JP2013021850A - Overheat protection circuit and communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overheat protection circuit and a communication device, capable of securely performing the overheat protection of a device and the cancellation of an overheat cause.SOLUTION: An overheat protection circuit 101 is operated by receiving a source power voltage, and includes a comparison circuit 22 for outputting a control signal to switch off a power circuit 13, provided for generating an operation power voltage from the source power voltage, when a detection voltage level output from a temperature detection circuit 11 is larger than a first reference voltage level, until the detection voltage level becomes smaller than a second reference voltage level smaller than the first reference voltage level. A temperature when the detect voltage level becomes equal to the second reference voltage level is out of a predetermined use temperature range of a device having the power circuit 13.

Description

  The present invention relates to an overheat protection circuit and a communication device, and more particularly to an overheat protection circuit and a communication device that control a power source of the device.

  As an example of a configuration for overheating protection of a device using a temperature sensor, for example, Japanese Patent Laid-Open No. 9-222448 (Patent Document 1) discloses the following configuration. That is, in a circuit provided with switch means that can be switched between an on state for conducting a power supply and a load and an off state for shutting off, a positive temperature coefficient thermistor is arranged in series with the switch means, and the both-end potential of the positive temperature coefficient thermistor Failure determination means for determining the presence / absence of a failure based on at least one of the potentials and outputting a determination signal.

Japanese Patent Laid-Open No. 9-222448

  As another example of the configuration for overheating protection of the apparatus using the temperature sensor, a configuration in which the CPU (Central Processing Unit) is interrupted by the output signal of the temperature sensor and the CPU performs overheat protection control such as power-off is conceivable. .

  However, in such a configuration, when the CPU is running out of control, the overheat protection control is not executed and the overheat state may continue.

  Also, an abnormality that causes the device to become overheated, such as a blanket over the device installed in the home, is often not resolved without human intervention. If the cause of overheating has not been eliminated, the overheating state may be repeated even if the temperature in the apparatus once decreases due to overheating protection control.

  Further, Non-Patent Document 1 does not disclose a configuration for solving such a problem.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an overheat protection circuit and a communication device that can more reliably perform overheat protection of the device and eliminate the cause of overheat. It is.

  In order to solve the above-described problem, an overheat protection circuit according to an aspect of the present invention is an overheat protection circuit used in an apparatus including a power supply circuit for generating an operation power supply voltage from an original power supply voltage. A temperature detection circuit that operates in response to a power supply voltage, detects a temperature, and outputs a detection voltage having a level corresponding to the detected temperature, operates in response to the original power supply voltage, and the level of the detection voltage is When the level of the reference voltage is higher than 1, the level of the detection voltage is turned off until the level of the detection voltage becomes lower than the level of the second reference voltage that is lower than the first reference voltage. A comparison circuit for outputting a control signal, and the temperature when the level of the detection voltage becomes equal to the level of the second reference voltage is outside a predetermined operating temperature range of the device.

  With such a configuration, once the power supply circuit is turned off by the control signal, it is possible to prevent the operating power supply voltage from returning unless a human intervenes. It is possible to prevent the power supply circuit from repeatedly turning on and off. Further, it is possible to control the operating power supply voltage of the above apparatus without performing power control by the CPU or separately from the power control by the CPU. Therefore, overheating protection of the apparatus and elimination of the cause of overheating can be more reliably performed.

  Preferably, the comparison circuit generates the first reference voltage and the second reference voltage based on the detection voltage, and the overheat protection circuit further includes the original reference based on a level change of the original power supply voltage. A correction circuit for correcting the original reference voltage so as to cancel the voltage level change is provided.

  With such a configuration, it is possible to suppress a change in temperature at which the power supply circuit is switched on and off by the control signal, and to stabilize control of the power supply circuit by the control signal.

  More preferably, the correction circuit cancels the level change of the original reference voltage in a state where the level of the detection voltage is substantially equal to the level of the first reference voltage.

  When trying to correct the original reference voltage with respect to fluctuations in the power supply, the voltage value of the original reference voltage follows a complicated locus, and the circuit for realizing this correction also becomes complicated. However, the fluctuation range of the original power supply voltage is normally determined by the specification to be about several percent with respect to the target voltage value. If the fluctuation is at most several percent, the original reference voltage corrected within the range can be approximated by a straight line. That is, the correction circuit can be simplified because it can cancel the fluctuation of the original power supply voltage approximated by a straight line.

  More preferably, the correction circuit includes a voltage dividing circuit for dividing the original power supply voltage, a constant voltage circuit for outputting a constant voltage, a voltage divided by the voltage dividing circuit, and the constant voltage circuit. And a differential amplifier circuit for amplifying a difference from the output voltage and outputting it as the original reference voltage.

  The original reference voltage correction circuit can be easily configured with a constant voltage source and a differential amplifier circuit. Generally, a high voltage constant voltage source is not stable and has poor accuracy. On the other hand, the output voltage of the constant voltage source used in the correction circuit is amplified. With such a configuration, a constant voltage source with a low voltage can be used, so that power consumption can be kept low with an inexpensive circuit configuration.

  Preferably, the overheat protection circuit further includes an amplification circuit for amplifying the detection voltage and outputting the amplified detection voltage to the comparison circuit, and the amplification circuit increases the level of the detection voltage after amplification. When it becomes substantially equal to the level of the reference voltage of 1, the gain is switched to a higher gain.

  As described above, in the amplifier circuit, the change in the output voltage of the amplifier circuit due to the change in the original power supply voltage can be suppressed by steeply setting the change in the output voltage of the amplifier circuit with respect to the change in the input voltage, that is, the detection voltage. it can. That is, it is possible to prevent the temperature at which the power supply circuit is switched on and off by the control signal from fluctuating and to stabilize the control of the power supply circuit by the control signal.

  More preferably, the amplification circuit switches to a high gain when the level of the detection voltage after amplification decreases and becomes substantially equal to the level of the second reference voltage.

  With such a configuration, the fluctuation of the output voltage of the amplifier circuit due to the fluctuation of the level of the original power supply voltage in the vicinity of the temperature corresponding to the second reference voltage can also be suppressed, so that the temperature setting corresponding to the second reference voltage is set. Can increase the degree of freedom.

  Preferably, the overheat protection circuit further includes a differential amplifier circuit for outputting a differential amplification voltage obtained by amplifying a difference between the detection voltage and an amplification reference voltage to the comparison circuit, and the comparison circuit includes: When the level of the differential amplification voltage becomes higher than the level of the first reference voltage, the level of the differential amplification voltage becomes lower than the level of the second reference voltage that is lower than the first reference voltage. Until the control signal for turning off the power supply circuit is output and the level of the differential amplification voltage becomes lower than the level of the second reference voltage, the level of the differential amplification voltage is A control signal for turning on the power supply circuit is output until the level becomes higher than the level of the reference voltage of 1.

  As described above, since the offset of the input voltage of the comparison circuit can be canceled by the configuration in which the detection voltage is differentially amplified, the level range of the input voltage of the comparison circuit can be expanded. As a result, the accuracy of power supply control based on temperature detection can be increased as compared with a configuration in which the amplification circuit performs simple amplification instead of differential amplification.

  In order to solve the above problems, a communication apparatus according to an aspect of the present invention includes a power supply circuit for generating an operation power supply voltage from an original power supply voltage, an arithmetic processing unit that operates in response to the operation power supply voltage, and an overheating. A temperature detecting circuit for operating the receiving power source voltage, detecting a temperature, and outputting a detection voltage having a level corresponding to the detected temperature. And when the level of the detection voltage becomes higher than the level of the first reference voltage, the level of the detection voltage is lower than the level of the first reference voltage. And a comparator circuit for outputting a control signal for turning off the power supply circuit until the level of the reference voltage becomes smaller than the level of the second reference voltage. The temperature of the time is a predetermined operating temperature range of the communication device.

  With such a configuration, once the power supply circuit is turned off by the control signal, it is possible to prevent the operating power supply voltage from returning unless a human intervenes. It is possible to prevent the power supply circuit from repeatedly turning on and off. Further, it is possible to control the operating power supply voltage of the above apparatus without performing power control by the CPU or separately from the power control by the CPU. Therefore, overheating protection of the apparatus and elimination of the cause of overheating can be more reliably performed.

  ADVANTAGE OF THE INVENTION According to this invention, the overheat protection of an apparatus and elimination of the overheat cause can be performed more reliably.

It is a figure which shows the structure of the communication apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure of the overheat protection circuit in the communication apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure of the temperature detection circuit in the overheat protection circuit which concerns on the 1st Embodiment of this invention. It is a figure which shows the temperature characteristic of the temperature detection element in the overheat protection circuit which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure of the amplifier circuit in the overheat protection circuit which concerns on the 1st Embodiment of this invention. It is a figure which shows the output characteristic of the amplifier circuit in the overheat protection circuit which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure of the comparison circuit in the overheat protection circuit which concerns on the 1st Embodiment of this invention. It is a figure which shows the production | generation of the reference voltage by the comparison circuit which concerns on the 1st Embodiment of invention. It is a figure which shows the production | generation of the reference voltage by the comparison circuit which concerns on the 1st Embodiment of this invention. It is a figure which shows the relationship between ambient temperature and a power supply control signal in the overheat protection circuit which concerns on the 1st Embodiment of this invention. It is a figure which shows the fluctuation | variation of the temperature which the fluctuation | variation of the amplification voltage in the overheat protection circuit which concerns on the 1st Embodiment of this invention, and a power supply control signal switches. In the overheat protection circuit which concerns on the 1st Embodiment of this invention, it is a figure which shows the structure of the comparison circuit which provided the correction circuit. It is a figure which shows the structure of the correction circuit in the overheat protection circuit which concerns on the 1st Embodiment of this invention. It is a figure which shows the correction effect by the correction circuit in the overheat protection circuit which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure of the amplifier circuit in the overheat protection circuit which concerns on the 2nd Embodiment of this invention. It is a figure which shows the output characteristic of the amplifier circuit in the overheat protection circuit which concerns on the 2nd Embodiment of this invention. It is a figure which shows the effect by the fluctuation | variation of the amplification voltage in the overheat protection circuit which concerns on the 2nd Embodiment of this invention, and the gain switching of an amplification circuit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<First Embodiment>
[Configuration and basic operation]
FIG. 1 is a diagram showing a configuration of a communication apparatus according to the first embodiment of the present invention.

  Referring to FIG. 1, a communication device 201 is an embedded device equipped with a CPU (Central Processing Unit). The communication device 201 includes a temperature detection circuit 11, a power supply control circuit 12, a system power supply (power supply circuit) 13, a CPU (arithmetic processing unit) 14, a PHY processing unit 15, and a VOIP (Voice Over IP) processing unit 16. And a peripheral circuit 17.

  The system power supply 13 converts an original power supply voltage Vcc of, for example, 12V supplied from the outside of the communication apparatus 201 into an operation power supply voltage VP such as 3.3V, and supplies it to each circuit in the communication apparatus 201.

  The CPU 14, the PHY processing unit 15, the VOIP processing unit 16, and the peripheral circuit 17 operate with the operating power supply voltage VP supplied from the system power supply 13.

  The CPU 14 is connected to the peripheral circuit 17 and controls each unit in the communication device 201.

  The PHY processing unit 15 performs physical layer signal processing according to a predetermined communication protocol on the communication signal received from the network, generates communication data, and outputs the communication data to the CPU 14.

  The CPU 14 outputs the communication data received from the PHY processing unit 15 to the VOIP processing unit 16.

  The VOIP processing unit 16 generates an audio signal from the communication data received from the CPU 14 and outputs the audio signal to a telephone or the like outside the communication device 201.

  In addition, the VOIP processing unit 16 generates communication data from a voice signal received from a telephone or the like outside the communication device 201 and outputs the communication data to the CPU 14.

  The CPU 14 outputs the communication data received from the VOIP processing unit 16 to the PHY processing unit 15.

  The PHY processing unit 15 performs physical layer signal processing on the communication data received from the CPU 14 in a predetermined communication protocol, generates a communication signal, and outputs the communication signal to the network.

  The temperature detection circuit 11 is disposed at a location where the heat generation amount is large in the communication device 201, operates by receiving the original power supply voltage Vcc, and detects the ambient temperature.

  The power supply control circuit 12 operates in response to the original power supply voltage Vcc, generates a power supply control signal PSEN based on the temperature detection result by the temperature detection circuit 11, and outputs it to the system power supply 13.

  System power supply 13 stops generating and outputting operation power supply voltage VP when power supply control signal PSEN received from power supply control circuit 12 becomes a logic high level, for example.

  FIG. 2 is a diagram illustrating a configuration of an overheat protection circuit in the communication device according to the first embodiment of the present invention.

  Referring to FIG. 2, overheat protection circuit 101 includes a temperature detection circuit 11 and a power supply control circuit 12. The power supply control circuit 12 includes an amplifier circuit 21 and a comparison circuit 22.

  The temperature detection circuit 11 detects the ambient temperature and outputs a detection voltage TDET having a level corresponding to the detected temperature.

  The amplifier circuit 21 amplifies the detection voltage TDET received from the temperature detection circuit 11 and outputs the amplified detection voltage TDET as the amplified voltage VAMP.

  Comparison circuit 22 generates power supply control signal PSEN based on amplified voltage VAMP received from amplifier circuit 21.

  FIG. 3 is a diagram showing a configuration of the temperature detection circuit in the overheat protection circuit according to the first embodiment of the present invention.

  Referring to FIG. 3, temperature detection circuit 11 includes a temperature detection element 71 and a resistor 72.

  Resistor 72 has a first end connected to the original power supply node to which original power supply voltage Vcc is supplied, and a second end. Temperature detecting element 71 is, for example, a diode, and has an anode connected to the second end of resistor 72 and a cathode connected to a ground node to which a ground voltage is supplied.

  The voltage at the connection node between the temperature detection element 71 and the resistor 72 is output as the detection voltage TDET.

  FIG. 4 is a diagram illustrating temperature characteristics of the temperature detection element in the overheat protection circuit according to the first embodiment of the present invention.

  Referring to FIG. 4, the diode that is the temperature detecting element 71 has a characteristic that the forward voltage VF decreases as the ambient temperature increases. In the circuit shown in FIG. 3, the forward voltage VF is the detection voltage TDET. The temperature characteristic of the forward voltage VF of this diode is, for example, -2 mV / ° C.

  FIG. 5 is a diagram showing a configuration of an amplifier circuit in the overheat protection circuit according to the first embodiment of the present invention.

  Referring to FIG. 5, amplifier circuit 21 includes a differential amplifier circuit 31 and resistors 32 to 35. The differential amplifier circuit 31 includes an inverting input terminal connected to the first end of the resistor 32 and the first end of the resistor 33, and a non-inverting input terminal connected to the first end of the resistor 34 and the first end of the resistor 35. And an output terminal connected to the second end of the resistor 33. Resistor 32 receives detection voltage TDET at the second end. The resistor 34 receives the amplified reference voltage AVref at the second end. A second end of the resistor 35 is connected to the ground node.

  The differential amplifier circuit 31 operates in response to the original power supply voltage Vcc, amplifies the difference between the detection voltage TDET and the amplified reference voltage AVref, and outputs the amplified voltage as the amplified voltage VAMP.

  FIG. 6 is a diagram showing output characteristics of the amplifier circuit in the overheat protection circuit according to the first embodiment of the present invention.

  Referring to FIG. 6, amplifier circuit 21 has a characteristic that the level of amplified voltage VAMP increases when the ambient temperature increases and the level of detection voltage TDET decreases.

  As described above, since the amplifier circuit 21 is provided in the overheat protection circuit 101, the level range of the output voltage to the comparison circuit 22 can be expanded even when the level change of the detection voltage TDET with respect to the temperature change is small. Power control can be performed.

  Referring to FIG. 2 again, the comparison circuit 22 is a hysteresis comparator having hysteresis characteristics. Specifically, when the level of the amplified voltage VAMP becomes higher than the level of the reference voltage VT1, the comparison circuit 22 makes the level of the amplified voltage VAMP lower than the level of the reference voltage VT2 that is lower than the reference voltage VT1. Until this time, a power control signal PSEN of a logic high level for turning off the system power supply 13 is output. When the level of the amplified voltage VAMP becomes lower than the level of the reference voltage VT2, the comparison circuit 22 is used to turn on the system power supply 13 until the level of the amplified voltage VAMP becomes higher than the level of the reference voltage VT1. A logic low level power supply control signal PSEN is output.

  FIG. 7 is a diagram showing a configuration of a comparison circuit in the overheat protection circuit according to the first embodiment of the present invention.

  Referring to FIG. 7, comparison circuit 22 includes resistors 41 and 42 and a comparator 43.

  The comparator 43 has an inverting input terminal that receives a comparison reference voltage (original reference voltage) CVref, a non-inverting input terminal connected to the first end of the resistor 41 and the first end of the resistor 42, and a second end of the resistor 42. And an output terminal connected thereto. The resistor 41 receives the amplified voltage VAMP at the second end.

  The comparator 43 operates in response to the original power supply voltage Vcc. The comparator 43 compares the comparison reference voltage CVref with the voltage Nref at the non-inverting input terminal. When the amplified voltage VAMP is larger than the voltage Nref, the comparator 43 outputs a logic high level signal as the power supply control signal PSEN, and the amplified voltage VAMP is When the voltage is smaller than the voltage Nref, a logic low level signal is output as the power supply control signal PSEN.

  FIG. 8 is a diagram illustrating generation of the reference voltage by the comparison circuit according to the first embodiment of the present invention.

  Referring to FIG. 8, when comparator 43 outputs a logic low level signal, in comparison circuit 22, resistor 41 and resistor 42 are connected in series, receive amplified voltage VAMP at one end, and ground at the other end. A voltage dividing circuit for receiving a voltage is formed. At this time, the voltage Nref at the connection node of the resistors 41 and 42 becomes the reference voltage VT1.

  FIG. 9 is a diagram illustrating generation of the reference voltage by the comparison circuit according to the first embodiment of the present invention.

  Referring to FIG. 9, when comparator 43 outputs a logic high level signal, in comparison circuit 22, resistor 41 and resistor 42 are connected in series, receive one source voltage Vcc at one end, and at the other end. A voltage dividing circuit for receiving the amplified voltage VAMP is formed. At this time, the voltage Nref at the connection node of the resistors 41 and 42 becomes the reference voltage VT2.

  That is, the comparison circuit 22 generates the reference voltage VT1 and the reference voltage VT2 based on the amplified voltage VAMP.

  FIG. 10 is a diagram showing the relationship between the ambient temperature and the power supply control signal in the overheat protection circuit according to the first embodiment of the present invention.

  Referring to FIG. 10, first, when the ambient temperature is within a predetermined operating temperature range of communication device 201, comparison circuit 22 outputs a power control signal PSEN at a logic low level. At this time, system power supply 13 generates and outputs operating power supply voltage VP.

  When the ambient temperature rises and exceeds T1, the amplified voltage VAMP exceeds the reference voltage VT1. Then, the comparison circuit 22 outputs a power control signal PSEN having a logic high level. As a result, the system power supply 13 stops generating and outputting the operating power supply voltage VP.

  Thereafter, even if the ambient temperature falls and falls below T1, the comparison circuit 22 maintains the power supply control signal PSEN at a logic high level until the ambient temperature falls below T2. Therefore, the system power supply 13 maintains a state where generation and output of the operation power supply voltage VP are stopped.

  When the ambient temperature further decreases and falls below T2, the amplified voltage VAMP becomes less than the reference voltage VT2. Then, the comparison circuit 22 outputs a power control signal PSEN having a logic low level. As a result, the system power supply 13 resumes the generation and output of the operating power supply voltage VP.

  Here, in the overheat protection circuit 101, the temperature T2 when the level of the amplified voltage VAMP becomes equal to the level of the reference voltage VT2 is set outside the predetermined operating temperature range of the communication device 201.

  Specifically, if the use temperature range of the communication device 201 is, for example, 0 ° C. or more and 60 ° C. or less, T1 is set to a temperature higher than 60 ° C., for example, and T2 is set to a temperature lower than 0 ° C., for example. This setting can be easily set by adjusting the resistance value of each resistor in the amplifier circuit 21 or the comparison circuit 22, for example.

  With such a configuration, once the power supply control signal PSEN becomes a logic high level, the power supply control signal PSEN does not return to a logic low level unless a person operates the communication device 201, and the operation power supply voltage VP is output from the power supply control circuit 12. Will not be. Thereby, it can prevent that the power supply of the communication apparatus 201 repeats on / off in the vicinity of the boundary of the use temperature range of the communication apparatus 201. Further, the operation power supply voltage VP of the communication device 201 can be controlled without performing power control by the CPU or separately from the power control by the CPU.

  FIG. 11 is a diagram showing fluctuations in the amplification voltage and fluctuations in temperature at which the power supply control signal is switched in the overheat protection circuit according to the first embodiment of the present invention.

  The original power supply voltage Vcc varies within a certain range according to the state of the power supply that generates the original power supply voltage Vcc.

  Referring to FIG. 11, for example, when generating amplified reference voltage AVref of amplifier circuit 21 from original power supply voltage Vcc, amplified reference voltage AVref varies according to original power supply voltage Vcc, and the output of amplifier circuit 21 is thereby generated. The amplified voltage VAMP, which is a voltage, varies. For this reason, the temperature at which the logic level of the power supply control signal PSEN that is the output voltage of the comparison circuit 22 changes also varies according to the original power supply voltage Vcc. Further, when the comparison reference voltage CVref of the comparison circuit 22 is generated from the original power supply voltage Vcc, although not shown, since the comparison reference voltage CVref varies according to the original power supply voltage Vcc, the power supply control signal PSEN The temperature at which the logic level switches varies according to the amplified voltage VAMP and the comparison reference voltage CVref.

  Here, it is complicated and difficult to adjust the values of the amplification reference voltage AVref and the comparison reference voltage CVref in order to keep the operating point of the overheat protection circuit 101 constant with respect to the change of the original power supply voltage Vcc.

  Further, for example, a configuration using a constant voltage circuit to generate the amplified reference voltage AVref and the comparison reference voltage CVref can be considered. However, in such a configuration, it is necessary to keep each reference voltage constant over the entire range of the operating temperature of the communication device 201, which increases the manufacturing cost of the constant voltage circuit. In particular, since the amplified reference voltage AVref is lower in level than the comparison reference voltage CVref, the manufacturing cost of the constant voltage circuit for the amplified reference voltage AVref becomes higher.

  Therefore, the overheat protection circuit 101 is provided with a correction circuit 71. The correction circuit 71 is included in the comparison circuit 22, for example.

  FIG. 12 is a diagram showing a configuration of a comparison circuit provided with a correction circuit in the overheat protection circuit according to the first embodiment of the present invention.

  Referring to FIG. 12, correction circuit 71 generates comparison reference voltage CVref from original power supply voltage Vcc, and also compares reference voltage CVref so as to cancel the level change of comparison reference voltage CVref due to the level change of original power supply voltage Vcc. Correct.

  Here, in the overheat protection circuit 101, as described above, the temperature T2 is set outside the operating temperature range of the communication device 101, so it is sufficient to consider only the level fluctuation of the original power supply voltage Vcc in the vicinity of the temperature T1. .

  Since the level fluctuation of the original power supply voltage Vcc is generally about several percent, the fluctuation of the original power supply voltage Vcc when the level of the original power supply voltage Vcc is, for example, around 12 V can be approximated by a straight line.

  The correction circuit 71 cancels the level change of the comparison reference voltage CVref due to the level change of the original power supply voltage Vcc when the original power supply voltage Vcc is near 12V and the level of the amplified voltage VAMP is substantially equal to the level of the reference voltage VT1. To do.

  In this way, the correction circuit 71 can be simplified because it is sufficient to cancel the level change of the original power supply voltage Vcc approximated by a straight line.

  FIG. 13 is a diagram showing a configuration of a correction circuit in the overheat protection circuit according to the first embodiment of the present invention.

  Referring to FIG. 13, correction circuit 71 includes a differential amplifier circuit 61, resistors 62 to 67, and a constant voltage circuit 68. The differential amplifier circuit 61 includes an inverting input terminal connected to the first end of the resistor 62 and the first end of the resistor 63, and a non-inverting input terminal connected to the first end of the resistor 64 and the first end of the resistor 65. And an output terminal connected to the second end of the resistor 63. The resistor 64 receives the output voltage of the constant voltage circuit 68 at the second end. A second end of resistor 65 is connected to the ground node.

  Resistor 66 and resistor 67 constitute a voltage dividing circuit, which divides original power supply voltage Vcc and outputs it to the second end of resistor 62.

  The differential amplifier circuit 61 operates in response to the original power supply voltage Vcc, amplifies the difference between the output voltage of the voltage dividing circuit composed of the resistors 66 and 67 and the output voltage of the constant voltage circuit 68, and compares the amplified voltages. Output as the reference voltage CVref.

  FIG. 14 is a diagram showing a correction effect by the correction circuit in the overheat protection circuit according to the first embodiment of the present invention.

  Referring to FIG. 14, in overheat protection circuit 101, comparison reference voltage CVref changes so as to cancel the level change of original power supply voltage Vcc in the vicinity of temperature T1, that is, in the state where amplified voltage VAMP is in the vicinity of reference voltage VT1. As a result, it is possible to prevent the temperature at which the logic level of the power control signal PSEN switches from fluctuating and to stabilize the control of the system power supply 13 by the power control signal PSEN.

  In addition, the reference voltage of the differential amplifier circuit 61 in the correction circuit 71, that is, the output voltage of the constant voltage circuit 68 is, for example, several V higher than the constant voltage circuit for generating the amplified reference voltage Aref in the amplifier circuit 21. . For this reason, the constant voltage circuit 68 is not required to have high accuracy, and the manufacturing cost can be reduced. Further, it is sufficient to provide one constant voltage circuit for the correction circuit 71, and the configuration can be simplified.

  The correction circuit 71 does not cancel the level change of the original power supply voltage Vcc near the temperature T2. For this reason, it is preferable to set the reference voltage VT2 as follows. That is, after the power supply control signal PSEN becomes a logic high level and the power supply control circuit 12 stops operating, the power supply control signal PSEN is switched to a logic low level due to the level fluctuation of the original power supply voltage Vcc, and the power supply control circuit 12 is erroneously changed. In order not to resume the operation, the reference voltage VT2 is set to a value having a sufficient margin with respect to the level fluctuation of the original power supply voltage Vcc. The setting of the reference voltage VT2 can be easily performed by adjusting the resistance value of each resistor in the amplifier circuit 21 or the comparison circuit 22, for example.

  By the way, in the configuration in which the CPU is interrupted by the output signal of the temperature sensor and the CPU performs overheat protection control such as turning off the power, when the CPU is out of control, the overheat protection control is not executed and the overheat state continues. There is a possibility. Also, an abnormality that causes the device to become overheated, such as a blanket over the device installed in the home, is often not resolved without human intervention. If the cause of overheating has not been eliminated, the overheating state may be repeated even if the temperature in the apparatus once decreases due to overheating protection control.

  In contrast, in the overheat protection circuit according to the first embodiment of the present invention, the temperature detection circuit 11 detects the temperature and outputs a detection voltage TDET having a level corresponding to the detected temperature. When the level of the amplified voltage VAMP obtained by amplifying the detection voltage TDET becomes larger than the level of the reference voltage VT1, the comparison circuit 22 makes the level of the amplified voltage VAMP smaller than the level of the reference voltage VT2 that is lower than the reference voltage VT1. Until that time, the power supply control signal PSEN for turning off the system power supply 13 is output. The temperature at which the level of the amplified voltage VAMP becomes equal to the level of the reference voltage VT2 is outside the predetermined use temperature range of the communication device 201.

  That is, the comparison circuit 22 has hysteresis, and sets the threshold temperature on the low temperature side, that is, the return temperature T2 of the power supply control signal PSEN to the logic low level outside the operating temperature range of the communication device 201. With such a configuration, once the power supply control signal PSEN becomes a logic high level, the operation power supply voltage VP can be prevented from returning unless a human intervenes. Therefore, communication is performed near the boundary of the operating temperature range of the communication device 201. It is possible to prevent the power supply of the apparatus 201 from being repeatedly turned on and off. Further, the operation power supply voltage VP of the communication device 201 can be controlled without performing power control by the CPU or separately from the power control by the CPU.

  Therefore, in the overheat protection circuit according to the first embodiment of the present invention, the overheat protection of the apparatus and the cause of overheat can be more reliably performed.

  In the overheat protection circuit according to the first embodiment of the present invention, the comparison circuit 22 generates the reference voltage VT1 and the reference voltage VT2 based on the amplified voltage VAMP. Then, the correction circuit 71 corrects the comparison reference voltage CVref so as to cancel the level change of the comparison reference voltage CVref due to the level change of the original power supply voltage Vcc.

  With such a configuration, it is possible to suppress a change in temperature at which the logic level of the power supply control signal PSEN switches, and to stabilize the control of the system power supply 13 by the power supply control signal PSEN.

  In the overheat protection circuit according to the first embodiment of the present invention, the correction circuit 71 cancels the level change of the comparison reference voltage CVref when the level of the amplified voltage VAMP is substantially equal to the level of the reference voltage VT1. To do.

  When trying to correct the original reference voltage with respect to fluctuations in the power supply, the voltage value of the original reference voltage follows a complicated locus, and the circuit for realizing this correction also becomes complicated. However, the fluctuation range of the original power supply voltage is normally determined by the specification to be about several percent with respect to the target voltage value. If the fluctuation is at most several percent, the original reference voltage corrected within the range can be approximated by a straight line. That is, the correction circuit 71 can be simplified because it is sufficient to cancel the fluctuation of the original power supply voltage Vcc approximated by a straight line.

  In the overheat protection circuit according to the first embodiment of the present invention, the voltage dividing circuit including the resistor 66 and the resistor 67 in the correction circuit 71 divides the original power supply voltage Vcc. The constant voltage circuit 68 outputs a constant voltage. Then, the differential amplifier circuit 61 amplifies the difference between the voltage divided by the voltage dividing circuit and the output voltage of the constant voltage circuit 68, and outputs it as a comparison reference voltage CVref.

  The original reference voltage correction circuit can be easily configured with a constant voltage source and a differential amplifier circuit. Generally, a high voltage constant voltage source is not stable and has poor accuracy. On the other hand, the output voltage of the constant voltage source used in the correction circuit is amplified. With such a configuration, a constant voltage source with a low voltage can be used, so that power consumption can be kept low with an inexpensive circuit configuration.

  In the overheat protection circuit according to the first embodiment of the present invention, the amplifier circuit 21 outputs the amplified voltage VAMP obtained by amplifying the difference between the detection voltage TDET and the amplified reference voltage AVref to the comparison circuit 22.

  As described above, the differential amplification of the detection voltage TDET can cancel the offset of the input voltage of the comparator 43 in the comparison circuit 22, so that the level range of the input voltage of the comparator 43 can be expanded. Thereby, the accuracy of power supply control based on temperature detection can be improved as compared with a configuration in which the amplification circuit 21 performs simple amplification instead of differential amplification.

  In the overheat protection circuit according to the first embodiment of the present invention, the amplifier circuit 21 is provided. However, the present invention is not limited to this. When the level change of the detection voltage TDET with respect to the temperature change is sufficiently large, the overheat protection circuit 101 may be configured not to include an amplifier circuit.

  In the overheat protection circuit according to the first embodiment of the present invention, the amplifier circuit 21 is configured to invert the slope of the detection voltage TDET. However, the present invention is not limited to this. The amplifier circuit 21 may output the amplified voltage VAMP from the amplifier circuit 21 without inverting the slope of the detection voltage TDET, for example, while maintaining a negative slope. In this case, the subsequent-stage comparator 43 is an inverting type.

  Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Second Embodiment>
The present embodiment relates to an overheat protection circuit in which a countermeasure against level fluctuation of the original power supply voltage Vcc, which is different from the overheat protection circuit according to the first embodiment, is taken. The contents other than those described below are the same as those of the overheat protection circuit according to the first embodiment.

  FIG. 15 is a diagram showing a configuration of an amplifier circuit in the overheat protection circuit according to the second embodiment of the present invention.

  Referring to FIG. 15, overheat protection circuit 102 includes an amplifier circuit 23 instead of amplifier circuit 21 as compared with the overheat protection circuit according to the first embodiment of the present invention.

  The amplifier circuit 23 includes a differential amplifier circuit 51, resistors R1 to R4, diodes D1 and D2, and Zener diodes ZD1 and ZD2.

  The differential amplifier circuit 51 includes an inverting input terminal connected to the first end of the resistor R1, the first end of the resistor R2, the first end of the resistor R4, and the cathode of the diode D1, and a non-inverting input terminal that receives the detection voltage TDET. And an output terminal connected to the second end of the resistor R2 and the first end of the resistor R3. Zener diode ZD1 has an anode connected to the anode of diode D1 and a cathode connected to the second end of resistor R3. Zener diode ZD2 has an anode connected to the anode of diode D2 and a cathode connected to the second end of resistor R4. The second end of resistor R1 and the cathode of diode D2 are connected to the ground node. The differential amplifier circuit 51 operates in response to the original power supply voltage Vcc.

  FIG. 16 is a diagram illustrating output characteristics of the amplifier circuit in the overheat protection circuit according to the second embodiment of the present invention.

  Referring to FIG. 16, amplification circuit 23 switches to a high gain when amplification voltage VAMP rises and becomes substantially equal to the level of reference voltage VT1 corresponding to temperature T1.

  The amplifier circuit 23 switches to a high gain when the amplified voltage VAMP drops and becomes substantially equal to the level of the reference voltage VT2 corresponding to the temperature T2.

  FIG. 16 shows the relationship between the detection voltage TDET and the amplified voltage VAMP. Specifically, the relationship between the detection voltage TDET and the amplified voltage VAMP is expressed by a linear function. When the detection voltage TDET is less than the voltage V1, the slope is (1 + R2 / R1), and the detection voltage TDET is equal to or higher than the voltage V1. The slope is (1+ (R2 || R3) / R1) when it is less than V2, and the slope is (1+ (R2 || R3) / (R1 || R4)) when the detection voltage TDET is equal to or higher than the voltage V2. It becomes. Here, “A || B” indicates a combined resistance of the resistors A and B connected in parallel.

Further, assuming that the voltage across the diode D1 is VD1, the voltage across the diode D2 is VD2, the voltage across the Zener diode ZD1 is VZD1, and the voltage across the Zener diode ZD2 is VZD2, the voltages V1 and V2 are expressed by the following equations: It is represented by
V1 = R1 / R2 × (VD1 + VZD1)
V2 = VD2 + VZD2

  R2 is sufficiently larger than R3, and R1 is sufficiently larger than R4.

  FIG. 17 is a diagram illustrating the effect of fluctuations in amplification voltage and gain switching of the amplifier circuit in the overheat protection circuit according to the second embodiment of the present invention.

  Referring to FIG. 17, when the ambient temperature rises due to the characteristics of the amplifier circuit 23 as shown in FIG. 16 and near the temperature T1, that is, the amplified voltage VAMP is near the reference voltage VT1, the amplified voltage VAMP with respect to the change in ambient temperature When the change becomes steep and the ambient temperature decreases and the vicinity of the temperature T2, that is, the amplified voltage VAMP becomes near the reference voltage VT2, the change of the amplified voltage VAMP with respect to the change of the ambient temperature becomes steep.

  In this manner, in the amplifier circuit 23, the change in the output voltage, that is, the amplified voltage VAMP is steeply set with respect to the change in the input voltage, that is, the detection voltage TDET. VAMP fluctuations can be suppressed.

  That is, it is possible to prevent the temperature at which the logic level of the power supply control signal PSEN switches from fluctuating and to stabilize the control of the system power supply 13 by the power supply control signal PSEN.

  In addition, since the fluctuation of the amplified voltage VAMP due to the fluctuation of the level of the original power supply voltage Vcc in the vicinity of the temperature T2 can be suppressed, the setting of the temperature T2 can be made as compared with the overheat protection circuit according to the first embodiment of the present invention. The degree of freedom can be increased.

  However, in the overheat protection circuit according to the first embodiment of the present invention, compared with the overheat protection circuit according to the second embodiment of the present invention, the characteristic of the amplifier circuit 21, that is, the amplified voltage VAMP with respect to a change in ambient temperature. It is not necessary to make the change of the steep, and the circuit configuration becomes simple.

  Since other configurations and operations are the same as those of the overheat protection circuit according to the first embodiment, detailed description thereof will not be repeated here.

  In the overheat protection circuit according to the second embodiment of the present invention, the amplifier circuit 23 uses a differential amplifier circuit. However, the present invention is not limited to this. A configuration using an amplifier circuit instead of the differential amplifier circuit may be used.

  The above embodiment should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

11 Temperature Detection Circuit 12 Power Supply Control Circuit 13 System Power Supply (Power Supply Circuit)
14 CPU (arithmetic processing unit)
DESCRIPTION OF SYMBOLS 15 PHY process part 16 VOIP process part 17 Peripheral circuit 21,23 Amplification circuit 22 Comparison circuit 31 Differential amplification circuit 32-35 Resistance 41,42 Resistance 43 Comparator 51 Differential amplification circuit 61 Differential amplification circuit 62-67 Resistance 68 Constant Voltage circuit 71 Temperature detection element 72 Resistance 101, 102 Overheat protection circuit 201 Communication device D1, D2 Diode R1-R4 Resistance ZD1, ZD2 Zener diode

Claims (8)

An overheat protection circuit used in a device including a power supply circuit for generating an operation power supply voltage from an original power supply voltage,
A temperature detection circuit that operates by receiving the original power supply voltage, detects a temperature, and outputs a detection voltage having a level corresponding to the detection temperature;
When receiving the original power supply voltage and operating, and when the level of the detection voltage becomes higher than the level of the first reference voltage, the second level of the detection voltage is lower than the level of the first reference voltage. A comparison circuit for outputting a control signal for outputting a control signal for turning off the power supply circuit until it becomes smaller than a level of a reference voltage;
The overheat protection circuit, wherein the temperature when the level of the detection voltage becomes equal to the level of the second reference voltage is outside a predetermined operating temperature range of the device. The comparison circuit generates the first reference voltage and the second reference voltage based on the detection voltage,
The overheat protection circuit further includes:
The overheat protection circuit according to claim 1, further comprising: a correction circuit for correcting the original reference voltage so as to cancel the level change of the original reference voltage due to the level change of the original power supply voltage.   The overheat protection circuit according to claim 2, wherein the correction circuit cancels a level change of the original reference voltage in a state where the level of the detection voltage is substantially equal to the level of the first reference voltage. The correction circuit includes:
A voltage dividing circuit for dividing the original power supply voltage;
A constant voltage circuit for outputting a constant voltage;
4. The differential amplifier circuit for amplifying a difference between the voltage divided by the voltage dividing circuit and the output voltage of the constant voltage circuit and outputting the amplified voltage as the original reference voltage. The overheat protection circuit described. The overheat protection circuit further includes:
An amplification circuit for amplifying the detection voltage and outputting the amplified voltage to the comparison circuit;
2. The overheat protection circuit according to claim 1, wherein the amplification circuit switches to a high gain when the level of the detection voltage after amplification rises and becomes substantially equal to the level of the first reference voltage. 3.   The overheat protection circuit according to claim 5, wherein the amplification circuit switches to a high gain when the level of the detection voltage after amplification decreases and becomes substantially equal to the level of the second reference voltage. The overheat protection circuit further includes:
A differential amplification circuit for outputting a differential amplification voltage obtained by amplifying the difference between the detection voltage and the amplification reference voltage to the comparison circuit;
When the level of the differential amplification voltage is higher than the level of the first reference voltage, the comparison circuit has a second reference whose level of the differential amplification voltage is lower than that of the first reference voltage. A control signal for turning off the power supply circuit is output until the voltage level becomes lower than the voltage level. When the level of the differential amplification voltage becomes lower than the level of the second reference voltage, the differential amplification is performed. The overheat protection circuit according to any one of claims 1 to 6, wherein a control signal for turning on the power supply circuit is output until a voltage level becomes higher than a level of the first reference voltage. A power supply circuit for generating an operating power supply voltage from the original power supply voltage;
An arithmetic processing unit that operates in response to the operating power supply voltage;
A communication device comprising an overheat protection circuit,
The overheat protection circuit is
A temperature detection circuit that operates by receiving the original power supply voltage, detects a temperature, and outputs a detection voltage having a level corresponding to the detection temperature;
When receiving the original power supply voltage and operating, and when the level of the detection voltage becomes higher than the level of the first reference voltage, the second level of the detection voltage is lower than the level of the first reference voltage. A comparison circuit for outputting a control signal for turning off the power supply circuit until it becomes lower than a reference voltage level,
The communication device, wherein the temperature when the level of the detection voltage becomes equal to the level of the second reference voltage is outside a predetermined operating temperature range of the communication device.

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