JP2009011105A - Portable information terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that, in a portable information terminal that is operable with a battery even if an external power supply is removed, when efficiency of a power supply circuit is dropped, loss is increased and a battery operating time is reduced, and consequently, device performance deteriorates. <P>SOLUTION: A portable information terminal 4A is provided with a plurality of switching transistors Q1, Q2 driven so as to be alternately turned on/off by a switching power supply circuit 5 of the portable information terminal, a drive control part 12 for drivingly controlling the switching transistors Q1, Q2, an output-side capacitor C2 charged with a voltage generated by switching the switching transistors Q1, Q2, and a snubber circuit 2 connected to each output-side line of the switching transistors Q1, Q2. The snubber circuit 2 is drivingly controlled on the basis of a detection signal outputted from a detection part 6 for detecting a power-supply state so as to suppress noise of P1, P2 occurring in the point E. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a portable information terminal including a notebook personal computer (notebook PC), a mobile phone, a PDA, a car navigation (which can be removed from a car and used in a house) having a function of automatically suppressing unwanted radiation. Is.

(1): Conventional example 1
FIG. 5 shows an example of a conventional switching power supply circuit. Hereinafter, it will be described as Conventional Example 1 including FIG. 5 and a general background art of the portable information terminal.

  In recent years, although the performance of portable information terminals has been remarkably improved, the power consumption of portable information terminals tends to increase accordingly. The portable information terminal is mounted with a switching power supply circuit such as a DC-DC converter in order to generate a high-voltage power supply supplied from the outside, that is, a low-voltage power supply used inside the circuit from the external power supply. . One example is shown in FIG.

  In FIG. 5, Q1 and Q2 are switching transistors (in this example, bipolar transistors), C1 and C2 are capacitors, CH is a choke coil, 11 is an output voltage detection unit, 12 is a drive control unit, + V1 is a DC input voltage, + V2 is a DC output voltage, GND is a ground potential, and E is a connection point between the emitter of the transistor Q1 and the collector of the transistor Q2.

  This switching power supply circuit feeds back the voltage detected by the drive controller 12 by the output voltage detector 11 and applies a drive signal to the transistors Q1 and Q2 by an internal circuit. At this time, this drive signal alternately applies a low level signal and a high level signal to the bases of the transistors Q1 and Q2, thereby turning on and off the transistors Q1 and Q2 alternately.

  That is, when the transistor Q1 is on, the transistor Q2 is driven off, and when the transistor Q1 is off, the transistor Q2 is driven on. When the transistors Q1 and Q2 are driven in this way, the voltage (or potential) at the connection point E between the emitter of the transistor Q1 and the collector of the transistor Q2 alternately changes between a low level and a high level. A current flows to the output-side capacitor C2 through CH.

  That is, the potential at the point E is high when the transistor Q1 is on and the transistor Q2 is off, and is low when the transistor Q1 is off and the transistor Q2 is on. Thus, an output voltage that fluctuates in a pulse shape is generated at the point E by turning on / off the transistors Q1 and Q2, but a large noise is generated when the output voltage changes.

  Thus, this switching power supply circuit has the property of generating large noises. As the power consumption of the portable information terminal increases, this noise also tends to increase.

  This power supply noise is sometimes radiated to the outside in the form of propagation directly from the printed circuit board of the portable information terminal, sometimes through the circuit, and via the external interface of the portable information terminal. These unwanted propagation radiations are regulated in countries around the world to stay within the prescribed level. European regulations such as EN 60950 fall under this category. In response to these regulations, the portable information terminal must take measures against unwanted radiation. If the noise generated by the switching power supply circuit can be reduced, it will be an effective measure against unwanted radiation.

(2): Conventional example 2
Hereinafter, Patent Document 1 will be described as Conventional Example 2. Conventional Example 2 describes the following contents.

  (a): “a power supply voltage detection circuit for detecting whether the input power supply voltage is the first power supply voltage or the second power supply voltage; and the power supply voltage detected by the power supply voltage detection circuit Accordingly, the snubber constant switching means for switching the snubber constant of the snubber circuit to be small at the first power supply voltage and large at the second power supply voltage is provided. See claim 1 of the claims.

(b): “In order to provide a switching power supply with a snubber circuit and a current limiting circuit, the switching power supply is low in loss and does not require the use of a device with a higher rating than necessary.” ・ ・-See paragraph number [0004]
(3): Conventional example 3
Hereinafter, Patent Document 2 will be described as Conventional Example 3. Conventional Example 3 describes the following contents.

(a): “Providing a switching power supply unit that can reduce the heat generation of the snubber circuit resistor so that a resistor with a small rated power can be used.”… See the Summary section
(b): “At least one of the snubber circuits has a plurality of resistors and switching means for selecting one of the resistors that is not overheated”. -See claim 1 of the claims.

(4): Conventional example 4
Hereinafter, Patent Document 3 will be described as Conventional Example 4. Conventional Example 4 describes the following contents.

(a): “In the converter circuit that self-resets by the open inductance of the input winding of the transformer and the capacity of the snubber capacitor, the capacity of the snubber capacitor is increased or decreased in accordance with the input voltage. Refer to the claims.
(b): “Efficient operation can be performed by automatically selecting a snubber capacitor capacity suitable for a low level DC input voltage and a snubber capacitor capacity suitable for a high level DC input voltage. Refer to the column of action.
JP 2001-224177 A JP-A-8-182317 Japanese Patent Laid-Open No. 2-168858

  (1) In the first conventional example, the noise generated by the switching power supply circuit has a property of increasing as the efficiency of the power supply circuit increases. That is, unnecessary radiation can be suppressed by intentionally reducing the efficiency of the power supply circuit (efficiency = output power / input power). In this case, the lower the efficiency, the greater the energy loss in the power supply circuit. For example, by providing a snubber circuit for the switching power supply circuit, switching noise can be reduced, but the efficiency of the power supply is reduced.

  Even if the external power supply is removed, in a portable information terminal that can be operated by a battery, if the efficiency of the power supply circuit is reduced, the loss increases and the battery operation time is shortened. This means that the performance of the device is degraded and is a serious problem.

  (2): Conventional Example 2 is intended to provide a switching power supply device having a snubber circuit and a current limiting circuit, which has a low loss and does not require the use of a device with a larger rating than necessary. According to the power supply voltage detection circuit that detects whether the input power supply voltage is the first power supply voltage or the second power supply voltage, and the power supply voltage detected by the power supply voltage detection circuit, The snubber circuit is provided with snubber constant switching means for switching so that the snubber constant of the snubber circuit is small at the first power supply voltage and large at the second power supply voltage.

  However, in Conventional Example 2, the portable information terminal, which is one of the essential components of the present invention, detects the power supply state from the outside, etc., and automatically reduces power efficiency to reduce unnecessary radiation. Therefore, there is no content of taking measures against unnecessary radiation without impairing the operation time of the battery, and the content is about the background art of the present invention.

  (3): Conventional Example 3 aims to provide a switching power supply device that can reduce the heat generation of a resistor of a snubber circuit so that a resistor with a small rated power can be used. At least one of the snubber circuits is provided. Relates to a switching power supply device comprising a plurality of resistors and switching means for selecting one of the resistors that is not overheated.

  However, in Conventional Example 3, the portable information terminal, which is one of the essential components of the present invention, detects the power supply state from the outside, etc., and automatically reduces power efficiency to reduce unnecessary radiation. Therefore, there is no content of taking measures against unnecessary radiation without impairing the operation time of the battery, and the content is about the background art of the present invention.

  (4): Conventional Example 4 is such that in a converter circuit that self-resets with the open inductance of the transformer input winding and the capacity of the snubber capacitor, the capacity of the snubber capacitor is increased or decreased according to the input voltage. It is the content that the capacity of the snubber capacitor suitable for the low level DC input voltage and the capacity of the snubber capacitor suitable for the high level DC input voltage can be automatically selected to perform efficient operation. .

  However, in the conventional example 4, the portable information terminal, which is one of the essential components of the present invention, detects the state of power supply from the outside, etc., and automatically reduces the power efficiency to reduce unnecessary radiation. Therefore, there is no content of taking measures against unnecessary radiation without impairing the operation time of the battery, and the content is about the background art of the present invention.

  The present invention has been made in order to solve the conventional problems, and the portable information terminal detects the power supply state or connection state from the outside and automatically reduces the power efficiency to reduce unnecessary radiation, thereby reducing the battery. The objective is to take measures against unwanted radiation without compromising the operating time of the power supply.

  In order to achieve the above object, the present invention is configured as follows.

  (1): In a portable information terminal equipped with a switching power supply circuit that operates by supplying power from a built-in battery power supply or an external power supply, the switching power supply circuit is for a plurality of switching devices that are driven to be turned on / off alternately. A transistor, a drive control unit for driving and controlling the switching transistor, an output-side capacitor charged with a voltage generated by switching of the switching transistor, and an output-side line of the switching transistor A snubber circuit is provided, and the snubber circuit is driven and controlled based on a detection signal output from a detection unit that detects a power supply state or a connection state.

  (2): In the portable information terminal of (1), the detection unit includes an external power supply detection unit that detects a connection state of an external power supply, and the external power supply is connected by the external power supply detection unit. Is detected, the snubber circuit is driven to an ON state based on the detection signal of the external power supply detection unit, the noise of the line is absorbed by the function of the snubber circuit, and the external power supply is shut off. Is detected, the snubber circuit is driven to an off state based on a detection signal of the external power source detection unit, and the function of the snubber circuit is stopped.

  (3): In the portable information terminal of (1), the detection unit includes a docking station / port replicator detection unit that detects a connection state of a docking station / port replicator that is fed from an external power source, When the docking station / port replicator detection unit detects that the docking station / port replicator is connected, the snubber circuit is driven to an ON state based on the detection signal of the docking station / port replicator detection unit. When the noise of the line is absorbed by the function of the snubber circuit and it is detected that the docking station / port replicator is not connected, the detection is performed based on the detection signal of the docking station / port replicator detection unit. It drives the snubber circuit in the OFF state, and wherein the stopping function of the snubber circuit.

  (4): In the portable information terminal of (1), the detection unit includes an I / F connection detection unit that detects a connection state of an external interface, and the interface is connected by the I / F connection detection unit. When it is detected that the signal is detected, the snubber circuit is driven to an ON state based on the detection signal of the I / F connection detection unit, and the noise of the line is absorbed by the function of the snubber circuit. When it is detected that is not connected, the snubber circuit is driven to an OFF state based on a detection signal of the I / F connection detection unit, and the function of the snubber circuit is stopped.

  (5): In the portable information terminal of (1), the snubber circuit is connected to the output-side line of the plurality of switching transistors that are driven so as to be alternately turned on / off. It is configured to include a series circuit of a transistor, a resistor, and a capacitor. When the snubber circuit switching transistor is turned on and a current flows through the snubber circuit, the noise in the line is absorbed and the snubber circuit switching is performed. When the transistor is turned off and no current flows through the snubber circuit, the line noise is not absorbed, and the detection unit includes an external power supply detection unit for detecting a connection state of an external power supply, and an external power supply. That detects the connection status of a docking station / port replicator that is powered from Each of the detection means of the connection / port replicator detection unit and the I / F connection detection unit for detecting the connection state of the external interface, and the snubber circuit generates the logical sum output of the detection signals from the plurality of detection units. The drive is controlled.

(Function)
FIG. 1 is a diagram illustrating the principle of the present invention. The operation of the present invention based on the above configuration will be described below with reference to FIG.

  The capacitor C1 is connected between the DC input voltage + V1 and GND, and applies the DC input voltage + V1 to the collector of the switching transistor Q1. An internal voltage is applied to the drive control unit 12, and control for alternately turning on / off the switching transistors Q1 and Q2 is performed. In this case, the drive control unit 12 takes in the output voltage detected by the output voltage detection unit 11 as a feedback signal (FB signal), and performs control to alternately turn on / off the switching transistors Q1 and Q2.

  The voltage at the point E as a result of the switching transistors Q1 and Q2 being alternately turned on / off is a voltage having a waveform as shown in FIG. 1, and this voltage causes a current to flow to the capacitor C2 via the choke coil CH. Flow and charge capacitor C2. And the charge voltage of the capacitor | condenser C2 is taken out as DC output voltage (+ V2).

  Further, the snubber circuit 2 (a circuit constituted by a series circuit of a transistor, a resistor, and a capacitor) includes logic of detection signals from the external power supply detection unit 13, the I / F connection detection unit 14, and the docking station / port replicator detection unit 15. Drive controlled with sum output. That is, the detection signals from the external power source detection unit 13, I / F connection detection unit 14, and docking station / port replicator detection unit 15 are driven and controlled by the OR output of the OR gate circuit 1.

  As the switching transistors Q1 and Q2 are driven on / off in this way, an output voltage as shown is generated at the connection point E between the emitter of the switching transistor Q1 and the collector of the transistor Q2. This output voltage instantaneously becomes a large voltage as indicated by P1 and P2 when the switching transistors Q1 and Q2 are switched, and this causes noise. However, when the snubber circuit 2 is turned on, the voltage generated at the point E (a momentary large voltage indicated by P1 and P2 that causes noise) is absorbed by the snubber circuit 2 to suppress the noise. The When the power source is only the battery power source, the snubber circuit 2 stops its operation.

  In this way, the portable information terminal detects the power supply state or connection state from the outside and automatically reduces the power efficiency to reduce unnecessary radiation, thereby reducing unnecessary radiation without impairing the operation time of the battery power source. Measures can be taken.

  The present invention has the following effects in claims 1 to 5.

  (1): The portable information terminal detects the power supply state or connection state from the outside and automatically reduces power efficiency to reduce unnecessary radiation, thereby reducing unnecessary radiation without sacrificing the operating time of the battery power supply. Measures can be taken.

  (2): In a portable information terminal that has an external power supply and a battery power supply and can control the efficiency of the switching power supply circuit, it detects the connection of an external power supply such as an AC adapter to the device body, and automatically In particular, by reducing the efficiency of the switching power supply circuit, the generation of noise can be suppressed without impairing the operation time of the battery power supply.

  (3): In a portable information terminal that has an external power supply and a battery power supply and can control the efficiency of the switching power supply circuit, it can detect the connection of an external power supply such as an AC adapter to the device body or By detecting the connection state of the powered docking station / port replicator or detecting the connection state of the external interface, the efficiency of the switching power supply circuit is automatically reduced depending on the state, thereby Noise generation can be suppressed without impairing the operating time of the power supply.

  In the following description, an example in which the portable information terminal is applied to a notebook personal computer (hereinafter also simply referred to as “notebook PC”) will be described. 1 to 4, 1 is an OR gate circuit, 2 is a snubber circuit, 4A is a portable information terminal (for example, a notebook PC), 5 is a switching power supply circuit, 6 is a detection unit, 11 is an output voltage detection unit, and 12 is Drive control unit, 13 is an external power supply detection unit, 14 is an I / F connection detection unit (interface connection detection unit), 15 is a docking station / port replicator detection unit, Q1 and Q2 are switching transistors, C1 and C2 are capacitors, CH is a choke coil, P1 and P2 are peak voltages, GND is a ground potential, D1, D2 and D3 are diodes, Qs is a snubber circuit transistor, Rs is a snubber circuit resistor, Cs is a snubber circuit capacitor, and E is a transistor Q1 And V2, V1 is the DC input voltage, V2 is the DC output voltage, Vx is the internal voltage, and the FB signal is the feedback. It shows the signal.

§1: Outline Description FIG. 1 is a diagram illustrating the principle of the present invention. The outline of the present invention will be described below with reference to FIG.

  (1): In a portable information terminal 4A (for example, a notebook PC) provided with a switching power supply circuit 5 that operates by supplying power from a built-in battery power supply or an external power supply, the switching power supply circuit 5 is turned on / off alternately. A plurality of switching transistors Q1 and Q2, which are driven at the same time, a drive control unit 12 for driving and controlling the switching transistors Q1 and Q2, and an output side charged with a voltage generated by switching of the switching transistors Q1 and Q2 Capacitor C2 and a snubber circuit 2 connected to the output-side line of the switching transistors Q1 and Q2, and drives the snubber circuit 2 based on a detection signal output from the detection unit 6 that detects the power supply state or connection state. Control.

  (2): In the portable information terminal 4A (for example, notebook PC) of (1), the detection unit 6 is provided with an external power supply detection unit 13 for detecting the connection state of the external power supply. When it is detected that an external power supply is connected, the snubber circuit 2 is driven to an ON state based on a detection signal from the external power supply detection unit 13, and the noise of the line is absorbed by the function of the snubber circuit 2. When it is detected that the external power source has been shut off, the snubber circuit 2 is driven to the OFF state based on the detection signal from the external power source detection unit 13 to stop the function of the snubber circuit 2.

  (3): In the portable information terminal 4A (for example, notebook PC) of (1), the detection unit 6 detects the connection state of the docking station / port replicator supplied with power from an external power source. When the docking station / port replicator detection unit 15 detects that the docking station / port replicator is connected, a snubber is provided based on the detection signal of the docking station / port replicator detection unit 15. When the circuit 2 is driven to be on and the noise of the line is absorbed by the function of the snubber circuit 2 and it is detected that the docking station / port replicator is not connected, the docking station / port replicator detector 15 A snubber circuit 2 is driven to the OFF state based on the detection signal, it stops the function of the snubber circuit 2.

  (4): In the portable information terminal 4A (for example, notebook PC) of (1), the detection unit 6 is provided with an I / F connection detection unit 14 for detecting the connection state of the external interface, and the I / F When the connection detection unit 14 detects that the interface is connected, the snubber circuit 2 is driven to the ON state based on the detection signal of the I / F connection detection unit 14, and the function of the snubber circuit 2 is used. When the noise of the line is absorbed and it is detected that the interface is not connected, the snubber circuit 2 is driven to the OFF state based on the detection signal of the I / F connection detection unit 14 to function the snubber circuit 2 Stop.

  (5): In the portable information terminal 4A (for example, notebook PC) of (1), the snubber circuit 2 is a line on the output side of a plurality of switching transistors Q1, Q2 that are driven so as to be alternately turned on / off. Is connected to a ground potential (GND) and includes a series circuit of a snubber circuit switching transistor, a resistor, and a capacitor. The snubber circuit switching transistor is turned on, and a current is supplied to the snubber circuit 2. When the current flows, the noise of the line is absorbed, the snubber circuit switching transistor is turned off, and when the current does not flow to the snubber circuit 2, the noise of the line is not absorbed, and the detection unit 6 includes An external power source detection unit 13 for detecting the connection state of the external power source, and a docking station / There are provided detection means for the docking station / port replicator detection unit 15 for detecting the connection state of the replicator and the I / F connection detection unit 14 for detecting the connection state of the external interface, and detection signals from these detection means The snubber circuit 2 is driven and controlled by the logical OR output (the output of the OR gate circuit 1).

§2: Description of notebook PC FIG. 2 is an explanatory diagram of a notebook PC. As shown in FIG. 2, the notebook PC 4 is provided with a switching power supply circuit 5 and a detection unit 6. The switching power supply circuit 5 is provided in the power supply unit of the notebook PC 4, and the switching power supply circuit 5 in the power supply unit converts an external power supply from a commercial power supply (for example, a commercial power supply with a voltage of 100 V) to a DC power supply through an AC adapter. DC power (hereinafter referred to as “external power”) and a DC power from a battery power (for example, a battery in the notebook PC 4) are supplied.

  The detection unit 6 includes an external power supply detection unit 13, an I / F connection detection unit 14, and a docking station / port replicator detection unit 15. The external power supply detection unit 13 detects whether or not external power is supplied (for example, detects a power supply stop state due to a power failure).

  In this case, as the external power source, for example, a commercial AC power source (for example, AC 100V) is input, and the AC power source is converted into a direct current, and a smoothed and stabilized direct current output (a constant voltage DC output) is obtained. Use what you can. Accordingly, since the external power input to the apparatus (notebook PC) is input as a DC input power, the external power detection unit 13 monitors the DC input power and determines whether the DC input power is supplied. By detecting, it is possible to detect the supply or stop state of the external power supply.

  The I / F connection detection unit 14 detects whether or not an I / F (interface) is connected. In this case, the I / F (interface) is, for example, a LAN, USB, or the like, and whether the I / F (interface) is connected or not is acquired by the OS in the apparatus. Thus, the I / F connection detection unit 14 detects.

  The docking station / port replicator detection unit 15 detects whether the docking station or the port replicator is connected to the notebook PC 4. In this case, the docking station / port replicator detection unit 15 detects whether the docking station or the port replicator is connected to the notebook PC 4 by acquiring information obtained by the OS in the apparatus.

  The switching power supply circuit 5 is provided with two switching transistors Q1 and Q2, an OR gate circuit 1, a snubber circuit 2, a choke coil CH, a capacitor C2, and the like. E represents a connection point between the transistors Q1 and Q2.

  In the switching power supply circuit 5, the transistors Q1 and Q2 are alternately turned on / off, and a current flows to the capacitor C2 via the choke coil CH by the voltage (or potential) at the point E. Charged. The voltage of the capacitor C2 is supplied to the load as a DC output voltage.

  In this case, a voltage that becomes noise is generated at the point E by the switching operation of the transistors Q1 and Q2. Therefore, in order to suppress this noise, the snubber circuit 2 is connected to the point E. An OR gate circuit 1 is provided to drive the snubber circuit 2. The OR gate circuit 1 includes an external power supply detection unit 13, an I / F connection detection unit 14, a docking station / port. An output signal from the replicator detection unit 15 is input.

  In this way, the snubber circuit 2 is operated by the output signal from the detection unit 6 via the OR gate circuit 1 so as to suppress the noise voltage generated at the point E.

  The meanings of the terms are as follows.

  (a): A port replicator is an expansion unit equipped with various types of connectors such as a serial port, a parallel port, and a keyboard connector.

  (b): Docking Station is a function expansion device for notebook computers. It is also called a docking bay or expansion unit depending on the manufacturer.

§3: Description of Snubber Circuit Example FIG. 3 is an explanatory diagram of a snubber circuit example. FIG. 3A shows a snubber circuit example 1 and FIG.

(1): Snubber circuit example 1
In this example, the two switching transistors Q1 and Q2 and the transistor Qs of the snubber circuit 2 are bipolar transistors.

  In FIG. 3A, Q1 and Q2 are switching transistors, C2 is an output side capacitor, 1 is an OR gate circuit, and 2 is a snubber circuit. In this case, the snubber circuit 2 is composed of a series circuit of a transistor (bipolar transistor) Qs, a resistor Rs, and a capacitor Cs, and includes a point E (output lines of the switching transistors Q1 and Q2), GND (ground potential), Connected between.

  The OR gate circuit 1 has a function of taking the outputs of the respective units of the detection unit 6 and applying the logical sum outputs of the three diodes D1 to D3 to the base of the transistor Q1 of the snubber circuit 2. For example, the diode D1 of the OR gate circuit 1 inputs the output of the external power supply detection unit 13 of the detection unit 6, the diode D2 inputs the output of the I / F connection detection unit 14 of the detection unit 6, and the diode D3 The output of the docking station / port replicator detection unit 15 of the detection unit 6 is input, and the logical sum output from the diodes D1 to D3 is applied to the base of the transistor Q1 of the snubber circuit 2.

  The operation of this circuit is as follows. The transistors Q1 and Q2 are driven on / off alternately by applying a driving pulse to the base. For example, at timing t1, the transistor Q1 is turned on and the transistor Q2 is driven off. At the next timing t2, the transistor Q1 is turned off and the transistor Q2 is driven on. At the next timing t3, the transistor Q1 is turned on and the transistor Q2 is turned off. Driven by.

  Thus, by turning on / off the transistors Q1 and Q2, an output voltage as shown is generated at the connection point E between the emitter of the transistor Q1 and the collector of the transistor Q2. As for this output voltage, when the transistors Q1 and Q2 are switched, large voltages such as P1 and P2 are instantaneously generated, which causes noise generation.

  Due to the voltage generated at the point E, a current flows from the point E through the choke coil CH to the output-side capacitor C2, and the capacitor C2 is charged. The voltage of the capacitor C2 becomes the DC output voltage + V2.

(2): Snubber circuit example 2
In this example, the two switching transistors Q1 and Q2 and the transistor Qs of the snubber circuit 2 are composed of MOS-FETs (for example, N-MOS-Power-FETs).

  In FIG. 3B, Q1 and Q2 are switching transistors (for example, N-MOS-Power-FET), C2 is an output side capacitor, 1 is an OR gate circuit, and 2 is a snubber circuit. In this case, the snubber circuit 2 is configured by a series circuit of a transistor Qs (for example, N-MOS-Power-FET), a resistor Rs, and a capacitor Cs, and a point E (output lines of the switching transistors Q1 and Q2) It is connected to GND (ground potential).

  The OR gate circuit 1 has a function of taking the output of each part of the detection unit 6 and applying the logical sum output of the three diodes D1 to D3 to the gate of the transistor Q1 of the snubber circuit 2. For example, the diode D1 of the OR gate circuit 1 inputs the output of the external power supply detection unit 13 of the detection unit 6, the diode D2 inputs the output of the I / F connection detection unit 14 of the detection unit 6, and the diode D3 The output of the docking station / port replicator detection unit 15 of the detection unit 6 is input, and the logical sum output from the diodes D1 to D3 is applied to the gate of the transistor Q1 of the snubber circuit 2.

  The operation of this circuit is as follows. Transistors Q1 and Q2 have their gates applied with drive pulses and are alternately turned on / off by the drive pulses. For example, at timing t1, the transistor Q1 is turned on and the transistor Q2 is driven off. At the next timing t2, the transistor Q1 is turned off and the transistor Q2 is driven on. At the next timing t3, the transistor Q1 is turned on and the transistor Q2 is turned off. Driven by.

  Thus, by turning on / off the transistors Q1 and Q2, an output voltage as shown is generated at the connection point E between the emitter of the transistor Q1 and the collector of the transistor Q2. As for this output voltage, when the transistors Q1 and Q2 are switched, large voltages such as P1 and P2 are instantaneously generated, which causes noise generation.

  Due to the voltage generated at the point E, a current flows from the point E through the choke coil CH to the output-side capacitor C2, and the capacitor C2 is charged. The voltage of the capacitor C2 becomes the DC output voltage + V2.

§4: Description of an example of a switching power supply circuit of a notebook PC FIG. 4 is an explanatory diagram of an example of a switching power supply circuit of a notebook PC. Hereinafter, an example of the switching power supply circuit will be described with reference to FIG.

A: Description of Configuration This switching power supply circuit is provided in the power supply section of the notebook PC, and only the basic circuit portion is shown. This switching power supply circuit includes an input-side capacitor C1, two switching transistors Q1 and Q2, a drive control unit 12 that drives and controls these switching transistors Q1 and Q2, and a connection between the switching transistors Q1 and Q2. A choke coil CH having one end connected to the point E, an output-side capacitor C2 connected to the other end of the choke coil CH, and an output voltage connected to a connection point of the choke coil CH and the output-side capacitor C2. A detection unit 11 and a snubber circuit including a series circuit of a transistor Qs, a resistor Rs, and a capacitor Cs connected to the point E are provided.

  A snubber circuit composed of a series circuit of a transistor Qs, a resistor Rs, and a capacitor Cs is connected to an external power supply detection unit 13 and an I / F connection detection unit 14 via an OR gate circuit composed of diodes D1, D2, and D3. The detection signal of the docking station / port replicator detection unit 15 is inputted, and the transistor Qs of the snubber circuit is driven and controlled by a signal that has passed through the OR gate circuit among these input signals.

B: Description of Operation In the above circuit, the capacitor C1 is connected between the DC input voltage + V1 and GND, and applies the DC input voltage + V1 to the collector of the transistor Q1. An internal voltage + Vx (arbitrary voltage) is applied to the drive control unit 12, and a control for alternately turning on / off the transistors Q1 and Q2 is performed. In this case, the drive control unit 12 feeds back the output voltage (DC, + V2) detected by the output voltage detection unit 11, and controls to turn on / off the transistors Q1 and Q2 alternately.

  The voltage (or potential) at the point E as a result of the transistors Q1 and Q2 being alternately turned on / off is a voltage having a waveform as shown in FIG. 3, and this voltage causes the capacitor C2 to pass through the choke coil CH. A current flows and charges the capacitor C2. Then, the charging voltage of the capacitor C2 is taken out as a DC output voltage.

  A snubber circuit composed of a series circuit of a transistor Qs, a resistor Rs, and a capacitor Cs includes a logical sum of detection signals from the external power supply detection unit 13, the I / F connection detection unit 14, and the docking station / port replicator detection unit 15. Drive controlled by output. That is, detection signals from the external power source detection unit 13, the I / F connection detection unit 14, and the docking station / port replicator detection unit 15 are driven and controlled by a logical sum output by a logical sum circuit composed of diodes D1, D2, and D3. .

§5: Other description The present invention is not limited to a notebook PC, but can be applied to a portable information terminal such as a mobile phone, a PDA, or a car navigation system (which can be removed from a car and used in a house).

It is a principle explanatory view of the present invention. It is explanatory drawing of the portable information terminal in embodiment. It is explanatory drawing of the snubber circuit example in embodiment, A figure shows snubber circuit example 1, B figure shows snubber circuit example 2. FIG. It is an example of the switching power supply circuit of the portable information terminal in an embodiment. It is an example of the conventional switching power supply circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 OR gate circuit 2 Snubber circuit 4A Portable information terminal 4 Notebook PC (notebook personal computer)
DESCRIPTION OF SYMBOLS 5 Switching power supply circuit 6 Detection part 11 Output voltage detection part 12 Drive control part 13 External power supply detection part 14 I / F connection detection part (interface connection detection part)
15 Docking station / port replicator detector Q1, Q2 Transistor C1, C2 Capacitor CH Choke coil P1, P2 Peak voltage GND Ground potential D1, D2, D3 Diode Qs Snubber circuit transistor Rs Snubber circuit resistance Cs Snubber circuit capacitor E Transistor Connection point between Q1 and Q2 V1 DC input voltage V2 DC output voltage Vx Internal voltage (arbitrary voltage)
FB signal Feedback signal

Claims (5)

In a portable information terminal having a switching power supply circuit that operates by power supply from a built-in battery power supply or an external power supply,
A plurality of switching transistors driven to alternately turn on / off in the switching power supply circuit;
A drive control unit for driving and controlling the switching transistor;
An output-side capacitor charged with a voltage generated by switching of the switching transistor;
A snubber circuit connected to the output-side line of the switching transistor;
A portable information terminal that controls driving of the snubber circuit based on a detection signal output from a detection unit that detects a power supply state or a connection state. The detection unit is provided with an external power supply detection unit for detecting a connection state of an external power supply. When the external power supply detection unit detects that an external power supply is connected, the detection of the external power supply detection unit is performed. Drive the snubber circuit based on the signal to absorb the noise of the line by the function of the snubber circuit,
The function of the snubber circuit is stopped when the snubber circuit is driven to an off state based on a detection signal of the external power supply detection unit when it is detected that the external power supply is shut off. 1. A portable information terminal according to 1. The detection unit includes a docking station / port replicator detection unit that detects a connection state of the docking station / port replicator that is fed from an external power source,
When the docking station / port replicator detection unit detects that the docking station / port replicator is connected, the snubber circuit is driven to an ON state based on a detection signal from the docking station / port replicator detection unit. Then, the noise of the line is absorbed by the function of the snubber circuit,
When it is detected that the docking station / port replicator is not connected, the snubber circuit is driven to an off state based on the detection signal of the docking station / port replicator detection unit, and the function of the snubber circuit is stopped. The portable information terminal according to claim 1. The detection unit is provided with an I / F connection detection unit for detecting a connection state of an external interface. When the I / F connection detection unit detects that an interface is connected, the I / F connection detection unit Based on the detection signal of the F connection detection unit, the snubber circuit is driven to an ON state, and the noise of the line is absorbed by the function of the snubber circuit,
When it is detected that the interface is not connected, the snubber circuit is driven to an OFF state based on a detection signal of the I / F connection detection unit, and the function of the snubber circuit is stopped. The portable information terminal according to claim 1. The snubber circuit includes a series circuit of a snubber circuit switching transistor, a resistor, and a capacitor connected to an output side line of the plurality of switching transistors driven to alternately turn on and off. Has been
When the snubber circuit switching transistor is turned on and a current flows through the snubber circuit, the noise of the line is absorbed, and when the snubber circuit switching transistor is turned off and no current flows through the snubber circuit, the line In addition to having the function of preventing noise absorption,
The detection unit includes an external power source detection unit that detects a connection state of an external power source, a docking station / port replicator detection unit that detects a connection state of a docking station / port replicator that is fed from the external power source, and an external interface Each detection means of the I / F connection detection unit for detecting the connection state is provided,
The portable information terminal according to claim 1, wherein the snubber circuit is driven and controlled by a logical sum output of detection signals from the plurality of detection means.

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