flows through the fourth resistor connected to the collector terminal of the third transistor, causing a voltage drop. Therefore, it can be detected that the monitored voltage exceeds the threshold voltage.
Further, by arranging each transistor and each resistor in a configuration similar to that of a so-called band gap reference circuit, variation in threshold voltage due to temperature change can be suppressed.

At least one diode may be further provided on the current path between the detection terminal and the fixed voltage terminal.
By providing the diode, the voltage to be monitored can be level shifted, and the threshold voltage can be adjusted by adjusting the number of diode stages. Further, the temperature characteristics of the diode can be canceled by the above-described transistor.

  The first voltage detection unit may include a reference voltage source that generates the first threshold voltage, and a voltage comparator that compares the voltage to be monitored with the first threshold voltage.

By providing the first voltage detection unit with the reference voltage source and the voltage comparator, it is possible to accurately detect the transition to the reduced voltage state.
The reference voltage source may be a band gap reference circuit.

Another aspect of the present invention relates to a voltage detection circuit having a first voltage and a second voltage higher than the first voltage as monitoring thresholds. The voltage detection circuit includes a first monitoring unit that starts comparison between the monitoring target voltage and the second voltage when the monitoring target voltage falls below the first voltage, and when the monitoring target voltage exceeds the second voltage. A second monitoring unit that starts comparison between the monitored voltage and the first voltage. The first monitoring unit is off during the period when the second monitoring unit monitors the monitoring target voltage, and the second monitoring unit is off during the period when the first monitoring unit monitors the monitoring target voltage.
According to this aspect, it can be used in place of the hysteresis comparator and the like, and by providing the first monitoring unit and the second monitoring unit, current consumption and detection accuracy required in each state are individually set. be able to.

First, an outline of an embodiment of the present invention will be described. The voltage detection circuit according to the present embodiment is used in battery-driven small information devices such as mobile phones and PDAs, and stably drives each electronic circuit used inside from a rechargeable battery such as lithium ion. Monitor whether the necessary voltage is output.
This voltage detection circuit detects when the monitored battery voltage is below the threshold voltage (hereinafter referred to as a reduced voltage state) or when the battery voltage is higher than the threshold voltage (hereinafter referred to as a normal voltage state). Then, the control unit that controls the entire small information device is notified.

Hereinafter, the voltage detection circuit according to the present embodiment will be described in detail with reference to the drawings.
FIG. 1 shows a configuration of a voltage detection circuit 1000 according to the present embodiment. The voltage detection circuit 1000 includes an input terminal 1002 and an output terminal 1004 as input / output terminals. A battery voltage Vbat is input to the input terminal 1002 from a battery (not shown). Further, a control unit (not shown) is connected to the output terminal 1004. The voltage detection circuit 1000 outputs from the output terminal 1004 a detection signal SIG10 in which the normal voltage state and the reduced voltage state are associated with the high level and the low level, respectively.

  The voltage detection circuit 1000 includes a first voltage detection unit 100, a second voltage detection unit 200, and an output unit 300.

  The first voltage detector 100 monitors the battery voltage Vbat in the normal voltage state, and detects the transition to the reduced voltage state. The battery voltage Vbat is input to the detection terminal 102 of the first voltage detection unit 100, and the first threshold voltage Vth1 is compared with the battery voltage Vbat. The output terminal 104 of the first voltage detector 100 outputs a first detection signal SIG1 that is at a low level when Vbat> Vth1 and at a high level when Vbat <Vth1. The first detection signal SIG1 is output to the output unit 300.

  The first voltage detection unit 100 includes an enable terminal 106. The first voltage detection unit 100 is turned on when the enable signal input to the enable terminal 106 is at a high level and monitors the battery voltage Vbat, and is turned off when the enable signal is at a low level, and monitors the battery voltage Vbat. Stop and reduce current consumption.

  The second voltage detection unit 200 monitors the battery voltage Vbat in the reduced voltage state, and monitors the return to the normal voltage state. Similar to the first voltage detector 100, the battery voltage Vbat is input to the detection terminal 202, and the second threshold voltage Vth2 is compared with the battery voltage Vbat. The output terminal 204 of the second voltage detector 200 outputs a high level when Vbat> Vth2, and a low level when Vbat <Vth1. The second detection signal SIG2 is input to the output unit 300. The second threshold voltage Vth2 used in the second voltage detector 200 is set higher than the first threshold voltage Vth1.

  The second voltage detection unit 200 also includes an enable terminal 206. The second voltage detector 200 is turned on when the enable signal input to the enable terminal 206 is at a high level and monitors the battery voltage Vbat, and is turned off when the enable signal is at a low level, and monitors the battery voltage Vbat. Stop to reduce current consumption.

The output unit 300 receives the first detection signal SIG1 and the second detection signal SIG2 output from the first voltage detection unit 100 and the second voltage detection unit 200.
The output unit 300 includes an RS flip-flop 30, transistors M1 and M2, and a resistor R30.

The second detection signal SIG2 output from the second voltage detection unit 200 is input to the set terminal S of the RS flip-flop 30, and the first detection signal output from the first voltage detection unit 100 is input to the reset terminal R. SIG1 is input.
The output terminal Q of the RS flip-flop 30 is connected to the gate terminal of the transistor M1 and to the enable terminal 106 of the first voltage detector 100. Further, the inverting output terminal Q ′ is connected to the enable terminal 206 of the second voltage detector 200. Since the two output terminals Q and Q ′ of the RS flip-flop 30 output signals in which high and low are inverted, one of the first voltage detection unit 100 and the second voltage detection unit 200 is the battery voltage Vbat. When the other is monitored, the other stops the monitoring operation.

The transistor M <b> 1 is an N-type MOSFET (Metal Oxide Field Effect Effect Transistor), and has a gate terminal connected to the output terminal Q of the RS flip-flop 30. The source terminal of the transistor M1 is grounded. A resistor R30 is connected to the drain terminal of the transistor M1, and the battery voltage Vbat is applied.
The transistor M2 is a P-type MOSFET, and the gate terminal is connected to the drain terminal of the transistor M1. The battery voltage Vbat is applied to the source terminal of the transistor M2, and the drain terminal is the output terminal 1004 of the voltage detection circuit 1000.

When the RS flip-flop 30 is set and a high level is input to the gate terminal of the transistor M1, the transistor M1 is turned on and a current flows through the resistor R30. Therefore, the gate voltage of the transistor M2 drops and the transistor M2 is turned on. . When the transistor M2 is turned on, the drain-source voltage decreases, and therefore, a high level detection signal SIG10 close to the battery voltage Vbat is output from the output terminal 1004.
Conversely, when the RS flip-flop 30 is reset and a low level is input to the gate terminal of the transistor M1, the transistor M1 is turned off, so that no current flows through the resistor R30 and the transistor M2 is not turned on. Outputs a low level detection signal SIG10.

  Based on the first detection signal SIG1 and the second detection signal SIG2, the output unit 300 configured in this way has a second threshold value after the battery voltage Vbat to be monitored becomes lower than the first threshold voltage Vth1. A period until the voltage Vth2 is reached is output as a reduced voltage state, and the first voltage detector 100 is turned off in the reduced voltage state.

  Next, detailed circuit configurations of the first voltage detection unit 100 and the second voltage detection unit 200 will be described.

  FIG. 2 is a circuit diagram showing a configuration of the first voltage detection unit 100. As described above, the first voltage detection unit 100 monitors the battery voltage Vbat in the normal voltage state, and detects the transition to the reduced voltage state. The first voltage detection unit 100 includes a reference voltage source 110, a voltage comparison unit 120, a constant current source 10, a transistor Q10, a first switch SW1, and an inverter INV1.

  The constant current source 10 generates a constant current to be supplied to the reference voltage source 110 and the voltage comparison unit 120. A first switch SW1 is provided between the constant current source 10 and the ground terminal. The first switch SW1 is an N-type MOSFET, and is turned on when the enable signal input to the enable terminal 106 is at a high level and turned off when the enable signal is at a low level. When the first switch SW1 is turned off, the current supply to the reference voltage source 110 and the voltage comparison unit 120 is stopped, and the voltage detection operation is stopped.

The reference voltage source 110 is a band gap reference circuit, and generates a substantially constant reference voltage Vref regardless of temperature fluctuations. Reference voltage source 110 includes transistors Q11-Q16 and resistors R10, R11.
Transistors Q11 and Q12 constitute a current mirror circuit, and resistors R10 and R11 are connected as collector loads of the respective transistors. A resistor R12 is connected to the emitter terminal of the transistor Q12. The transistor Q13 is supplied with a constant current from the transistor Q16, and compensates for temperature fluctuations. The transistors Q15 and Q16 constitute a current mirror circuit with the transistor Q10, and operate as a constant current source obtained by multiplying the constant current Ic generated by the constant current source 10 by a constant. The transistor Q14 increases the sink current of the reference voltage source 110 and decreases the output impedance. The reference voltage source 110 configured in this way outputs the potential at the connection point of the resistors R10 and R11 as the reference voltage Vref.

The voltage comparison unit 120 compares the second threshold voltage Vth2 with the battery voltage Vbat.
Voltage comparison unit 120 includes transistors Q17-Q22. Transistors Q18 and Q19 constitute a differential input pair, and transistors Q20 and Q21 function as a current mirror load. A reference voltage Vref and a battery voltage Vbat ′ are input to the base terminals of the transistors Q18 and Q19 constituting the differential input pair, respectively. The battery voltage Vbat ′ is a voltage obtained by dividing the battery voltage Vbat by the resistors R13 and R14 and multiplying it by R14 / (R13 + R14).
The collector terminal of the transistor Q19 is connected to the base terminal of the transistor Q22 and is subjected to current-voltage conversion by the resistor R15. The inverter INV1 inverts the collector voltage of the transistor Q22 and outputs it from the output terminal 104.

In this voltage comparison unit 120, when Vbat ′ <Vref, the base current and the collector current of the transistor Q22 increase, and the voltage drop at the resistor R15 increases. As a result, the collector voltage of the transistor Q22 decreases and a high level is output from the output terminal 104.
Further, when Vbat ′> Vref, the base current and the collector current of the transistor Q22 are reduced, so that the voltage drop at the resistor R15 is reduced and the collector voltage of the transistor Q22 is increased. As a result, a low level is output from the output terminal 104.

If the first threshold voltage Vth1 is written as Vth1 = Vbat × (R13 + R14) / R14, the first voltage detector 100 compares the battery voltage Vbat with the first threshold voltage Vth1. When Vbat <Vth1, that is, when a reduced voltage state is detected, a high level is output, and when Vbat> Vth1, that is, in a normal voltage state, a low level is output.
When the first switch SW1 is off, no current flows through the voltage comparison unit 120, and no voltage drop occurs at the resistor R15, so the first detection signal SIG1 is at a low level.

  In the first voltage detection unit 100, the first threshold voltage Vth1 is set based on the reference voltage Vref generated by the bandgap reference circuit, so that the transition to the reduced voltage state can be detected with high accuracy. it can.

Next, the configuration of the second voltage detection unit 200 will be described with reference to FIGS. 3 and 4. FIG. 3 is a circuit diagram illustrating a configuration of the second voltage detection unit 200.
As described above, the second voltage detection unit 200 is a circuit that monitors the battery voltage Vbat in the reduced voltage state and detects the return to the normal voltage state. The battery voltage Vbat is input to the detection terminal 202, and the output terminal The second detection signal SIG2 is output from 204.

The second voltage detector 200 includes a first transistor Q1, a second transistor Q2, a third transistor Q3, a first resistor R1, a second resistor R2, a third resistor R3, transistors Q30 to Q32, a second switch SW2, and an inverter INV2. including.
Transistors Q30 to Q32 each have a base-collector connected to form a diode. Assuming that the forward voltage between the base and emitter of the bipolar transistor is Vf, the voltage at the emitter terminal of the transistor Q32 is given by (Vbat−3 × Vf), and the battery voltage Vbat is level-shifted.

A first resistor R1 and a second resistor R2 are connected to the detection terminal 202 via transistors Q30 to Q32 functioning as diodes.
The first transistor Q1 and the second transistor Q2 are NPN-type bipolar transistors, and constitute a current mirror circuit having base terminals connected in common. The first resistor R1 and the second resistor R2 are connected to the collector terminal as loads of the first and second transistors Q1 and Q2, respectively. The third resistor R3 is connected to the emitter terminal of the second transistor Q2. A fixed voltage is supplied to the emitter terminal of the first transistor Q1 and the third resistor R3 via the second switch SW2.
The third transistor Q3 is an NPN-type bipolar transistor, and its base terminal is connected to the collector terminal of the second transistor Q2. A fourth resistor R4 is provided between the collector terminal of the third transistor Q3 and the detection terminal 202. The second voltage detector 200 inverts the voltage appearing at the collector terminal of the third transistor Q3 by the inverter INV2, and outputs the inverted signal from the output terminal 204 as the second detection signal SIG2.

  A second switch SW2 composed of an N-type MOSFET is provided in the current path from the detection terminal 202 to the ground terminal. When the second switch SW2 is on, voltage detection is performed by the second voltage detector 200, and the second switch SW2 is turned on. When the switch SW2 is off, the voltage detection by the second voltage detector 200 is stopped.

  The resistance values of the first resistor R1 to the fourth resistor R4 used in the second voltage detection unit 200 are preferably set high in order to suppress current consumption. For example, by setting the resistance values of the first resistor R1 and the second resistor R2 to several MΩ and the resistance value of the fourth resistor R4 to several tens MΩ, the second voltage detection unit 200 in a state where the second switch SW2 is turned on. Current consumption can be suppressed to 1 μA or less. The current consumption of the second voltage detector 200 is almost zero when the battery voltage Vbat is somewhat lower than the second threshold voltage during the voltage monitoring period, because the first and second transistors Q1 and Q2 are off. When the battery voltage approaches the second threshold voltage and the first and second transistors Q1 and Q2 start to turn on, only a very small current flows, so that the current consumption is very small.

FIG. 4 is a diagram illustrating input / output characteristics of the second voltage detection unit 200 configured as described above. 4, the horizontal axis represents the battery voltage Vbat applied to the detection terminal 202, and the vertical axis represents the second detection signal SIG2 output from the output terminal 204 and the collector voltage Vc3 of the third transistor Q3.
As shown in the figure, in the region where the battery voltage Vbat is small, the transistors Q30 to Q32 functioning as diodes are not turned on, so the first transistor Q1 to the third transistor Q3 are also turned off, and the fourth resistor R4 In this case, the collector voltage Vc3 of the third transistor Q3 is substantially equal to the battery voltage Vbat.

When the battery voltage Vbat rises and becomes higher than the predetermined second threshold voltage Vth2, the transistors Q30 to Q32 are turned on, current flows through the first transistor Q1 and the second transistor Q2, and the third transistor Q3 is turned on. A voltage drop occurs at the fourth resistor R4, and the collector voltage Vc3 of the third transistor Q3 decreases.
The second threshold voltage Vth2 is obtained by using the voltage Vsw across the second switch SW2, the base-emitter voltage Vbe of the first transistor Q1, the resistance value of the first resistor R1, and the current Iq1 flowing through the first transistor Q1. Vth2 = Vf × 3 + Vsw + R1 × Iq1 + Vbe1.

  Since the collector voltage of the third transistor Q3 is output from the detection terminal 202 of the second voltage detector 200 via the inverter INV2, the high level is obtained when the battery voltage Vbat is higher than the second threshold voltage Vth2. When the voltage Vbat is lower than the second threshold voltage Vth2, a low level is output. In the region where the battery voltage Vbat is lower than the voltage indicated by Vx in FIG. 4, the logic of the second detection signal SIG2 is inverted. However, in the voltage detection circuit 1000 according to the present embodiment, the logic is used in the region where Vbat> Vx. To do.

  When the second switch SW2 is turned off in the second voltage detection unit 200, the third transistor Q3 is turned off, so that no voltage drop occurs in the fourth resistor R4, and the second detection signal SIG2 is at a low level. .

  Hereinafter, the operation of the voltage detection circuit 1000 configured as described above will be described with reference to FIG. FIG. 5 is a time chart showing an operation state of the voltage detection circuit 1000 according to the present embodiment.

  At a certain time T0, the battery voltage Vbat input to the first voltage detection unit 100 is in a normal voltage state that is higher than both the first threshold voltage Vth1 and the second threshold voltage Vth2. At this time, a high level is output from the output terminal Q of the RS flip-flop 30 in FIG. 1, and a high level detection signal SIG10 indicating a normal voltage state is output from the output terminal 1004.

The battery voltage Vbat gradually decreases with battery power consumption. When the high level is output from the output terminal Q of the RS flip-flop 30, the first voltage detection unit 100 is turned on and the second voltage detection unit 200 is turned off. The voltage Vth1 is compared with the battery voltage Vbat.
When the battery voltage Vbat becomes lower than the first threshold voltage Vth1 at time T1, a high level is output from the output terminal 104 of the first voltage detector 100. When the first detection signal SIG1 output from the first voltage detection unit 100 becomes a high level, the RS flip-flop 30 is reset and a low level is output from the output terminal Q.

When the RS flip-flop 30 is reset at time T1, a low level is input to the enable terminal 106 of the first voltage detection unit 100, and the first voltage detection unit 100 is turned off. The first detection signal SIG1 is lowered to a low level.
On the other hand, when the RS flip-flop 30 is reset, a high level is input to the enable terminal 206 of the second voltage detector 200, and the second voltage detector 200 is turned on. The second voltage detector 200 starts comparing the battery voltage Vbat and the second threshold voltage Vth2.

  When charging of the battery is started at time T2, the battery voltage Vbat starts to increase. After time T2, the battery voltage Vbat rises, and when it becomes higher than the second threshold voltage Vth2 at time T3, the second detection signal SIG2 output from the second voltage detection unit 200 becomes high level. When the second detection signal SIG2 becomes high level, the RS flip-flop 30 is set, and the output of the RS flip-flop 30, that is, the detection signal SIG10 becomes high level.

  When a high level is output from the output terminal Q of the RS flip-flop 30, the second voltage detection unit 200 is turned off and the first voltage detection unit 100 is turned on. Thereafter, the first voltage detection unit 100 again starts comparing the first threshold voltage Vth1 and the battery voltage Vbat.

  Thus, the voltage detection circuit 1000 generates the detection signal SIG10 during a period from time T1 when the battery voltage Vbat becomes lower than the first threshold voltage Vth1 to time T3 when the battery voltage Vbat becomes higher than the second threshold voltage Vth2. The control unit is notified of the low voltage state as a low level.

According to voltage detection circuit 1000 according to the present embodiment, in the normal voltage state from time T0 to time T1 and after time T3, reference voltage source 110 and voltage comparison unit 120 are included, and highly accurate voltage detection is possible. The first voltage detector 100 can be turned on to accurately detect the transition to the reduced voltage state.
Further, when the voltage is shifted to the reduced voltage state at time T1, battery consumption can be reduced by performing voltage detection using the second voltage detection unit 200 with low current consumption. Furthermore, even if the detection accuracy in the second voltage detection unit 200 deteriorates by setting the second threshold voltage Vth2 in the second voltage detection unit 200 higher than the first threshold voltage Vth1, the normal voltage state It is possible to prevent erroneous detection of return to.

  Those skilled in the art will understand that the above-described embodiment is an exemplification, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  In the embodiment, the transistors constituting the first voltage detection unit 100 and the second voltage detection unit 200 may be configured by replacing bipolar transistors and field effect transistors. In addition, the NPN type and PNP type substitution of the bipolar transistor and the N type and P type substitution of the field effect transistor are naturally included in the scope of the present invention.

  In the embodiment, all the elements constituting the voltage detection circuit 1000 may be integrated or may be configured separately in another integrated circuit, and a part thereof may be configured by discrete components. It may be. Which part is integrated may be determined according to cost, occupied area, application, and the like.

It is a figure which shows the structure of the voltage detection circuit which concerns on embodiment. It is a circuit diagram which shows the structure of a 1st voltage detection part. It is a circuit diagram which shows the structure of a 2nd voltage detection part. It is a figure which shows the input-output characteristic of a 2nd voltage detection part. It is a time chart which shows the operation state of the voltage detection circuit which concerns on embodiment.

Explanation of symbols

  1000 voltage detection circuit, 100 first voltage detection unit, 110 reference voltage source, 200 second voltage detection unit, 300 output unit, R2 second resistance, R3 third resistance, R4 fourth resistance, Q1 first transistor, Q2 first 2 transistors, Q3 3rd transistor.

Claims (7)

A voltage detection circuit that detects a reduced voltage state in which a voltage to be monitored is lower than a predetermined threshold voltage,
A first voltage detector for comparing the voltage to be monitored with a first threshold voltage;
During the period from when the voltage to be monitored becomes lower than the first threshold voltage to the second threshold voltage set higher than the first threshold voltage, the voltage to be monitored and the voltage A second voltage detector for comparing the second threshold voltage;
A period from when the voltage to be monitored becomes lower than the first threshold voltage to when the voltage reaches the second threshold voltage is output as a reduced voltage state, and the first voltage detector in the reduced voltage state An output section for turning off,
A voltage detection circuit comprising:   The output unit includes a flip-flop that is set and reset by outputs of the first voltage detection unit and the second voltage detection unit, and based on the output of the flip-flop, the first voltage detection unit and the second voltage detection unit The voltage detection circuit according to claim 1, wherein any one of the voltage detection units is turned on. A voltage detection circuit for detecting a voltage to be monitored input to a detection terminal,
First and second resistors connected to the detection terminal;
First and second transistors having a base terminal connected in common and forming a current mirror pair using the first and second resistors as collector loads;
A third resistor connected to the emitter terminal of the second transistor;
A fixed voltage terminal connected to the emitter terminal of the first transistor and the third resistor to supply a fixed voltage;
A third transistor having a base terminal connected to the collector terminal of the second transistor and an emitter terminal connected to the fixed voltage terminal;
A fourth resistor connected between the collector terminal of the third transistor and the detection terminal;
And a voltage detection circuit that performs voltage detection based on a voltage appearing at a collector terminal of the third transistor.   The voltage detection circuit according to claim 3, further comprising at least one diode on a current path between the detection terminal and the fixed voltage terminal.   The voltage detection circuit according to claim 1, wherein the second voltage detection unit is the voltage detection circuit according to claim 3. The first voltage detector is
A reference voltage source for generating the first threshold voltage;
A voltage comparator that compares the monitored voltage with the first threshold voltage;
The voltage detection circuit according to claim 1, further comprising: A voltage detection circuit having a first voltage and a second voltage higher than the first voltage as monitoring thresholds,
A first monitoring unit that starts comparison between the monitoring target voltage and the second voltage when the monitoring target voltage falls below the first voltage;
A second monitoring unit that starts a comparison between the monitored voltage and the first voltage when the monitored voltage exceeds the second voltage;
The first monitoring unit is off during the period when the second monitoring unit monitors the monitoring target voltage, and the second monitoring unit is off during the period when the first monitoring unit monitors the monitoring target voltage. A voltage detection circuit characterized by:

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