JP2012042419A - Battery voltage detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct a discharge time of a secondary battery for supply of a backup power source.SOLUTION: A comparator compares a detection voltage of a secondary battery Vb and a reference voltage corresponding to a discharge termination voltage of the secondary battery Vb. Based on the result of the comparison made by the comparator, a switch SW stops the supply of power to a load Lo from the secondary battery Vb. An AC correction circuit 10a corrects early timing of output inversion of the comparator by a ripple component superposed on the voltage of the secondary battery Vb during discharge to the AC load Lo. The AC correction circuit 10a can convert the ripple component into a DC component and reduce the reference voltage so as to correspond to the DC voltage.

Description

  The present invention relates to a battery voltage detection circuit for detecting the voltage of a battery used in an uninterruptible power supply.

  There is an uninterruptible power supply (hereinafter referred to as a backup power supply) as an apparatus for supplying power to a device for a certain period of time when an instantaneous voltage drop or a power failure occurs (see, for example, Patent Document 1). The backup power supply device is used for devices that require high reliability, for example, communication devices such as broadcast devices and relay devices, medical devices, and data storage devices in a data center.

  The backup power supply device is provided with a secondary battery (storage battery), and the secondary battery is discharged when an instantaneous voltage drop or power failure occurs. When the secondary battery is settled, it is repeatedly used by charging from a commercial power supply (AC power supply). Secondary batteries include lead batteries, lithium ion batteries, nickel metal hydride batteries, and the like. Secondary batteries have the property of shortening battery life when overdischarged. Overdischarge refers to discharging until the discharge end voltage specified for each battery falls below. Moreover, the secondary battery has a property that the discharge end voltage decreases as the discharge current increases.

  FIG. 1 is a diagram illustrating a configuration example of a battery voltage detection circuit 100p for detecting a voltage of a secondary battery mounted on a backup power supply device according to the related art. When an instantaneous voltage drop or a power failure occurs, the switch (relay contact rl in FIG. 1) closes, and power is supplied from the secondary battery Vb to the load Lo. In this specification, an example in which a lead battery is used as the secondary battery Vb will be described. The battery voltage detection circuit 100p detects the voltage of the secondary battery Vb and prevents overdischarge of the secondary battery Vb.

  The battery voltage detection circuit 100p includes a first operational amplifier OP1 that functions as a comparator, and a relay drive coil RL. The detection voltage of the secondary battery Vb is input to the inverting input terminal of the first operational amplifier OP1 through the first resistor R1. The reference voltage Vref is input to the non-inverting input terminal of the first operational amplifier OP1 through the second resistor R2. This reference voltage Vref is a voltage corresponding to the specified voltage of the secondary battery Vb (that is, its discharge end voltage). The end-of-discharge voltage is a threshold voltage for determining whether or not there is an overdischarge.

  The relay drive coil LR is connected between the power supply voltage terminal Vdd and the output terminal of the first operational amplifier OP1. A first diode D1 is connected to both ends of the relay drive coil RL in parallel with the relay drive coil RL. The first diode D1 protects the relay drive coil RL itself from the back electromotive voltage generated by the relay drive coil RL.

  While the detection voltage of the secondary battery Vb exceeds the reference voltage Vref, the first operational amplifier OP1 outputs a low level, and current continues to flow through the relay drive coil RL. Thereby, the relay contact rl maintains a closed state. When the detection voltage of the secondary battery Vb reaches the reference voltage Vref, the output of the first operational amplifier OP1 is inverted to a high level, and the current flowing through the relay drive coil RL stops. Thereby, the relay contact rl is opened, and the secondary battery Vb and the load Lo are electrically disconnected.

  FIG. 2 is a diagram showing the voltage V-time T characteristics of the secondary battery Vb in FIG. When the relay contact rl is closed at time t1 and the discharge from the secondary battery Vb to the load Lo is started, the DC voltage component of the battery voltage decreases while the ripple voltage increases with time.

JP 2002-325465 A

  When the detection voltage of the secondary battery Vb reaches the end-of-discharge voltage Vth (corresponding to the reference voltage Vref described above), the relay contact rl is opened, the secondary battery Vb and the load Lo are electrically disconnected, and the discharge is performed. finish. Originally, if the ripple component that is an alternating current component is not superimposed on the detection voltage of the secondary battery Vb, the discharge end voltage Vth is reached at time t3, and the discharge ends. Therefore, if the load does not generate an AC component (hereinafter referred to as a DC load), the discharge ends at time t3.

  On the other hand, in a load that generates an AC component (hereinafter referred to as an AC load), a ripple component may be superimposed on the DC power supply. In FIG. 2, the ripple component touches the discharge end voltage Vth at time t2, and the discharge ends at time t2. Thus, a difference occurs in the detected voltage between the DC load and the AC load. The AC load reduces the discharge time (backup time) by Δt (t3-t2) than the DC load. This means that the discharge performance inherent to the secondary battery Vb cannot be fully exhibited, and as a result, the battery life is shortened. The same thing occurs with sudden load fluctuations.

  Originally, a secondary battery such as a lead battery decreases its discharge end voltage with an increase in load current. However, in the detection circuit shown in FIG. 1, the ripple characteristic increases with an increase in load current, contrary to the battery characteristics. As a result, the final discharge voltage increases.

  This invention is made | formed in view of such a condition, The objective is to provide the technique which optimizes the discharge time of the secondary battery for supplying backup power supply.

  In order to solve the above problems, a battery voltage detection circuit according to an aspect of the present invention is a battery voltage detection circuit that detects a voltage of a secondary battery for backing up a power supply of a load, and the detection voltage of the secondary battery. And a reference voltage corresponding to the discharge end voltage of the secondary battery, a switch for stopping power supply from the secondary battery to the load based on the comparison result of the comparator, and an AC load An AC correction circuit for correcting that the output inversion timing of the comparator is advanced by a ripple component superimposed on the voltage of the secondary battery during discharging.

  According to this aspect, the shortening of the discharge time due to the ripple component touching the discharge end voltage can be suppressed.

  The AC correction circuit may convert the ripple component into a DC component and reduce the reference voltage corresponding to the DC voltage. To achieve this, the AC correction circuit includes a DC cut capacity that cuts the DC component of the detection voltage of the secondary battery, a smoothing capacity that smoothes the AC component that has passed through the DC cut capacity, and a smoothing capacity. An inverting amplifier that inverts and amplifies the smoothed voltage and a variable resistor that adjusts the voltage inverted and amplified by the inverting amplifier may be included. The voltage adjusted by the variable resistor may be added to the reference voltage.

  You may further provide the direct-current correction circuit which correct | amends a reference voltage according to the discharge current which flows into a load from a secondary battery. Thereby, the change of the discharge end voltage due to the change of the discharge current from the secondary battery can be automatically corrected.

  ADVANTAGE OF THE INVENTION According to this invention, the discharge time of the secondary battery for supplying backup power can be optimized.

It is a figure which shows the structural example of the battery voltage detection circuit for detecting the voltage of the secondary battery mounted in the backup power supply device which concerns on a prior art. It is a figure which shows the voltage-time characteristic of the secondary battery in FIG. It is a functional block diagram of the battery voltage detection circuit which concerns on Embodiment 1 of this invention. It is a figure which shows the circuit structural example of the battery voltage detection circuit which concerns on Embodiment 1 of this invention. It is a figure which shows the voltage-time characteristic of the secondary battery in FIG. It is a functional block diagram of the battery voltage detection circuit which concerns on Embodiment 2 of this invention. It is a figure which shows the circuit structural example of the battery voltage detection circuit which concerns on Embodiment 2 of this invention. It is a figure which shows the voltage-time characteristic of the secondary battery in FIG.

  FIG. 3 is a functional block diagram of the battery voltage detection circuit 100a according to Embodiment 1 of the present invention. The battery voltage detection circuit 100a detects the voltage of the secondary battery Vb for backing up the power supply of the load Lo. In the following embodiments, an AC load such as an inverter is assumed as the load Lo.

  The battery voltage detection circuit 100 a includes an effective value voltage detection correction unit 10 and a comparison unit 20. The effective value voltage detection correction unit 10 converts an AC component included in the detection voltage of the secondary battery Vb into an effective value, and adds the effective value to the detection voltage of the secondary battery Vb, or the secondary battery Vb. Subtract from the reference voltage corresponding to the discharge end voltage. This effective value may be a pseudo value. The comparison unit 20 compares the detection voltage of the secondary battery Vb with the reference voltage, and controls the switch SW according to the comparison result. The switch SW stops the power supply from the secondary battery Vb to the load Lo based on the comparison result of the comparison unit 20. Specifically, when the detection voltage of the secondary battery Vb reaches the reference voltage, the switch SW is turned off. Hereinafter, a specific circuit configuration example for realizing the functional block will be described.

  FIG. 4 is a diagram showing a circuit configuration example of the battery voltage detection circuit 100a according to Embodiment 1 of the present invention. This circuit configuration example is an example in which the effective value (negative voltage) is added to the reference voltage. In this circuit configuration example, the comparison unit 20 in FIG. 3 is configured by a hysteresis comparator, and the switch SW in FIG. 3 is configured by a relay.

  The detection voltage of the secondary battery Vb is input to the inverting input terminal of the first operational amplifier OP1 through the first resistor R1. A third resistor R3 is connected between a connection point between the first resistor R1 and the non-inverting input terminal and the ground. The detected voltage of the secondary battery Vb after being resistance-divided by the first resistor R1 and the third resistor R3 is input to the non-inverting input terminal.

  The reference voltage Vref is input to the non-inverting input terminal of the first operational amplifier OP1 through the second resistor R2. This reference voltage Vref is a voltage corresponding to the discharge end voltage of the secondary battery Vb. A fourth resistor R4 is connected between the output terminal of the first operational amplifier OP1 and the connection point between the second resistor R2 and the non-inverting input terminal of the first operational amplifier OP1. A dead zone can be created by inserting the fourth resistor R4 as a feedback resistor.

  The relay drive coil LR is connected between the power supply voltage terminal Vdd and the output terminal of the first operational amplifier OP1. A first diode D1 is connected to both ends of the relay drive coil RL in parallel with the relay drive coil RL.

  While the detection voltage of the secondary battery Vb exceeds the reference voltage Vref, the first operational amplifier OP1 outputs a low level, and current continues to flow through the relay drive coil RL. Thereby, the relay contact rl maintains a closed state. When the detection voltage of the secondary battery Vb reaches the reference voltage Vref, the output of the first operational amplifier OP1 is inverted to a high level, and the current flowing through the relay drive coil RL stops. Thereby, the relay contact rl is opened, and the secondary battery Vb and the load Lo are electrically disconnected.

  In the circuit configuration example of FIG. 4, the effective value voltage detection correction unit 10 of FIG. 3 is configured by an AC correction circuit 10a. The AC correction circuit 10a corrects that the output inversion timing of the comparator is advanced by the ripple component superimposed on the voltage of the secondary battery when discharging to the AC load. For this purpose, the ripple component is converted into a DC voltage (effective value), and the reference voltage Vref is lowered corresponding to the DC voltage. This will be specifically described below.

  The AC correction circuit 10a includes a first capacitor C1, a fifth resistor R5, a second diode D2, a second capacitor C2, a sixth resistor R6, a seventh resistor R7, a second operational amplifier OP2, an eighth resistor R8, and a third diode D3. And a first variable resistor Rv1.

  The detection voltage of the secondary battery Vb is input to the inverting input terminal of the second operational amplifier OP2 via the first capacitor C1, the second diode D2, and the seventh resistor R7. A fifth resistor R5 is connected between the connection point of the first capacitor C1 and the second diode D2 and the ground. A parallel circuit of the second capacitor and the sixth resistor R6 is connected between the connection point of the second diode D2 and the seventh resistor R7 and the ground.

  The first capacity C1 acts as a direct current cut capacity for cutting the direct current component of the secondary battery Vb. The second diode D2 prevents current from flowing from the second operational amplifier OP2 or the second capacitor to the secondary battery Vb or the load Lo. The second capacitor C2 functions as a smoothing capacitor that charges and smoothes the AC component that has passed through the first capacitor and the second diode D2. With this smoothing capacitor, it is possible to smooth sudden voltage changes other than ripple components and prevent malfunctions due to short-time voltage changes such as noise.

  The non-inverting input terminal of the second operational amplifier OP2 is connected to the ground. An eighth resistor R8 is connected as a feedback resistor between the output terminal of the second operational amplifier OP2 and the connection point between the seventh resistor R7 and the inverting input terminal of the second operational amplifier OP2. The second operational amplifier OP2, the seventh resistor R7, and the eighth resistor R8 constitute an inverting amplifier. The inverting amplifier inverts and amplifies the voltage smoothed by the second capacitor C2.

  The output voltage of the inverting amplifier is input to the first variable resistor Rv1 via the third diode D3. The third diode D3 prevents current from flowing from the inverting amplifier to the hysteresis comparator. The first variable resistor Rv1 adjusts the voltage inverted and amplified by the inverting amplifier. The designer can adjust the volume of the first variable resistor Rv1 in consideration of temperature characteristics and the like. The voltage (negative voltage) adjusted by the first variable resistor Rv1 is added to the reference voltage Vref. That is, the reference voltage Vref can be lowered by an amount corresponding to the effective voltage corresponding to the ripple component.

  FIG. 5 is a diagram showing the voltage V-time T characteristics of the secondary battery Vb in FIG. When the relay contact rl is closed at time t1 and the discharge from the secondary battery Vb to the load Lo is started, the DC voltage component of the battery voltage decreases while the ripple voltage increases with time.

  In the battery voltage detection circuit 100a in FIG. 4, the reference voltage Vref of the hysteresis comparator decreases as the amplitude of the ripple voltage increases. FIG. 5 shows a state where the discharge end voltage Vth of the secondary battery Vb is lowered to the discharge end voltage Vth ′. Thereby, as shown in FIG. 2, it can be avoided that the ripple component touches the discharge end voltage Vth at the time t2 and the discharge ends.

  In FIG. 5, the discharge ends when the ripple component touches the reduced discharge end voltage Vth ′ at time t <b> 3. That is, it is shown that the reduction of the discharge time (backup time) of Δt (t3−t2) shown in FIG. 2 can be avoided. This indicates that the discharge from the secondary battery Vb is completed at the original end timing when the DC voltage detected from the secondary battery Vb reaches the original discharge end voltage Vth. That is, it shows that the secondary battery Vb has fully exhibited the discharge performance originally possessed.

  FIG. 6 is a functional block diagram of the battery voltage detection circuit 100b according to Embodiment 2 of the present invention. The battery voltage detection circuit 100b according to the second embodiment has a configuration in which an effective value current detection correction unit 30 is added to the battery voltage detection circuit 100a according to the first embodiment. In the second embodiment, a shunt resistor Rs is connected between the low potential side terminal of the load Lo and the low potential side terminal of the secondary battery Vb.

  The effective value current detection correction unit 30 detects the discharge current flowing from the secondary battery Vb to the load Lo by detecting the voltage across the shunt resistor Rs, and the discharge end voltage of the secondary battery Vb according to the discharge current. Or the detection voltage of the secondary battery Vb is corrected. When the discharge current is an alternating current, it is detected by an effective value. Here, as described above, when the discharge current from the secondary battery to the load increases, the end-of-discharge voltage decreases. The DC correction circuit 30a automatically reduces the end-of-discharge voltage according to the nature of the secondary battery. Hereinafter, a specific circuit configuration example for realizing the functional block will be described.

  FIG. 7 is a diagram showing a circuit configuration example of the battery voltage detection circuit 100b according to Embodiment 2 of the present invention. This circuit configuration example is an example in which a decrease (negative voltage) of the discharge end voltage accompanying an increase in the discharge current is added to the reference voltage. In this circuit configuration example, a DC correction circuit 30a is added to the circuit configuration example shown in FIG. The DC correction circuit 30a includes a ninth resistor R9, a third operational amplifier OP3, a tenth resistor R10, a fourth diode D4, and a second variable resistor Rv2.

  The voltage detected from the connection point between the shunt resistor Rs and the load Lo is input to the inverting input terminal of the third operational amplifier OP3 via the ninth resistor R9. When the discharge current flowing through the load Lo is an alternating current, it is converted into an effective value voltage by an unillustrated AC-DC conversion circuit and input to the inverting input terminal of the third operational amplifier OP3. The reference voltage Vrefd for DC component correction is input to the non-inverting input terminal of the third operational amplifier OP3. A tenth resistor R10 is connected as a feedback resistor between the output terminal of the third operational amplifier OP3 and a connection point between the ninth resistor R9 and the inverting input terminal of the third operational amplifier OP3. The third operational amplifier OP3, the ninth resistor R9, and the tenth resistor R10 constitute an inverting amplifier. The inverting amplifier inverts and amplifies the voltage corresponding to the discharge current flowing through the load Lo.

  The output voltage of the inverting amplifier is input to the second variable resistor Rv2 via the fourth diode D4. The fourth diode D4 prevents current from flowing from the inverting amplifier to the hysteresis comparator. The second variable resistor Rv2 adjusts the voltage inverted and amplified by the inverting amplifier. The designer can adjust the volume of the second variable resistor Rv2 in consideration of temperature characteristics and the like. The voltage (negative voltage) adjusted by the second variable resistor Rv2 is added to the reference voltage Vref. That is, the reference voltage Vref can be lowered by an amount corresponding to the voltage corresponding to the discharge current. The reference voltage Vref greatly decreases as the discharge current increases.

  FIG. 8 is a diagram showing the voltage V-time T characteristics of the secondary battery Vb in FIG. In FIG. 8, the AC component generated in the load Lo is ignored. Alternatively, a DC load is assumed as the load Lo. When the relay contact rl is closed at time t1 and discharging from the secondary battery Vb to the load Lo is started, the battery voltage decreases with time.

  In the supply of backup power, the discharge current from the secondary battery usually increases with time. Accordingly, the reference voltage Vref of the hysteresis comparator is lowered. FIG. 8 shows a state in which the discharge end voltage Vth of the secondary battery Vb has decreased to the discharge end voltage Vth ″. Thereby, the time to reach the discharge end voltage Vth ″ is Δt (t4−t3), It can be extended, and the discharge performance inherent to the secondary battery Vb can be fully exhibited.

  As described above, according to the first and second embodiments, by adding a circuit for automatically correcting the discharge end voltage of the secondary battery for supplying the backup power, the discharge time of the secondary battery is reduced. Can be optimized. That is, by adding the AC correction circuit 10a according to the first embodiment, it is possible to reduce the discharge time due to the AC component as close to zero as possible. Further, by adding the DC correction circuit 30a according to the second embodiment, it is possible to reduce the discharge time due to the increase of the DC current as close to zero as possible. By these, the performance of the discharge time which a secondary battery originally has can be fully exhibited, and, as a result, battery life can be maximized.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art 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.

  The battery voltage detection circuit 100b according to the second embodiment includes both the AC correction circuit 10a and the DC correction circuit 30a. However, when the load Lo is a DC load, the AC correction circuit 10a is not required and the comparison unit 20 In addition, it is only necessary to provide the DC correction circuit 30a.

  100p, 100a, 100b Battery voltage detection circuit, Lo load, Vb secondary battery, SW switch, 10 RMS voltage detection correction unit, 10a AC correction circuit, 20 comparison unit, 30 RMS value current detection correction unit, 30a DC correction circuit .

Claims (5)

A battery voltage detection circuit for detecting a voltage of a secondary battery for backing up a load power source,
A comparator that compares the detected voltage of the secondary battery with a reference voltage corresponding to a discharge end voltage of the secondary battery;
Based on the comparison result of the comparator, a switch for stopping the power supply from the secondary battery to the load,
An AC correction circuit for correcting that the output inversion timing of the comparator is advanced by a ripple component superimposed on the voltage of the secondary battery when discharging to an AC load;
A battery voltage detection circuit comprising:   The battery voltage detection circuit according to claim 1, wherein the AC correction circuit converts the ripple component into a DC component, and reduces the reference voltage corresponding to the DC voltage. The AC correction circuit is:
DC cut capacity for cutting the DC component of the detection voltage of the secondary battery,
A smoothing capacitor that smoothes the AC component that has passed through the DC cut capacitor;
An inverting amplifier for inverting and amplifying the voltage smoothed by the smoothing capacitor;
A variable resistor that adjusts the voltage inverted and amplified by the inverting amplifier, and
The battery voltage detection circuit according to claim 1, wherein the voltage adjusted by the variable resistor is added to the reference voltage.   4. The battery voltage detection circuit according to claim 1, further comprising a DC correction circuit that corrects the reference voltage in accordance with a discharge current flowing from the secondary battery to a load. 5.   The battery voltage detection circuit according to claim 4, wherein the DC correction circuit decreases the reference voltage as an effective value of a discharge current flowing through the load is higher.

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