JP2003180040A - Battery backup circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To downsize a power source and reduce the cost by sharply reducing the number of parts. <P>SOLUTION: This battery backup circuit uses a cutoff FET 3 as a cutoff element within a cutoff circuit, and a body diode built in the cutoff FET 3 is so connected as to be directed in a forward direction to the direction of a battery charge current, and this is equipped with a DC/DC converter 7 which generates the optimum charge voltage for the battery voltage, a charge circuit 2 which charges a battery 11 with a specified value of fixed current or a specified value of fixed voltage, and a cutoff circuit which cuts off the battery 11 when the battery 11 goes into an overdischarged state or the battery voltage drops under the preset value. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a battery connection on the secondary side of a DC output power supply, which charges the battery when the input is in a power supply state, and from the secondary side battery when a power failure occurs. The present invention relates to a battery backup circuit that performs an output backup operation by supplying power.

Further, the present invention relates to a battery backup circuit that charges a battery when the input is energized or backs up the output to the load by discharging the battery when the input is interrupted.

[0003]

2. Description of the Related Art FIG. 9 shows a block diagram of a conventional battery backup circuit. As shown in FIG. 9, the conventional battery backup circuit includes a DC / DC converter 100, a charging circuit 110, a disconnection circuit 120, an overdischarge prevention circuit 130, and a battery 140. In the disconnection circuit 120, the disconnection element uses a power relay, and the charging circuit 110 uses a PNP electrode transistor as a charging constant current circuit element.

At the time of AC power supply, the DC / DC converter 100 shown in FIG. 9 generates an optimum charging voltage of the battery voltage. The charging operation is a constant voltage current method, and in a state where the battery 140 is little charged and is almost empty, the battery 140 is charged with a predetermined constant current value while limiting the current. On the other hand, when the battery 140 is close to full charge, the battery voltage and the voltage of the DC / DC converter 100 become small, so the constant current circuit cannot flow the set constant current, and constant voltage charging is performed. When fully charged, the battery voltage and the voltage generated by the DC / DC converter become almost equal,
The charging current is almost gone.

When the defective battery is connected or the battery terminals are short-circuited, a large power loss occurs in the constant current circuit,
Leading to component failure. In order to prevent this, heat protection of the element is required. In case of power failure, DC / DC converter 100
Since the operation of is stopped, the power supply voltage on the load side drops due to the battery voltage. As a result, the discharging diode 150 in FIG. 9 becomes conductive and supplies power to the load side to perform the backup operation.

When the battery 140 is in an over-discharged state, problems such as shortening of life occur. Therefore, when the battery voltage drops below a certain set value, a circuit for disconnecting (disconnecting circuit 120) is required. Further, in order to prevent the battery 140 from being discharged when the battery is not energized, the leakage current after disconnection must be sufficiently smaller than the self-discharge current of the battery 140. When the load is short-circuited,
A protection circuit for preventing overcurrent from the battery 140 is required.

However, in FIG. 9, the battery 14
A relay is used as a circuit element that disconnects when 0 is over-discharged and the battery voltage drops below a certain set value. This relay has mechanical contact, so the reliability is low, especially DC large current Relays that can flow current are expensive. Further, similarly, since a bipolar type transistor is used as a charging element, it is necessary to flow a relatively large current as a base current, which causes heat generation and efficiency deterioration.

Furthermore, since it is constructed so as to protect against heating when the charging is abnormal, an element for detecting heating,
Circuits and the like were required, which was a factor of increasing the number of parts and cost. Since the conventional circuit as shown in FIG. 9 is used for a relatively expensive power source, it is designed with emphasis on performance and is not suitable for a mass-produced power source that requires low cost.

FIG. 10 shows an example of a block diagram of another conventional battery backup circuit. A more specific case will be described using the conventional example of FIG. The first converter 50 is connected to the commercial input, and the output voltage V11 of the first converter 50 is connected to the load 1 via the overcurrent protection circuit 51. In addition, the voltage V of the output of the first converter 50
11 is connected to the second converter 52, and its voltage V12 is connected to the load 2. Furthermore, the voltage V11 of the first converter 50 is connected to the charging circuit 53 and the disconnection circuit 54, becomes the voltage V13, and is connected to the battery 55.

First, the configuration and operation of each block will be described. The first converter 50 is composed of a forward type insulated converter. The commercial input is rectified by the diode bridge D1 and smoothed by the capacitor C1. A voltage is generated in the primary winding Np of the transformer T1 by turning on / off the switching element Q1, and the voltage induced in the secondary winding Ns of the transformer T1 is rectified by the diodes D2 and D3 and smoothed by the inductor L1 and the capacitor C2. , Voltage V11. The voltage V11 is fed back to the on / off state of the switching element Q1 by the control circuit 61,
Stabilized to a predetermined voltage.

The voltage induced in the auxiliary winding Na of the transformer T1 is rectified by the diode D4 and smoothed by the capacitor C3 to become the voltage V10. The voltage V10 is applied to the logic circuit 6
0, the control circuit 61, etc.

The logic circuit 60 detects the energization and power failure of the commercial input and outputs a signal as a logic to the secondary side of the battery backup circuit. In this way, the state of the commercial input is transmitted to the device on the load side, the computer (not shown) or the like via the logic.

The second converter 52 is a step-down converter. The voltage V11 is generated in the inductor L2 by turning on and off the switching element Q2, rectified by the diode D5, and the inductor L2 and the capacitor C are rectified.
Smoothing at 4 results in voltage V12. The voltage V12 is fed back to the on / off state of the switching element Q2 by the control circuit 62 and stabilized at a predetermined voltage.

The charging circuit 53 is composed of a series regulator. PN as charge control element Q3 for electric power
P-transistors are used. The control circuit 63 controls the charge control element Q3 so that the battery voltage V13 becomes a predetermined voltage. The control circuit 64 controls the charge control element Q3 so that the voltage generated in the resistor R1 has a predetermined value.

Specifically, the control circuit 63 and the control circuit 64 are error amplifiers, and are integrated circuits with the common potential COM as a reference.

The emitter of the charge control element Q3 is connected to the voltage V11, and the collector voltage V14 is the resistance R2.
It is connected to the voltage V13 of the battery 55 through a series circuit of 0 and the diode D20. The voltage V14 at the collector of the charge control element Q3 is connected to the relay S1 of the disconnection circuit 54 and the anode of the diode 30.

In the disconnecting circuit 54, the relay S1 is used as a disconnecting element for electric power. The monitoring circuit 65 is
Charge control element Q3 using thermistor or posistor
The temperature is measured, and when the temperature exceeds a predetermined temperature, the relay S1 is turned off. The monitoring circuit 66 measures the voltage V13 of the battery 55 and turns off the relay S1 when the voltage V13 drops below a predetermined voltage.

Specifically, the monitoring circuit 65 and the monitoring circuit 66 are composed of comparators, and are composed of an integrated circuit with the common potential COM as a reference. Since the output terminal and the control terminal of the relay S1 are insulated, the relay S1 can be easily driven.

Further, one end of the relay S1 has a voltage V14 and is connected to the voltage V11 via a diode D30. The other end of the relay S1 is connected to the voltage V14 of the battery 55.

Next, the overall operation of the conventional battery backup circuit of FIG. 10 will be described. When the input is energized, the first converter 50 operates and the voltage V1
1 is generated. The voltage V11 is set to a value higher than the charging voltage of the battery 55.

The operation of the charging circuit 53 will be described in detail. When the voltage V13 of the battery 55 is low, the relay S1
Is off, and the charging current supplied from the charging control element Q3 flows to the battery 55 via the resistor R20 and the diode D20.

When the battery 55 is charged and the voltage V13 rises, the relay S1 is turned on and the charge control element Q
The charging current supplied from 3 flows to the battery 55 via the relay S1.

When the voltage V13 of the battery 55 is not sufficient, the charging current increases, the voltage of the resistor R1 increases, and the control of the control circuit 64 becomes effective. If the voltage generated in the resistor R1 is controlled to a predetermined value, the resistor R1
The charging current flowing through is controlled to a predetermined value. And then
The battery 55 is charged with a predetermined charging current. At this time, the control circuit 63 does not reach the predetermined voltage and does not operate.

When the voltage V13 of the battery 55 increases, the charging current decreases and the control of the control circuit 63 becomes effective. Then, the battery 55 is charged with a predetermined charging voltage. At this time, in the control circuit 64, the voltage of the resistor R1 does not reach the predetermined value and does not work.

When the battery 55 is fully charged, the voltage V1
When 3 becomes higher than the predetermined voltage, the charge control element Q3 is turned off and the charging circuit 53 is stopped. In this way, the charging circuit 53 charges the battery 55.

Further, in charging the battery 55, when the temperature of the charge control element Q3 exceeds a predetermined temperature due to the charging current, the monitoring circuit 65 turns off the relay S1 and the charging current passes through the resistor R20 and the diode D20. Flowing. When the charging current is suppressed by the resistor R20, the loss in the charging control element Q3 decreases, the temperature decreases, and the relay S1 turns on again. In this way, the temperature of the charge control element Q3 is suppressed so as not to become excessive.

Next, the operation at the time of power failure of the input will be described. The first converter 50 is stopped. Battery 5
5 is connected to the voltage V11 via the relay S1 and the diode D30, and discharges. Electric power is supplied to the load 1 and the load 2.

In this way, at the time of power failure of the input, the backup operation of the output is performed without interruption of the power supply to the load 1 and the load 2.

When the battery 55 is over-discharged during the discharging of the battery 55 and the voltage V13 becomes lower than a predetermined voltage, the monitoring circuit 66 turns off the relay S1. The battery 55 is released from the stress of over-discharge, and the reliability is improved. If there is no monitoring circuit 66,
The stress of over-discharging may shorten the life of the battery 55.

On the other hand, when a defective battery 55 is connected, or a battery connecting terminal is short-circuited,
The current of the charge control element Q3 increases, the temperature of the charge control element Q3 rises, the monitoring circuit 65 turns off the relay S1, and suppresses the destruction of the battery backup circuit.

When an accident such as a short circuit occurs in the load 1, the overcurrent protection circuit 51 limits the current to the load 1 and the excessive discharge current from the battery 55 to improve the reliability. . If there is no overcurrent protection circuit 51,
The battery backup circuit may be damaged by the overcurrent of the battery 55.

The first converter 50 is generally constructed so as to detect the current of the switching element Q1 (not shown), limit this value, and prevent a failure due to a short circuit of the output or the like.

[0033]

However, the conventional examples shown in FIGS. 9 and 10 have the following problems. In the disconnection circuit 54, the relay S1 has a mechanical contact, has a problem of low reliability of operation and high cost.

Further, the charging circuit 53 and the disconnecting circuit 54
However, there is a problem that the number of parts is large and it is difficult to reduce the size and cost.

Further, after the charge of the battery 55 is completed, the voltage of the battery 55 may be overcharged and rise due to a change in environment. At this time, there is a problem that the logic output is stopped when the input is energized. While the output of the logic is stopped, it is not known whether the commercial input is energized or a power failure occurs, and the reliability of the device on the load side decreases.

More specifically, when the voltage of the battery 55 rises during the energization of the input, the relay S1 is turned on and the diode D31 is turned on to raise the voltage V11. When the voltage V11 rises, the control circuit 61 turns off the switching element Q1, the voltage V10 falls, the logic circuit 60 stops, and the logic output stops.

Furthermore, after the relay S1 is once turned off due to over discharge of the battery 55, the voltage V of the battery 55 is
13 recovers and rises, and the monitoring circuit 67 again relays S1.
Is turned on, the battery 55 is discharged again, and the battery 5
5 has a problem that stress is generated.

Further, the charge control element Q3 is a series regulator, has a large loss, and has a problem that a large heat sink is required. Furthermore, the charge control element Q3
Is a pnp transistor, which has a problem that the DC amplification factor is low, a large base current is required, and the loss becomes large. Further, the overcurrent protection circuit 51 also has a problem that a power element and a heat sink corresponding to heat generation are separately required.

Furthermore, there is a problem that the battery 55 is excessively discharged when the battery backup circuit is stopped for a long period of time. More specifically, the control circuit 63 and the monitoring circuit 66 constantly measure the voltage V13 of the battery 55, so that the discharge of the battery 55 is promoted.

The present invention has been made in view of the above circumstances, and ensures the same operation as the conventional one with the minimum necessary number of parts. In particular, at the time of battery backup, the battery is used as a power source and a voltage different from that of the battery is output. It is an object of the present invention to provide a low-cost battery backup circuit by reducing the number of parts applied to a multi-output power supply.

Further, an object of the present invention is to solve the problems described above, and to provide a battery backup circuit having a small number of parts, a low loss, a small size, a low cost and a high reliability. is there.

[0042]

In order to achieve the above object, the invention according to claim 1 provides a DC / DC converter for generating an optimum charging voltage of a battery voltage, and a battery with a predetermined constant current. A battery backup circuit that includes a charging circuit that charges the battery with a predetermined value or a predetermined constant voltage, and a disconnecting circuit that disconnects the battery when the battery becomes over-discharged and the battery voltage drops below a set value. The FET is used as a disconnecting element in the disconnecting circuit, and the body diode with the built-in FET is connected so as to be in the forward direction with respect to the battery charging current direction.

Therefore, according to the invention described in claim 1,
An FET is used as a disconnecting element, and a body diode built in the FET is connected so as to be in the forward direction with respect to the battery charging current direction, so that discharging of the battery can be suppressed when not charged.

The invention described in claim 2 is the same as claim 1
In addition to the configuration described in (3), the power source for driving the gate of the separation element is obtained from the auxiliary winding of the coil of the secondary converter.

Therefore, according to the invention described in claim 2,
Since the auxiliary winding of the coil of the secondary converter is used as the power source for driving the gate of the disconnection element, the parts can be shared, the number of parts can be reduced, and a simple circuit can be realized.

Further, in addition to the structure described in claim 1, the invention described in claim 3 is characterized in that the power source for driving the gate of the separation element is obtained from a charge pump circuit configured as a backup power source.

Therefore, according to the invention described in claim 3,
The gate driving power supply for the disconnecting element is obtained from the charge pump circuit configured as the backup power supply, and it is possible to reduce the number of parts and cost.

The invention described in claim 4 is the same as claim 1.
In addition to the configuration described in (1), an overcurrent protection circuit is provided between the output of the DC / DC converter for charging the battery and the load.

Therefore, according to the invention described in claim 4,
By providing the overcurrent protection circuit between the output of the DC / DC converter for charging the battery and the load, it becomes possible to prevent the overcurrent from the battery when the load is short-circuited.

Further, in addition to the structure of claim 1, the invention of claim 5 turns on the FET that is a disconnecting element of the battery only when a power failure is detected by the power failure detection circuit, and turns on the FET when energized. The feature is that the battery is charged through the body diode.

Therefore, according to the invention of claim 5,
Only when there is a power failure detected by the power failure detection circuit, turn on the FET that is the battery disconnection element, and when power is applied, FE
Since the battery is charged through the body diode of T, it is possible to avoid the converter from stopping due to the overcharged battery.

According to a sixth aspect of the present invention, a bipolar transistor or FET is used as the current limiting element, and the voltage generated in the current detection resistor connected to the emitter or source and the base of the current detection transistor are used.
A battery charging circuit is provided, which compares the voltage between the emitters and changes the potential of the base or gate of the current limiting element by the collector current of the current detection transistor to perform constant current control.

Therefore, according to the invention of claim 6,
The voltage generated in the current detection resistor connected to the emitter or the source using the current limiting element is compared with the voltage between the base and emitter of the current detecting transistor, and the base of the current limiting element is adjusted by the collector current of the current detecting transistor. Or because the constant current control is performed by changing the gate potential,
It is possible to reduce the cost of the entire battery backup circuit.

Further, in addition to the configuration of claim 6, the invention of claim 7 further reduces the charging current when the voltage drop of the battery charging circuit increases and reduces the power loss of the current limiting element. It is characterized by having a limiting circuit.

Therefore, according to the invention described in claim 7,
Since the power limiting circuit reduces the power loss of the current limiting element when the voltage drop of the battery charging circuit becomes large, the current limiting element can be protected.

The invention described in claim 8 is the same as claim 7
In addition to the configuration described in (3), a Zener diode and a resistor are connected in series to the base of the current detecting transistor, and the current limiting element is limited according to the voltage between the collector (drain) and the emitter (source) of the current limiting element. Change the current value,
A battery charging circuit for limiting the power of the current limiting element is provided.

Therefore, according to the invention described in claim 8,
It is a more specific version of the invention described in claim 7,
A Zener diode and a resistor are connected in series to the base of the current detection transistor, and the limiting current value of the current limiting element is changed according to the voltage between the collector (drain) and the emitter (source) of the current limiting element to change the power. Since the limit is applied, the power loss can be reduced and the charging current can be reduced.

Further, the invention according to claim 9 comprises a charging circuit for charging the battery with a predetermined current or voltage, and a disconnecting circuit for disconnecting the battery from the load on the basis of the voltage drop of the battery. In the battery backup circuit, as a disconnecting element in the disconnecting circuit, a battery backup is provided, which includes a MOSFET that connects an anode of a built-in body diode to the charging circuit and a cathode of the body diode to the battery. Circuit.

Therefore, according to the invention described in claim 9, the reliability of the operation due to the mechanical contact is not lowered, the cost is reduced, and the diode of the charging circuit can be eliminated.

According to a tenth aspect of the present invention, in a battery backup circuit including a disconnecting circuit for disconnecting the battery from the load based on a decrease in the voltage of the battery, the disconnecting element in the disconnecting circuit is:
A battery backup circuit, which is turned off when a current flowing through the disconnecting element or a voltage generated in a resistor in series with the disconnecting element exceeds a predetermined value.

Therefore, according to the invention of claim 10,
A separate overcurrent protection circuit and a heat sink for the same are not required, which is low cost and simple.

Further, in the invention according to claim 11, in a battery backup circuit comprising a disconnecting circuit for disconnecting the battery from the load based on a decrease in the voltage of the battery, the disconnecting element in the disconnecting circuit is the disconnecting element. The battery backup circuit is characterized in that it is turned off when the voltage generated at the voltage exceeds a predetermined value.

Therefore, according to the invention of claim 11,
It is a low-cost and simple circuit that can prevent damage when the load is short-circuited.

According to a twelfth aspect of the present invention, in a battery backup circuit provided with a disconnection circuit for disconnecting the battery and the load based on a decrease in the voltage of the battery, the disconnection element in the disconnection circuit is:
A battery backup circuit is characterized in that it is turned off based on the detection of energization of the input and turned on based on the detection of the power failure of the input.

Therefore, according to the invention of claim 12,
The logic output can be stably obtained without interruption when the input is energized.

Furthermore, the invention according to claim 13 is characterized in that the disconnection element is turned off when the voltage of the load drops, and the battery backup circuit according to any one of claims 9 to 12, Is characterized by.

Therefore, according to the invention of claim 13,
When the battery 55 is over-discharged, the discharge is stopped and maintained (latch) until the input is energized, so that the reliability of the battery can be improved.

The invention as set forth in claim 14 is provided with a charging circuit for charging the battery with a predetermined current or voltage, and a disconnecting circuit for disconnecting the battery from the load on the basis of the voltage drop of the battery. In the battery backup circuit, as a charge control element in the charging circuit, a battery is provided that includes a MOSFET that connects an anode of a built-in body diode to the disconnection circuit and connects a cathode of the body diode to the load. It features a backup circuit.

Therefore, according to the invention of claim 14,
You can remove the diode in the disconnect circuit.

Further, the invention according to claim 15 is a battery backup circuit comprising a charging circuit for charging a battery with a predetermined current or voltage, comprising a converter for converting an input voltage into a charging voltage for the battery, A battery backup circuit, wherein the charging control element in the charging circuit is turned off when a current flowing in the charging control element or a voltage generated in a resistor in series with the charging control element exceeds a predetermined value. Is characterized by.

Therefore, according to the invention of claim 15,
The loss in the charging circuit is reduced, the control is simple, and the cost is low.

In a sixteenth aspect of the present invention, in a battery backup circuit including a charging circuit for charging a battery with a predetermined current or voltage, the charging control element in the charging circuit is generated in the charging control element. A battery backup circuit, which is turned off when the voltage exceeds a predetermined value.

Therefore, according to the invention of claim 16,
With a low-cost and simple circuit, it is possible to suppress the connection of the defective battery 55 and the breakage of the connection terminal of the battery due to a short circuit or the like. Moreover, a thermistor or a posistor becomes unnecessary.

Further, in the invention according to claim 17, the charging circuit uses a transistor or a MOSFET as a charging control element in the charging circuit, and the resistor is connected to an emitter or a source of the charging control element. A second transistor having a base and an emitter connected to the resistor and a collector connected to the base or the gate of the charge control element, and a cathode connected to the collector or the source of the charge control element, The battery backup circuit according to claim 15 or 16, further comprising: a Zener diode having an anode connected to the base.

Therefore, according to the invention of claim 17,
A circuit can be easily realized at low cost.

The invention according to claim 18 is characterized by comprising a converter for supplying electric power to the charging circuit or the disconnecting circuit.
The battery backup circuit according to any one of items 1 to 5 above.

Therefore, according to the invention of claim 18,
A circuit can be easily realized at low cost.

The battery backup circuit according to any one of claims 9 to 17, further comprising a charge pump circuit for supplying electric power to the charging circuit or the disconnecting circuit.

Therefore, according to the invention of claim 19,
A circuit can be easily realized at low cost.

[0080]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of the battery backup circuit of the present invention. Like the conventional battery backup circuit, it is provided with a DC / DC converter, a charging circuit, an overdischarge prevention circuit, and the like. In the battery backup circuit 1 of the present invention, unlike the conventional case, the DC / DC converter 9 is provided, and a voltage higher than the + voltage of the battery 11 is generated and used to drive the FET (disconnect FET 3).

As shown in FIG. 1, the Nch-FET (N channel-FET) is used as the disconnecting FET 3 and the battery 11 as the disconnecting SW. Further, the body diode having the disconnection FET 3 built therein is connected so as to be in the forward direction with respect to the battery charging current direction. The battery 11 is electrically connected when the gate potential exceeds a certain threshold voltage with respect to the source, and is disconnected below that. In general, FET (disconnect FE
In T3), the body diode is formed inside, and the battery 11 cannot be separated in the charging direction in FIG. 1, but it is sufficient if only the discharge of the battery 11 can be suppressed when not energized in actual use. So it doesn't matter.

The battery charging circuit 2 is characterized in that a current limiting circuit and a power limiting circuit (instead of the conventional heating protection circuit) are provided as protection circuits. In this embodiment, an Nch-FET is used as a charging element, but a bipolar transistor or Pch-F is used.
A similar circuit configuration is possible with ET.

The current limiting circuit 2a, as shown in FIG.
Transistor base-emitter voltage (hereinafter Vbe
Abbreviated) is compared with the voltage drop that occurs in the current sense resistor Rs. The current is Ichg to Vbe (0.4 to 0.7).
V) / Rs.

The power limiting circuit 2b is the battery charging circuit 2
In order to reduce the power loss when the voltage drop becomes large, the charging voltage is reduced. The Zener diode 4 and the resistor 6 shown in FIG. 2 correspond to them, and when the voltage drop becomes large and the Zener diode 4 starts to conduct, the base voltage of the transistor that senses the current gradually rises. The charging current limit value can be reduced. By optimizing the ratio of the Zener voltage and each resistance, it is possible to make the loss of the charging FET approximately the same value regardless of the value of the voltage drop.

In order to insert the disconnection element on the + side (+ voltage) of the battery 11, it is necessary to drive the disconnection element to generate a voltage higher than the + voltage of the battery 11. FIG. 3 shows a step-down chopper circuit. Specifically, it is a circuit for generating a voltage higher than the battery + terminal from the step-down chopper converter, forming an insulated auxiliary winding in the coil of the chopper converter, and adding two elements, a diode 29 and a capacitor 30. It is realized in. In addition, step-up chopper converters and isolated DC
Even in the case of the / DC converter, it is possible to easily obtain a voltage higher than the battery voltage by the same method.

Further, as shown in FIG. 4, the load source battery backup circuit can be realized by a similar circuit, for example, when the battery + terminal is connected to the GND of the power source and the battery power is taken out as the negative power source. .
In that case, as the disconnection FET 3 of the battery 11, a Pch-FET is connected to the negative terminal side of the battery 11, and a voltage lower than the battery 11 negative terminal voltage is generated from the DC / DC converter 7 to be used for gate drive. However, the same operation can be realized. Also here, a voltage higher than the + voltage of the battery 11 is generated, and the DC / DC converter 9 is used to drive the FET (disconnect FET3).
Is used.

Further, in the case of controlling the battery backup circuit by the power failure detection circuit, as shown in FIG. 5, by combining the power failure detection circuits, the FET 13 is turned off only when there is a power failure, and the FET 13 is turned off when there is an input. Battery 21 via the body diode of FET13
Can also be charged. In this case, the DC / D when the overcharged battery 21 is connected
The operation stop of the C converter 17 can be avoided.

Next, FIG. 6 shows a case where a charge pump circuit is used for generating the gate drive voltage. As shown in FIG. 6, a charge pump circuit is connected to the oscillation circuit 25 connected to DC + and GND to generate a gate drive voltage. In other words, like a single output power supply, DC / D on the secondary side
If there is no C converter, the voltage for driving the SW-FET gate cannot be generated by disconnecting from the winding as described above. Since the gate of the FET is insulated and the power is very small, it is necessary to generate the gate drive voltage 27 using the charge pump circuit as shown in FIG. 6 in terms of the number of parts and the cost. Be advantageous.

The present invention will be described in detail below with reference to FIG. FIG. 7 shows another embodiment according to the present invention. In addition,
The same elements as those in the conventional example of FIG. 10 are designated by the same reference numerals and the description thereof will be omitted.

The feature of the embodiment shown in FIG. 7 is that N-channel MOS is used for the charge control element Q4 and the disconnection element Q6 for electric power.
A monitoring circuit 67 that uses an FET and turns off the element Q6 based on the voltage of the load voltage V11 is provided, a charging circuit 53 having an overcurrent protection function and a short-circuit protection function is provided, and the second converter 52 is connected to the charging circuit 53 and Arranged to supply power to the disconnection circuit 54, the first converter 50 is at the point of outputting the charging voltage of the battery.

First, the configuration and operation of each block will be described. The second converter 52 includes a primary winding N of a transformer T2 instead of the inductor L2 as compared with the conventional example of FIG.
Use 1. The voltage induced in the secondary winding N2 of the transformer T2 is rectified by the diode D6 and smoothed by the capacitor C5, and becomes a voltage (V15-V14). Voltage (V15-
V14) supplies power to the charging circuit 53 and the disconnection circuit 54.

Switching element Q2, transformer T2, diode D5 and capacitor C5 form a flyback converter. The flyback converter supplies power to the charging circuit 53 and the disconnecting circuit 54.

In the charging circuit 53, the charge control element Q4 for electric power uses an N-channel MOSFET, the drain thereof is connected to the voltage V11, and the emitter thereof is the resistor R5.
To the voltage V14 via. In addition, the charge control element Q
The gate of 4 is connected to voltage V15 via resistor R2.

The diode D31 is a body diode containing the charge control element Q4. When using a transistor for the charge control element Q4, connect an external diode D3
Add 1. The anode of the diode D31 is a resistor R5
And to disconnect circuit 54 via voltage V14,
The cathode of the diode D31 is connected to the load 1 via the voltage V11 and the overcurrent protection circuit 51.

The charge control element Q4 has an N-channel MOSF.
By using ET, the parts of the diode D30 are unnecessary and the loss corresponding to the base current of the charge control element Q3 is reduced as compared with the conventional example of FIG.

Compared with the conventional example of FIG. 10, the control circuit 63
The control of the voltage corresponding to is deleted, and the control of the current corresponding to the control circuit 63 does not use an error amplifier or the like.

The resistor R5 is connected in series to the emitter of the charge control element Q4 and detects the charge current. Charge control element Q
If 4 is a multi-emitter N-channel MOSFET, it may be connected to this terminal.

In the second transistor Q5, the base is connected to the source of the charge control element Q4 and one end of the resistance R5 via the resistance R4, the emitter is connected to the other end of the resistance R5 and the voltage V14, and the collector is connected to the charge control element. It is connected to the gate of Q4 and it is judged whether the voltage generated in the resistor R5 exceeds a predetermined value.

In the Zener diode D7, the cathode is connected to the source of the charge control element Q4 and the voltage V11, and the anode is connected through the resistor R3 to the second transistor Q5.
And determines whether the voltage generated in the charge control element Q4 exceeds a predetermined value.

In the disconnecting circuit 54, the power disconnecting element Q6 uses an N-channel MOSFET, the drain thereof is connected to the voltage V13 of the battery 55, and the emitter thereof is connected to the voltage V14.

The diode D32 is a body diode having a built-in disconnecting element Q6. When using a transistor for the disconnection element Q6, use an external diode D3
Add 2. The anode of the diode D32 has a voltage V1.
4 is connected to the charging circuit 53, and the cathode of the diode D32 is connected to the battery 55 via the voltage V13.

N-channel MOSF is used as the disconnecting element Q6.
By using ET, compared with the conventional example of FIG. 10, the parts of the diode D20 and the resistor R20 are unnecessary, the reliability of the operation due to mechanical contacts is not reduced, and the cost is reduced.

The monitoring circuit 67 measures the voltage V11 of the load, and when it drops below a predetermined voltage, the disconnecting element Q
Turn off 6. Specifically, the monitoring circuit 67 is composed of a comparator, and is composed of an integrated circuit based on the voltage V14. Electric power is supplied from the voltage V15.

The voltage V11 is the voltage of the load and is the voltage applied to the load via the overcurrent protection circuit 51. The voltage V11 is also the voltage of the output of the first converter 50. Further, the voltage V11 is the battery 55 when the charge control element Q4 and the disconnection element Q6 are both on.
Is almost equal to the voltage V13.

Compared to the conventional example of FIG. 10, the control circuit 63
Since the monitoring circuit 67 is not connected to the voltage V13 of the battery 55, the battery 55 is not excessively discharged when the battery backup circuit is stopped for a long time.

Next, the overall operation of the embodiment shown in FIG. 7 will be described. The description of the same components as those in the conventional example of FIG. 10 will be omitted. When the input is energized, the first converter 50 operates to generate the voltage V11. The voltage V11 is set to be a suitable charging voltage for the battery 55.

The operation of the charging circuit 53 will be described in detail. When the voltage V13 of the battery 55 is not sufficient, the charging current increases, and when the voltage of the resistor R5 increases and reaches a predetermined voltage, the base current of the second transistor Q5 increases,
The voltage of the collector of the second transistor Q5 decreases, the voltage of the gate of the charge control element Q4 decreases, and the charge control element Q4 decreases.
In No. 4, the drain-emitter voltage in the active state increases and the increase in charging current is suppressed.

Then, the charging current is almost Vbe / R5.
Constant current. The charging circuit 53 has an overcurrent protection function. Here, Vbe is the base-emitter voltage of the second transistor Q5.

Further, the drain-emitter voltage of the charge control element Q4 increases, and the drain-emitter voltage of the charge control element Q4 increases.
When the voltage between the emitters reaches a predetermined voltage, the Zener diode D7 is turned on, the base current of the second transistor Q5 increases, the collector voltage of the second transistor Q5 decreases, and the gate voltage of the charge control element Q4 changes. Positive feedback occurs in which the drain-emitter voltage of the charge control element Q4 decreases and increases. As a result, the increase in charging current is further suppressed.

Then, the voltage V13 of the battery 55
However, when the voltage becomes approximately V11 + Vz + Vbe or less, charging is stopped. The charging circuit 53 has a short circuit protection function. Here, V11 is the output voltage of the first converter, Vz is the Zener voltage of the Zener diode D7, Vbe is the base-emitter voltage of the second transistor Q5, and the voltage V1
4 and the voltage V13 are almost equal.

By appropriately selecting the value of the resistor R5, the value of the Zener diode D7, and the value of the resistor R3, heat generation in the charge control element Q4 can be suitably suppressed.

When the voltage V13 of the battery 55 increases, the charging current decreases, the voltage of the resistor R5 decreases, the Zener diode D7 and the second transistor Q5 both turn off, the gate of the charge control element Q4 rises, and the charge control element Q4 rises. The control element Q4 becomes saturated and turns on.

Charge control element Q4 and disconnection element Q6
Battery 55 because both are fully on in saturation
Is charged with a suitable charging voltage of the voltage V11 output from the first converter. In addition, since it is completely turned on in the saturated state, the loss in the charging circuit 53 is small.

When charging is completed, voltage V11 and voltage V1
It becomes the same as 3 and the charging current stops flowing. In this way, the charging circuit 53 charges the battery 55.

Next, the operation at the time of power failure of the input will be described. The first converter 50 is stopped. The disconnection element Q6 and the charge control element Q4 are both on. The battery 55 is connected to the voltage V11 via the disconnection element Q6, the resistor R5, and the charge control element Q4, and discharges. Load 1
And the load 2 is supplied with electric power.

In this way, at the time of power failure of the input, the backup operation of the output is performed without interruption of the power supply to the load 1 and the load 2.

Further, in discharging the battery 55,
The battery 55 is over-discharged, the voltage V13 drops,
When the voltage V14 decreases, the load voltage V11 decreases, and the load voltage V11 becomes equal to or lower than a predetermined voltage, the monitoring circuit 67.
The disconnecting element Q6 is turned off. Separation element Q
When 6 is turned off, the voltage V14 drops, the voltage V11 drops, and the supply of electric power to the load 1 and the load 2 also stops.
The battery 55 is released from the stress of over discharge.

Thereafter, even if the voltage V13 of the battery 55 recovers and rises, the voltage V14 keeps decreasing and the voltage V13
11 keeps falling and the decoupling element Q6 remains off.

After that, when the input current is turned on, the first
The converter operates, the voltage V11 rises, the second converter 52 operates, and the voltage (V15-V14) is generated,
The charge control element Q4 of the charging circuit 53 is turned on, and a charging current flows in the battery 55.

As described above, when the battery 55 is over-discharged, the disconnecting circuit 54 stops discharging and maintains (latches) until the input is energized, so that the reliability of the battery is improved.

When a defective battery 55 is connected or a battery connecting terminal is short-circuited, the drain-emitter voltage of the charge control element Q4 rises,
The Zener diode D7 is turned on, the current of the resistor R3 increases, the base current of the second transistor Q5 increases, the collector-emitter voltage of the second transistor Q5 decreases, and the gate voltage of the charge control element Q4 decreases. , The charge control element Q4 is turned off. In this way, damage to the battery backup circuit is suppressed.

In the above-mentioned example, the second converter 52 is arranged so as to supply electric power to the charging circuit 53 and the disconnecting circuit 54, but separately from this, the first converter 50 is provided.
The same effect can be obtained by arranging (not shown) so as to supply electric power from the charging circuit 53 to the disconnecting circuit 54.

More specifically, a second auxiliary winding (not shown) is added to the transformer T1 of the first converter 50, and the voltage induced in this winding is smoothed and rectified to obtain the voltage (V15-V1).
4), and power is supplied to the charging circuit 53 and the disconnection circuit 54.

The present invention will be described in detail below with reference to FIG. FIG. 8 shows another embodiment according to the present invention. In addition,
The same elements as those in the embodiment of FIG. 7 are designated by the same reference numerals and the description thereof will be omitted.

The feature of the embodiment shown in FIG. 8 is that power is supplied from the charge pump circuit 57 to the charging circuit 53 and the disconnection circuit 54, and the disconnection circuit 54 having an overcurrent protection function and a short circuit protection function is provided. The circuit 51 is deleted, and the monitoring circuit 68 turns off the disconnecting element Q6 based on the detection of the energization of the input, and turns off and turns on the disconnecting element Q6 based on the detection of the energization of the input and the power failure.

First, the structure and operation of each block will be described. In the charge pump circuit 57, the output V20 of the oscillator U1 is connected to the base of the transistor Q7 and the base of the transistor Q8, respectively. The collectors of the transistors Q7 and Q8 are connected to the voltage V11 and the common potential COM, and the emitters are commonly connected to the voltage V
21 and connected to one end of the capacitor C6. The other end V22 of the capacitor C6 is connected to the cathode of the diode D9 and the anode of the diode D10. Diode D9
Of the diode D10 is connected to the voltage V11, and the cathode of the diode D10 is connected to the voltage V15. Capacitor C7 is connected to voltage V11 and voltage V15, respectively.

The operation of the charge pump circuit 57 will be described. When the output V20 of the oscillator U1 is Low, the transistor Q7 is turned off, the transistor Q8 is turned on, and the voltage V
21 becomes the common potential COM, the diode D9 is turned on, the diode D10 is turned off, and the capacitor C6 is charged.

Next, the output V20 of the oscillator U1 becomes High.
Then, the transistor Q7 turns on, and the transistor Q7
8 off, diode D9 off, diode D10
Is turned on, the capacitor C6 is discharged, and the capacitor C7 is charged.

The charge charged in the capacitor C6 is charge pumped. As a result, the voltage V15 becomes higher than V11. Then, the voltage of the capacitor C7 (V
15-V11) is almost V11.

In this way, the charge pump circuit 57
The voltage (V15-V11) of the capacitor C7 supplies the electric power to the charging circuit 53 and the disconnecting circuit 54. When the charge control element Q4 is on, the voltage V11 and the voltage V14 are almost the same.

In the above-mentioned example, the oscillator U1 was used, but separately from this, the rectangular voltage generated in the secondary winding Ns of the transformer T1 of the first converter 50 is used instead of the oscillator U1. Even if the charge pump circuit 57 is configured (not shown), the same effect can be obtained.

The structure in the vicinity of the disconnecting element Q6 of the disconnecting circuit 54 is almost the same as the structure of the charging circuit 53, and the direction of the corresponding current is reversed. The operation is similar.

The monitoring circuit 68 of the disconnecting circuit 54 has the first
The converter 50 is arranged so as to obtain detection results of energization and power failure of commercial input from the logic circuit 60 of the converter 50. The monitoring circuit 68 turns off the disconnecting element Q6 when the input is energized, and turns on the disconnecting element Q6 when the input is in a power failure.

Next, the overall operation of the embodiment shown in FIG. 8 will be described. The description of the same components as those in the embodiment of FIG. 7 is omitted. When the input is energized, the first converter 50 operates to generate the voltage V11, but the logic circuit 60 detects the energization, and the monitoring circuit 68 turns off the disconnection element Q6. The charging circuit 53 charges the battery 55 via the diode 32. When the battery 55 is fully charged, the diode 32 turns off.

After that, the battery 5 is
Even if the voltage of 5 rises due to overcharge, the disconnection element Q
6 and diode D32 are both off and battery 5
5 does not discharge. Therefore, the voltage V11 does not change,
The first converter 50 also continues to operate, the voltage V10 does not change, and the logic circuit 60 continues to operate.

In this way, the logic does not stop when the input is energized. Whether the commercial input is energized or a power outage can always be confirmed by a device on the load side.

After that, when the input is in a power failure, the logic circuit 60 detects the power failure, and the monitoring circuit 68 disconnects the element Q.
Turn on 6. The battery 55 is a disconnecting element Q6,
It is connected to the voltage V11 via the resistor R9, the resistor R5 and the charge control element Q4 and is discharged. Electric power is supplied to the load 1 and the load 2.

In this way, at the time of power failure of the input, the backup operation of the output is performed without interruption of the power supply to the load 1 and the load 2.

When an accident such as a short circuit occurs in the load 1, the discharge current from the battery 55 increases and the resistance R
When the voltage of 9 increases to reach a predetermined voltage, the base current of the transistor Q9 increases, the collector voltage of the transistor Q9 decreases, the gate voltage of the disconnecting element Q6 decreases, and the disconnecting element Q6 becomes active. The drain-emitter voltage increases, and the increase in discharge current is suppressed.

Further, the drain-emitter voltage of the disconnecting element Q6 increases, and the drain-emitter voltage of the disconnecting element Q6 increases.
When the voltage between the emitters reaches a predetermined voltage, the Zener diode D11 is turned on, the base current of the transistor Q9 increases, the collector voltage of the transistor Q9 decreases, the gate voltage of the disconnecting element Q6 decreases, and the disconnecting element Q6 decreases. Positive feedback that the drain-emitter voltage of Q6 increases causes the disconnection element Q6 to turn off. In this way, damage to the battery backup circuit is suppressed.

In the above example, the charging circuit 53 and the disconnecting circuit 54 have the overcurrent protection function and the short circuit protection function. However, in addition to this, only the short circuit protection function is provided and the overcurrent protection function is provided. Even if it is configured with a separate circuit,
The same effect can be obtained.

More specifically, in the embodiment shown in FIG.
4, the resistor R5, the resistor R9, and the resistor R8 are deleted, and a separate overcurrent protection circuit (not shown) is added.

[0144]

According to the present invention, an FET is used as a battery disconnecting element, and Vbe of a transistor is used for limiting the current of a charging circuit, so that the power of the charging circuit is limited by a Zener diode and a resistor. By implementing a simple circuit with the addition of, the element is protected,
Also, because the gate drive power supply for the disconnection element is realized by a simple circuit that uses the auxiliary winding of the coil of the secondary converter, the number of parts can be significantly reduced compared to the conventional battery backup circuit. , Miniaturization of power supply,
It is possible to reduce costs.

[0145]

[Brief description of drawings]

FIG. 1 is a block diagram of a battery backup circuit of the present invention.

FIG. 2 is a circuit diagram of a charging circuit.

FIG. 3 is a circuit diagram for generating a gate drive voltage using a step-down chopper circuit.

FIG. 4 is a block diagram of a load source battery backup circuit of the present invention.

FIG. 5 is a block diagram in which a battery backup circuit of the present invention is combined with a power failure detection circuit.

FIG. 6 is a circuit diagram for generating a gate drive voltage using a charge pump circuit.

FIG. 7 is a configuration diagram showing another embodiment of the present invention.

FIG. 8 is a configuration diagram showing another embodiment of the present invention.

FIG. 9 is a block diagram of a conventional battery backup circuit.

FIG. 10 is a configuration diagram of another conventional battery backup circuit.

[Explanation of symbols]

1 Battery backup circuit 2 charging circuit 2a Current control circuit 2b Electrode limiting circuit 3, 13 Separated FET 4 Zener diode 5 Step-down chopper converter 7, 9, 17 DC / DC converter 11, 21 battery 25 oscillator circuits 26 Charge pump circuit 27 Gate drive voltage 50 First Converter 51 Overcurrent protection circuit 52 Second converter 2,53,110 charging circuit 54 disconnection circuit 55 battery 26, 57 Charge pump circuit 60 logic circuits 61, 62, 63, 64 control circuit 65, 66, 67, 68 Monitoring circuit Q3, Q4 Charge control element Q6 Separation element S1 relay R5, R9 resistance

Continued front page    (72) Inventor Takuya Hiyoshi             2-9-32 Nakamachi, Musashino City, Tokyo Yokogawa             Electric Co., Ltd. F-term (reference) 5G003 AA01 BA01 CA03 CC02 DA05                       DA16 GA01 GB03                 5H030 AA04 BB02 BB03 BB23 BB27

Claims (19)

[Claims] 1. A DC / DC converter for generating an optimum charging voltage of a battery voltage, a charging circuit for charging a battery with a predetermined constant current value or a predetermined constant voltage value, and a battery A battery backup circuit comprising: a disconnecting circuit that disconnects the battery when the battery voltage drops below a set value in an over-discharged state, wherein an FET is used as a disconnecting element in the disconnecting circuit, A battery backup circuit in which a body diode is connected so as to be in a forward direction with respect to a battery charging current direction. 2. A power source for driving the gate of the disconnecting element is set to 2
The battery backup circuit according to claim 1, wherein the battery backup circuit is obtained from an auxiliary winding of a coil of the secondary converter. 3. A power source for driving the gate of the disconnecting element,
The battery backup circuit according to claim 1, wherein the battery backup circuit is obtained from a charge pump circuit configured as a backup power source. 4. The battery backup circuit according to claim 1, wherein an overcurrent protection circuit is provided between the output of the DC / DC converter for charging the battery and the load. 5. A FET, which is a battery disconnecting element, is turned on only when a power failure is detected by the power failure detection circuit,
The battery backup circuit according to claim 1, wherein the battery is charged through the body diode of the FET when energized. 6. A current limiting element such as a bipolar transistor or FET is used to compare a voltage generated in a current detecting resistor connected to an emitter or a source with a voltage between a base and an emitter of a current detecting transistor to obtain a current. A battery backup circuit comprising a battery charging circuit that performs constant current control by changing the potential of the base or gate of the current limiting element by the collector current of the detection transistor. 7. The battery backup according to claim 6, further comprising a power limiting circuit that reduces the charging current when the voltage drop of the battery charging circuit increases and reduces the power loss of the current limiting element. circuit. 8. A zener diode and a resistor are connected in series to the base of a current detection transistor, and the current limiter value of the current limiter element is changed according to the collector-emitter voltage of the current limiter element to change the current. The battery backup circuit according to claim 7, further comprising a battery charging circuit that limits the power of the limiting element. 9. A battery backup circuit comprising: a charging circuit for charging a battery with a predetermined current or voltage; and a disconnecting circuit for disconnecting the battery from a load based on a decrease in the voltage of the battery. 5. A battery backup circuit comprising a MOSFET for connecting the anode of a built-in body diode to the charging circuit and connecting the cathode of the body diode to the battery as a disconnecting element. 10. A battery backup circuit comprising a disconnecting circuit for disconnecting the battery from a load based on a voltage drop of a battery, wherein the disconnecting element in the disconnecting circuit is a current flowing through the disconnecting element or a series connection to the disconnecting element. A battery backup circuit, which is turned off when the voltage generated in the resistance of the battery exceeds a predetermined value. 11. A battery backup circuit comprising a disconnecting circuit for disconnecting the battery from a load on the basis of a decrease in the voltage of the battery, wherein the disconnecting element in the disconnecting circuit has a voltage generated in the disconnecting element with a predetermined value. A battery backup circuit that is turned off when it exceeds. 12. A battery backup circuit comprising a disconnecting circuit for disconnecting the battery from a load on the basis of a decrease in the voltage of the battery, wherein a disconnecting element in the disconnecting circuit is turned off based on detection of energization of the input, and the input is disconnected. A battery backup circuit that is turned on when a power failure is detected. 13. The battery backup circuit according to claim 9, wherein the disconnection element is turned off when the load voltage drops. 14. A battery backup circuit comprising: a charging circuit for charging a battery with a predetermined current or voltage; and a disconnecting circuit for disconnecting the battery from a load based on a drop in the voltage of the battery. As a charging control element of the above, a battery backup circuit comprising a MOSFET for connecting an anode of a built-in body diode to the disconnection circuit and connecting a cathode of the body diode to the load. 15. A battery backup circuit comprising a charging circuit for charging a battery with a predetermined current or voltage, comprising a converter for converting an input voltage into a charging voltage for the battery, wherein the charge control element in the charging circuit is A battery backup circuit, which is turned off when a current flowing through the charge control element or a voltage generated in a resistor in series with the charge control element exceeds a predetermined value. 16. A battery backup circuit comprising a charging circuit for charging a battery with a predetermined current or voltage, wherein the charging control element in the charging circuit is configured to operate when a voltage generated in the charging control element exceeds a predetermined value. Battery backup circuit characterized by turning off. 17. The charging circuit uses a transistor or a MOSFET as a charge control element in the charging circuit, the resistor is connected to an emitter or a source of the charge control element, and a base and an emitter are connected to the resistor. Second transistors connected to each other and having a collector connected to the base or gate of the charge control element, and a Zener diode having a cathode connected to the collector or source of the charge control element and an anode connected to the base of the second transistor 16. The method according to claim 15 or claim 16 further comprising:
Battery backup circuit described. 18. The battery backup circuit according to claim 9, further comprising a converter that supplies electric power to the charging circuit or the disconnection circuit. 19. The battery backup circuit according to claim 9, further comprising a charge pump circuit that supplies electric power to the charging circuit or the disconnecting circuit.