Patent Description:
Inrush current is a transient phenomenon that occurs depending on the size of a load when an input voltage is applied in an electrical and electronic system. The inrush current needs to be limited because it may cause permanent damage, faults, or abnormal operation of the system. In general, a battery management system (BMS) applied to a battery pack is also applied with a technology for limiting an inrush current.

Meanwhile, in the case of vehicles, which are one of the representative systems in which a battery pack is mounted, most of them use a lead acid battery as a low voltage (LV) power source. Accordingly, due to influence of inductive and capacitive loads connected to the lead acid battery, a system should normally operate in a very wide supply voltage range (e.g., at a maximum of <NUM> V) in an electromagnetic compatibility (EMC) test.

However, in the case of the conventional inrush current limiter designed for a high voltage (HV: high voltage) system, when the supply voltage is lowered below a certain level, there is a problem that an erroneous operation is caused, and thus needs improvement.

<CIT> discloses an inrush current limited for limiting current surges on a power supply bus.

The above information disclosed in this background section is only for enhancement of understanding of the background of the invention, and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.

The problem to be solved through exemplary embodiments of the present invention relates to an inrush current limiter and a system including the same, which enables normal operation of the system even in an EMC test environment by improving an operation voltage range of an inrush current limiting circuit.

In accordance with an aspect of the present invention, there is provided an inrush current limiter according to claim <NUM>. Embodiments of the invention are set out in the dependent claims.

The transistor may include a first terminal connected to the first input node and a second terminal connected to the first output node, and turn-on of the transistor may be controlled by a voltage between the first terminal and the control terminal.

The transistor may be a metal-oxide semiconductor field-effect transistor (MOSFET), the first terminal and the second terminal may be respectively a source and a drain of the transistor, and the control terminal may be a gate of the transistor.

The second input node may be connected to a ground.

The inrush current limiter may include a gate driver that gradually increases a voltage between the first terminal and the control terminal when the input voltage is input.

The gate driver may include a first resistor connected in parallel between the first terminal and the control terminal, and a first capacitor; and a third resistor that is connected between the control terminal and the second input node.

The gate driver may further include a Zener diode that is connected between the first terminal and the control terminal and limits a voltage between the first terminal and the control terminal.

The inrush current limiter may further include a feedback portion that is connected between the second terminal and the control terminal, and may stabilize a voltage between the first terminal and the control terminal.

The feedback portion may include a second capacitor that is connected in series between the first terminal and the control terminal, and a second resistor.

The mode controller may include a comparator, wherein the comparator may include: a first input terminal to which a comparison voltage corresponding to the input voltage is input, a second input terminal to which a reference voltage is input, and an output terminal that outputs an output signal corresponding to a comparison result of voltages input through the first and second input terminals to a control terminal of the switch.

The mode controller may include a fourth resistor and a fifth resistor that are connected in series, and may further include a voltage divider circuit that outputs the comparison voltage divided from the input voltage to the first input terminal.

The mode controller may further include a sixth resistor that connects between the second input terminal and the output terminal of the comparator, and the comparator may operate as a hysteresis comparator based on a hysteresis band having a lower limit that is lower than the reference voltage and an upper limit that is higher than the reference voltage, and may output an output signal that turns on the switch to the output terminal when the comparison voltage is lower than the lower limit and outputs an output signal that turns off the switch when the comparison voltage is higher than the upper limit.

The fourth resistor and the fifth resistor may be connected between the first output node and the ground, and the comparator may be activated after a predetermined time lapses after application of the input voltage.

The fourth resistor and the fifth resistor may be connected between the first input node and the ground.

A system according to claim <NUM> may include the inrush current limiter of the present invention.

According to the present invention, the operation voltage range of the inrush current limiting circuit is improved to enable normal operation of the system even in an EMC test environment.

Hereinafter, with reference to the accompanying drawings, effects and features of an exemplary embodiment and a method of implementing the same will be described in detail. In the drawings, the same reference numerals denote the same constituent elements, and redundant descriptions thereof are omitted.

Accordingly, processes, elements, and techniques that are not considered necessary to those having ordinary skill in the art for a complete understanding of the aspects and features of the present invention may not be described.

Further, the use of "may" or "can" when describing embodiments of the present invention refers to "one or more embodiments of the present invention. " In the following description of embodiments of the present invention, the terms of a singular form may include plural forms unless the context clearly indicates otherwise.

The terms "first" and "second" are used to describe elements of various configurations, but these constituent elements are not limited by these terms. These terms are only used to distinguish one constituent element from another. For example, a second constituent element may be named a first constituent element without departing from the right range of the present invention, and similarly, a first constituent element may be named a second constituent element.

Hereinafter, an inrush current limiter according to the present invention will be described in detail with reference to necessary drawings.

<FIG> schematically illustrates an inrush current limiter.

Referring to <FIG>, an inrush current limiter 100A includes input nodes IN1 and IN2 that are connected with a power source (not shown), output nodes OUT1 and OUT2 that are connected with a load (not shown), an inrush current limiting portion <NUM>, a mode control switch SW1, and a mode controller <NUM>.

The inrush current limiting portion <NUM> is a circuit that is connected between the input nodes IN1 and IN2 and the output nodes OUT1 and OUT2 and performs an inrush current limitation function when power is connected. The inrush current limiting portion <NUM> includes a transistor Q1 connected between the input node IN1 and the output node OUT1, and may include a gate driver <NUM> connected between an input terminal and a control terminal, and a feedback portion <NUM> connected between an output terminal and a control terminal of the transistor Q1.

The gate driver <NUM> controls the turn on of the transistor Q1 when an input voltage Vin of a first voltage level or higher is input, and may gradually increase a voltage between the control terminal and an input terminal of the transistor Q1 such that the transistor Q1 is fully turned on after a predetermined time period elapses after application of the input voltage Vin. On-resistance of the transistor Q1 is gradually decreased during the predetermined time period by the gate driver <NUM> after application of the input voltage Vin, and accordingly, a sudden current fluctuation due to the turn-on of the transistor Q1 does not occur, thereby limiting the inrush current.

The feedback portion <NUM> is a negative feedback portion that is connected between the output terminal and the control terminal of the transistor Q1, and performs a function of suppressing the inrush current by stabilizing (or planarizing) a voltage between the control terminal and the input terminal of the transistor Q1. That is, the inrush current can be suppressed by suppressing the sudden fluctuation of the voltage between the control terminal and the input terminal of the transistor Q1.

The mode control switch SW1 is connected between the control terminal of the transistor Q1 and the input node IN2 in the inrush current limiting portion <NUM>, and performs a function of switching electrical connection between the input node IN2 and the control terminal of the transistor Q1. When the mode control switch SW1 is turned off, the transistor Q1 operates in an inrush current limitation mode during which the turning-on is controlled by the gate driver <NUM> in the inrush current limiting portion <NUM>. On the contrary, when the mode control switch SW1 is turned on, the control terminal of the transistor Q1 is electrically connected with the input node IN2, and the transistor Q1 operates in a mode (e.g., an EMC test mode) during which the turning-on is controlled according to the input voltage Vin regardless of operation of the gate driver <NUM>.

When the mode control switch SW1 is turned on, the control terminal of the transistor Q1 is directly connected to the input node IN2, and the input voltage Vin corresponds to a voltage between the input terminal and the control terminal of the transistor Q1. Accordingly, the transistor Q1 may be turned on when a voltage level of the input voltage Vin is equal to or higher than a threshold voltage level (hereinafter referred to as a second voltage level) of the transistor Q1.

When the mode control switch SW1 is turned off, that is, when the transistor Q1 operates in the inrush current limitation mode, the transistor Q1 is turned on by the gate driver <NUM> when the voltage level of the input voltage Vin is equal to or higher than a first voltage level. The gate driver <NUM> transmits a voltage divided from the input voltage Vin through a voltage divider circuit (not shown) to the control terminal of the transistor Q1, and this will be described later. Thus, the first voltage level that determines turning-on of the transistor Q1 in the inrush current limitation that the transistor Q1 is fully turned on after a predetermined time period elapses after application of the input voltage Vin. On-resistance of the transistor Q1 is gradually decreased during the predetermined time period by the gate driver <NUM> after application of the input voltage Vin, and accordingly, a sudden current fluctuation due to the turn-on of the transistor Q1 does not occur, thereby limiting the inrush current.

The mode control switch SW1 is connected between the control terminal of the transistor Q1 and the input node IN2 in the inrush current limiting portion <NUM>, and performs a function of switching electrical connection between the input node IN2 and the control terminal of the transistor Q1. When the mode control switch SW1 is turned off, the transistor Q1 operates in an inrush current limitation mode during which the turning-on is controlled by the gate driver <NUM> in the inrush current limiting portion <NUM>. On the contrary, when the mode control switch SW1 is turned on, the control terminal of the transistor Q1 is electrically connected with the input node IN2, and the transistor Q1 may operate in a mode (e.g., an EMC test mode) during which the turning-on is controlled according to the input voltage Vin regardless of operation of the gate driver <NUM>.

When the mode control switch SW1 is turned off, that is, when the transistor Q1 operates in the inrush current limitation mode, the transistor Q1 may be turned on by the gate driver <NUM> when the voltage level of the input voltage Vin is equal to or higher than a first voltage level. The gate driver <NUM> transmits a voltage divided from the input voltage Vin through a voltage divider circuit (not shown) to the control terminal of the transistor Q1, and this will be described later. Thus, the first voltage level that determines turning-on of the transistor Q1 in the inrush current limitation mode may be higher than the above-stated second voltage level.

The mode controller <NUM> receives the input voltage Vin supplied from the power source, and controls turn-on/turn-off of the mode control switch SW1 according to a level of the received input voltage Vin. That is, the mode controller <NUM> compares the input voltage Vin or the voltage level of the voltage divided from the input voltage Vin with a predetermined reference voltage Vref or a reference voltage range, and controls switching of the mode control switch SW1 according to a comparison result.

For example, the mode controller <NUM> may turn on the mode control switch SW1 when the voltage level of the input voltage Vin or the voltage divided from the input voltage Vin is lower than the predetermined reference voltage Vref or lower than the lower limit of the predetermined reference voltage range in the turn-off state of the mode control switch SW1.

In addition, for example, the mode controller <NUM> may turn off the mode control switch SW1 when the voltage level of the input voltage Vin or the voltage divided from the input voltage Vin is higher than the predetermined reference voltage Vref or higher than the upper limit of the predetermined reference voltage range in the turn-on state of the mode control switch SW1. Here, the upper limit and the lower limit of the reference voltage range may be set based on a reference voltage Vref input to the mode controller <NUM>.

<FIG> shows a system where the inrush current limiter according to the exemplary embodiment of the present invention is applied.

Referring to <FIG>, a system 10A may include an inrush current limiter 100A that is connected between a power source <NUM> and a load <NUM>. Such a system 10A may be, for example, a vehicle system.

The power source <NUM> is electrically connected to the input nodes IN1 and IN2 of the inrush current limiter 100A and supplies an input voltage Vin to the inrush current limiter 100A. For example, when the system 10A includes a high voltage battery pack, the power source <NUM> may be a high voltage battery back. In addition, for example, the power source <NUM> may be an external power source for an EMC test. When the power source <NUM> is an external power source, the power source <NUM> may supply an input voltage Vin from approximately <NUM> V to <NUM> V to the inrush current limiter 100A.

The system 10A further includes a main switch SW2, and a connection with the inrush current limiter 100A may be controlled by the power source <NUM>.

As described above, the inrush current limiter 100A may include an inrush current limiting portion <NUM>, a mode control switch SW1, and a mode controller <NUM>. In addition, the inrush current limiting portion <NUM> may include a transistor Q1, a gate driver <NUM>, and a feedback portion <NUM>.

The transistor Q1 may operate as a switch that is connected between an input node IN1 and an output node OUT1 to block or allow a current flow between the two nodes. As shown in <FIG>, when the input node IN1 is connected to a positive output of the power source <NUM> and the input node IN2 is connected to a negative output of the power source <NUM>, the transistor Q1 may be, for example, a P-channel metal-oxide semiconductor field-effect transistor (P-channel MOSFET). However, the exemplary embodiment of the present invention is not limited thereto, and the transistor Q1 may be an N-channel MOSFET. In this case, the input node IN2 of the inrush current limiter 100A may be connected to the positive output of the power source <NUM> and the input node IN1 may be connected to the negative output of the power source <NUM>.

Hereinafter, for better understanding and ease of description, the case where the transistor Q1 is a P-channel MOSFET will be described as an example.

The gate driver <NUM> may include a first capacitor C1 and a first resistor R1 that are connected in parallel between a source and a gate of the transistor Q1, and a third resistor R3 that is connected between the gate of the transistor Q1 and the second input node IN2.

When the main switch SW2 is turned on and an input voltage of higher than a first voltage level is input from the power source <NUM>, a current supplied from the power source <NUM> flows via the first resistor R1 and the third resistor R3, and the first capacitor C1 is charged by the supply voltage of the power source <NUM>. Accordingly, a gate voltage Vg of the transistor Q1 is gradually decreased by charging of the first capacitor C1, and a gate-source voltage Vgs of the transistor Q1 is gradually increased. Thereafter, when the gradually increasing gate-source voltage Vgs of the transistor Q1 reaches a threshold voltage Vth of the transistor Q1, the transistor Q1 is turned on. In this case, a time constant that determines the time when the gate-source voltage Vgs of the transistor Q1 reaches the threshold voltage Vth of the transistor Q1 may be determined by capacitance of the first capacitor C1 and resistance values of the first resistor R1 and the third resistor R3. In addition, a voltage level of the input voltage Vin that turns on the transistor Q1 may be determined by the resistance values of the first resistor R1 and the third resistor R3.

Meanwhile, the gate driver <NUM> may further include a Zener diode ZD1 that includes a cathode connected to the source of the transistor Q1 and an anode connected to the gate of the transistor Q1. The Zener diode ZD1 may serve to limit the gate-source voltage Vgs of the transistor Q1 within its rated voltage. Thus, a voltage between lateral ends of the first capacitor C1 connected with the Zener diode ZD1 in parallel may be limited by the Zener diode ZD1.

The feedback portion <NUM> may include a second capacitor C2 connected in series between a drain and the gate of the transistor Q1, and a second resistor R2. Such a feedback portion <NUM> provides a feedback path between the drain and the gate of the transistor Q1 to provide a function of suppressing an inrush current transmitted to a load-side capacitor C_L by stabilizing the gate-source voltage Vgs of the transistor Q1.

The mode controller <NUM> may include a comparator U1 and voltage divider circuits R4 and R5.

The voltage divider circuits R4 and R5 include a fourth resistor R4 and a fifth resistor R5 that are connected in series between the output node OUT1 and the input node IN2 (i.e., a ground), and divide a voltage, transmitted to the output node OUT1, through the transistor Q1 and transmit it as an input voltage of the comparator U1. For this, the fourth resistor R4 is connected between the output node OUT1 and a first input terminal of the comparator U1, and the fifth resistor R5 may be connected between the first input terminal of the comparator U1 and the second input node IN2, that is, the ground.

The comparator U1 may include a first input terminal (e.g., a negative input) that receives a voltage divided from the voltage divider circuits R4 and R5, a second input terminal (e.g., a positive input) to which the reference voltage Vref is input, and an output terminal outputting a control signal to the mode control switch SW1.

The comparator U1 may output a signal (e.g., a high level signal) to turn on the mode control switch SW1 to the output terminal when the voltage received through the first input terminal is lower than the reference voltage Vref. On the other hand, the comparator U1 may output a signal (e.g., a high level signal) to turn off the mode control switch SW1 to the output terminal when the voltage input through the first input terminal is higher than the reference voltage Vref.

The comparator U1 may be a hysteresis comparator. The hysteresis comparator U1 may operate by a hysteresis band (referred to as a reference voltage range in this specification) defined by an upper limit and a lower limit. When the comparator U1 operates as a hysteresis comparator, the mode controller <NUM> may further include a sixth resistor R6 that is connected between the second input terminal and the output terminal of the comparator U1 and determines the hysteresis band of the comparator U1. The hysteresis band of the hysteresis comparator U1, that is, the reference voltage range, is determined by a lower limit determined at a lower level and an upper limit determined at a higher level based on the reference voltage Vref input to the second input terminal of comparator U1, and the upper and lower limits may be determined by the sixth resistor R6.

Such a hysteresis comparator U1 may output a signal (e.g., a high level signal) to turn on the mode control switch SW1 to the output terminal when a voltage input to the first input terminal is lower than the lower limit of the reference voltage range, and outputs a signal (e.g., a low level signal) to turn off the mode control switch SW1 to the output terminal when the voltage input to the first input terminal is higher than the upper limit of the reference voltage range.

The above-described reference voltage Vref or the reference voltage range may be set so that the mode control switch SW1 can be turned on when the input voltage Vin has a lower voltage level than the first voltage level.

Meanwhile, the mode controller <NUM>, that is, the comparator U1 of the mode controller <NUM>, is prevented from malfunctioning due to transmission of a part of the input voltage Vin to the output node OUT1 at the early connection stage of the power source <NUM>, that is, while the inrush current limiting portion <NUM> performs an inrush current limitation operation, and in order to prevent power wastage due to unnecessary operation of the comparator U1 while performing the inrush current limiting operation, the comparator U1 may be controlled to be activated after a predetermined time after power from the power source <NUM> is applied. That is, an operation voltage for operating the comparator U1 is applied after a predetermined delay after the power source <NUM> is connected such that the comparator U1 operates in a state in which the voltage transmitted to the load <NUM> through the output node OUT1 is stabilized. In such a state, the transistor Q1 is completely turned on (fully turned on) to operate in saturation, and an input voltage Vin may be applied to the output node OUT1.

Meanwhile, in the above-described exemplary embodiment, a case that the mode controller <NUM> is connected to the output node OUT1 of the inrush current limiter 100A to monitor the input voltage Vin input from the power source <NUM> is described, but the exemplary embodiment of the present invention is not limited thereto.

<FIG> schematically illustrates an inrush current limiter 100B according to another exemplary embodiment of the present invention, and <FIG> schematically illustrates a system 10B to which the inrush current limiter of <FIG> is applied.

Referring to <FIG> and <FIG>, the inrush current limiter 100B and the system 10B according to another exemplary embodiment of the present invention are different from the inrush current limiter 100A and the system 10A according to the above-described exemplary embodiment of the present invention in that voltage divider circuits R4 and R5 are not connected to a first output node OUT1 but are connected to a first input node IN1. Therefore, hereinafter, in order to avoid unnecessary redundant description, descriptions of the remaining constituent elements that operate similarly to the inrush current limiters 100A and the system 10A described above will be omitted.

As in the above-described exemplary embodiment, when the voltage divider circuits R4 and R5 are connected to the first output node OUT1, a predetermined delay occurs until a voltage Vin supplied by a power source <NUM> is normally transmitted to an output node OUT1 due to operation of the inrush current limiting portion <NUM>, and accordingly, a predetermined delay occurs until voltage divider circuits R4 and R5 transmit a voltage corresponding to the normal input voltage Vin to the comparator U1.

On the contrary, as shown in <FIG> and <FIG>, when the first input terminal of the comparator U1 is connected to the first input node IN1 through voltage divider circuits R4 and R5, the input voltage Vin is transmitted directly to the voltage divider circuits R4 and R5 when the power source <NUM> is connected, and accordingly, the comparator U1 also directly receives the voltage corresponding to the normal input voltage Vin.

Meanwhile, as in the above-described exemplary embodiment, in the inrush current limiter 100B, the comparator U1 may be activated after a predetermined time lapses after connection of the power source <NUM> so as to prevent occurrence of power waste due to unnecessary operation of the comparator U1 while the inrush current limiter 100B performs inrush current limitation operation.

Hereinafter, referring to <FIG>, a method for operating the inrush current limiters 100A and 100B according to the exemplary embodiments of the present invention will be described in more detail.

<FIG> schematically illustrates an operation timing diagram of the inrush current limiters 100A and 100B according to the exemplary embodiments of the present invention, and exemplarily illustrates a case that a low-voltage test voltage is applied for an EMC test after connection of the power source <NUM> to the systems 10A and 10B.

Although it is not illustrated in <FIG>, when the main switch SW2 is turned on and thus the input voltage Vin starts to be supplied from the power source <NUM>, an inrush current may occur at the input terminal due to the charging voltage of the load capacitor C_L, which is close to a zero potential (<NUM> V) at the early stage. Thus, the inrush current limiter 100A at the beginning of the connection of the power supply <NUM> operates in the inrush current limiting mode to suppress the inrush current transmitted to the load <NUM>.

After that, when the transistor Q1 is turned on and a predetermined time lapses and the input current is stabilized, the comparator U1 is activated for monitoring of the input voltage Vin, and the inrush current limiters 100A and 100B continuously monitor a voltage level of the input voltage Vin through the comparator U1 (Mode <NUM>). In this case, the transistor Q1 is completely turned on and the comparator U1 operates in saturation.

The mode controller <NUM> turns on the mode control switch SW1 when it detects that the input voltage Vin drops below the rated voltage of the system 10A for EMC tests while monitoring the input voltage Vin through the comparator U1 (Mode <NUM>). That is, when the voltage input corresponding to the input voltage Vin is lower than a first threshold value VHL, an output signal V_out_comp for controlling the mode control switch SW1 to turn on is transmitted to a control terminal of the mode control switch SW1. Here, the first threshold value VHL corresponds to the lower limit of the hysteresis band of the hysteresis comparator U1.

In a section in which the mode control switch SW1 is turned on (Mode <NUM>), when the voltage level of the input voltage Vin is higher than the threshold voltage level of the transistor Q1, the transistor Q1 may be completely turned on. Therefore, it is possible to operate the transistor Q1 even when a lower voltage than the rated voltage of systems 10A and 10B is input as in the case of the EMC test.

Meanwhile, the mode controller <NUM> continuously monitors the voltage level of the input voltage Vin through the comparator U1 even in the Mode <NUM> section, and turns off the mode control switch SW1 when it is detected that the input voltage Vin increases within the rated voltage range of the system 10A due to the termination of the EMC situation during the monitoring (Mode <NUM>). That is, the comparator U1 controls an output signal V_out_comp to control the mode control switch SW1 to the turn off state when the voltage input corresponding to the input voltage Vin is higher than the second threshold value VHU. Here, the second threshold value VHU corresponds to the upper limit of the hysteresis band of the hysteresis comparator U1.

As the mode control switch SW1 is turned off, the inrush current limiters 100A and 100B return to the inrush current limit mode, and the turn on of the transistor Q1 is controlled by the gate driver <NUM> (Mode <NUM>).

According to the above-described exemplary embodiments, in the inrush current limiters 100A and 100B of the systems 10A and 10B, the transistor Q1 is turned on even when the input voltage Vin is lower than the rated voltage of the systems 10A and 10B is input as in the EMC test process such that it is possible to prevent a situation where power is not supplied to the load <NUM> due to malfunction of the transistor Q1.

An electronic or electrical device and/or any other related device or constituent element according to the exemplary embodiments of the present invention described herein can be implemented using any suitable hardware, firmware (e.g., application-specific integrated circuits), software, or a combination of software, firmware, and hardware. For example, the elements of various configurations of the devices can be formed on a single integrated circuit (IC) chip or on separate IC chips. In addition, the elements of various configurations of the devices can be implemented as a flexible printed circuit film, a tape carrier package (TCP), or a printed circuit board (PCB), or may be implemented on a single substrate. The electrical connection or interconnection described in the present specification can be implemented by wire or conductive elements on, for example, a PCB or other type of circuit carrier. The conductive element may include metallization such as surface metallization and/or pins, and may include conductive polymers or ceramics. In addition, electrical energy may be transmitted through a wireless connection using, for example, electron radiation or light.

In addition, the various configurations elements of the devices may be a process or a thread that runs on at least one processor and at least one computing device to perform the various functions described herein, executes computer program instructions, and interacts with other system constituent elements. The computer program instructions are stored in a memory that can be implemented in a computing device using standard memory devices, such as a random access memory (RAM). The computer program instructions may also be stored on other non-transitory computer readable media such as, for example, a CD-ROM, a flash drive, and the like.

Claim 1:
An inrush current limiter (100A, 100B) comprising:
a first input node, IN1, and a second input node, IN2, that receive an input voltage, Vin, from a power source (<NUM>);
a first output node, OUT1, and a second output node, OUT2, that are connected to a load (<NUM>);
an inrush current limiting portion (<NUM>) that includes a transistor, Q1, that has a first terminal connected to the first input node, IN1, a second terminal connected to the first output node, OUT1, and a control terminal, wherein turn-on of the transistor is controlled by a voltage between the first terminal and the control terminal;
a switch, SW1, connected between the control terminal of the transistor and the second input node, IN2; and
a mode controller (<NUM>) configured to:
turn the switch off when a voltage level of the input voltage is higher than a first level, VHU, and
turn the switch on when the voltage level of the input voltage is lower than a second level, VHL, wherein the second level is lower than the first level,
wherein when the switch is off, the inrush current limiting portion (<NUM>) is configured to control the transistor to turn on gradually to limit an inrush current, and
when the switch is on and a voltage level of the input voltage is equal to or higher than the second level, the input voltage is applied between the second input node and the control terminal of the transistor to turn on the transistor.