JP2005184904A - Circuit for preventing rush current - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a rush current preventing circuit for preventing rush current, which flows from an electronic apparatus to an external device at the moment of connecting the external device via a connecting means with a low cost in the electronic apparatus, having a structure which supplies the output voltage of a power source to the internal load unit and which can supply the output voltage of the power source to the external device connected via the connecting means. <P>SOLUTION: In the rush current preventing circuit, the base current of a transistor Q2 flows, to turn ON the transistor Q2 at the time point of connecting a USB device 20 to a USB host apparatus 10; the voltage of an input terminal IP rises from 0V to 5V; and the output voltage of an output control signal OP is switched from an OFF control voltage to an ON-control voltage and is held. After the gate voltage of a transistor Q1 is controlled so as to limit the drain current to about 0.9 A or smaller for a predetermined time, starting from the time point that the output voltage of the output control terminal OP becomes the ON control voltage, the gate voltage which becomes a state where the transistor Q1 completely becomes ON, is held. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention includes a power supply device and has a configuration capable of supplying an output voltage of the power supply device to an internal load device and supplying an output voltage of the power supply device to an external device connected through a connection unit. The present invention relates to an inrush current preventing circuit for preventing an inrush current from an electronic device to an external device when the external device is connected via a connection means in the electronic device.

  In an electronic apparatus having a configuration that includes a power supply device and that can supply the output voltage of the power supply device to an internal load device and that can supply the output voltage of the power supply device to an external device connected via a connecting means. A large inrush current may flow from the electronic device to the external device at the moment when the external device is connected via the connection means. For example, an electronic device equipped with a USB host controller as a known USB (Universal / Serial / Bus) host device is connected to a USB device equipped with a USB bus interface connected via a USB connector via a VBAS terminal and a GND terminal. The USB standard stipulates that the power supply of 0.5 A must be supplied at DC 5 V, and a capacitor of several tens to several hundreds μF is provided between the VBAS terminal and the GND terminal. Is common. Therefore, from the moment when a USB device equipped with a USB bus interface is connected to the USB connector of an electronic device equipped with a USB host controller, until the capacitor provided between the VBAS terminal and the GND terminal on the USB device side is charged, A current flows instantaneously, and an inrush current called a so-called inrush current always flows. This inrush current causes an instantaneous drop in the power supply voltage of the power supply device of the electronic device equipped with the USB host controller, and the microcomputer control device of the electronic device is reset. There was a problem of coming. As a conventional technique for solving such a problem, an inductance of several μH is provided in a VBAS line of an electronic device equipped with a USB host controller so as to reduce an inrush current which is an instantaneous inrush current. The thing is common (for example, refer patent document 1).

JP 2002-51449 A

  However, since the inductance is generally an expensive electronic component compared to a resistor, a transistor, or the like, there is a problem that the cost of the interface circuit of the electronic device is increased by providing the inductance described above in the VBAS line. It was.

  The present invention has been made in view of such a situation, and the problem is that the power supply device is provided, the output voltage of the power supply device is supplied to the internal load device, and the external device is connected via the connection means. In an electronic device having a configuration capable of supplying the output voltage of the power supply device to the device, an inrush current prevention circuit for preventing an inrush current flowing from the electronic device to the external device at the moment when the external device is connected via the connection means It is to be realized at low cost.

  In order to achieve the above object, according to a first aspect of the present invention, there is provided a power supply device, wherein an output voltage of the power supply device is supplied to an internal load device and the power supply to an external device connected via a connecting means. In an electronic device having a configuration capable of supplying an output voltage of the device, inrush current prevention for preventing an inrush current from the electronic device to the external device when the external device is connected via the connection means A switch circuit for turning ON / OFF the output voltage to the external device, switch circuit control means for ON / OFF control of the switch circuit, and the external device connected via the connection means And an external device connection detection circuit for detecting that, when the control signal from the switch circuit control means is switched from OFF control to ON control, ON current limiting means for limiting the current flowing from the power supply device to the connection means via the switch circuit to a constant current value or less for a certain period of time, and the switch circuit control means via the connection means When the device is not connected, the control signal to the switch circuit is set to OFF control, and the control signal to the switch circuit is set to ON control when the external device is connected through the connection means. Is an inrush current prevention circuit.

  In the state where the external device is not connected via the connecting means, the external device is connected via the connecting means by setting the control signal to the switch circuit to OFF control and turning off the power output to the connecting means. At the moment, power is not supplied from the electronic device to the external device. When the external device connection detection circuit detects that the external device is connected via the connection means, the control signal of the switch circuit is turned on, and the power output to the external device is turned on. At that time, the current flowing from the power supply device to the connection means via the switch circuit by the ON current limiting means is limited to a constant current value or less for a certain period of time, and therefore flows at the moment when the external device is connected via the connection means. The inrush current to be attempted can be limited to a certain current value or less. In other words, if the switch circuit is turned on before the external device is connected as in the prior art, an inrush current flows at the moment the external device is connected, so it corresponds to the instantaneous inrush current. Although it is extremely difficult to control the switch circuit, the present invention turns off the switch circuit before the external device is connected, and turns on the switch circuit after the external device is connected. The inrush current can be prevented from flowing at the moment of connection, and the switch circuit corresponding to the inrush current that is about to flow instantaneously can be reliably controlled. Therefore, it is possible to prevent an inrush current flowing from the electronic device to the external device at the moment when the external device is connected to the electronic device via the connection means. In addition, since it is not necessary to provide an inductance such as an expensive coil in the power supply line to the external device as in the prior art, there is an effect that the inrush current prevention circuit can be configured at low cost.

  According to a second aspect of the present invention, in the first aspect, the external device connection detection circuit is configured such that an output voltage of the power supply device is applied between an emitter and a collector, and a base is connected via a base current limiting resistor. The PNP type transistor connected to the connection means has a configuration in which a base current flows when the external device is connected via the connection means, and the switch circuit control means is configured to turn on the PNP transistor. An inrush current prevention circuit characterized in that an operation state is detected and a control signal to the switch circuit is held by ON control when the PNP transistor is turned from OFF to ON. Since it is not necessary to provide an inductance such as an expensive coil in the power supply line to the external device as in the prior art, the inrush current prevention circuit can be configured at low cost.

  According to a third aspect of the present invention, in the second aspect described above, the switch circuit includes a MOSFET provided between the output of the power supply device and the voltage output of the connection means, and a gate voltage of the MOSFET. A gate voltage control circuit that controls the drain current of the MOSFET for a certain period of time when the control signal of the switch circuit control means switches from OFF control to ON control. The inrush current prevention circuit is characterized in that the gate voltage of the MOSFET is controlled so as to be limited to a value below the value.

  In this way, when the control signal of the MOSFET and the switch circuit control means switches from OFF control to ON control, the gate voltage of the MOSFET is controlled so as to limit the drain current of the MOSFET to a constant current value or less for a certain period of time. By configuring the switch circuit with the gate voltage control circuit, it is possible to prevent an inrush current flowing from the electronic device to the external device at the moment when the external device is connected to the electronic device via the connecting means.

  According to a fourth aspect of the present invention, in the second aspect or the third aspect described above, the electronic device includes a communication unit that communicates with the external device via the connection unit, and the switch circuit control The means switches the control signal to the switch circuit from ON control to OFF control when it is detected from the communication state of the communication means that the external device connected via the connection means has been disconnected. Is an inrush current prevention circuit. As described above, in the electronic apparatus having the communication unit that communicates with the external device via the connection unit, it is detected that the external device is disconnected by detecting the communication state with the external device. Can do.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects described above, the electronic device includes a USB host controller, and the output voltage of the power supply device passes through the switch circuit. It is an electronic device having a configuration applied between a VBAS terminal and a GND terminal of a USB connector, the connection means is a USB connector, and the external device is a USB device equipped with a USB bus interface. This is a featured inrush current prevention circuit.

  As described above, when a USB device equipped with a USB bus interface is connected to a USB connector of an electronic device equipped with a USB host controller, the capacitor provided between the VBAS terminal and the GND terminal on the USB device side is charged at the moment of connection. During this time, a current flows instantaneously, and a so-called inrush current called an inrush current always flows. Therefore, according to the inrush current prevention circuit shown in the fifth aspect of the present invention, in the inrush current prevention circuit of the electronic device equipped with the USB host controller, any one of the first to fourth aspects described above. The effects of the described invention can be obtained, and the inrush current that flows when a USB device equipped with a USB bus interface is connected can be reduced.

According to a sixth aspect of the present invention, there is provided an electronic apparatus including the inrush current preventing circuit according to any one of the first to fifth aspects.
According to the electronic device shown in the sixth aspect of the present invention, the operational effect according to any one of the first to fifth aspects described above can be obtained in the electronic device.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram of an inrush current preventing circuit according to the present invention, and FIG. 2 is a timing chart thereof. First, the circuit configuration of an inrush current prevention circuit according to the present invention will be described with reference to FIG.

  The USB host device 10 as an “electronic device” according to the present invention includes a USB connector 3 as a “connecting means” with a USB device 20 as an “external device”. The USB host device 10 is equipped with a USB host controller 13 as a “communication means” on the host side, and a USB device 20 equipped with a USB bus interface 22 as a “communication means” on the device side is connected via the USB connector 3. Can be connected. The USB connector 3 is a USB standard connector having four terminals: a VBAS terminal as a power supply line, a GND terminal, and a D + terminal and a D− terminal as communication signal lines.

  The USB host device 10 equipped with the USB host controller 13 is connected to the load 21 of the USB device 20 equipped with the USB bus interface 22 connected via the USB connector 3 with DC5V / 0.5A via the VBAS terminal and the GND terminal. The power supply can be supplied. A capacitor C1 of several tens to several hundreds μF is provided between the VBAS terminal on the USB host device 10 side and the GND terminal, and several tens of times are also provided between the VBAS terminal on the USB device 20 side and the GND terminal. A capacitor C21 of up to several hundred μF is provided. Further, the USB host controller 13 and the USB bus interface 22 are connected by two signal lines of the D + terminal and the D− terminal of the USB connector 3 to perform bidirectional communication.

  The VBAS line of the USB host device 10 is provided with a switch circuit 1 for turning on / off the output voltage to the USB device 20, and an ASIC as “switch circuit control means” for performing ON / OFF control of the switch circuit 1. (Application-specific integrated circuit) 11 is ON / OFF controlled. The switch circuit 1 includes a field effect transistor Q1 (MOSFET) connected so that the VBAS line can be turned ON / OFF, and a gate voltage control circuit 12 that controls the gate voltage of the transistor Q1. The gate voltage control circuit 12 sets the transistor Q1 within a certain current value (approximately 0.9 A) for a certain time (several milliseconds to several tens of milliseconds) immediately after the output control signal OP of the ASIC 11 switches from OFF control to ON control. The circuit configuration controls the gate voltage of the transistor Q1 so as to limit the drain current.

  The USB host device 10 also has a USB device connection detection circuit 2 as an “external device connection detection circuit” that detects that the USB device 20 is connected via the USB connector 3. The USB device connection detection circuit 2 has a PNP transistor Q2 to which a voltage of DC 5 V is applied between the emitter and collector, the base connected to the VBAS terminal of the USB connector 3, a bias resistor R1 at the base of the transistor Q2, and a transistor The transistor has a base current limiting resistor R2 for Q2 and a collector current limiting resistor R3 for the transistor Q2. The emitter voltage of the transistor Q2 is input to the input terminal IP of the ASIC 11. The ASIC 11 monitors the communication state between the USB host controller 13 and the USB bus interface 22 and detects that the USB device 20 is disconnected from the USB connector 3 of the USB host device 10.

Next, the operation of the inrush current prevention circuit according to the present invention will be described with reference to the timing chart shown in FIG.
When the USB device 20 is connected to the USB host device 10 via the USB connector 3 (reference S in FIG. 2), the base current of the transistor Q2 of the USB device connection detection circuit 2 flows (reference A in FIG. 1). The transistor Q2 is turned on, and the voltage at the input terminal IP of the ASIC 11 rises from 0V to 5V. The ASIC 11 switches the output voltage of the output control signal OP from the OFF control voltage (5V) to the ON control voltage (0V) and holds it when the input voltage at the input terminal IP rises from 0V to 5V. The gate voltage control circuit 12 limits the drain current of the transistor Q1 to about 0.9 A or less for a certain period of time (symbol B in FIG. 2) from when the output voltage of the output control terminal OP of the ASIC 11 becomes the ON control voltage. After controlling the gate voltage of the transistor Q1, the gate voltage at which the transistor Q1 is completely turned on is held. The voltage of the VBAS line gradually increases from 0V to 5V for a certain period of time (symbol B) from when the output voltage of the output control terminal OP of the ASIC 11 becomes the ON control voltage. The current value of the VBAS line is the time during which an inrush current flows from when the output voltage of the output control terminal OP of the ASIC 11 becomes the ON control voltage until the capacitor C21 on the USB device 20 side is charged ( After the current is limited to about 0.9 A or less in FIG. 2C, the standard value of USB is 0.5 A.

  The ASIC 11 monitors the communication state of the USB host controller 13, and the USB device 20 is disconnected from the USB connector 3 of the USB host device 10, and the USB host controller 13 and the USB bus interface 22 on the USB device 20 side are connected. When the communication is interrupted, the output voltage of the output control terminal OP is switched from the ON control voltage (0 V) to the OFF control voltage (5 V) and held.

  As described above, when it is detected that the USB device 20 is connected via the USB connector 3, the control signal of the switch circuit 1 is turned on and the power output to the USB device 20 is turned on. At this time, the current flowing to the USB device 20 via the switch circuit 1 is limited to a certain current value (approximately 0.9 A) or less for a certain time (several milliseconds to several tens of milliseconds). The inrush current that flows at the moment when the device 20 is connected can be limited to a certain current value (about 0.9 A) or less. Therefore, an inrush current (inrush current) flowing from the USB host device 10 to the USB device 20 at the moment when the USB device 20 is connected to the USB host device 10 via the USB connector 3 can be prevented. Further, since it is not necessary to provide an inductance such as an expensive coil in the VBAS line on the USB host device 10 side as in the prior art, the inrush current prevention circuit can be configured at low cost.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Needless to say.

  The present invention includes a power supply device and has a configuration capable of supplying an output voltage of the power supply device to an internal load device and supplying an output voltage of the power supply device to an external device connected through a connection unit. It can be used in electronic equipment.

It is a circuit diagram of the inrush current prevention circuit which concerns on this invention. 3 is a timing chart of an inrush current prevention circuit according to the present invention.

Explanation of symbols

  1 switch circuit, 2 USB device connection detection circuit, 3 USB connector, 10 USB host device, 11 ASIC, 12 gate voltage control circuit, 13 USB host controller, 20 USB device, 22 USB bus interface

Claims (6)

An electronic device comprising a power supply device, wherein the output voltage of the power supply device is supplied to an internal load device and can supply the output voltage of the power supply device to an external device connected via a connection means In the inrush current prevention circuit for preventing an inrush current from the electronic device to the external device when the external device is connected through the connection means,
A switch circuit for turning ON / OFF the output voltage to the external device, and a switch circuit control means for performing ON / OFF control of the switch circuit;
An external device connection detection circuit for detecting that the external device is connected via the connection means;
When the control signal from the switch circuit control means is switched from OFF control to ON control, the switch circuit is configured to change a current flowing from the power supply device to the connection means via the switch circuit at a constant current value for a predetermined time. ON current limiting means for limiting to:
The switch circuit control means sets the control signal to the switch circuit to OFF control in a state where the external apparatus is not connected via the connection means, and when the external apparatus is connected via the connection means An inrush current prevention circuit characterized in that the control signal to the switch circuit is turned on. 2. The external device connection detection circuit according to claim 1, wherein an output voltage of the power supply device is applied between an emitter and a collector, and a PNP transistor having a base connected to the connection means via a base current limiting resistor is provided. When the external device is connected via the connection means, the base current flows and is turned ON. The switch circuit control means detects the operating state of the PNP transistor, and the PNP transistor is turned OFF. An inrush current prevention circuit, wherein a control signal to the switch circuit is held by ON control when the switch is turned on. 3. The switch circuit according to claim 2, wherein the switch circuit includes a MOSFET provided between an output of the power supply device and a voltage output of the connection means, and a gate voltage control circuit that controls a gate voltage of the MOSFET, The gate voltage control circuit sets the gate voltage of the MOSFET so as to limit the drain current of the MOSFET to a constant current value or less for a certain period of time when the control signal of the switch circuit control means switches from OFF control to ON control. An inrush current prevention circuit characterized by controlling. 4. The electronic device according to claim 2, wherein the electronic device includes a communication unit that communicates with the external device via the connection unit, and the switch circuit control unit is connected from the communication state of the communication unit via the connection unit. An inrush current prevention circuit, wherein the control signal to the switch circuit is switched from ON control to OFF control when it is detected that the connected external device is disconnected. 5. The electronic device according to claim 1, wherein the electronic device includes a USB host controller, and an output voltage of the power supply device is applied between a VBAS terminal and a GND terminal of the USB connector via the switch circuit. An inrush current prevention circuit, wherein the connection means is a USB connector, and the external device is a USB device equipped with a USB bus interface. The electronic device provided with the inrush current prevention circuit of any one of Claims 1-5.

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