Entrance protection device

Abstract

An input protection device according to one aspect of the present invention is equipped with: a switching unit that is arranged between a power source and a load and can switch the connection and disconnection of the power source and the load; a switching control unit that controls the switching unit in response to an externally supplied start signal and connects the power source and the load; an undervoltage protection unit that, when an input voltage from the power source is equal to or lower than a prescribed voltage threshold, controls the switching unit and disconnects the power source and the load; a current limiting unit that limits a current supplied to the load to equal to or lower than a limit value;and a threshold value changing unit which, upon receipt of the start signal, causes the threshold value to increase over time so that the input voltage does not become equal to or lower than the voltage threshold value.;

Description

TECHNICAL FIELDThe present invention relates to an input protection device.PRIOR ARTJP H09-056058 A discloses a device that prevents an inrush current from flowing from the power supply to a load when the power supply is turned on.SUMMARY OF THE INVENTIONIt is desirable to provide a better input protection device.An aspect of the present invention is characterized by an input protection device that limits a current supplied from a power supply to a load when the power supply is turned on, the input protection device comprising: a switching unit that is disposed between the power supply and the load and is configured to switch between connection and disconnection between the power supply and the load; a switching control unit that is configured to control the switching unit in response to an activation signal supplied from the outside to connect the power supply and the load; an under-voltage protection unit that is configured to control the switching unit to disconnect 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 configured to limit the current supplied to the load to a threshold value or less; and a threshold value changing unit configured to increase the threshold value with time so that the input voltage does not become equal to or lower than the voltage threshold value after the activation signal is received.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a block diagram of an electrical device; FIG. 2 is a circuit diagram of an input protection device according to a first embodiment; FIGS. 3A to 3E are time charts showing a temporal change of each value of a reference example; FIGS. 4A to 4H are timing charts showing a temporal change in 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 a second embodiment; and FIGS. 6A to 6H are timing charts showing a temporal change of each value of the input protection device according to the second embodiment.DETAILED DESCRIPTION OF THE INVENTION[1. Electrical Device 10]FIG. 1 is a block diagram of an electric device 10. the electric device 10 (including an electronic device) includes a power supply 12, an input protector 14, and a follower circuit (load) 16. The subsequent stage 16 is operated by the power supplied from the power supply 12. The subsequent stage 16 includes a capacitor 20 (electrolytic capacitor or the like) having a large capacitance. The input protection device 14 is arranged between the power supply device 12 and the subsequent stage 16.The terms used in the present specification are defined as follows:Input voltage VIN: the value of a voltage supplied from the power supply 12 to the input protector 14;COUNTER ELECTROMOTIVE FORCE ΔVIN_R: the value of a counter electromotive force generated by a resistance of a cable connecting the power supply device 12 and the input protector 14;COUNTER ELECTROMOTIVE FORCE ΔVIN_L: the value of a counter electromotive force generated by an inductance of the cable connecting the power supply 12 and the input protector 14;Current lin: the value of a current supplied from the input protection device 14 to the subsequent stage 16;current limit value ILIM': a limit value (variable value) of current lin set in input protector 14;Current limit value ILIM: the upper limit of current limit value ILIM';Charging voltage VIN_INT: the value of a voltage of the capacitor 20 of the subsequent circuit stage 16;variable resistor Rset': the value of a resistor (variable value) of a resistor adjustment circuit 40 (FIG. 2 ); andSet resistance Rset: the lower limit of variable resistance Rset'.[2. Configuration of Input Protection Device 14]The input protector 14 protects the subsequent stage 16 by separating the power supply 12 from the subsequent stage 16 when an abnormality occurs in the power supplied from the power supply 12 to the subsequent stage 16. The input protection device 14 includes an input protection unit 22 and a limit value changing unit 24.The input protection unit 22 includes a switching unit 26, a switching control unit 28, an under voltage protection unit 30, and a current limiting unit 32. the switching unit 26 is disposed between the power supply device 12 and the subsequent circuit stage 16, and switches between connection and disconnection between the power supply device 12 and the subsequent circuit stage 16. The switching control unit 28 controls the switching unit 26 in response to an activation signal supplied from the outside, thereby connecting the power supply device 12 and the subsequent circuit stage 16. The under voltage protection unit 30 controls the switching unit 26 to disconnect the power supply unit 12 from the subsequent circuit stage 16 when the input voltage VIN of the power supply unit 12 is equal to or lower than a predetermined voltage threshold Vth. That is, the under voltage protection unit 30 has an under voltage protection function. The current limiting unit 32 limits the current lin supplied to the subsequent circuit stage 16 to the current limit value ILIM' or less. That is, the current limiting unit 32 has an inrush current suppressing function.The limit value changing unit 24 increases the current limit value ILIM' used by the current limiting unit 32 with time so that the input voltage VINby the power supply device 12 does not become equal to or less than the predetermined voltage threshold value Vthafter the activation signal supplied from the outside is received. The limit value changing unit 24 increases the current limit value ILIM' with time, thereby suppressing a rapid increase in the current lin supplied from the input protector 14 to the subsequent stage 16.[3. Specific Example of Input Protection Device 14][3-1. First Embodiment][Configuration]FIG. 2 is a circuit diagram of the input protection device 14 according to a first embodiment. The input protection device 14 includes an electronic fuse 36, an RC low-pass filter circuit (resistance capacitance) 38, and a resistance adjustment 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 adjustment circuit 40 correspond to the limit value change unit 24 shown in FIG. 1.The electronic fuse 36 is also referred to as eUSE. The electronic fuse 36 is an integrated circuit including a switching element 42 and a control circuit 44. the switching element 42 is, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The switching element 42 corresponds to the switching unit 26 illustrated in FIG. 1, and the control circuit 44 includes an electronic circuit for realizing the functions of the switching control unit 28, the under-voltage protection unit 30, the current limiting unit 32, and the like illustrated in FIG. 1. That is, the control circuit 44 sets the voltage threshold value Vth to a constant value. The control circuit 44 turns off the switching element 42 when the input voltage VIN falls below the voltage threshold Vth. The control circuit 44 limits the current lin to the current limit value ILIM'. The control circuit 44 changes the current limit value ILIM' according to the variable resistor Rset'.The electronic fuse 36 includes an input terminal 46 (INPUT), an output terminal 48 (OUTPUT), an EN terminal (enable terminal) 50, and an ILIM terminal 52. The EN terminal 50 and the ILIM terminal 52 are connected to the control circuit 44, respectively. The input terminal 46 is connected to the power supply 12. The output terminal 48 is connected to the follower circuit 16. The EN terminal 50 is connected to a device (not shown) that outputs the activation signal. The ILIM terminal 52 is connected to the resistance adjusting circuit 40. Although not illustrated, a voltage monitoring device formed on a single circuit board together with the electronic fuse 36, other electrical devices, and the like are indicated as devices that output the activation signal. The voltage monitor and other electrical devices output the activation signal when the input voltage VIN überschreitet a predetermined voltage.The RC low pass filter circuit 38 includes a resistor 54 and a capacitor 56. a first terminal of the resistor 54 is connected to the EN terminal 50 provided in the electronic fuse 36 and to a device (not shown) that outputs the 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 an FET (Field Effect Transistor) 60 provided in the resistance adjustment circuit 40. A second terminal of the capacitor 56 is connected to ground. The RC low-pass filter circuit 38 gradually increases the voltage of the activation signal supplied from the outside and supplies, as the gate signal, the voltage to the gate terminal of the FET 60 provided in the resistance adjustment circuit 40.The resistance adjustment circuit 40 includes a series circuit in which a fixed resistor 58 and the 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 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. As a result, the resistance value between the drain and the source of the FET 60 gradually decreases. As a result, the variable resistance Rset' of the resistance adjusting circuit 40 gradually decreases. The variable resistor Rset' is the resistance value (variable value) of the resistor adjusting circuit 40 as described above. The control circuit 44 is configured to set the current limit value ILIM' corresponding to the variable resistor Rset'. Therefore, the control circuit 44 increases the current limit value ILIM' according to the decrease of the variable resistor Rset'. As described above, the current limit value ILIM' is a limit value (variable value) of the current lin set in the input protector 14. As the current limit value ILIM' gradually increases, the current lin also gradually increases. As described above, the current lin is a value of the current supplied from the input protector 14 to the subsequent stage 16. As described above, since the RC low pass filter circuit 38 and the resistance adjustment circuit 40 are provided, the current lin can be gradually increased.[Comparison between the First Embodiment and Reference Example]The input protection device 14 is characterized by being provided with a variable resistor Rset'. Here, the operation of the input protector 14 in the case where no variable resistor Rset' is provided and the operation of the input protector 14 in the case where the variable resistor Rset' is provided are compared.[Operation of Reference Example]The input protector 14 is used as a reference example in the case where no variable resistor Rset' is provided. Each of FIGS. 3A to 3E is a time chart showing a temporal change of each value of the input protection device 14 according to the reference example. FIG. 3A is a timing diagram of the input voltage VIN. FIG. 3B is a timing diagram of the back EMF DVIN_R. FIG. 3C is a timing diagram of the back EMF DVIN_L. FIG. 3D is a timing diagram of current lin. FIG. 3E is a timing diagram of the charging voltage VIN_INT. Note that FIGS. 3A to 3E are exaggerated for convenience of description.At a time ta 1 when the power supply is turned on, the input voltage VIN increases. Thereafter, at a time ta 2, the current lin rapidly increases to the current limit value ILIM. Due to the rapid increase of the current lin, a large counter electromotive force ΔVIN_R is generated by the resistance of the cable between the power supply device 12 and the input protection device 14. In addition, due to the rapid increase of the current lin, a large counter electromotive force ΔVIN_L is generated by the inductance of the cable between the power supply device 12 and the input protection device 14. The input voltage VIN is greatly reduced by the counter electromotive forces ΔVIN_R and ΔVIN_L. When the input voltage VIN falls below the voltage threshold Vth, the control circuit 44 (the under-voltage protection unit 30) switches the switching element 42 from ON to OFF to disconnect the power supply 12 and the subsequent switching circuit 16.At a time ta 3 at which the switching element 42 is switched, the current lin rapidly decreases. By rapidly decreasing the current lin, the counter electromotive force ΔVIN_L is generated in the opposite direction to the counter electromotive forces ΔVIN_R and ΔVIN_L generated at the time ta 2. The input voltage VIN is greatly increased by the counter electromotive force ΔVIN_L generated in the opposite direction in this manner. At the time when the counter electromotive forces ΔVIN_R and ΔVIN_L are not generated, the input voltage VIN corresponds to the input voltage VIN at the time ta 1. Such a behavior occurs repeatedly.The capacitor 20 of the subsequent stage 16 is charged while the current lin is supplied from the input protection device 14 to the subsequent stage 16. That is, as illustrated in FIG. 3E, the charging voltage VIN_INT steigt up only while the current linis supplied from the input protection device 14 to the subsequent stage 16.At a time ta4, the charging voltage VIN_INT becomes substantially equal to the input voltage VIN. Then, the current lin decreases and the counter electromotive forces ΔVIN_R and ΔVIN_L decrease. Since the counter electromotive forces ΔVIN_R and ΔVIN_L are reduced, the variation of the input voltage VIN is also reduced. As a result, the input voltage VIN does not fall below the voltage threshold Vth, and thus the activation of the charge voltage VIN_INT is completed. Thereafter, the current lin increases with an increase in the current consumption due to the start of operation of the subsequent circuit stage 16.As described above, in the input protection device 14 according to the reference example, the peak of the input voltage VIN becomes excessively large. Therefore, there is a possibility that the components of the input protection device 14 are damaged. In the input protector 14 according to the reference example, the current lin is intermittently supplied from the input protector 14 to the subsequent circuit stage 16. Therefore, it takes a long time to charge the capacitor 20 of the subsequent stage 16.[Operation of Input Protection Apparatus 14 According to First Embodiment]Each of FIGS. 4A to 4H is a timing chart showing a temporal change of each value of the input protector 14 according to the first embodiment.FIG. 4A is a timing diagram of the input voltage VIN.FIG. 4B is a time chart of the counter electromotive force ΔVIN_R.FIG. 4C is a time chart of the counter electromotive force ΔVIN_L.FIG. 4D is a time chart of current lin.FIG. 4E is a timing diagram of the activation signal.FIG. 4F is a timing diagram of the variable resistor Rset'.FIG. 4G is a time chart of the current limit value ILIM'. FIG. 4H is a timing diagram of the charging voltage VIN_INT.Note that FIGS. 4A to 4H are exaggerated like FIGS. 3A to 3E.At a time tb 1 when the power supply is turned on, the input voltage VIN increases. Further, after the input voltage VIN rises, the activation signal is supplied at time tb2. Then, the output voltage of the RC low pass filter circuit 38 starts to rise from zero (not shown). As time goes on, the output voltage of the RC low pass filter circuit 38 gradually rises. The degree of increase in the output voltage of the RC low pass filter 38 is determined by the time constant (RC). The output voltage of the RC low pass filter 38 is applied to the gate terminal of the FET 60. As a result, the resistance value between the drain and the source of the FET 60 starts to decrease from infinity. With time, the resistance value between the drain and the source of the FET 60 gradually decreases. Therefore, the variable resistor Rset' starts decreasing as shown in FIG. 4F. With time, the variable resistor Rset' gradually decreases. Then, as shown in FIG. 4G, the current limit value ILIM' starts to increase. The current limit value ILIM' gradually increases with time. As shown in FIG. 4D, the current lin gradually increases according to the increase of the current limit value ILIM'. Since the current limit value ILIM' gradually increases, the current lin does not rapidly increase. Therefore, as shown in FIGS. 4B and 4C, the magnitude of the counter electromotive forces ΔVIN_R and ΔVIN_L is smaller than the magnitude of the counter electromotive forces ΔVIN_R and ΔVIN_L shown in FIG. 3C. Therefore, the decrease of the input voltage VIN is small accordingly. As a result, the input voltage VIN does not fall below the voltage threshold Vth.At time tb 3, the resistance value between the drain and the source of the FET 60 becomes substantially zero. As shown in FIG. 4F, the variable resistor Rset' becomes equal to the set resistor Rset which is the lower limit. As shown in FIG. 4G, the current limit value ILIM' becomes the current limit value ILIM that is the upper limit. As shown in FIG. 4D, the current lin also becomes equal to the current limit value ILIM. Accordingly, when the current lin no longer changes, the counter electromotive forces ΔVIN_R and ΔVIN_L are no longer generated and the input voltage VIN no longer changes.In the first embodiment, the current lin does not rapidly increase between the time tb 1 and the time tb 3. Therefore, the change in the input voltage VIN due to the counter electromotive force ΔVIN_R and the counter electromotive force ΔVIN_L becomes small, and thus the input voltage VIN does not fall below the voltage threshold value Vth. Therefore, according to the first embodiment, the input voltage VINcan be prevented from becoming excessively large, and thus there is no possibility that the components of the input protection device 14 are damaged.In the first embodiment, the input voltage VIN does not fall below the voltage threshold Vth, and thus the control circuit 44 (the under-voltage protection unit 30) maintains the connection state of the switching element 42. That is, the connection state between the power supply device 12 and the follower circuit 16 is maintained until the capacitor 20 of the follower circuit 16 is charged. Therefore, the capacitor 20 of the subsequent circuit stage 16 according to the first embodiment can be charged quickly.[3-2. Second Embodiment]FIG. 5 is a circuit diagram of the input protection device 14 according to a second embodiment. The second embodiment is an improvement 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 accurately set the current limit value ILIM due to noise or the like. In the second embodiment, the resistance adjustment circuit 40 includes 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 Rset 2 of the noise prevention resistor 62 is larger than the resistance value Rset 1 of the fixed resistor 58.FIGS. 6A to 6H are time charts showing a temporal change of each value of the input protection device 14 according to the second embodiment, respectively. Figs. 6A to 6E and 6H are the same as Figs. 4A to 4E and 4H. FIG. 6F is a timing diagram of the variable resistor Rset'. FIG. 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 value Rset1 and the resistance value Rset2. Since the FET 60 is bypassed by the noise prevention resistor 62, the variable resistor Rset' does not become excessively large. Therefore, the current limiting unit 32 can accurately set the current limit value ILIM without being affected by noise.[3-3. Other Embodiments]In the above embodiment, the case where the activation signal supplied from the outside is supplied as a gate signal to the gate terminal of the FET 60 provided in the resistance adjustment circuit 40 via the RC low pass filter circuit 38 has been described as an example, but the present invention is not limited thereto. The gate signal output from another output circuit (e.g., a processor or the like) 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. Supplemental Annotations]The following supplementary notes are further disclosed with respect to the above embodiments and modifications.(Supplementary Note 1) The input protection device (14) that limits a current (Iin) supplied from the power supply (12) to the load (16) when the power supply is turned on comprises: the switching unit (26) that is disposed between the power supply and the load and is configured to switch between connection and disconnection between the power supply and the load; the switching control unit (28) that is configured to control the switching unit to connect the power supply and the load in response to an activation signal supplied from the outside; the under-voltage protection unit (30) that is configured to control the switching unit to disconnect the power supply and the load when the input voltage (VIN) from the power supply is equal to or lower than a predetermined voltage threshold; the current limiting unit (32) configured to limit the current supplied to the load to the threshold value (ILIM') or less; and the threshold value changing unit (24) configured to increase the threshold value with time so that the input voltage does not become equal to or lower than the voltage threshold value after the activation signal is received.(Supplementary Note 2) In the input protection device according to Supplementary Note 1, the switching unit, the switching control unit, the under-voltage protection unit, and the current limiting unit may be included in the single integrated circuit (36).(Supplementary Note 3) In the input protection device according to Supplementary Note 2, the limit value changing unit may include the resistance setting circuit (40) connected to the integrated circuit, the resistance setting circuit having the resistance value (Rset') that can be lowered to the lower limit value (Rset) set in advance, and the limit value may change according to the resistance value of the resistance setting circuit.(Supplementary Note 4) In the input protection device according to Supplementary Note 3, the resistance adjustment circuit may include the series circuit in which the fixed resistor (58) having a constant resistance value and the FET (Field Effect Transistor) (60) are connected in series, and the limit value changing unit may include the output circuit that outputs the gate signal for changing the resistance value of the resistance adjustment circuit to the Field Effect Transistor.(Supplementary Note 5) In the input protection device according to Supplementary Note 4, the output circuit may further include the RC low-pass filter circuit (resistor capacitance) ( 38) that changes the resistance value of the resistor adjustment circuit using the activation signal.(Supplementary Note 6) In the input protection device according to Supplementary Note 4 or 5, the threshold value changing unit may include the noise suppression resistor ( 62) connected to the source terminal of the FET and the drain terminal of the FET and having a resistance value larger than the resistance value of the fixed resistor.Although the present invention has been described in detail, it is not limited to the above-described individual embodiments. In these embodiments, various additions, substitutions, modifications, partial deletions, and the like can be made without departing from the spirit and scope of the present invention or without departing from the spirit and scope of the present invention that arises from the contents described in the claims and their equivalents. These embodiments may also be implemented in combination. For example, in the above-described embodiments, the order of the operations and the order of the processes are shown as examples, and the present invention is not limited to these. The same applies to the case where numerical values or mathematical equations are used in the description of the above-described embodiments.LIST OF REFERENCE CHARACTERS12 Power supply device (power supply) 14 Input protection device 16 Series stage circuit (load) 24 Limit value changing unit 26 Switching unit 28 Switching control unit 30 Under-voltage protection unit 32 Current limiting unit 36 Electronic fuse (integrated circuit) 38 RC low-pass filter circuit 40 Resistance adjusting circuit 58 Fixed resistor 60 FET 62 Noise suppression resistorReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedJP H09-056058 A

[0002]

Claims

An input protection device that limits a current supplied from a power supply to a load when the power supply is turned on, the input protection device comprising: a switching unit disposed between the power supply and the load and configured to switch between connection and disconnection of the power supply and the load; a switching control unit configured to control the switching unit in response to an activation signal supplied from the outside to connect the power supply and the load; an under-voltage protection unit configured to control the switching unit to disconnect 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 configured to limit the current supplied to the load to a threshold value or less; and a threshold changing unit configured to increase the threshold with time so that the input voltage does not become equal to or less than the voltage threshold after the activation signal is received.The input protection device according to claim 1, wherein the switching unit, the switching control unit, the under voltage protection unit, and the current limiting unit are included in a single integrated circuit.The input protection device according to claim 2, wherein the limit value changing unit includes a resistance adjustment circuit connected to the integrated circuit, the resistance adjustment circuit has a resistance value configured to be lowered to a lower limit value set in advance, and the limit value changes according to the resistance value of the resistance adjustment circuit.The input protection device according to claim 3, wherein the resistance adjustment circuit includes a series circuit in which a fixed resistor having a constant resistance value and a field effect transistor are connected in series, and the limit value changing unit includes an output circuit configured to output a gate signal for changing the resistance value of the resistance adjustment circuit to the field effect transistor.The input protection device according to claim 4, wherein the output circuit includes a resistance-capacitance low pass filter circuit configured to change the resistance value of the resistance adjustment circuit using the activation signal.The input protection device according to claim 4 or 5, wherein the threshold changing unit includes a noise suppression resistor connected to a source terminal of the field effect transistor and a drain terminal of the field effect transistor and having a resistance value larger than the resistance value of the fixed resistor.

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