JP2010282574A - Electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic apparatus capable of achieving, without using an I/O port of a microcomputer, overcurrent protection for a power supply line connected to a power supply pin of a USB port. <P>SOLUTION: The electronic apparatus includes: a USB port 1; a stabilized DC power supply (transistor Q1, Zener diode ZD1); current detection parts (resistances R1, R2) provided on the input side of the power supply for detecting currents flowing in a power supply line connected to a power supply pin 11; a transistor Q3 that turns on when an output voltage of the current detection parts becomes equal to or higher than a reference overcurrent value; a transistor Q5 that turns off as the transistor Q3 turns on; and control parts (transistor Q4 and resistances R7-R9) that control the transistor Q3 to keep the transistor Q3 on even if the output voltage of the current detection parts drops to less than the reference overcurrent value after the transistor Q3 is temporarily turned on. While the transistor Q5 is off, the operation of the power supply stops. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electronic device having a USB (Universal Serial Bus) port.

  In recent years, electronic devices having a USB port have been provided in various markets. In the USB 2.0 standard, the maximum value of the current supplied to the power supply pin of the USB port is 500 [mA], and the voltage supplied to the power supply pin of the USB port is 5 [V] ± 5% (= 4 .75 to 5.25 [V]). Therefore, when the current supplied to the power supply pin of the USB port exceeds 500 [mA], the electronic device including the USB port has overcurrent protection for the current supply line connected to the power supply pin of the USB port. Such a configuration is desirable.

  In the USB 3.0 standard, the maximum value of the current supplied to the power supply pin of the USB port is 900 [mA]. Therefore, when the USB 3.0 standard is supported, the current is supplied to the power supply pin of the USB port. It is desirable that the current supply line connected to the power supply pin of the USB port is protected against overcurrent when the current to be applied exceeds 900 [mA].

  Further, in an electronic device having a USB port, a specific USB medium storing update data for updating firmware (hereinafter referred to as “service USB medium”) is connected to the USB port in a service-compatible manner. Therefore, it can be considered that the firmware can be updated. When the USB port is a port dedicated to the specific USB media, the current supplied from the USB port to the service USB media does not require 500 [mA] (the maximum supply current of the USB 2.0 standard). The maximum rated current of the power supply circuit connected to the power supply pin of the port via the power supply line can be made less than 500 [mA], and the cost of the power supply circuit can be reduced. However, even if the USB port is a dedicated port for service USB media and this is clearly stated in the instruction manual or the electronic device body, USB media other than the service USB media (hereinafter referred to as "non-service It is physically possible to connect the USB media). For this reason, the user may connect a non-service USB medium to the USB port. If the current consumption of the non-service USB media is less than the maximum rated current of the power supply circuit connected to the power supply pin of the USB port via the power supply line, the user connects the non-service USB media to the USB port. However, there is no particular problem. On the other hand, if the consumption current of the non-service USB media is larger than the maximum rated current of the power supply circuit connected to the power supply pin of the USB port via the power supply line, the user does not service the USB port. When the USB media is connected, problems such as abnormal heat generation and breakage of the power supply circuit connected to the power supply pin of the USB port via the power supply line occur. Therefore, if the current supplied to the power supply pin of the USB port exceeds the maximum rated current of the power supply circuit connected to the power supply pin of the USB port via the power supply line, the power supply pin of the USB port It is desirable that the overcurrent protection is applied to the current supply line connected to the.

  As described above, various values can be considered for the overcurrent setting value. In any case, an electronic device equipped with a USB port has overcurrent protection for the current supply line connected to the power supply pin of the USB port. Such a configuration is desirable. When overcurrent protection is applied to the current supply line connected to the power supply pin of the USB port, a voltage and a reference corresponding to the current flowing through the current supply line connected to the power supply pin of the USB port are used. Comparing the voltage with a comparator (see, for example, Patent Document 3), the microcomputer determines whether or not it is an overcurrent from the comparison result of the comparator, and if the microcomputer determines that it is an overcurrent, the microcomputer A general overcurrent protection configuration is a configuration in which the current supply line connected to the power supply pin of the USB port is cut off by controlling a switch unit that switches between energization and cutoff of the current supply line connected to the power supply pin. is there.

JP 10-97352 A (summary) JP 2008-9898 A (summary) JP 11-85291 A (summary)

  However, in the above general overcurrent protection configuration, the two I / O ports of the microcomputer are used for overcurrent protection of the power supply line connected to the power supply pin of the USB port. There is a problem that the I / O port of the used microcomputer cannot be allocated to other uses.

  Patent Document 1 describes overcurrent protection for a current supply line connected to a power supply pin of a USB port, but does not disclose any specific configuration of the overcurrent protection circuit.

  Patent Document 2 relates to an electronic device (personal computer) having a USB port and a USB device connected to the USB port. Patent Document 2 discloses that an overcurrent protection circuit is provided on the USB device side, but does not disclose provision of an overcurrent protection circuit on the electronic device side including the USB port.

  In view of the above situation, the present invention is an electronic device equipped with a USB port, and does not use an I / O port of a microcomputer for overcurrent protection of a power supply line connected to a power supply pin of the USB port. An object is to provide an electronic device that can be realized.

  In order to achieve the above object, an electronic device according to the present invention is provided on the input side of a USB port, a DC stabilized power supply for supplying a voltage to a power supply pin of the USB port, and the DC stabilized power supply, A current detection unit that detects a current flowing through a power supply line connected to a power supply pin of the USB port, and a first that is turned on when a voltage output from the current detection unit exceeds a predetermined overcurrent reference value; A transistor, a second transistor that is turned off when the first transistor is turned on, and a voltage that is output from the current detector after the first transistor is turned on once is less than the overcurrent reference value A control unit that controls the first transistor so that the first transistor remains on even if the second transistor is off. Is a structure in which the operation of the DC stabilized power supply is stopped.

  According to such a configuration, overcurrent protection of the power supply line connected to the power supply pin of the USB port can be realized without using the I / O port of the microcomputer. Further, according to such a configuration, since the current detection unit is provided on the input side of the DC stabilized power supply, even when a large current flows, a voltage drop at the current detection unit is supplied to the power supply pin of the USB port. The effect on the voltage is reduced, the voltage supplied to the power supply pin of the USB port can be easily kept within the range specified by the USB standard, and the accuracy of the circuit constants of each circuit element is not required so much, so the cost is low. Can be achieved.

  Also, a bypass path for bypassing the input side and output side of the DC stabilized power supply is provided, and the bypass path is cut off when the current flowing through the power supply line connected to the power supply pin of the USB port is less than a predetermined value. When the current flowing through the power supply line connected to the power supply pin of the USB port is equal to or greater than the predetermined value, the bypass path is conducted, and the predetermined value is connected to the power supply pin of the USB port. You may make it make it smaller than the overcurrent of the electric current which flows through a power supply line. In addition, the bypass path may include a third transistor for switching the blocking / conduction of the bypass path.

  In the case of the configuration including the bypass path as described above, from the viewpoint of cost reduction, the stabilized DC power source includes an output transistor and a Zener diode connected to a base of the output transistor, and the output It is desirable not to provide a heat sink around the transistor.

  According to the present invention, in an electronic device having a USB port, overcurrent protection of a power supply line connected to a power supply pin of the USB port can be realized without using an I / O port of a microcomputer.

It is a block diagram which shows one schematic structural example of the liquid crystal television which concerns on this invention. It is a figure which shows the equivalent circuit of the part relevant to the power supply to the power supply pin of a USB port in case the electric current supplied to the power supply pin of a USB port is less than 389 [mA]. It is a figure which shows the equivalent circuit of the part relevant to the power supply to the power supply pin of a USB port in case the electric current supplied to the power supply pin of a USB port is 389 [mA] or more and less than 520 [mA]. It is a figure which shows the equivalent circuit of the part relevant to the power supply to the power supply pin of a USB port in case the electric current supplied to the power supply pin of a USB port is 520 [mA] or more.

  Embodiments of the present invention will be described below with reference to the drawings. Here, a liquid crystal television will be described as an example of the electronic apparatus according to the present invention. FIG. 1 shows a schematic configuration example of a liquid crystal television according to the present invention.

  The liquid crystal television according to the present invention shown in FIG. 1 includes a terminal T1, a USB port 1, a microcomputer (hereinafter referred to as a microcomputer) 2, a load 3, a remote control light receiving unit 4, an operation key 5, and capacitors C1 to C1. C3, diodes D1 and D2, transistors Q1 to Q5, resistors R1 to R12, and a Zener diode ZD1. The USB port 1 has a power supply pin 11, a data + pin 12, a data−pin 13, and a ground pin 14. Transistors Q1 and Q4 are each an NPN transistor, and transistors Q2, Q3, and Q5 are each a PNP transistor. The transistor Q3 is an example of the “first transistor” recited in the claims, the transistor Q5 is an example of the “second transistor” recited in the claims, and the transistor Q2 is defined in the claims. It is an example of the described “third transistor”.

  The liquid crystal television according to the present invention shown in FIG. 1 naturally has a power supply unit that supplies a voltage of 6.5 [V] to the terminal T1, a microcomputer 2, a load 3, a remote control light receiving unit 4, and operation keys. Although the power supply unit for 4 is provided, the power supply unit is not a characteristic part of the present invention, and therefore illustration and description thereof are omitted here. Further, the data + pin 12 of the USB port 1, the data−pin 13 of the USB port 1, the load 3, the remote control light receiving unit 4, and the operation key 4 are each connected to each I / O port of the microcomputer 2. The illustration of these I / O ports is omitted in FIG.

  The load 3 includes a tuner unit 31, a video circuit 32, an audio circuit 33, a liquid crystal display unit 34, and a speaker 35. The tuner unit 31 selects and demodulates a television broadcast signal received from an antenna (not shown). The video circuit 32 performs various processes (for example, luminance correction and gamma correction) on the video signal received from the tuner unit 31, and outputs the video signal subjected to the various processes to the liquid crystal display unit 34. The liquid crystal display unit 34 performs display based on the output signal of the video circuit 32. The audio circuit 33 performs various processes (for example, volume adjustment) on the audio signal received from the tuner unit 31 and outputs the audio signal subjected to the various processes to the speaker 35. The speaker 35 emits sound based on the output signal of the sound circuit 33.

  The remote control light receiving unit 4 outputs an instruction signal corresponding to an infrared signal from a remote control transmitter (not shown) to the microcomputer 2. The operation key 5 outputs an instruction signal corresponding to the user's key operation to the microcomputer 2. The microcomputer 2 controls the operation of the load 3 (for example, a channel selection operation by the tuner unit 31 and a volume adjustment operation by the audio circuit 33) based on an instruction signal from the remote control light receiving unit 4 or the operation key 5.

  Next, a circuit configuration of a portion related to power supply to the power supply pin 11 of the USB port 1 will be described.

  A parallel circuit composed of resistors R1 and R2 and a parallel circuit composed of resistors R3 and R4 are inserted in a power supply line between the terminal T1 and the collector of the transistor Q1. One end of the resistor R1 and one end of the resistor R2 are connected to the terminal T1 to which 6.5 [V] is applied, and one end of the resistor R3 and one end of the resistor R4 are connected to the other end of the resistor R1 and the other end of the resistor R2. The collector of the transistor Q1 is connected to the other end of the resistor R3 and the other end of the resistor R4.

  A capacitor C1 and a capacitor C2 are provided on a power supply line between the emitter of the transistor Q1 and the power supply pin 11 of the USB port 1. One end of the capacitor C1 and one end of the capacitor C2 are connected to a power supply line between the emitter of the transistor Q1 and the power supply pin 11 of the USB port 1, and the other end of the capacitor C1 and the other end of the capacitor C2 are connected to the ground potential. Is done.

  The cathode of the Zener diode ZD1 is connected to the base of the transistor Q1, and the anode of the Zener diode ZD1 is connected to the ground potential.

  The emitter of transistor Q2 is connected to one end of resistor R3 and one end of resistor R4, the base of transistor Q2 is connected to the other end of resistor R3, the other end of resistor R4, and the collector of transistor Q1, and the collector of transistor Q2 is the resistor It is connected to the emitter of the transistor Q1 through R5.

  The emitter of the transistor Q3 is connected to one end of the resistor R1 and one end of the resistor R2. The base of the transistor Q3 is connected to the other end of the resistor R1 and the other end of the resistor R2 through the resistor R6, and the transistor through the resistor R7. Connected to the collector of Q4. The emitter of the transistor Q4 is connected to the ground potential, the base of the transistor Q4 is connected to the collector of the transistor Q3 via the resistor R8, and is connected to the ground potential via the resistor R9.

  The anode of the diode D1 is connected to one end of the resistor R1 and one end of the resistor R2, and the cathode of the diode D1 is connected to the emitter of the transistor Q5 via the resistor R10. The collector of the transistor Q5 is connected to the connection node of the base of the transistor Q1 and the cathode of the Zener diode ZD1, and the base of the transistor Q5 is connected to the ground potential via the resistor R11. The anode of the diode D2 is connected to the collector of the transistor Q3, the anode of the diode D2 is connected to the base of the transistor Q5, and is connected to the emitter of the transistor Q5 via the resistor R12. Further, the anode of the diode D2 is connected to one end of the capacitor C3, and the other end of the capacitor C3 is connected to the ground potential.

  Next, the circuit operation of the portion related to the power supply to the power supply pin 11 of the USB port 1 having the above circuit configuration will be described.

  Note that the circuit constants of each circuit element in the portion related to the power supply to the power supply pin 11 of the USB port 1 are the transistor Q2 when the current supplied to the power supply pin 11 of the USB port 1 is 389 [mA] or more. Is turned on, and the transistor Q3 is set to be turned on when the current supplied to the power supply pin 11 of the USB port 1 becomes 520 [mA] or more.

  Further, the transistor Q1 and the Zener diode ZD1 function as a direct current stabilizing power source.

  The parallel circuit composed of resistors R1 and R2 and the parallel circuit composed of resistors R3 and R4 each function as a current detection circuit that detects a current supplied to the power supply pin 11 of the USB port 1. In the circuit configuration in which the current detection circuit is provided on the output side of the DC stabilized power supply, when a large current flows, the voltage supplied to the power supply pin of the USB port due to the voltage drop in the current detection circuit is 4.75 to 5 It is difficult to keep the voltage within the range of .25 [V], and the accuracy of the circuit constant of each circuit element is required, which increases the cost. On the other hand, in the circuit configuration in which the current detection circuit is provided on the input side of the stabilized DC power supply as in the present invention, even when a large current flows, the voltage drop in the current detection circuit is the power supply pin of the USB port 1. 11 is reduced, and the voltage supplied to the power supply pin 11 of the USB port 1 can be easily kept within the range of 4.75 to 5.25 [V]. Since the accuracy of the constant is not so required, the cost can be reduced.

  First, a case where the current supplied to the power supply pin 11 of the USB port 1 is less than 389 [mA] will be described.

  When the current supplied to the power supply pin 11 of the USB port 1 is less than 389 [mA], the voltage drop in the parallel circuit composed of the resistors R3 and R4 is smaller than the base-emitter threshold voltage of the transistor Q2, so that the transistor Q2 is turned off, and a bypass path that bypasses one end of the resistor R3 and one end of the resistor R4 and the emitter of the transistor Q1 is blocked by the transistor Q2.

  When the current supplied to the power supply pin 11 of the USB port 1 is less than 389 [mA], the voltage drop in the parallel circuit composed of the resistors R1 and R2 is smaller than the base-emitter threshold voltage of the transistor Q3. The transistor Q3 is turned off.

  As the transistor Q3 is turned off, the transistor Q5 is turned on, the Zener diode ZD1 is turned on, the transistor Q1 is turned on, and the voltage is stepped down by the collector-emitter voltage of the transistor Q1 4.75-5.25 [ The voltage stabilized in the range of V] is supplied to the power supply pin 11 of the USB port 1.

  Therefore, when the current supplied to the power supply pin 11 of the USB port 1 is less than 389 [mA], an equivalent circuit of the portion related to the power supply to the power supply pin 11 of the USB port 1 is as shown in FIG. become.

  Next, a case where the current supplied to the power supply pin 11 of the USB port 1 is 389 [mA] or more and less than 520 [mA] will be described.

  When the current supplied to the power supply pin 11 of the USB port 1 is not less than 389 [mA] and less than 520 [mA], the voltage drop in the parallel circuit composed of the resistors R3 and R4 is not less than the threshold voltage between the base and emitter of the transistor Q2. Therefore, the transistor Q2 is turned on, and the bypass path that bypasses one end of the resistor R3 and one end of the resistor R4 and the emitter of the transistor Q1 is conducted.

  When the bypass path becomes conductive, a voltage drop due to the collector-emitter saturation voltage generated in the transistor Q1 can be reduced. Accordingly, since heat generation in the transistor Q1 can be suppressed, it is not necessary to provide a heat sink near the transistor Q1. Further, since the step-down amount due to the collector-emitter voltage of the transistor Q1 does not fluctuate greatly, it is not necessary to finely control the base voltage of the transistor Q1, and the Zener voltage of the Zener diode ZD1 does not need to be controlled as in this embodiment. Control becomes possible.

  It is possible to eliminate the bypass path and the transistor Q2 and the resistor R5 on the bypass path. However, when implementing such abolition, measures to provide a heat sink near the transistor Q1, Instead of the zener diode ZD1, a measure may be taken to provide a voltage dividing circuit that divides the voltage supplied to the power supply pin 11 and supplies it to the reference terminal of the shunt regulator. Even when the bypass Q and the transistor Q2 and the resistor R5 on the bypass path are not abolished, a power supply pin can be used instead of a configuration in which a heat sink is provided in the vicinity of the transistor Q1, or the Zener diode ZD1 is replaced with a shunt regulator. 11 may be provided with a voltage dividing circuit that divides the voltage supplied to 11 and supplies it to the reference terminal of the shunt regulator.

  When the current supplied to the power supply pin 11 of the USB port 1 is 389 [mA] or more and less than 520 [mA], the voltage drop in the parallel circuit composed of the resistors R1 and R2 is the base-emitter threshold of the transistor Q3. Since it is less than the voltage, transistor Q3 is turned off.

  As the transistor Q3 is turned off, the transistor Q5 is turned on, the Zener diode ZD1 is turned on, the transistor Q1 is turned on, and the voltage is stepped down by the collector-emitter voltage of the transistor Q1 to 4.75-5.25 [ The voltage stabilized in the range of V] is supplied to the power supply pin 11 of the USB port 1.

  Therefore, when the current supplied to the power supply pin 11 of the USB port 1 is 389 [mA] or more and less than 520 [mA], an equivalent circuit of a portion related to power supply to the power supply pin 11 of the USB port 1 is as follows. As shown in FIG.

  Finally, a case where the current supplied to the power supply pin 11 of the USB port 1 is 520 [mA] or more will be described.

  Immediately after the current supplied to the power supply pin 11 of the USB port 1 is switched from less than 520 [mA] to 520 [mA] or more, the transistors Q1 and Q2 are turned on, and at this time, the resistors R1 and R2 are connected in parallel. Since the voltage drop across the circuit is greater than or equal to the base-emitter threshold voltage of transistor Q3, transistor Q3 is turned on.

  As the transistor Q3 is turned on, the transistor Q5 is turned off, the Zener diode ZD1 is turned off, and the transistor Q1 is turned off. When the transistor Q1 is turned off, no current flows through the parallel circuit composed of the resistors R1 and R2, but the transistor Q3 is turned on and the transistor Q3 is kept on. A circuit including the transistor Q4 and the resistors R7 to R9 is an example of the “control unit” recited in the claims.

  Therefore, when the current supplied to the power supply pin 11 of the USB port 1 is 520 [mA] or more, the equivalent circuit of the portion related to the power supply to the power supply pin 11 of the USB port 1 is as shown in FIG. Thus, it can be seen that overcurrent protection is applied to the power supply line connected to the power supply pin 11 of the USB port 1. And once overcurrent protection is applied, it will not return from overcurrent protection unless the liquid crystal television according to the present invention shown in FIG. 1 is shut off.

  As apparent from FIGS. 1 and 4, in the liquid crystal television according to the present invention shown in FIG. 1, the overcurrent protection of the power supply line connected to the power supply pin 11 of the USB port 1 is protected by the I / O of the microcomputer 2. This can be realized without using the O port.

  Although recent electronic devices have been digitized and are increasingly dependent on firmware, the number of I / O ports of a microcomputer is limited. For this reason, as in the present invention, by implementing overcurrent protection of the power supply line connected to the power supply pin of the USB port without using the I / O port of the microcomputer, the microcomputer not used for overcurrent protection The I / O port can be effectively used for other purposes.

  As mentioned above, although embodiment which concerns on this invention was described, the range of this invention is not limited to this, A various change can be added and implemented in the range which does not deviate from the main point of invention.

DESCRIPTION OF SYMBOLS 1 USB port 2 Microcomputer 3 Load 4 Remote control light-receiving part 5 Operation key 11 Power supply pin 12 Data + pin 13 Data-pin 24 Ground pin 31 Tuner part 32 Video circuit 33 Audio circuit 34 Liquid crystal display part 35 Speaker C1-C3 Capacitor D1, D2 Diode Q1-Q5 Transistor R1-R12 Resistor ZD1 Zener diode

Claims (4)

USB port,
DC stabilized power supply for supplying voltage to the power supply pin of the USB port;
A current detection unit that is provided on the input side of the DC stabilized power supply and detects a current flowing through a power supply line connected to a power supply pin of the USB port;
A first transistor that is turned on when a voltage output from the current detection unit exceeds a predetermined overcurrent reference value;
A second transistor that is turned off as the first transistor is turned on;
The first transistor is maintained in an on state even when a voltage output from the current detector after the first transistor is once turned on is less than the overcurrent reference value. A control unit for controlling the transistor,
The electronic device is characterized in that the operation of the stabilized DC power supply is stopped when the second transistor is off. With a bypass path that bypasses the input side and output side of the DC stabilized power supply,
When the current flowing through the power supply line connected to the power supply pin of the USB port is less than a predetermined value, the bypass path is interrupted,
When the current flowing through the power supply line connected to the power supply pin of the USB port is greater than or equal to the predetermined value, the bypass path is conducted,
The electronic device according to claim 1, wherein the predetermined value is smaller than an overcurrent of a current flowing through a power supply line connected to a power supply pin of the USB port.   The electronic device according to claim 3, wherein the bypass path includes a third transistor for switching the cutoff / conduction of the bypass path.   4. The electronic device according to claim 2, wherein the DC-stabilized power supply includes an output transistor and a Zener diode connected to a base of the output transistor, and no heat sink is provided around the output transistor. .

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