JP7157865B1 - Protection circuit for built-in battery - Google Patents

Abstract

Kind Code: A1 A protection circuit is provided that protects a battery, prolongs the life of the battery, and improves the start-up capability of the external field device when power is supplied to the external field device by the device driven by the battery. A protection circuit according to one embodiment of the present invention is a protection circuit for a device that is driven by a battery and supplies power to an external field device, comprising a battery and a DC-DC converter that transforms the battery voltage of the battery. A power supply unit comprising a converter, a current monitoring unit that monitors the output current of the power supply unit, a control unit that controls the on/off state and output voltage of the power supply unit based on a signal from the current monitoring unit, and protects the battery. and a fuse, wherein the control unit reduces the output voltage and controls the on/off state of the power supply unit according to the state of overcurrent detected by the current monitoring unit. . [Selection drawing] Fig. 3

Description

The present invention relates to a protection circuit in a battery-driven device that supplies power to an external field device, for example, a circuit that protects a battery and peripheral circuits from a short-circuit fault in an external field device.

With recent advances in wireless network technology, wireless modules that wirelessly communicate measurement data are also being used in field devices.

Patent Literature 1 discloses a wireless field device in which wireless communication means is incorporated in the field device. Here, the field devices are pressure gauges, differential pressure gauges, thermometers, level gauges, flowmeters, various transmitters, etc., which are directly connected to processes and perform measurements, and are also called industrial transmitters.

The wireless signal converter of Patent Document 1 is assumed to be placed in a place where normal wiring is difficult, and a method of operating with a battery such as a lithium battery, for example, is considered and adopted.

Patent Document 2 discloses a wireless device connected to a two-wire transmitter that receives supply of power supply voltage via a loop signal line and outputs an analog DC current signal of 4-20 A according to a measured value or the like. there is

Patent Document 3 describes a power supply device that uses a battery as a power source and has an overcurrent reset unit that turns off the power supply when the output current becomes an overcurrent and turns on the power supply after a certain period of time.

Patent No. 5229592 Patent No. 6706424 JP 2016-1943 A

Battery-powered devices that supply power to external field devices need to protect the batteries and increase battery life.

Patent Literature 1 describes intermittent operation of the field wireless device to reduce the power consumption of the battery, but does not describe protection of the battery.

Patent Literature 2 incorporates a battery in a wireless device to enable wireless communication of signals from field devices, but does not describe protecting the battery and extending the battery life.

Japanese Patent Laid-Open No. 2002-201000 describes detecting an overcurrent in the output current of a power supply unit and controlling ON/OFF of the power supply. However, in Patent Document 3, since the inrush current after the power supply is applied to the external field device with a large input capacity becomes large, the power supply is immediately turned off, and the external field device cannot be activated.

In addition, a fuse is sometimes provided to protect the battery against a short-circuit failure of a semiconductor component in the power supply unit, but it is likely to blow unintentionally when power is supplied to an external field device. As a battery protection measure, an overcurrent suppression circuit having a fold-back characteristic is generally provided, but there is a problem that the power loss during current monitoring is large and the battery life is shortened.

Accordingly, the present invention has been made in view of these circumstances. It is an object of the present invention to provide a protection circuit with improved capabilities.

The above object of the present invention can be achieved by the following configurations. That is, the protection circuit of the first aspect of the present invention is a protection circuit for a device that is driven by a battery and supplies power to an external field device, comprising a battery and a DC-DC converter that transforms the battery voltage of the battery. and a current monitoring unit that monitors the output current of the power supply unit,
a control unit that controls the on/off state and output voltage of the power supply unit based on a signal from the current monitoring unit; and a fuse that protects the battery. According to the state of the current, the output voltage is reduced and the on/off state of the power supply unit is controlled , and the control unit reduces the output voltage when the current monitoring unit detects an overcurrent. a first control unit that outputs a reduction command to the power supply unit; and a second control unit that receives the output voltage reduction command, controls the on/off timing of the power supply unit, and determines an abnormality in the external field device. It is characterized by having

A protection circuit according to a second aspect of the present invention is the protection circuit according to the first aspect, wherein the first control section reduces the output voltage after a first period when the current monitoring section detects an overcurrent. An output voltage reduction command is sent to the power supply unit, the second control unit turns off the power supply unit after a second period from receiving the output voltage reduction command, and turns on the power supply unit after a third period. and determining whether the external field device is abnormal based on the number of times the power source is turned on and off.

A protection circuit according to a third aspect of the present invention is the protection circuit according to the first or second aspect, wherein the control unit includes a battery voltage monitoring unit that monitors the battery voltage, and the battery voltage is higher than a predetermined voltage. It is characterized by outputting an off command to the power supply section when it detects that the power supply has also decreased.

According to a fourth aspect of the present invention, in the protection circuit according to any one of the first to third aspects, the protection circuit is an explosion-proof device.

According to the protection circuit of the first aspect of the present invention, the control unit reduces the output voltage and controls the on/off state of the power supply unit according to the state of overcurrent detected by the current monitoring unit. When power is supplied to an external field device by a device driven by a battery, it is possible to protect the battery and extend its service life, as well as improve the start-up capability of the external field device.

Further, according to the protection circuit of the first aspect, the control section can reduce the output voltage according to the state of overcurrent detected by the current monitoring section, so that rapid overcurrent protection can be realized. Furthermore, it is possible to prevent overcurrent generated in the output current of the power supply unit from exceeding the rated current of the battery and the fusing current of the fuse at startup. In addition, the response of the first control unit is fast, and the power supply unit can be quickly controlled to reduce the voltage supplied to the external field device, thereby protecting the battery from instantaneous overcurrent. Furthermore, the second control unit receives the signal from the first control unit and controls the on/off state of the power supply unit, thereby improving the start-up capability of the external field device and diagnosing an abnormality in the external field device. be able to. For example, a temporary overcurrent supply required to start up an external field device can be separated from a sustained short circuit fault to protect the battery from continuous overcurrent occurrence.

According to the protection circuit of the second aspect of the present invention, the output voltage of the power supply section is detected immediately after detecting the overcurrent of the output current _IO of the power supply section, that is, after the first period (for example, the determination period t _d ), the output voltage of the power supply section Applying a low voltage _VOL to the external field device to power the input capacitance of the external field device for a period of time while reducing the current load on the battery and protecting it by reducing _VO to a low voltage _VOL . can do. After reducing the output voltage V _O of the power supply unit to the low voltage V _OL , the second control unit turns off the power supply unit after a second period (for example, an ON period t _on ), and further, after a third period (for example, an OFF After the period t _off ), the power is turned on again (hereinafter sometimes referred to as “retry”).

In this way, after the overcurrent is detected, the input capacitance of the external field device is charged with the low voltage _VOL , the power supply section is turned off after the second period, and the retry is performed after the third period, and the power supply is turned off. An output voltage _VO is applied from the unit to the external field device. As a result, the power supply section repeats the on-off operation by retry, the input capacitance of the external field device is gradually charged, and the external field device is started up. Therefore, it is possible to quickly start the external device while suppressing the inrush current at the time of retry, so that it is possible to improve both the start-up capability of the external device and the protection capability of the battery.

According to the protection circuit of the third aspect of the present invention, in addition to monitoring the overcurrent of the output current by the current monitoring unit, the battery voltage monitoring unit for monitoring the battery voltage is provided, and when the battery voltage drops below a predetermined voltage When this is detected, by outputting an off command to the power supply unit, the control unit prevents unnecessary blowing of the fuse due to a decrease in battery voltage due to a decrease in remaining battery power and an increase in fuse current _IH due to a decrease in battery voltage. In addition, by suppressing the fuse current IH to a certain _level or less, overdischarge of the battery can be prevented. In addition, determination of battery life is also possible.

According to the protection circuit of the fourth aspect of the present invention, the protection circuit can be used as an explosion-proof device. Conventionally, explosion-proof devices that can supply power from batteries to general-purpose external field devices with 4-20mA current signals have not been realized. According to the protection circuit of the fifth aspect of the present invention, it is possible to drive an external field device that consumes a maximum current of 20 mA or more with a battery incorporated in the explosion-proof device. This is because, in this embodiment, the input capacitance of the external field device is gradually charged while reducing the overcurrent that occurs at startup, and on the other hand, it is possible to determine an abnormality such as a short-circuit current that occurs when the external field device is short-circuited. Therefore, it is possible to achieve both current consumption, which is large compared to the battery rating, which occurs continuously, and protection from the short-circuit current that occurs when a short circuit occurs.

1 is a block diagram of a system including a protection circuit according to Embodiment 1 of the present invention; FIG. 2 is a waveform diagram of each part of the protection circuit of FIG. 1; FIG. FIG. 4 is a block diagram of a system including a protection circuit according to Embodiment 2 of the present invention;

A preferred embodiment of the protection circuit of the present invention will be described below with reference to the drawings. However, the embodiments shown below are examples for embodying the technical idea of the present invention, and do not limit the present invention to these, but are other embodiments included in the scope of claims. is equally applicable to

[Embodiment 1]
A protection circuit according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 and 2. FIG.

[Overall system configuration]
FIG. 1 is a block diagram of a system including a protection circuit 20 according to Embodiment 1 of the present invention. The radio signal converter 10 includes a protection circuit 20 and a radio signal conversion circuit 30, and although not particularly limited, is housed inside a pressure-resistant explosion-proof container to realize a pressure-resistant explosion-proof structure. . The pressure-resistant explosion-proof container has, for example, a rectangular parallelepiped shape, and at least one surface thereof is provided with tempered glass so that the indicator of the wireless signal converter 10 and the like can be checked from the outside.

The protection circuit 20 is connected to an external device 40 such as an external field device 41 , but not limited to, for example, a two-wire type external field device 41 via two-wire cables 42 and 43 . The external field device 41 is not particularly limited, but examples include pressure gauges, differential pressure gauges, thermometers, level gauges, flow meters, and various transmitters that directly connect to the process and perform measurements. be done.

As the external field device 41, a device having an explosion-proof structure, for example, a pressure-resistant explosion-proof external field device 41 is assumed. Therefore, when the radio signal converter 10 has an explosion-proof structure, the two-wire cables 42 and 43 are also housed in a pressure-resistant explosion-proof conduit, for example, in order to make them pressure-resistant explosion-proof cables. In order to provide an explosion-proof structure, for example, pressure-resistant packing fittings are provided at the insertion openings of the two-wire cables 42 and 43 of the pressure-resistant explosion-proof container.

The wireless signal converter 10 and the external field device 41 have been described as pressure-resistant and explosion-proof. The embodiments are not intended to be limited to pressure-resistant explosion-proof types, but include, for example, intrinsically safe explosion-proof structures. Applicable to any of the locations.

Here, regarding intrinsically safe explosion-proof, hazardous areas are defined as follows.
"Type 0 Hazardous Area": Locations where an explosive atmosphere may exist continuously or for a long period of time "Type 1 Hazardous Area": Explosive gas may be generated even under normal conditions Location "Type 2 Hazardous Area": Location where explosive gas may be generated only under abnormal circumstances "Non-hazardous area": There is no risk of explosive gas being generated even if an abnormal situation occurs place

Intrinsically safe explosion-proof structure means an explosion-proof structure that prevents explosions in equipment that could be ignited by sparks generated in an internal circuit, and that suppresses the effects of high-temperature parts in the equipment on surrounding parts. The intrinsically safe explosion-proof structure can be applied to any of Class 0, Class 1, Class 2 and non-hazardous areas.

A pressure-resistant explosion-proof structure means an explosion-proof structure that does not cause secondary damage outside the container when an explosion occurs in the device due to explosive gas inside the container. The pressure-resistant explosion-proof structure is designed to withstand an internal pressure of about 1 MPa, for example. The pressure-resistant explosion-proof structure can be applied to Class 1 hazardous areas, Class 2 hazardous areas, and non-hazardous areas, but cannot be applied to Class 0 hazardous areas. Although an explosion-proof structure has been described here, this is not intended to limit the present embodiment to an explosion-proof structure, and the protection circuit 20 of the present embodiment may be of a non-explosion-proof structure or of an explosion-proof structure. can also be applied to the equipment of

The external field device 41 is not particularly limited, but can employ an external field device 41 that outputs a standard 4-20 mA analog DC current signal, and is protected via two-wire cables 42 and 43. A voltage of V _O (eg, 14.3 V) is supplied from the circuit 20 . The two-wire cables 42 and 43 serve both as power lines and signal lines, and the wireless signal converter 10 can be installed near the external field device 41, so the wiring distance can be minimized.

It is widely used as an external field device 41 because it can supply and measure drive power for general-purpose 4-20mA current signals without being limited by the electrical parameters of the external field device 41. It is possible to connect with a general-purpose external field device 41 that is already in use, and it is possible to apply it to the external field device 41 that was used in the existing equipment, and furthermore, it is possible to divert it from the unnecessary line. .

The specifications of two-wire field devices are defined in NAMUR NE 43. Table 1 shows the current range of the analog DC current signal output from the external field device 41 .

A normal output signal is 4-20 mA. A normal lower limit range (3.8-4.0 mA) and a normal upper limit range (20.0-20.5 mA) are defined as the boundary values of this normal output signal. In addition, in the case of failure of the two-wire external field device 41 (transmitter failure), a current lower than the normal range (3.6-3.8mA) or a current higher than the normal range (20.5mA) -22.0 mA) is output. Further, the output signal is 0 to 3.6 mA when there is a possibility of an open failure, and the output signal is a current value greater than 22.0 mA when there is a possibility of a short circuit failure.

The voltage supplied from the two-wire cables 42 and 43 to the external field device 41 is, for example, 14.3 V, and the current as the device signal is normally in the range of 4 to 20 mA, with a maximum analog DC current of 25 mA. The external field device 41 returns, for example, a sensor detection value as an analog DC current signal. A 20mA analog DC signal is output. In this way, the external field device 41 can supply and measure drive power for a general-purpose 4-20 mA current signal, so it can be used as a widely used general-purpose external field device 41. can be combined, it can be applied to the external field device 41 used in the existing equipment, and further, it can be diverted from the unnecessary line.

The wireless signal converter 10 adopts a method of operating with a battery 21 that does not require preparation of an additional power source or the like, on the assumption that it will be placed in a place where normal wiring is difficult. Therefore, for example, if the radio signal conversion circuit 30 is set to operate intermittently, the power consumption of the battery 21 can be reduced, thereby achieving long-time operation.

The radio signal conversion circuit 30 includes an arithmetic unit 31 , a communication module 32 , a radio antenna 33 and the like, and is supplied with power from the battery 21 .

Based on the current value of the analog DC current (output current I _O ) of the two-wire cables 42 and 43 detected by the current monitoring unit 23, the calculation unit 31 detects the signal from the external field device 41, for example, the signal from the external field device 41 of the sensor. If so, the sensor detection value is calculated from the output current _IO .

The communication module 32 converts the sensor detection value calculated by the calculation unit 31 into a radio signal, and outputs the radio signal from the radio antenna 33 for transmission to a host device (not shown). The wireless antenna 33 is installed in the pressure-resistant explosion-proof container, but at least it is possible to output the wireless signal to the outside through the tempered glass. The host device can control the process, plant, etc. in which the external field device 41 is arranged, and can set various parameters of the wireless signal converter 10 . Various parameters of the wireless signal converter 10 may be set from an input device connected to the wireless signal converter 10 by wire or wirelessly, or from a console provided in the wireless signal converter 10. .

[Configuration of protection circuit]
The protection circuit 20 includes a battery 21, a fuse 22, a current monitoring section 23, a power supply section 24, a cutoff section 25, a first control section 26, a second control section 27, a battery voltage monitoring section 28, and the like. In order from the positive output of the battery 21, the fuse 22, the cutoff unit 25, the power supply unit 24, the current monitoring unit 23, the positive output terminal of the protective circuit 20, the positive cable 42, the external field device 41, the negative cable 43, and the protective circuit. 20 negative output terminal and a ground terminal are connected.

A primary battery is used as the battery 21 . Although the primary battery is not particularly limited, a lithium battery that has a long life and is capable of supplying a stable high output voltage V _O (about 6 V) is used.

A fuse 22 is provided on the output side of the battery 21 . This fuse 22 protects the battery 21 from failure of the semiconductor in the radio signal converter 10 .

The current monitoring unit 23 detects an analog direct current (output current I _O ) of the two-wire cables 42 and 43 and outputs a signal of the detected output current I _O to the first control unit 26 and the calculation unit 31 .

The power supply unit 24 uses the battery 21 as a power source to supply the external field device 41 with a constant voltage value set via the two-wire cables 42 and 43 based on the control command P1 of the _first control unit 26, which will be described later. (Output voltage V _O ), for example, a DC voltage of +14.3 V is supplied to the plus side cable 42 and 0 V (ground voltage) is supplied to the minus side cable 43 . The power supply unit 24 is a step-up DC-DC converter that supplies the voltage of the battery 21 (eg, 6 V) to the external field device 41 up to a predetermined voltage, such as a set voltage (eg, rated voltage V _OC =14.3 V). Increase pressure. The type of the step-up DC-DC converter is not particularly limited, but an insulation type is preferable from the viewpoint of explosion-proof performance, and a power-saving semiconductor device from the viewpoint of battery life, such as silicon carbide (SiC) or the like. , and those using gallium nitride (GaN) are preferable.

The cutoff unit 25 is a switching circuit that turns on and off the power of the battery 21 supplied to the power supply unit 24, and supplies the power of the battery 21 to the power supply unit 24 based on the control command P2 of the _second control unit 27, which will be described later. on-off control.

The first control unit 26 outputs a control command P ₁ for the output voltage _VO to the power supply unit 24 based on the current value _IO detected by the current monitoring unit 23 . When the current value I _O is greater than the reference current I _OS (eg, 25 mA) for a first period (determination period t _d ) or longer, the first control unit 26 determines that the output current I _O is an overcurrent. , outputs to the power supply unit 24 _a control command P1 for reducing the output voltage V _O to a low voltage V _OL (for example, 6.0 V). The determination period _td is set to a period shorter than 1 ms, for example. Therefore, since the first control section 26 has a fast response, it immediately controls the output voltage V _O of the power supply section 24, that is, the voltage supplied to the external field device 41, to the low voltage V _OL when an overcurrent of the output current I _O is detected. Thereby, the battery 21 can be protected from momentary overcurrent.

The second control unit 27 receives the control command P1 from the _first control unit 26 to reduce the output voltage _VO to the low voltage _VOL , and turns on/off the battery power supply to the power supply unit 24 by the cutoff unit 25. while outputting a control command P2 for controlling the external field device 41 and diagnosing an abnormality of the external field device 41, for example, a short _- circuit failure.

The protection circuit 20 can be set to intermittently enter a sleep state. The period of intermittent operation can be set in the protection circuit 20 . In the sleep state, functions other than the timer function of the protection circuit 20 or power supply is stopped, thereby reducing power consumption. Since the timer function of the protection circuit 20 continues even in the sleep state, the protection circuit 20 and the wireless signal converter 10 switch from the sleep state to the operation state at the start-up time corresponding to the set intermittent operation. and start supplying power to the external field device 41 .

The period of the intermittent operation is not particularly limited, but for example, the device signal, that is, the output current _IO is detected once an hour, and the measured value of the external field device 41 corresponding to the output current _IO is obtained. It is possible to set so as to output from the radio antenna 33 as a radio signal. Since the power consumption can be greatly reduced during the intermittent sleep state, the primary battery can ensure operation for about 10 years, and by extending the battery life, it can be placed in places where normal wiring is difficult. Furthermore, the maintenance cost associated with battery replacement can be reduced as the battery life is improved. The period of the intermittent operation is set according to the time required from the start of power supply to the external field device 41 to the stabilization of the device signal, that is, the time required for the external field device 41 to start up. Since the time required to start the external field device 41 is normally about 2 to 5 seconds, the user can determine the time required to start the external field device 41 within 2 to 60 seconds. there is Alternatively, it is also possible to acquire the time required to activate the two-wire external field device 41 from data when the second control unit 27 actually activates the two-wire external field device 41 .

In this embodiment, as described above, the user can set the startup time between 2 seconds and 60 seconds. Allows you to set. The shortest period of the intermittent operation corresponds to 1 minute (60 seconds), which is the longest activation time. On the other hand, one hour (60 minutes) is shown as an example of the maximum period of the intermittent operation cycle, but the maximum period is not directly related to the startup period of the two-wire external field device 41 and can be set arbitrarily. The maximum period of the intermittent operation cycle can be appropriately set to, for example, 2 hours, 6 hours, 12 hours, 24 hours, or 2 days, and there is no need to set a particular upper limit.

When the protection circuit 20 is activated, a control command P2 is output from the _second control unit 27 to the cutoff unit 25 to turn on the power supply to the power supply unit 24 . Next, when receiving _a control command P1 to reduce the output voltage V _O to the low voltage V _OL from the first control unit 26, the second control unit 27 sends the voltage to the cutoff unit 25 after the second period (ON period t _on ). A control command P2 for turning off the power supply to the power supply unit 24 is _output .

The _second control unit 27 further outputs a control command P2 to the cutoff unit 25 to turn on the power supply to the power supply unit 24 again after the third period (off period t _off ), that is, to retry.

Abnormalities in the external field device 41 can be diagnosed based on the time until the external field device 41 is activated. In this embodiment, the second control unit 27 can diagnose an abnormality in the external field device 41 based on the number of retries until activation. For example, when the number of retries is a predetermined number, but is not particularly limited, but is greater than 100, for example, it is possible to diagnose that the external field device 41 may have a short-circuit failure. . On the other hand, for example, if the number of retries is less than another predetermined number of times, but not particularly limited, for example, three times, an abnormality in the capacitive element of the external field device 41, such as an aluminum It is possible to diagnose the possibility that an electrolytic capacitor dry-up abnormality has occurred.

Battery voltage monitoring unit 28 detects battery voltage _VB and outputs the detected value of battery voltage _VB to second control unit 27 . The second control unit 27 determines whether the battery voltage _VB is lower than the reference voltage _VBS . When the battery voltage _VB is lower than the reference voltage _VBS , it is determined that the battery voltage is abnormally low, and a control command P2 is issued to the cutoff unit ₂₅ to turn off the power supply to the power supply unit 24. Output. Diagnosis based on the battery voltage _VB makes it possible to judge the life of the battery, and it is also possible to estimate the remaining battery capacity from the change history of the battery voltage _VB .

In addition to overcurrent monitoring of the output current _IO by the current monitoring unit 23, a battery voltage monitoring unit 28 for monitoring the battery voltage _VB is provided, and the battery voltage _VB is the end voltage (hereinafter referred to as “reference voltage _VBS ”). ), the power supply to the power supply unit 24 is turned off, causing the battery voltage to drop due to the decrease in the battery remaining amount and the fuse 22 to open due to the increase in the fuse current _IH accompanying the decrease in battery voltage. Unnecessary fusing can be prevented, and overdischarge of the battery 21 can be prevented by suppressing the fuse current IH to a certain _level or less. In addition, determination of battery life is also possible. Although not particularly limited, the reference voltage _VBS can be set to 4.0V, for example. By monitoring the battery voltage _VB with the battery voltage monitor 28, the life of the battery can be determined. Further, the remaining amount of the battery 21 can be predicted by analyzing the degree of decrease in the battery voltage _VB from the history of the waveform of the battery voltage _VB .

[Protection circuit operation]
FIG. 2 is a waveform diagram of each part of the protection circuit 20 of FIG. Battery voltage V _B , fuse current I _H , output voltage V _O , output current I _O , control command P ₁ , and control command P ₂ , which are waveform diagrams in FIG. corresponds to the sign attached to . The operation of the protection circuit 20 during the passage of time from t1 to t19 will be described below with reference to FIG. Note that the waveform diagram of FIG. 2 is a drawing for explanation, and shows a schematic representation of an actual current or voltage waveform, which is an example for making the explanation easier to understand. FIG. 2 shows an example in which the number of retries is 6, the output current _IO is stabilized at 4-20 mA, and the external field device 41 is activated. An external field device 41 having a relatively small capacitive element, such as an external field device 41, may be activated after about 10 retries. It is diagnosed that there is a possibility that a short-circuit fault has occurred in the field device 41 . For example, when the device is started after three retries, it is diagnosed that there is a possibility that there is an abnormality in the capacitive element of the external field device 41, for example, an aluminum electrolytic capacitor that has dried up.

(1) Time t1
At time t1, the protection circuit 20 is activated, and the second control section 27 outputs a control command _P2ON for turning on the cutoff section 25 . Thereby, the electric power of the battery 21 is supplied to the power supply unit 24 . The power supply unit 24 is controlled by the control command P ₁ from the first control unit 26 so that the output voltage V 0 becomes the set voltage V _OC (for example, _14.3 V). The output voltage VO is supplied to the external field device 41 via two-wire cables _42,43 . Immediately after the external field device 41 is energized, the capacitive element of the external field device 41 is in an uncharged state and the input resistance is small, so the output current _IO has a large value. Therefore, an output current I _O1 exceeding the reference current I _OS (eg, 25 mA) flows. Since a large output current _{IO1 flows, the fuse current IH also becomes a large IH1, and the battery voltage VB becomes a voltage VB2 which is a voltage drop of the fuse current IH1 with respect to the internal} resistance. When the battery voltage _VB becomes equal to or lower than the reference voltage _VBS , the _second control section 27 outputs a control command P2 to turn off the cutoff section 25 .

(2) Time t2
At time t2, when the output current _IO exceeds the reference current _IOs during the determination period _td , the first control unit 26 determines that an overcurrent has occurred in the output current _IO , and the power supply unit 24 output voltage reduction command _P1L for reducing the output voltage _VO . When receiving the output voltage reduction command _P1L , the power supply unit 24 reduces the output voltage _VO to the low voltage _VOL . When the output voltage V _O is reduced to a low voltage V _OL (eg, 6.0V), the output current I _O is reduced to I _O2 but still greater than the reference current I _OS . When the output voltage _VO is reduced to a low voltage _VOL , the fuse current _IH is reduced to a current _IH2 that is slightly greater than the reference current _IHS . In response, battery voltage _{VB recovers to voltage VB1 ,} which is the voltage level during normal operation. The reference current _IHS is the limit value of the fuse current _IH , that is, the limit value of the battery current, and is a limit value determined according to the conditions of the circuits such as the battery 21 and the fuse 22 . However, even if the fuse current _{IH momentarily exceeds} the reference current _IHS , the fuse 22 does not blow immediately. It is set so that the fuse 22 is not melted by the fuse current _IH during normal operation.

In FIG. 2, the time t2 is after the determination period _td from the time t1. Actually, there is a delay time such as the current detection time in the current monitoring unit 23 and the calculation time in the first control unit 26, etc. Therefore, the time t2 is the time after the judgment period _td plus the calculation delay time from the time t1. becomes. However, when the calculation speed, detection speed, etc. are sufficiently fast, the calculation delay time becomes so small that it can be ignored. Therefore, the calculation delay time is ignored in FIG. 2 in this embodiment.

(3) Time t3 to time t4
At time t3, the _first control unit 26 changes the control command P1 from _P1L to 0 level after a second period (interruption standby time, hereinafter sometimes referred to as "ON period t _on ") from time t2. At the same time as releasing the output voltage reduction command _P1L , the second control unit 27 is notified that the ON period t _on has elapsed, and the _second control unit 27 outputs a control command P2 to turn off the cutoff unit 25. . When the cutoff unit 25 is turned off, the output current _IO becomes zero at time t3. The ON period t _on can be, for example, 1 ms. When the output current _IO becomes zero, the fuse current _IH also becomes zero at time t3. On the other hand, since the capacitive element of the external field device 41 is slightly charged, the output voltage _VO gradually drops from _VOL to zero from time t3 to time t4.

(4) Time t5 to time t8
At time t5, after the third period from time t3 (retry waiting time (hereinafter sometimes referred to as "off period t _off ")), the second control unit 27 turns on the cutoff unit 25 again by retrying. Output P _{2on The} off period t _off can be set to 30 ms, for example.

When the cut-off unit 25 is turned on, the capacitive element of the external field device 41 is not yet charged to a sufficient voltage, so the output current _IO exceeds the reference current _IO as in (1) above, and the first Since the overcurrent continues for the period (determination period t _d ), the first control unit 26 outputs the output voltage reduction command P _1L to the power supply unit 24 (time t6). Further, when the second period (ON period t _on ) has elapsed, at time t7, the _first control unit 26 changes the control command P1 from _P1L to 0 level, and cancels the output voltage reduction command _P1L . The second control unit 27 is notified that the ON period t _on has elapsed, and the _second control unit 27 outputs a control command P2 to turn off the cutoff unit 25 . When the cutoff unit 25 is turned off, the output current _IO becomes zero at time t7. When the output current _IO becomes zero, the fuse current _IH also becomes zero at time t7. On the other hand, since the capacitive element of the external field device 41 was gradually charged, the output voltage _VO gradually drops from _VOL to zero from time t7 to time t8. The amount of time from when the cutoff unit 25 is turned off at time t7 until the output voltage _VO becomes zero at t8 by the amount of the increase in the voltage charged in the capacitive element of the external field device 41 is the same as that of the previous retry. This is longer than the time from when the cutoff unit 25 is turned off at time t3 until the output voltage _VO becomes zero at t4.

(5) Time t9 to time t12
At time t9, after the third period (off period t _off ) from time t7, the second control section 27 again outputs the control signal _P2on for turning on the cutoff section 25 by retrying. However, since the capacitive element of the external field device 41 is still not charged to a sufficient voltage, the output current _IO exceeds the reference current _IO as in (1) and (4) above, and the first period ( Determination period t _d ) Since the overcurrent continues, the first control unit 26 outputs the output voltage reduction command P _1L to the power supply unit 24 (time t10). Further, when the second period (ON period t _on ) elapses, at time t11, the first control unit 26 changes the control command P ₁ from P _1L to 0 level, cancels the output voltage reduction command P _1L , and at the same time, The second control unit 27 is notified that the ON period t _on has elapsed, and the _second control unit 27 outputs a control command P2 to turn off the cutoff unit 25 . When the cutoff unit 25 is turned off, the output current _IO becomes zero at time t11. When the output current _IO becomes zero, the fuse current _IH also becomes zero at time t11.

On the other hand, since the capacitive element of the external field device 41 was gradually charged, the output voltage _{VO did not drop to the low voltage VOL immediately after the output voltage reduction command P1L was output} at time t10, but instead dropped to the low voltage VOL at time t10. After the output voltage V ₀ drops from the set voltage V _OC at t10, the output voltage V 0 drops gradually from time _t10 to time t11. Furthermore, even if the cutoff unit 25 is turned off at time t11, since the charging of the capacitive element of the external field device 41 is progressing, the output voltage _VO does not decrease abruptly, and gradually decreases from time t11 to time t12. , the output voltage _VO drops. Since the capacitive element of the external field device 41 is slightly charged, the output voltage _VO does not become zero at time t12, but becomes a level close to the low voltage _VOL .

Since the output voltage V _O and the output current I _O are applied to the external field device 41 at each retry, the capacitive element of the external field device 41 is gradually charged and the residual energy increases. As a result, the required energy for charging the capacitive element necessary for starting the external field device 41 decreases each time the retry is repeated. For this reason, the output voltage _VO increases with each retry, approaching a state in which it is easy to start. Therefore, the state of the capacitive element of the external field device 41 can be estimated from the number of retries until the external field device 41 is activated. For example, as described above, the second control unit 27 can diagnose an abnormality in the external field device 41 based on the number of retries until activation.

(6) Time t12 to time t15
At time t12, after the third period (off period t _off ) from time t11, the second control section 27 again outputs the control signal _P2on for turning on the cutoff section 25 by retrying. However, since the capacitive element of the external field device 41 is still not charged to a sufficient voltage, the output current _IO exceeds the reference current _IO as in (1), (4), and (5) above. Since the overcurrent continues for the first period (determination period t _d ), the first control unit 26 outputs the output voltage reduction command P _1L to the power supply unit 24 (time t13). Further, when the second period (ON period t _on ) has elapsed, at time t14, the _first control unit 26 changes the control command P1 from _P1L to 0 level, and cancels the output voltage reduction command _P1L . The second control unit 27 is notified that the ON period t _on has elapsed, and the _second control unit 27 outputs a control command P2 to turn off the cutoff unit 25 . When the cutoff unit 25 is turned off, the output current _IO becomes zero at time t14. When the output current _IO becomes zero, the fuse current _IH also becomes zero at time t14.

On the other hand, since the charging of the capacitive element of the external field device 41 is progressing, the output voltage _VO does not decrease to the low voltage _VOL even if the output voltage reduction command _P1L is output at time t13. After the output voltage V 0 slightly drops from the set voltage V _OC at _t13 , the output voltage V 0 gently drops from time _t13 to time t14. Furthermore, at time t14, even if the cutoff unit 25 is turned off, since the charging of the capacitive element of the external field device 41 is progressing, the output voltage _VO does not decrease abruptly, and gradually decreases from time t14 to time t15. , the output voltage _VO drops. As the charging of the capacitive element of the external field device 41 progresses, the output voltage _VO does not become zero at time t15, but becomes a predetermined level lower than the set voltage _VOC .

(7) Time t15 to time t18
At time t15, after the third period (off period t _off ) from time t14, the second control unit 27 again outputs the control signal _P2on that turns on the cutoff unit 25 by retrying. However, although the capacitor element of the external field device 41 is being charged, it is still not charged to a voltage sufficient to start up completely. Similarly, the output current I _O exceeds the reference current I _OS , and the overcurrent continues for the first period (determination period t _d ). _1L is output (time t16). Further, when the second period (ON period t _on ) has elapsed, at time t17, the _first control unit 26 changes the control command P1 from _P1L to 0 level, and cancels the output voltage reduction command _P1L . The second control unit 27 is notified that the ON period t _on has elapsed, and the _second control unit 27 outputs a control command P2 to turn off the cutoff unit 25 . When the cutoff unit 25 is turned off, the output current _IO becomes zero at time t17. When the output current _IO becomes zero, the fuse current IH also becomes zero at time _t17 .

On the other hand, the output voltage _VO does not drop to _VOL even if the output voltage reduction command _P1L is output at time t16 because the charging of the capacitive element of the external field device 41 has progressed considerably. After the output voltage V ₀ slightly drops from the set voltage V _OC at , the output voltage V 0 gently drops from time _t16 to time t17. Furthermore, at time t17, even if the cutoff unit 25 is turned off, since the charging of the capacitive element of the external field device 41 is progressing, the output voltage _VO does not decrease abruptly, and gradually decreases from time t17 to time t18. , the output voltage _VO drops. Retrying is repeated, and even at time t18, the charging of the capacitive element of the external field device 41 progresses to a level at which the output voltage _VO does not drop significantly from the set voltage _VOC .

(8) Time t18 to time t19
At time t18, after the third period ( _off period toff) from time t17, the second control section 27 again outputs the control signal _P2on for turning on the cutoff section 25 by retrying. Since the charging of the capacitive element of the external field device 41 has progressed sufficiently to enable activation, the output current _{IO momentarily} exceeds the reference current IO due to the rush current between times t18 and t19. It is an instantaneous pulse-shaped current shorter than the period _td , the output current _IO immediately becomes a value lower than the reference current _IOs , and after time t19, the output current _IO is smaller than the reference current _IOs . values, specifically 4-20 mA, are stable. Therefore, after time _t18 , the first control unit 26 does not determine that the output current _IO is _overcurrent . No output.

If the first control unit 26 does not output the output voltage reduction command _P1L , which is a command to reduce the output voltage _VO , to the power supply unit 24, the second period (ON period t _on ) is not timed. Furthermore, the second control unit 27 does not time the third period (off period t _off ). Therefore, after time t18, the capacitive element of the external field device 41 is sufficiently charged, the output current _I.sub.O stabilizes at a value smaller than the reference current _I.sub.OS , and the start-up of the external field device 41 is completed.

After time _t18 , the output voltage V 0 stabilizes at the set voltage V _OC (eg, 14.3 V). Since the control command P2 of the _second control unit 27 remains _P2on , the cutoff unit 25 remains on unless an overcurrent or the like is detected, and the power supply unit 24 is supplied with the power of the battery 21. continue to be supplied.

Between times t18 and _t19 , the output current _IO includes a momentary inrush current, so the fuse current _IH also momentarily exceeds the reference current _IHS . It stabilizes at a small value. Also, between times t18 and _t19 , the fuse current _IH momentarily exceeds the reference current _IHS , so the battery voltage VB momentarily drops to _VB2 due to the voltage drop due to the internal resistance of the battery. However, after time t19, it stabilizes at _VB1 .

After the external field device 41 is activated, normally, the output current _IO detected by the current monitoring unit 23 is stabilized at a value of 4-20 mA corresponding to the detected value of the sensor. When the output current _IO exceeds the reference current _IOs , the first control unit 26 determines that an overcurrent abnormality has occurred, and reduces the output voltage _VO of the power supply unit 24 to the low voltage _VOL . Further, the _second control unit 27 outputs a control command P2 to turn off the cutoff unit 25 after the on period t _on , thereby turning off the power supply to the external field device 41 . If the overcurrent of the output current _IO continues even after a predetermined number of retries, the second control unit 27 determines that a short circuit has occurred in the external field device 41, and turns off the cutoff unit 25. Along with outputting the control command P2, the wireless signal from the communication module 32 notifies the host device that an abnormality has occurred in the _output current _IO .

According to the protection circuit 20 of the first aspect of the present invention, the first control unit 26 reduces the output voltage _VO according to the overcurrent state detected by the current monitoring unit 23, and the power supply unit 24 By controlling the ON/OFF state, when power is supplied to the external field device 41 by a device driven by the battery 21, in addition to protecting and extending the life of the battery 21, the startup capability of the external field device 41 is improved. can be done.

According to the protection circuit 20 of the present embodiment, the first control unit 26 can reduce the output voltage _VO according to the state of overcurrent detected by the current monitoring unit 23, so that rapid overcurrent protection can be achieved. can be realized. Furthermore, the overcurrent generated in the output current _IO of the power supply unit 24 at the time of start-up can be prevented from exceeding the rated current of the battery 21 and the fusing current of the fuse 22 .

In addition, according to the protection circuit 20 of the present embodiment, the response of the first control unit 26 is fast, and the power supply unit 24 is quickly controlled to reduce the output voltage _VO supplied to the external field device 41, thereby instantaneously Battery 21 can be protected from overcurrent. Further, the second control unit 27 receives the signal from the first control unit 26 and controls the on/off state of the power supply unit 24 , specifically, by controlling the on/off state of the cutoff unit 25 , the external field device 41 can be improved, and an abnormality of the external field device 41 can be diagnosed. For example, it is possible to separate the supply of a temporary overcurrent necessary for starting the external field device 41 from the continuously occurring short-circuit failure, and protect the battery 21 from continuous occurrence of overcurrent.

Further, according to the protection circuit 20 of the present embodiment, the output of the power supply unit 24 is detected immediately after detecting the overcurrent of the output current _IO of the power supply unit 24, that is, after the first period (for example, the determination period t _d ). By reducing the voltage _VO to a low voltage _VOL , the current load applied to the battery 21 is lowered and protected, while the low voltage _VOL is applied to the external field device 41, and the capacitive element of the external field device 41, for example, the input capacitance, is protected. power can be supplied over a period of time. After reducing the output voltage V _O of the power supply unit 24 to the low voltage V _OL , the second control unit 27 turns off the power supply unit 24 after a second period (for example, an ON period t _on ). The cutoff unit 25 is turned off, and after a third period (for example, off period t _off ), the cutoff unit 25 is turned on again to retry.

In this way, after the overcurrent is detected, the capacitive element of the external field device 41 is charged with the low voltage _VOL , the power supply unit 24 is turned off after the second period, and the retry is performed after the third period. , the output voltage _VO is applied to the external field device 41 from the power supply unit 24 . As a result, the power supply unit 24 repeats the ON/OFF operation by retry, the capacitive element of the external field device 41 is gradually charged, and the external field device 41 is activated. Therefore, the external field device 41 can be started quickly while suppressing the inrush current at the time of retry, so that both the improvement of the starting ability of the external field device 41 and the improvement of the protection ability of the battery 21 can be achieved. In addition, by preventing an excessive current from being output from the battery 21, the battery life can be further improved, and the external field device 41 can be protected.

Furthermore, according to the protection circuit 20 of the embodiment, in addition to the overcurrent monitoring of the output current _IO by the current monitoring unit 23, the battery voltage monitoring unit 28 for monitoring the battery voltage _VB is provided so that the battery voltage _VB (reference voltage V _BS ), outputting an off command to the power supply unit 24, specifically by turning off the cutoff unit 25, the first control unit 26 and the second control The part 27 can prevent unnecessary melting of the fuse 22 due to a decrease in battery voltage due to a decrease in remaining battery power and an increase in fuse current IH due to a decrease in battery voltage, and the fuse current _IH can be suppressed below a certain _level . Thus, overdischarge of the battery 21 can be prevented. In addition, determination of battery life is also possible.

Moreover, according to the protection circuit 20 of this embodiment, the protection circuit 20 can be used as an explosion-proof device. Conventionally, an explosion-proof device capable of supplying power from the battery 21 to a general-purpose external field device 41 having a current signal of 4-20 mA has not been realized. According to the protection circuit 20 of the present embodiment, it is possible to drive the external field device 41, which consumes a maximum current of 20 mA or more, with the battery 21 incorporated in the explosion-proof device. This is because, in the present embodiment, while the capacitive element of the external field device 41 is gradually charged while reducing the overcurrent that occurs at startup, an abnormality such as a short-circuit current that occurs when the external field device 41 is short-circuited is prevented. Therefore, it is possible to achieve both current consumption that is large compared to the battery rating, which occurs continuously, and protection from short-circuit current that occurs when a short circuit occurs.

[Embodiment 2]
A protection circuit 20 according to a second embodiment of the present invention will be described with reference to FIGS. 2 and 3. FIG. In FIG. 3, the same reference numerals are used for the same configuration as in the first embodiment, and the description thereof is omitted. In the first embodiment, the radio signal converter 10 including the protection circuit 20 and the radio signal conversion circuit 30 is described as an example. The waveform diagram of each part of the protection circuit 20 in FIG. 2 is common to the first embodiment.

FIG. 3 is a block diagram of a system including protection circuit 20 according to Embodiment 2 of the present invention. Since the structure of the protection circuit 20 is common to that of the first embodiment, detailed description thereof will be omitted. _A set voltage V _OC (for example, 14.3 V) of the external field device 41 is output from the power supply unit 24 as the output voltage V 0 and supplied to the external field device 41 via two-wire cables 42 and 43 .

The external field device 41 can be, for example, a two-wire type external field device 41 as in the first embodiment. The voltage supplied from the two-wire cables 42 and 43 to the external field device 41 is, for example, 14.3 V, and the output current I _O as the device signal is normally in the range of 4 to 20 mA, the reference current I _OS (overcurrent detection reference current I _OS =25 mA). As the external field device 41, for example, a sensor detection value is returned as an analog DC current signal in the range of 4 to 20 mA, and a widely used general-purpose external field device 41 can be used.

Also in the present embodiment, as in the first embodiment, the output current I The current load applied to the battery 21 is reduced by reducing the output voltage _VO of the power supply unit 24 to the low voltage _VOL immediately after detecting the overcurrent of _O , that is, after the first period (for example, the determination period t _d ). A low voltage _VOL can be applied to the external field device 41 to supply power to the input capacitance of the external field device 41 for a certain period of time while under voltage protection. After reducing the output voltage V _O of the power supply unit 24 to the low voltage V _OL , the second control unit 27 turns off the power supply unit 24 after a second period (for example, the ON period t _on ). is turned off, and a retry is performed after a third period (for example, an off period t _off ).

In this way, after the overcurrent is detected, the input capacitance of the external field device 41 is charged with the low voltage V _OL , the power supply unit 24 is turned off after the second period (on period t _on ), and then the third period After (off period t _off ), a retry is performed, and the output voltage V _O is applied from the power supply section 24 to the external field device 41 . As a result, the power supply unit 24 repeats the ON/OFF operation by retry, the input capacitance of the external field device 41 is gradually charged, and the external field device 41 is activated. Therefore, the external field device 41 can be started quickly while suppressing the inrush current at the time of retry, so that both the improvement of the starting ability of the external field device 41 and the improvement of the protection ability of the battery 21 can be achieved.

In a structure that supplies power to an external field device 41 while protecting the battery 21 by the protection circuit 20, how is the detection value of the output current _IO , which is the device current from the external field device 41, handled by the protection circuit 20? Various applications are possible in terms of whether they are used and what kind of additional circuits are provided. For example, the protection circuit 20 of the present embodiment can be employed to implement a control unit or a detection unit for configuring a control device in a process, plant, or the like in which the external field device 41 is installed.

Although several embodiments of the present invention have been described above, these embodiments illustrate the protection circuit 20 for embodying the technical idea of the present invention, and the present invention is limited to these. Instead, it is equally applicable to other embodiments, and it is possible to omit, add, or change some of these embodiments, or to combine aspects of each embodiment. .

For example, the description of the explosion-proof structure in Embodiment 1 is not intended to limit the present invention to explosion-proof structures only, and the present invention is equally applicable to equipment that does not have an explosion-proof structure.

DESCRIPTION OF SYMBOLS 10... Radio signal converter 20... Protection circuit 21... Battery 22... Fuse 23... Current monitoring part 24... Power supply part 25... Breaking part 26... First control Section 27 Second control section 28 Battery voltage monitoring section 30 Radio signal conversion circuit 31 Calculation section 32 Communication module 33 Radio antenna 40 External device 41・・・External field device 42, 43 ・・・Two-wire cable

Claims (4)

A protection circuit for a battery-powered device that supplies power to an external field device,
a battery;
a power supply unit comprising a DC-DC converter that transforms the battery voltage of the battery;
a current monitoring unit that monitors the output current of the power supply;
a control unit that controls the on/off state and output voltage of the power supply unit based on the signal from the current monitoring unit;
a fuse that protects the battery;
including
The control unit reduces the output voltage and controls the on/off state of the power supply unit according to the state of overcurrent detected by the current monitoring unit ,
The control unit
a first control unit that outputs an output voltage reduction command for reducing the output voltage to the power supply unit when an overcurrent is detected by the current monitoring unit;
a second control unit that receives the output voltage reduction command, controls the on/off timing of the power supply unit, and determines an abnormality in the external field device;
A protection circuit, comprising : The first control unit sends an output voltage reduction command to the power supply unit to reduce the output voltage after a first period when the current monitoring unit detects an overcurrent,
The second control unit is
After receiving the output voltage reduction command, the power supply unit is turned off after a second period, and the power supply unit is turned on after a third period,
2. The protection circuit according to claim 1 , wherein abnormality of said external field device is determined based on the number of times said power supply is turned on and off. The control unit
A battery voltage monitoring unit that monitors the battery voltage,
3. The protection circuit according to claim 1, wherein when it detects that the battery voltage has dropped below a predetermined voltage, it outputs an off command to the power supply unit. The protection circuit according to any one of claims 1 to 3 , wherein the protection circuit is an explosion-proof device.

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