WO2024089795A1

WO2024089795A1 - Input protection device

Info

Publication number: WO2024089795A1
Application number: PCT/JP2022/039906
Authority: WO
Inventors: 五嶋数哉
Original assignee: ファナック株式会社
Priority date: 2022-10-26
Filing date: 2022-10-26
Publication date: 2024-05-02
Also published as: JPWO2024089795A1; JP7239793B1

Abstract

An input protection device according to an aspect of the present disclosure is provided with: a switch unit that is interposed between a power source and a load and that can switch connection and disconnection of the power source and the load; a switch control unit that controls the switch unit in response to a start signal supplied from the outside and connects the power source and the load to each other; a low voltage protection unit that, when an input voltage from the power source is equal to or lower than a prescribed voltage threshold value, controls the switch unit and disconnects the power source and the load from each other; a current limitation unit that limits a current supplied to the load to equal to or less than a limitation value; and a limitation-value change unit that, after receiving the start signal, causes the limitation value to increase with the elapse of time such that the input voltage does not become equal to or lower than the voltage threshold value.

Description

Input Protection Device

This disclosure relates to an input protection device.

　JP Patent Publication No. 9-56058 discloses a device that prevents inrush current from flowing from a power source to a load when the power is turned on.

It would be desirable to provide a better input protection device.

One aspect of the present disclosure is an input protection device that limits the current supplied from a power source to a load when the power source is turned on, and includes a switch unit that is interposed between the power source and the load and is capable of switching between connection and disconnection of the power source and the load, a switch control unit that controls the switch unit to connect the power source and the load in response to an activation signal supplied from the outside, a low voltage protection unit that controls the switch unit to disconnect the power source and the load when the input voltage from the power source is equal to or lower than a predetermined voltage threshold, a current limiting unit that limits the current supplied to the load to a limit value or lower, and a limit value changing unit that increases the limit value over time after receiving the activation signal so that the input voltage does not become equal to or lower than the voltage threshold.

FIG. 1 is a block diagram of an electrical device. FIG. 2 is a circuit diagram of the input protection device according to the first embodiment. Each of FIGS. 3A to 3E is a time chart showing the change over time of each value in the reference example. Each of FIGS. 4A to 4H is a time chart showing the change over time of each value of the input protection device according to the first embodiment. FIG. 5 is a circuit diagram of an input protection device according to the second embodiment. Each of FIGS. 6A to 6H is a time chart showing the change over time of each value of the input protection device according to the second embodiment.

[1 Electrical Equipment 10]
1 is a block diagram of an electric device 10. The electric device 10 (including electronic devices) has a power supply device 12, an input protection device 14, and a subsequent circuit (load) 16. The input protection device 14 and the subsequent circuit 16 are formed on a single printed circuit board, for example. The subsequent circuit 16 operates with power supplied by the power supply device 12. The subsequent circuit 16 has a large-capacity capacitor 20 (such as an electrolytic capacitor). The input protection device 14 is interposed between the power supply device 12 and the subsequent circuit 16.

The terms used in this specification are defined as follows.
Input voltage VIN: the value of the voltage supplied from the power supply 12 to the input protection device 14.
Back electromotive force ΔVIN_R: the value of the back electromotive force generated by the resistance of the cable connecting the power supply device 12 and the input protection device 14.
Back electromotive force ΔVIN_L: the value of the back electromotive force generated by the inductance of the cable connecting the power supply device 12 and the input protection device 14.
Current Iin: the value of the current supplied from the input protection device 14 to the subsequent circuit 16.
Current limit value ILIM′: A limit value (variable value) of the current Iin set in the input protection device 14.
Current limit value ILIM: Upper limit value of current limit value ILIM'.
Charging voltage VIN_INT: the voltage value of the capacitor 20 in the subsequent circuit 16.
Variable resistor Rset': the resistance value (variable value) of the resistor setting circuit 40 (FIG. 2).
Set resistance Rset: The lower limit value of the variable resistance Rset'.

[2. Configuration of input protection device 14]
When an abnormality occurs in the power supplied from the power supply device 12 to the subsequent circuit 16, the input protection device 14 cuts off the power supply device 12 and the subsequent circuit 16 to protect the subsequent circuit 16. The input protection device 14 has an input protection unit 22 and a limit value changing unit 24.

The input protection unit 22 has a switch unit 26, a switch control unit 28, a low-voltage protection unit 30, and a current limiting unit 32. The switch unit 26 is interposed between the power supply device 12 and the rear circuit 16, and switches between connection and disconnection of the power supply device 12 and the rear circuit 16. The switch control unit 28 controls the switch unit 26 in response to a start-up signal supplied from the outside to connect the power supply device 12 and the rear circuit 16. The low-voltage protection unit 30 controls the switch unit 26 to disconnect the power supply device 12 and the rear circuit 16 when the input voltage VIN by the power supply device 12 is equal to or lower than a predetermined voltage threshold Vth. That is, the low-voltage protection unit 30 has a low-voltage protection function. The current limiting unit 32 limits the current Iin supplied to the rear circuit 16 to equal to or lower than the current limit value ILIM'. That is, the current limiting unit 32 has an inrush current suppression function.

After receiving a startup signal supplied from the outside, the limit value change unit 24 increases the current limit value ILIM' used by the current limit unit 32 over time so that the input voltage VIN from the power supply device 12 does not fall below a predetermined voltage threshold Vth. By increasing the current limit value ILIM' over time, the limit value change unit 24 suppresses a sudden increase in the current Iin supplied from the input protection device 14 to the subsequent circuit 16.

[3. Specific Examples of Input Protection Device 14]
[3-1 First embodiment]
[composition]
2 is a circuit diagram of the input protection device 14 according to the first embodiment. The input protection device 14 has an electronic fuse 36, an RC low-pass filter circuit 38, and a resistance setting circuit 40. The electronic fuse 36 corresponds to the input protection unit 22 shown in FIG 1. The RC low-pass filter circuit 38 and the resistance setting circuit 40 correspond to the limit value changing unit 24 shown in FIG 1.

The electronic fuse 36 is also called an eFUSE. The electronic fuse 36 is an integrated circuit having a switch element 42 and a control circuit 44. The switch element 42 is, for example, a MOSFET. The switch element 42 corresponds to the switch unit 26 shown in FIG. 1. The control circuit 44 has electronic circuits for realizing the functions of the switch control unit 28, the low voltage protection unit 30, the current limiting unit 32, and the like shown in FIG. 1. That is, the control circuit 44 sets the voltage threshold Vth to a constant value. The control circuit 44 also shuts off the switch element 42 when the input voltage VIN falls below the voltage threshold Vth. The control circuit 44 also limits the current Iin to a current limit value ILIM'. The control circuit 44 also changes the current limit value ILIM' according to the variable resistor Rset'.

The electronic fuse 36 has an input terminal 46 (INPUT), an output terminal 48 (OUTPUT), an EN terminal (enable terminal) 50, and an ILIM terminal 52. The input terminal 46 and the output terminal 48 are connected to each other via a switch element 42. The EN terminal 50 and the ILIM terminal 52 are each connected to a control circuit 44. The input terminal 46 is connected to the power supply device 12. The output terminal 48 is connected to the subsequent circuit 16. The EN terminal 50 is connected to a device (not shown) that outputs a start signal. The ILIM terminal 52 is connected to the resistance setting circuit 40. Although not shown, examples of the device that outputs the start signal include a voltage monitoring device and other electrical equipment formed on a single printed circuit board together with the electronic fuse 36. The voltage monitoring device and other electrical equipment output a start signal when the input voltage VIN exceeds a predetermined voltage.

The RC low-pass filter circuit 38 has a resistor 54 and a capacitor 56. A first terminal of the resistor 54 is connected to an EN terminal 50 provided in the electronic fuse 36 and to a device (not shown) that outputs an activation signal. A second terminal of the resistor 54 is connected to a first terminal of the capacitor 56 and to a gate terminal of a FET 60 provided in the resistance setting circuit 40. A second terminal of the capacitor 56 is connected to ground. The RC low-pass filter circuit 38 gradually increases the voltage due to the activation signal supplied from outside, and supplies it as a gate signal to the gate terminal of the FET 60 provided in the resistance setting circuit 40.

The resistance setting circuit 40 has a series circuit in which a fixed resistor 58 and a FET 60 are connected in series. The resistance value of the fixed resistor 58 is constant. A first terminal of the fixed resistor 58 is connected to the ILIM terminal 52 of the electronic fuse 36. A second terminal of the fixed resistor 58 is connected to the drain terminal of the FET 60. The FET 60 is, for example, a MOSFET. The drain terminal of the FET 60 is connected to the second terminal of the fixed resistor 58. The source terminal of the FET 60 is connected to ground. The gate terminal of the FET 60 is connected to the output terminal of the RC low-pass filter circuit 38 (the second terminal of the resistor 54 and the first terminal of the capacitor 56).

As described above, the RC low-pass filter circuit 38 gradually increases the voltage supplied to the gate terminal of the FET 60. This gradually decreases the drain-source resistance of the FET 60. This gradually decreases the variable resistance Rset' of the resistance setting circuit 40. As described above, the variable resistance Rset' is the resistance value (variable value) of the resistance setting circuit 40. The control circuit 44 is configured to set the current limit value ILIM' according to the variable resistance Rset'. For this reason, the control circuit 44 increases the current limit value ILIM' as the variable resistance Rset' decreases. As described above, the current limit value ILIM' is the limit value (variable value) of the current Iin set in the input protection device 14. When the current limit value ILIM' gradually increases, the current Iin also gradually increases. As described above, the current Iin is the value of the current supplied from the input protection device 14 to the subsequent circuit 16. In this way, the RC low-pass filter circuit 38 and the resistance setting circuit 40 are provided, so the current Iin can be gradually increased.

[Comparison between the first embodiment and the reference example]
One of the features of the input protection device 14 is that it is provided with a variable resistor Rset'. Here, the operation of the input protection device 14 when it is not provided with the variable resistor Rset' will be compared with the operation of the input protection device 14 when it is provided with the variable resistor Rset'.

[Reference Example Operation]
An input protection device 14 not including a variable resistor Rset' is taken as a reference example. Each of Figs. 3A to 3E is a time chart showing the time change of each value of the input protection device 14 according to the reference example. Fig. 3A is a time chart of the input voltage VIN. Fig. 3B is a time chart of the back electromotive force ΔVIN_R. Fig. 3C is a time chart of the back electromotive force ΔVIN_L. Fig. 3D is a time chart of the current Iin. Fig. 3E is a time chart of the charging voltage VIN_INT. For convenience of explanation, Figs. 3A to 3E are deformed.

At time ta1 when the power is turned on, the input voltage VIN rises. After that, at time ta2, the current Iin rises suddenly to the current limit value ILIM. As the current Iin rises suddenly, a large back electromotive force ΔVIN_R is generated due to the resistance of the cable between the power supply device 12 and the input protection device 14. As the current Iin rises suddenly, a large back electromotive force ΔVIN_L is generated due to the inductance of the cable between the power supply device 12 and the input protection device 14. These back electromotive forces ΔVIN_R and ΔVIN_L cause the input voltage VIN to drop significantly. When the input voltage VIN falls below the voltage threshold Vth, the control circuit 44 (low voltage protection unit 30) switches the switch element 42 from on to off to cut off the power supply device 12 and the subsequent circuit 16.

At timing ta3 when the switch element 42 is switched, the current Iin drops suddenly. As the current Iin drops suddenly, a back electromotive force ΔVIN_L is generated in the opposite direction to the back electromotive forces ΔVIN_R, ΔVIN_L generated at timing ta2. This back electromotive force ΔVIN_L in the opposite direction causes the input voltage VIN to rise significantly. At timings when the back electromotive forces ΔVIN_R, ΔVIN_L are not generated, the input voltage VIN is equal to the input voltage VIN at timing ta1. This phenomenon occurs repeatedly.

The capacitor 20 of the rear circuit 16 is charged while the current Iin is being supplied from the input protection device 14 to the rear circuit 16. That is, as shown in FIG. 3E, the charging voltage VIN_INT rises only while the current Iin is being supplied from the input protection device 14 to the rear circuit 16.

At timing ta4, the charging voltage VIN_INT becomes approximately equal to the input voltage VIN. Then, the current Iin decreases, and the back electromotive forces ΔVIN_R and ΔVIN_L decrease. Because these back electromotive forces ΔVIN_R and ΔVIN_L decrease, the fluctuation of the input voltage VIN also decreases. As a result, the input voltage VIN does not fall below the voltage threshold Vth, and the start-up of the charging voltage VIN_INT is completed. Thereafter, the current Iin increases as the consumption current increases due to the start of operation of the subsequent circuit 16.

As such, in the input protection device 14 of the reference example, the peak of the input voltage VIN becomes excessively large. This may cause damage to the components of the input protection device 14. Furthermore, in the input protection device 14 of the reference example, the current Iin is intermittently supplied from the input protection device 14 to the subsequent circuit 16. This means that it takes a long time for the capacitor 20 of the subsequent circuit 16 to be charged.

[Operation of the input protection device 14 according to the first embodiment]
Each of Figures 4A to 4H is a time chart showing the change over time of each value of the input protection device 14 according to the first embodiment. Figure 4A is a time chart of the input voltage VIN. Figure 4B is a time chart of the back electromotive force ΔVIN_R. Figure 4C is a time chart of the back electromotive force ΔVIN_L. Figure 4D is a time chart of the current Iin. Figure 4E is a time chart of the start-up signal. Figure 4F is a time chart of the variable resistor Rset'. Figure 4G is a time chart of the current limit value ILIM'. Figure 4H is a time chart of the charging voltage VIN_INT. Note that, like Figures 3A to 3E, Figures 4A to 4H are deformed.

At timing tb1 when the power is turned on, the input voltage VIN rises. Furthermore, at timing tb2 after the input voltage VIN has risen, a start-up signal is supplied. Then, the output voltage of the RC low-pass filter circuit 38 starts to rise from zero (not shown). As time passes, the output voltage of the RC low-pass filter circuit 38 gradually rises. The degree of rise in the output voltage of the RC low-pass filter circuit 38 is determined by the time constant (RC). The output voltage of the RC low-pass filter circuit 38 is supplied to the gate terminal of the FET 60. As a result, the resistance value between the drain and source of the FET 60 starts to decrease from infinity. As time passes, the resistance value between the drain and source of the FET 60 gradually decreases. Therefore, as shown in FIG. 4F, the variable resistor Rset' starts to decrease. As time passes, the variable resistor Rset' gradually decreases. Then, as shown in FIG. 4G, the current limit value ILIM' starts to increase. As time passes, the current limit value ILIM' gradually increases. As shown in FIG. 4D, the current Iin gradually increases in accordance with the increase in the current limit value ILIM'. Because the current limit value ILIM' increases gradually, the current Iin does not increase abruptly. Therefore, as shown in FIG. 4B and FIG. 4C, the magnitude of the back electromotive forces ΔVIN_R, ΔVIN_L is smaller than the magnitude of the back electromotive forces ΔVIN_R, ΔVIN_L shown in FIG. 3C. Therefore, the decrease in the input voltage VIN is also smaller. As a result, the input voltage VIN does not fall below the voltage threshold Vth.

At timing tb3, the resistance between the drain and source of FET 60 becomes approximately zero. As shown in FIG. 4F, variable resistance Rset' becomes equal to set resistance Rset, which is the lower limit value. As shown in FIG. 4G, current limit value ILIM' becomes equal to current limit value ILIM, which is the upper limit value. As shown in FIG. 4D, current Iin also becomes equal to current limit value ILIM. When current Iin stops changing, back electromotive forces ΔVIN_R and ΔVIN_L are no longer generated, and the input voltage VIN stops changing.

In the first embodiment, the current Iin does not rise suddenly between timing tb1 and timing tb3. Therefore, the change in the input voltage VIN caused by the back electromotive forces ΔVIN_R and ΔVIN_L becomes small, and the input voltage VIN does not fall below the voltage threshold Vth. Therefore, according to the first embodiment, it is possible to prevent the input voltage VIN from becoming excessively large, and as a result, there is no risk of damage to the components of the input protection device 14.

In addition, in the first embodiment, since the input voltage VIN does not fall below the voltage threshold Vth, the control circuit 44 (low voltage protection unit 30) maintains the connection state of the switch element 42. In other words, the connection state between the power supply device 12 and the subsequent circuit 16 is maintained until the capacitor 20 of the subsequent circuit 16 is charged. Therefore, according to the first embodiment, the capacitor 20 of the subsequent circuit 16 can be quickly charged.

[3-2 Second embodiment]
5 is a circuit diagram of the input protection device 14 according to the second embodiment. The second embodiment is an improved example of the first embodiment. The basic configuration of the input protection device 14 according to the second embodiment is the same as the configuration of the input protection device 14 according to the first embodiment.

In the first embodiment, the variable resistor Rset' starts decreasing from infinity. In this case, the current limiting unit 32 may not be able to accurately set the current limiting value ILIM due to noise or the like. In the second embodiment, the resistance setting circuit 40 has a noise prevention resistor 62 that bypasses the FET 60. A first terminal of the noise prevention resistor 62 is connected to the source terminal of the FET 60. A first terminal of the noise prevention resistor 62 is connected to the drain terminal of the FET 60. The resistance value Rset2 of the noise prevention resistor 62 is greater than the resistance value Rset1 of the fixed resistor 58.

Each of Figures 6A to 6H is a time chart showing the change over time of each value of the input protection device 14 according to the second embodiment. Figures 6A to 6E and 6H are the same as Figures 4A to 4E and 4H. Figure 6F is a time chart of the variable resistor Rset'. Figure 6G is a time chart of the current limit value ILIM'.

As shown in FIG. 6F, the upper limit of the variable resistor Rset' is the sum of the resistance values Rset1 and Rset2. In this way, the FET 60 is bypassed by the noise prevention resistor 62, so that the variable resistor Rset' does not become excessively large. Therefore, the current limiting unit 32 can accurately set the current limiting value ILIM without being affected by noise.

[3-3 Other embodiments]
In the above embodiment, an example has been described in which an externally supplied activation signal is supplied as a gate signal to the gate terminal of the FET 60 provided in the resistance setting circuit 40 via the RC low-pass filter circuit 38, but this is not limiting. A gate signal output by another output circuit (e.g., a processor, etc.) may be supplied to the gate terminal of the FET 60. In this case, the other output circuit gradually increases the magnitude of the gate signal.

[4 Supplementary Note]
The following supplementary notes are further disclosed regarding the above embodiment and modified examples.

(Note 1) An input protection device (14) that limits a current (Iin) supplied from a power source (12) to a load (16) when the power source is turned on includes a switch unit (26) that is interposed between the power source and the load and can switch between connection and disconnection of the power source and the load, a switch control unit (28) that controls the switch unit to connect the power source and the load in response to an activation signal supplied from the outside, a low voltage protection unit (30) that controls the switch unit to disconnect the power source and the load when an input voltage (VIN) from the power source is equal to or lower than a predetermined voltage threshold, a current limiting unit (32) that limits the current supplied to the load to a limit value (ILIM') or lower, and a limit value changing unit (24) that increases the limit value over time after receiving the activation signal so that the input voltage does not become equal to or lower than the voltage threshold.

(Appendix 2) In the input protection device described in Appendix 1, the switch unit, the switch control unit, the low voltage protection unit, and the current limiting unit may be included in a single integrated circuit (36).

(Appendix 3) In the input protection device described in Appendix 2, the limit value change unit has a resistance setting circuit (40) connected to the integrated circuit and capable of lowering the resistance value (Rset') to a preset lower limit value (Rset), and the limit value may change according to the resistance value of the resistance setting circuit.

(Appendix 4) In the input protection device described in Appendix 3, the resistance setting circuit may have a series circuit in which a fixed resistor (58) having a constant resistance value and a FET (60) are connected in series, and the limit value changing unit may have an output circuit that outputs a gate signal to the FET to change the resistance value of the resistance setting circuit.

(Appendix 5) In the input protection device described in Appendix 4, the output circuit may further include an RC low-pass filter circuit (38) that uses the activation signal to change the resistance value of the resistance setting circuit.

(Appendix 6) In the input protection device described in appendix 4 or 5, the limit value change unit may have a noise prevention resistor (62) connected to the source terminal of the FET and the drain terminal of the FET and having a resistance value greater than that of the fixed resistor.

Although the present disclosure has been described in detail, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible to these embodiments without departing from the gist of the present disclosure, or without departing from the gist of the present disclosure derived from the contents described in the claims and their equivalents. These embodiments can also be implemented in combination. For example, in the above-mentioned embodiments, the order of each operation and the order of each process are shown as examples, and are not limited to these. The same applies when numerical values or formulas are used to explain the above-mentioned embodiments.

REFERENCE SIGNS LIST 12 power supply device (power supply) 14 input protection device 16 subsequent circuit (load) 24 limit value change section 26 switch section 28 switch control section 30 low voltage protection section 32 current limit section 36 electronic fuse (integrated circuit)
38 RC low-pass filter circuit 40 Resistance setting circuit 58 Fixed resistor 60 FET
62: Noise prevention resistor

Claims

An input protection device that limits the current supplied from a power supply to a load when the power supply is turned on,
a switch unit interposed between the power source and the load and capable of switching between connection and disconnection between the power source and the load;
a switch control unit that controls the switch unit in response to an externally supplied start signal to connect the power source and the load;
a low voltage protection unit that controls the switch unit to cut off the power supply and the load when an input voltage from the power supply is equal to or lower than a predetermined voltage threshold;
a current limiting unit that limits a current supplied to the load to a limit value or less;
a limit value changing unit that increases the limit value over time after receiving the activation signal so that the input voltage does not become equal to or lower than the voltage threshold value;
An input protection device comprising:
2. An input protection device according to claim 1,
An input protection device, wherein the switch section, the switch control section, the under-voltage protection section and the current limiting section are included in a single integrated circuit.
3. An input protection device according to claim 2,
the limit value changing unit has a resistance setting circuit connected to the integrated circuit and capable of decreasing a resistance value to a preset lower limit value;
An input protection device, wherein the limit value varies depending on the resistance value of the resistance setting circuit.
4. An input protection device according to claim 3,
the resistance setting circuit has a series circuit in which a fixed resistor having a constant resistance value and an FET are connected in series,
The limit value changing unit has an output circuit that outputs a gate signal to the FET for changing the resistance value of the resistance setting circuit.
5. An input protection device according to claim 4,
The output circuit further includes an RC low-pass filter circuit that changes a resistance value of the resistance setting circuit using the activation signal.
6. An input protection device according to claim 4 or 5,
The limit value changing unit has a noise prevention resistor connected to a source terminal of the FET and a drain terminal of the FET, the noise prevention resistor having a resistance value greater than that of the fixed resistor.