JP2007288995A - Device for detecting disconnection from power source and device for protecting electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To immediately detect that a commercial AC power supply is not connected. <P>SOLUTION: A capacitor 24 is connected to both ends of an electrical outlet 10 which is connected to or disconnected from the commercial AC power supply. The both ends of the capacitor 24 are connected between input terminals 8IN-1, 8IN-2 of a DC power supply circuit 8. A light emitting diode 16L of a photocoupler 16 is connected between the both ends of the capacitor 24 via a high pass filter 21. When the electrical outlet 10 is disconnected from the commercial AC power source, the high pass filter 21 rapidly intercepts a current discharged from the capacitor 24, and rapidly stops the light emitting diode 16L emitting light. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power supply non-connection detection device that detects that an electronic device has changed from a connection state of a commercial AC power supply to a non-connection state, and a protection device for an electronic device using the same.

  In electronic devices, commercial AC power is often converted to DC by an AC-DC converter and supplied to a circuit. A smoothing capacitor may be used for the AC-DC converter, and even after the supply of commercial AC power to the AC-DC converter is stopped, the power supply in the circuit of the electronic device gradually increases due to the discharge from the smoothing capacitor. The circuit operates in an unstable manner when it drops. In order to improve this point, for example, in the technique disclosed in Patent Document 1, in the switching power supply, when the voltage across the smoothing capacitor is compared with the reference voltage, the voltage across the smoothing capacitor drops below the reference voltage. The starting circuit of the switching power supply connected between both ends of the smoothing capacitor is stopped.

JP 2001-309653 A

  However, with the technique of Patent Document 1, the switching power supply cannot be stopped until the voltage of the smoothing capacitor drops below the reference voltage. In particular, when a switching power supply is used, a noise removing capacitor may be connected to the input side of the switching power supply. In this case, the voltage of the smoothing capacitor does not become lower than the reference voltage unless the noise removing capacitor is sufficiently discharged. Therefore, the switching power supply does not stop unless a considerable time elapses after the commercial AC power supply is disconnected.

  An object of the present invention is to provide a power supply disconnection detection device that can immediately detect disconnection when a commercial AC power supply is disconnected, and to provide a protection device using the detection device. With the goal.

  The detection device of one embodiment of the present invention includes a pair of AC power input terminals that are connected to or disconnected from a commercial AC power supply. This AC power supply input terminal can be connected, for example. An AC-DC conversion means is connected between the AC power supply input terminals. A first capacitor is connected between the AC power supply input terminals. The first capacitor is for noise removal. A series circuit of the detection means and the filter is connected in parallel with the first capacitor. The detection means generates a detection signal in the disconnected state. The filter is configured to pass a frequency equal to or higher than the frequency of the commercial AC power supply.

  In the detection apparatus configured as described above, when a commercial AC power supply is connected to the AC power supply input terminal, the commercial AC power supply is connected to the AC-DC conversion means, and a DC output is generated. At this time, the first capacitor is charged and discharged. When the commercial AC power supply is disconnected from the power input terminal, a discharge current tends to flow from the first capacitor toward the detection means, but the frequency is lower than the frequency of the commercial AC power supply. Therefore, the discharge current that is about to flow to the detection means is interrupted by the filter connected in series with the detection means, and the detection of power disconnection by the detection means is quickly performed.

  The AC-DC conversion means can be a switching power supply. As the switching power supply, for example, a rectifying / smoothing means for rectifying and smoothing a commercial AC power supply voltage and a smoothing voltage from the rectifying / smoothing means are switched by the switching means, transformed by a transformer, and then rectified and smoothed by the rectifying / smoothing means. Can be. In such a configuration, the first capacitor is often used for noise removal.

  The filter can be a high-pass filter in which a current limiting resistor means to the detecting means and a second capacitor are connected in series. If comprised in this way, a high-pass filter can be comprised using the current limiting resistance means for a detection means, and reduction of cost can be aimed at.

  Further, the resistance means includes a plurality of parallel resistance circuits connected in series, and at least one of the parallel resistance circuits is configured to be able to replace a resistor constituting the circuit and to be short-circuited. Has been. For example, a chip resistor can be used as the resistor.

  With this configuration, by connecting a plurality of parallel resistance circuits in series and appropriately selecting the value, even when any one of commercial AC voltages having different voltages is supplied, the current flowing through the detection means can be reduced. Limiting to a predetermined value and setting the cut frequency of the high-pass filter to an appropriate value can be easily performed.

  The detection means has an insulated primary side and secondary side, the primary side is connected between the two input terminals, and the detection signal is generated on the secondary side. As the detection means, for example, one using a photocoupler or a transformer can be used. If comprised in this way, a detection signal can be insulated from the commercial AC power supply side.

  An electronic device protection device according to one embodiment of the present invention is such that the electronic circuit is connected to the output side of the AC-DC conversion means in the power supply disconnection detecting device described above. Furthermore, protection means for protecting the electronic circuit in response to generation of the detection signal is provided. With this configuration, when the commercial AC power supply is disconnected, the protection means can be operated immediately and the electronic circuit can be protected.

  Further, the AC-DC converting means can gradually reduce the output voltage from the time when it is in the disconnected state. In this case, the protection means is operated by the AC-DC conversion means. If comprised in this way, while a protection means is operate | moving with the output voltage of an AC-DC conversion means, a detection signal is supplied from a detection means, and a protection means can be operated. Therefore, it is not necessary to provide a special power source dedicated to the protection means.

  The electronic circuit can be a digital amplifier. In this case, the protection means is an open / close contact connected between the output side of the digital amplifier and the speaker, and is opened according to the generation of the detection signal.

  If comprised in this way, it can prevent instantaneously that the abnormal sound which may arise by a power supply disconnection is output from a speaker.

  According to another aspect of the present invention, there is provided an electronic device protection apparatus, wherein the AC-DC conversion unit includes a first rectification unit that rectifies the commercial AC power source, and the first rectification unit. Smoothing means for smoothing the output, switching means for switching the smoothed output, control means for controlling the switching means, and second rectifying means for rectifying the output of the switching means. Stop means for stopping the control means in response to the generation of the detection means is provided. As the control means, for example, the output of the second rectifying means, for example, the output current and the output voltage are detected, an error between the detected value and the reference value is obtained, and the switching means is controlled so that this error becomes zero. In particular, one using PWM control for switching control can be used. In this case, the oscillation circuit used for PWM control can be stopped. In addition, the oscillation can be stopped in the same manner even in an oscillation circuit of a self-excited oscillation type non-feedback type switching power supply.

  With this configuration, when the commercial AC power supply is disconnected, it is possible to stop the output of the power supply from the AC-DC converting means, and in particular, the capacity of the smoothing means is large and smoothing over a relatively long time. Even when the output is maintained, the power output from the AC-DC converter can be stopped immediately.

  According to another aspect of the present invention, there is provided an electronic device protection apparatus comprising the first and second detection means in which the detection means simultaneously generates a detection signal in the power supply disconnection detection apparatus described above. The first and second detection means can be connected in series or in parallel. The AC-DC converting means includes a first rectifying means for rectifying the commercial AC power supply, a smoothing means for smoothing the output of the first rectifying means, a switching means for switching the smoothed output, and the switching means. And a second rectifying means for rectifying the output of the switching means. The control means can be as described above. An electronic circuit is connected to the output side of the AC-DC converting means. The electronic circuit can be an amplifying means, such as the digital amplifier circuit described above. A protection means protects the electronic circuit in response to the generation of the detection signal of the first detection means. The stop means stops the control means in response to the occurrence of the second detection means. The stop means includes a delay means so that the protection means operates later in response to the generation of the first detection signal and the stop means operates in response to the generation of the second detection signal. . When both the stop means and the protection means have the delay means, the delay time of the stop means is set longer than the delay time of the protection means. If comprised in this way, after stopping an electronic circuit, an AC-DC conversion means can be stopped.

  As described above, according to the present invention, when the commercial AC power supply is disconnected, it can be immediately detected that the commercial AC power supply is disconnected. Further, in accordance with this detection, appropriate protection can be started for the electronic circuit and the AC-DC converting means.

  In the first embodiment of the present invention, the present invention is implemented in a digital amplifier. The digital amplifier has an electronic circuit, for example, a digital amplifier circuit 2 as shown in FIG. The digital amplifier circuit 2 converts an analog input signal into a pulse width modulation signal or a pulse density signal (hereinafter referred to as a digital signal) using a carrier signal in a pulse width modulator or a pulse density modulator, and this digital signal is converted into a digital signal. The power is amplified by an amplifier using a class D amplification method. The amplified digital signal is converted into an output analog signal by removing the carrier signal component contained in the digital signal by the LC output filter 4 including the inductor 4L and the capacitor 4c.

  This output analog signal is supplied to a plurality of speakers 6 connected in parallel. These speakers are of high impedance type and are arranged at different positions in a building or a store. The output analog signal is supplied to the closed switch 7 connected in series to the speaker 6. Of the switches 7, those to which a control signal is supplied from a control circuit (not shown) are often closed, and the volume is often adjusted by an attenuator (attenuator) at the speaker installation destination. That is, the load of the digital amplifier circuit 2 frequently changes.

  A DC voltage for operating the digital amplifier circuit 2 is generated by AC-DC conversion means, for example, a DC power supply circuit 8. The DC power supply circuit 8 has output terminals 8P and 8N, the output terminal 8P is connected to the positive power supply terminal 2P of the digital amplifier circuit 2, and the output terminal 8N and the negative power supply terminal 2N of the digital amplifier circuit 2 are set to a reference potential, for example Connected to ground potential.

  The DC power supply circuit 8 has two input terminals 8IN-1 and 8IN-2, which are connected or disconnected to a commercial AC power supply (not shown) via a commercial AC power supply input terminal, for example, the outlet 10. Put into a state. The commercial AC power source has, for example, an effective value of 100 V and a commercial AC frequency of 50 Hz or 60 Hz.

  The DC power supply circuit 8 is a switching power supply, for example, and rectifies the commercial AC voltage supplied to the input terminals 2IN-1 and 2IN-2 by a rectifier, for example, a full-wave rectifier circuit or a half-wave rectifier circuit. Is smoothed by a smoothing means such as a smoothing capacitor. This smoothed voltage is converted into a high frequency voltage by a switching circuit such as a chopper circuit or an inverter circuit, and supplied to the primary winding of the insulation transformer. The high frequency voltage induced in the secondary winding of the isolation transformer is rectified by an output side rectifying / smoothing means, for example, a rectifying diode, and smoothed by a smoothing reactor or a smoothing capacitor, and a DC voltage is generated between the two output terminals 8P and 8N. To do.

  The DC power supply circuit 8 can have a reference potential terminal 8R in addition to the output terminals 8P and 8N. In this case, the DC power supply circuit 8 is configured such that the output terminal 8P generates a positive voltage from the reference potential terminal 8R and the output terminal 8N generates a negative voltage from the reference potential terminal 8R. Note that a first capacitor, for example, a noise removing capacitor 24 is connected between both ends of the outlet 10, that is, between the input terminals 8IN-1 and 8IN-2 of the DC power supply circuit 8.

  An open / close contact, for example, a relay open / close contact 12 is disposed between the LC output filter 4 and the switch 7 of each speaker 6. The relay switching contact 12 is normally closed and is opened when a drive signal is supplied from the drive circuit 14. As will be described later, when the outlet 10 is disconnected from the commercial AC power source, the drive circuit 14 instantaneously opens the relay switching contact 12 and generates abnormal noise based on the fluctuation of the voltage supplied to the digital amplifier circuit 2. This is to prevent the occurrence of The relay switching contact 12 and the drive circuit 14 constitute a protection circuit, for example, an output side protection circuit.

  In order to operate the output side protection circuit, detection means, for example, a detection circuit 16 is provided. The detection circuit 16 has a primary side and a secondary side, both of which are insulated, and is composed of, for example, a photocoupler. That is, the detection circuit 16 has a light emitting element such as a light emitting diode 16L on the primary side and a light receiving element such as a phototransistor 16P on the secondary side. In a state where the outlet 10 is connected to a commercial AC power source, the light emitting diode 16L emits light, and the phototransistor 16P generates a light reception signal due to the light emission. When the outlet 10 is disconnected from the commercial power source, the light emitting diode 16L stops emitting light, and the phototransistor 16P does not generate a light reception signal. As a result, the comparison circuit 18 sends an energizing signal to the drive circuit 14, and the drive circuit 14 opens the contact 12. Note that 16I is a diode connected in reverse parallel to the light emitting diode 16L, and is used for supplying a commercial alternating current having a polarity opposite to the polarity in which the light emitting diode 16L is conducted.

  As the photocoupler, an AC input compatible type can be used. In this case, since the two light emitting diodes are connected in antiparallel, no additional circuit is required. When a standard type is used, a diode is connected in antiparallel to the light emitting diode as an additional circuit.

  The light emitting diode 16L is connected to the outlet 10 through a filter means, for example, a high-pass filter 21. The high pass filter 21 is constituted by a resistance means, for example, a series circuit of a resistor network 20 and a second capacitor, for example, a capacitor 22. The cut frequency of the high pass filter 21 is set to a frequency somewhat lower than the frequency of the commercial AC power supply, for example, a frequency somewhat lower than 50 Hz.

  The resistance network 20 is originally provided for limiting the current of the light emitting diode 16L, and is configured by a plurality of, for example, two parallel circuits 20a and 20b in series as shown in FIG. The two resistors of the parallel circuit 20a are of a predetermined value, for example, 68 kΩ chip type. The parallel circuit 20b can connect three chip resistors in parallel. In the parallel circuit 20b, all the resistors are removed and the connection ends of one resistor are short-circuited by a jumper wire, for example, 68 kΩ resistors are used for the two resistors, and the remaining one resistor It is possible to remove the resistor, use, for example, a 150 kΩ resistor for the two resistors and remove the remaining one resistor. That is, the configuration of the parallel circuit 20b can be changed.

  By changing the configuration of the parallel circuit 20b in this way, even when this digital amplifier is used in an area other than Japan, the voltage of a commercial AC power supply such as the United States is 120 V and the frequency is 60 Hz. Even when used in a region or in a region where the voltage of a commercial AC power supply such as Europe is 230 V and the frequency is 50 Hz, the current flowing through the light emitting diode 16L is limited to a predetermined current. Can do. Also, in any region, the cut frequency of the high-pass filter 21 configured with the capacitor 22 can be set to a frequency somewhat lower than 50 Hz. In addition, this configuration can be changed very easily.

  As shown in FIG. 2, the comparison circuit 18 has a switching element, for example, a PNP transistor 28, having a control electrode, for example, a base connected to the collector of the phototransistor 16P through a resistor 26. The emitter of the phototransistor 16P is connected to a reference potential point, for example, a ground potential, and the collector is connected to the power supply terminal + V via the resistor 30. The voltage at the power supply terminal + V is obtained from the output voltage of the DC power supply circuit 8. The common electrode, for example, the emitter of the transistor 28 is connected to the power supply terminal + V, and the output electrode, for example, the collector is connected to the sensitivity adjustment circuit 34 via the resistor 32. The sensitivity adjustment circuit 34 is a time constant circuit in which a capacitor 36 and a resistor 38 are connected in parallel, and is connected between the end of the resistor 32 opposite to the collector and the ground potential. The end of the parallel circuit 34 opposite to the ground side of the resistor 38 is connected to the switching element, for example, the control electrode, for example, the base, of the NPN transistor 42 via the resistor 40, and the common electrode, for example, the emitter is grounded. Yes. Therefore, the output voltage of the sensitivity adjustment circuit 34 is supplied to the base. The collector of the transistor 42 is connected to the power supply terminal + V through the resistor 44. Although not shown, the operating voltage of the drive circuit 14 is also supplied from the + V terminal.

  Since the cutoff frequency of the high-pass filter 21 is lower than the frequency of the commercial AC power supply, when the outlet 10 is connected to the commercial AC power supply, the commercial AC voltage is supplied to the light emitting diode 16 via the high-pass filter 21. As a result, the light emitting diode 16L emits light, and the phototransistor 16P is conductive. As a result, the transistors 28 and 42 are both turned on, the input side voltage of the driving circuit 14 is at the ground potential, and the contact 12 remains closed. At this time, the capacitor 36 of the sensitivity adjustment circuit 34 is charged. Further, the capacitor 24 is repeatedly charged and discharged by a commercial AC voltage.

  In this state, when the outlet 10 is disconnected from the commercial AC power supply, the light emitting diode 16L stops emitting light and the phototransistor 16P is turned off. As a result, the transistor 28 is also turned off, and the capacitor 36 starts discharging. When this discharge voltage falls below the voltage (reference voltage) that needs to be applied between the base and the emitter in order to maintain the conduction of the transistor 42, the transistor 42 becomes non-conductive, and the voltage at the + V terminal is used as an energizing signal. The drive circuit 14 is supplied to the drive circuit 14, and the drive circuit 14 opens the contact 12. The reason why the sensitivity adjustment circuit 34 is provided is to prevent the contact 12 from being opened in the event of a momentary power failure due to a problem with the commercial AC power supply and a subsequent power recovery. .

  The above description is a case where it is assumed that when the outlet 10 is disconnected from the commercial AC power supply, the light emission of the light emitting diode 16L is immediately stopped. However, in practice, since the noise suppressing capacitor 24 is connected to both ends of the outlet 10, the light emission of the light emitting diode 16L does not stop immediately.

  That is, when the outlet 10 is connected to a commercial AC power supply, the capacitor 24 is repeatedly charged and discharged. Therefore, when the outlet 10 is disconnected from the commercial AC power source, the capacitor 24 is charged to a certain positive or negative voltage, and discharging starts from that voltage. FIG. 3 shows a state where the outlet 24 is disconnected from the commercial AC power source and the capacitor 24 starts discharging while the capacitor 24 is charged to a positive peak voltage. The discharge current due to this discharge gradually flows to the light emitting diode 16L, and the light emission does not stop immediately, and the contact 12 is kept closed. Therefore, there is a high possibility that abnormal noise is generated from the speaker 6 as the output voltage of the DC power supply circuit 8 decreases.

  By the way, the frequency of the discharge current is lower than the frequency of the commercial AC power supply. Accordingly, since the cutoff frequency of the high-pass filter 21 constituted by the capacitor 22 and the resistor network 20 is higher than the frequency of the discharge current, the high-pass filter 21 rapidly causes the discharge current to flow through the light emitting diode 16L. The light emission of the light emitting diode 16L is rapidly stopped. When the outlet 10 is disconnected, the voltage at the + V terminal also decreases due to the discharge of the smoothing capacitor or the like in the DC power supply circuit 8, but the voltage at the + V terminal causes the comparison circuit 18 and the drive circuit 14 to operate normally. The light emitting diode 16L stops light emission while maintaining the voltage capable of generating the light, and the contact 12 is opened. Therefore, no abnormal sound is output from the speaker 6.

  Returning to FIG. 1, the LC output filter 4 converts the digital signal output from the digital amplifier circuit 2 into an analog signal, that is, removes the carrier signal from the waveform including the carrier signal output from the digital amplifier circuit 2. This is a low-pass filter. The cutoff frequency of the LC output filter 4 is lower than the carrier frequency in the modulator of the digital amplifier circuit 2, for example, 350 kHz or less, and is 20 kHz which is the upper limit frequency of the quality assurance band of the digital amplifier, for example, 20 Hz to 20 kHz. Is also set high.

  Incidentally, an analog signal input to the digital amplifier circuit 2 or an analog signal amplified in the digital amplifier circuit 2 may be excessive. In this case, the digital signal output from the digital amplifier circuit 2 is distorted. This distorted digital signal includes various harmonic components, and may include the resonance frequency of the LC output filter 4 and a frequency component in the vicinity thereof. In this case, a large current flows through the LC output filter 4. Therefore, the digital amplifier circuit 2 and the DC power supply circuit 8 may be damaged.

  The LC output filter 4 has a predetermined load impedance when all the switches 7 are closed and all the high-impedance speakers 6 are connected to the LC output filter 4, and a low pass as shown by a solid line in FIG. The filter characteristics are shown. However, the number of the speakers 6 in which the switch 7 is closed is not always constant and is changed variously. Alternatively, the volume may be adjusted individually by the attenuator at the speaker installation destination. Therefore, when the load impedance varies depending on the number of speakers 6 connected to the LC output filter 4, and particularly when the number of speakers 6 connected to the LC output filter 4 is small, the LC output filter 4 is indicated by a broken line in FIG. As shown, a sharp peak is generated at the resonance frequency. In this state, if a resonance frequency component is included in the current flowing through the LC output filter 4, a resonance current flows and a resonance voltage is generated. In particular, when a high impedance speaker 6 is used, the rated output voltage of each speaker 6 is as high as 100 V in Japan and 70 V in the United States, so that the resonance current flowing through the LC output filter 4 is excessive, and the resonance voltage Is too large. Therefore, the LC output filter 4, the digital amplifier circuit 2, the DC power supply circuit 8, and the connected speaker are overrated due to an excessive voltage and are likely to be damaged.

  Therefore, as shown in FIG. 5, a voltage obtained by dividing the voltage across the capacitor 4C of the LC output filter 4 by a voltage dividing circuit, for example, a resistance voltage dividing circuit 46, is supplied to the band pass filter 48. The bandpass filter 48 has a peak near a frequency somewhat lower than the resonance frequency of the LC output filter 4, for example, has a Q peak as shown in FIG. When the output voltage of the band pass filter 48 is supplied to the comparison circuit 50 and a resonance current is flowing through the LC output filter 4, the comparison circuit 50 generates an energizing signal. In response to this, the drive circuit 52 operates a signal attenuating means provided in the digital amplifier circuit 2, for example, a mute circuit (not shown), and a distorted digital signal is output from the digital amplifier circuit 2. It is preventing that. As a result, excessive current flows through the digital amplifier circuit 2 and the DC power supply circuit 8 to prevent them from being damaged.

  The band-pass filter 48 includes two operational amplifiers 54 and 56, resistors 58, 60, 62, 64, 66 and 68, and capacitors 70 and 72 as shown in FIG. The output filter 4 has a Q peak at a resonance frequency, for example, a frequency somewhat lower than 41 kHz, and its gain is the lowest value in the lower limit frequency of the quality assurance frequency band of the digital amplifier circuit 2, for example, around 20 Hz. The gain gradually increases as the frequency increases. However, it is still a negative gain even in the vicinity of the upper limit frequency of the quality assurance frequency band, for example, 20 kHz, the gain becomes positive at a frequency somewhat lower than the Q peak frequency, and becomes the maximum gain at the Q peak frequency. Thereafter, the gain decreases as the frequency increases, but it never becomes a negative gain, and is configured to have a positive constant gain even when the carrier frequency of the digital amplifier circuit 2 exceeds 350 kHz. Note that the gain is a negative value in a high frequency region not shown. As described above, when a frequency component higher than a frequency slightly lower than the resonance frequency of the LC output filter 4 is generated in the LC output filter 4, a voltage larger than the voltage of the component is generated in the bandpass filter 48 as an output voltage. .

  The comparison circuit 50 includes a semiconductor switching element such as an NPN transistor 74 to which the output voltage of the bandpass filter 48 is supplied to a control electrode, for example, a base via a resistor 68 and a diode 69, and a common electrode such as an emitter is It is connected to a reference potential, for example a ground potential. The output electrode, for example, the collector is connected to the + V terminal via the resistor 76. The collector of the transistor 74 is connected to a semiconductor switching element, for example, a control electrode of the PNP transistor 80, for example, a base, via a resistor 78. The transistor 80 is connected to the emitter. The output electrode, for example, the collector is connected to the ground potential via the resistor 82 and is connected to the drive circuit 52. A capacitor 84 is connected between the base and the collector. The capacitor 84 and the resistor 78 constitute a sensitivity adjuster.

  When the level of the input signal to the digital amplifier circuit 2 is low and the output signal of the digital amplifier circuit 2 is not distorted, or when the frequency is away from the resonance frequency of the LC output filter 4, a resonance current is supplied to the LC output filter 4. Is not flowing. Therefore, the output voltage of the band-pass filter 48 is lower than the input voltage, and the base-emitter voltage necessary for making the transistor 74 conductive is not supplied between the base-emitter of the transistor 74, and the transistor 74 is not turned on. It is continuity. Therefore, neither the base-emitter voltage required for making the transistor 80 conductive nor the base-emitter of the transistor 80 is obtained, and the transistor 80 is also non-conductive. Therefore, the ground potential is supplied to the drive circuit 52, and the drive circuit 52 is not operating. At this time, the capacitor 84 is charged.

  When the level of the input signal to the digital amplifier circuit 2 is high and the output waveform of the digital amplifier circuit 2 is distorted or when the frequency is close to the resonance frequency of the LC output filter 4, a large resonance current flows through the LC output filter 4. . As a result, the output voltage of the bandpass filter 48 becomes larger than the input voltage. The transistor 74 is turned on, the capacitor 84 is rapidly discharged, the transistor 80 is turned on, and the voltage at the + V terminal is supplied to the drive circuit 52 as an energizing signal. The mute circuit in the digital amplifier circuit 2 is activated, and the generation of the distorted output signal in the digital amplifier circuit 2 is stopped. As a result, the resonance current does not flow to the LC output filter 4, and damage to the LC output filter 4, the digital amplifier circuit 2, and the DC power supply circuit 8 can be prevented. Even if the output voltage of the band pass filter 84 decreases and the transistor 74 becomes non-conductive, the conductive state of the transistor 80 is maintained while the capacitor 84 is charged, and the operation of the mute circuit is continued. The

  A third embodiment is shown in FIG. In this embodiment, a transformer 86 in which the primary winding 86P and the secondary winding 86S are insulated instead of the photocoupler 16 is used. Primary winding 86 </ b> P is connected in series with resistance network 20. A rectifying / smoothing circuit 92 including a rectifying diode 88 and a smoothing capacitor 90 is connected to the secondary winding 86S. The output voltage of the smoothing circuit 92 is supplied to the comparison circuit 18. Other configurations are the same as those of the first embodiment.

  A third embodiment is shown in FIGS. In this embodiment, when the outlet 10 is disconnected from the commercial AC power supply in the first embodiment, the DC power supply circuit 8 is also stopped. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In this digital amplifier, as shown in part in FIG. 8, the DC power supply circuit 8 includes a rectifier, for example, a full-wave rectifier circuit 100. The input side of the full-wave rectifier circuit 100 is connected to both ends of the outlet 10. Smoothing means, for example, smoothing capacitors 102 and 104 connected in series, are connected between the output terminals of the full-wave rectifier circuit 100.

  The smoothed output voltage between the smoothing capacitors 102 and 104 is supplied to the switching means shown in FIG. The inverter 106 is a bridge circuit composed of semiconductor switching elements such as bipolar transistors, MOSFETs, or IGBTs. The semiconductor switching elements are turned on / off based on the PWM signal from the PWM circuit 108, and the input smoothed output voltage is converted to high frequency. The voltage is converted into voltage, transformed by an insulation transformer 110, rectified by an output side rectifier, for example, a rectifier diode 112, smoothed by a smoothing unit, for example, a smoothing capacitor 114, and supplied to the digital amplifier circuit 2 as a load. . This load output, eg, load voltage, is detected by a detection means, eg, voltage detector 116, and this detected voltage is supplied to a comparison means, eg, error amplifier 118, where a predetermined reference voltage from reference voltage source 120 is provided. And the difference is supplied to the PWM circuit 108. The PWM circuit 108 changes the duty ratio of the PWM signal so that this error becomes zero. An oscillation circuit 122 is connected to the PWM circuit 108 in order to generate this PWM signal. These PWM circuit, voltage detector 116, error amplifier 118, reference voltage source 120, and oscillation circuit 122 constitute the control means. The smoothing capacitors 102 and 104 have large capacities in order to stabilize the operating voltage of the digital amplifier circuit 2. In particular, in the case of a power supply for a digital amplifier having a large output, the smoothing capacitor of the power supply must be increased in proportion to the output.

  As described above, since the smoothing capacitors 102 and 104 have large capacities, even when the outlet 10 is disconnected from the commercial AC power supply, the voltage supplied from the smoothing capacitors 102 and 104 to the inverter 106 is very low. In addition, the operating voltage supplied to the digital amplifier circuit 2 does not decrease. When the outlet 10 is disconnected from the commercial AC power supply, it is desirable to stop the DC power supply circuit 8 immediately.

  Therefore, as shown in FIG. 9, the primary side of the other detection circuit 124 as the second detection means in series with the primary side of the detection circuit 16 as the first detection means, that is, the light emitting diode 16L as the light emitting element. The light-emitting diodes 124L that are light-emitting elements are connected with the same polarity. When the outlet 10 is connected to a commercial AC power supply, a light emission signal is supplied from the light emitting diode 124L to the secondary side of the detection circuit 124, that is, the phototransistor 124P which is a light receiving element. 124I is a diode connected in antiparallel with the light emitting diodes 16L and 124L.

  The collector electrode of the phototransistor 124L is connected to the positive power supply terminal + V through the resistor 126. The positive power supply terminal + V is a connection point between the Zener diode 130 and the resistor 128, in which a resistor 128 and a Zener diode 130 of a predetermined size are connected in series between both ends of the smoothing capacitors 102 and 104. However, the Zener diode 130 has its cathode connected to the resistor 128 side. The emitter of the phototransistor 124L is connected to the reference potential. This reference potential is on the anode side of the Zener diode 128. Note that the reference potential is not affected by the commercial AC power supply by connecting the connection point of the smoothing capacitors 102 and 104 to one input side of the full-wave rectifier circuit 100. In the state where the outlet 10 is connected to the commercial AC power source, a predetermined voltage determined by the rating is generated between both ends of the Zener diode 128. When the outlet 10 is disconnected from the commercial AC power source, the voltage gradually increases. It will drop to.

  The connection point between the collector of the phototransistor 124P and the resistor 126 is connected to the control electrode, for example, the base of the PNP transistor 134 via the resistor 132, and the common electrode, for example, the emitter is connected to the positive power supply terminal + V. Yes. An output electrode, for example, a collector, of the transistor 134 is connected to a reference potential via a series circuit of a resistor 136 and a capacitor 138. A connection point between the capacitor 138 and the resistor 136 is connected to the base of the NPN transistor 142 via the resistor 140. The collector of the transistor 142 is connected to the positive power supply terminal + V via the resistor 144, and the emitter is connected to the reference potential.

  The collector of the transistor 142 is connected to the base of an NPN-type Darlington transistor 148 via a resistor 146, and this base is connected to a reference potential via a capacitor 150. The resistor 146 and the capacitor 150 constitute a delay circuit, for example, a sensitivity adjustment circuit 151. The time constant of the sensitivity adjustment circuit 151 is set larger than the time constant of the sensitivity adjustment circuit 34 shown in FIG. A series circuit of a diode 152 and a resistor 154 is connected in parallel with the resistor 146. The diode 152 is connected such that its cathode faces the collector side of the transistor 142. The collector of the Darlington transistor 148 is connected to the positive power supply terminal + V through the resistor 156, and the emitter is connected to the reference electric point.

  The collector of the Darlington transistor 148 is connected to the base of the PNP transistor 160 via the resistor 158, the emitter thereof is connected to the positive power supply terminal + V, the collector is connected to the reference potential via the resistor 162, The collector is connected to the base of the NPN transistor 166 via the resistor 164, the emitter is connected to the reference potential, and the collector is connected to the oscillation circuit 122. The oscillation circuit 122 oscillates when the transistor 166 is non-conductive, and stops oscillation when the transistor 166 is conductive.

  When the outlet 10 is connected to a commercial AC power source, the light emitting diode 16L emits light, and the relay switching contact 12 is closed as described in the first embodiment. The light emitting diode 124L also emits light, so that the phototransistor 124P is conductive and the transistors 134 and 142 are conductive. Therefore, the capacitor 150 of the sensitivity adjustment circuit 151 is not charged, the Darlington transistor 148 is non-conductive, and the transistors 160 and 166 are non-conductive. Therefore, the oscillation circuit 122 operates and a DC operating voltage is supplied from the DC power supply circuit 8 to the digital amplifier circuit 2.

  When the outlet 10 is disconnected from the commercial AC power source, the light emitting diode 16L stops emitting light, and the relay switching contact 12 is opened as in the first embodiment. Further, simultaneously with the light emission stop of the light emitting diode 16L, the light emitting diode 124L stops the light emission. Then, the phototransistor 124P is turned off, and the transistors 134 and 142 are turned off. As a result, the capacitor 150 is charged by the resistor 146 of the sensitivity adjustment circuit 151. Eventually, when the charging voltage of the capacitor 150 becomes higher than the necessary base-emitter voltage between its base and emitter to make the Darlington transistor 148 conductive, the Darlington transistor 148 becomes conductive and the transistors 160 and 166 become conductive. The oscillation circuit 122 stops operating. As a result, the operating voltage is not supplied from the DC power supply circuit 8 to the digital amplifier circuit 2, and the digital amplifier circuit 2 stops.

  Since the outlet 10 is disconnected from the commercial AC power supply, the voltage of the positive power supply terminal + V gradually decreases, but the capacity of the smoothing capacitors 102 and 104 is large. Thus, the voltage is sufficient to stop the oscillation circuit 122. Since the time constant of the sensitivity adjustment circuit 151 is larger than the time constant of the sensitivity adjustment circuit 34, the oscillation circuit 122 stops oscillating after the relay opening contact 12 is opened. Furthermore, when the outlet 10 is disconnected from the commercial AC power supply and then immediately connected to the commercial AC power supply, that is, when a momentary power failure occurs, the electric charge charged in the capacitor 150 is a resistance. Since the capacitor 154 and the diode 154 are immediately discharged, the oscillation circuit 122 starts operation immediately. Therefore, the resistor 154 is selected to have a sufficiently small value as compared with the resistor 146.

  In the above three embodiments, the present invention is implemented in a digital amplifier, but a device that needs to quickly detect that it is disconnected from a commercial AC power source, such as an uninterruptible power supply device or an electronic memory, is provided. It can also be used for devices that need instant backup in installed equipment. In each of the above embodiments, the high-pass filter 21 is configured by the current limiting resistor network 20 and the capacitor 22 of the light emitting diode 16L. However, the present invention is not limited to this. For example, the resistor network 20 is used for current limiting. A high pass filter can be provided separately. Further, a band pass filter may be used instead of the high pass filter. In the second embodiment, the detection circuits 16 and 124 are provided to control the relay switching contact 12 and the oscillation circuit 122. However, the detection circuit 16 is removed and only the oscillation circuit 122 is controlled. You can also. In the third embodiment, the light emitting diodes 16L and 124L of the detection circuits 16 and 124 are connected in series. However, they can be connected in antiparallel. In this case, a diode connected in antiparallel with the light emitting diode is unnecessary.

1 is a block diagram of a digital amplifier according to a first embodiment of the present invention. FIG. 2 is a circuit diagram of a portion that detects a non-connection state of the digital amplifier of FIG. 1 to a commercial power source. It is a figure which shows the change of the voltage of the capacitor | condenser 24 of the digital amplifier of FIG. It is a figure which shows the change of the frequency characteristic accompanying the change of the load of LC output filter 4 of the digital amplifier of FIG. FIG. 2 is a circuit diagram of a portion for detecting a resonance state of an LC filter output filter in the digital amplifier of FIG. 1. It is a frequency characteristic part of the band pass filter used in the digital amplifier of FIG. It is a block diagram of a part of digital amplifier of the 2nd Embodiment of this invention. It is a block diagram of a part of digital amplifier of the 3rd Embodiment of this invention. It is a block diagram of a part of DC power supply circuit of the digital amplifier of FIG.

Explanation of symbols

8 DC power supply circuit (AC-DC conversion means)
16 Photocoupler (detection means)
22 Capacitor (first capacitor)
24 capacitor (second capacitor)

Claims (10)

A pair of AC power input terminals that are connected to or disconnected from a commercial AC power supply;
AC-DC conversion means connected between the AC power input terminals,
A first capacitor connected between the AC power input terminals;
A detection circuit and a series circuit of filters connected in parallel with the first capacitor;
The power supply non-connection detection device includes: the detection means generates a detection signal in the non-connection state, and the filter passes a frequency equal to or higher than a frequency of the commercial AC power supply.   2. The power disconnection detecting device according to claim 1, wherein the AC-DC converting means is a switching power supply.   2. The power supply disconnection detecting device according to claim 1, wherein the filter is a high-pass filter in which a current limiting resistor means to the detection means and a second capacitor are connected in series.   4. The power disconnection detecting device according to claim 3, wherein the resistance means includes a plurality of parallel resistance circuits connected in series, and at least one of the parallel resistance circuits replaces a resistor constituting the resistance circuit. A power disconnection detecting device configured to be capable of being short-circuited.   2. The power disconnection detecting device according to claim 1, wherein the detection means has an insulated primary side and secondary side, the primary side is connected between the two input terminals, and the detection signal is connected to the secondary side. A power disconnection detection device that generates In the power disconnection detecting device according to claim 1,
An electronic circuit connected to the output side of the AC-DC converting means;
A protection circuit for protecting the electronic circuit in response to generation of the detection signal;
A protection device for electronic equipment.   7. The protection apparatus for an electronic device according to claim 6, wherein the AC-DC conversion means gradually decreases its output voltage from the time when it is in the disconnected state, and the protection circuit operates according to the output voltage of the AC-DC conversion means. Protection device for electronic equipment.   7. The protection apparatus for an electronic device according to claim 6, wherein the electronic circuit is a digital amplifier circuit, and the protection circuit is an open / close contact connected between an output side of the digital amplifier circuit and a speaker. A protection device for electronic devices that is opened in response to signal generation. In the power disconnection detecting device according to claim 1,
The AC-DC converting means includes a first rectifying means for rectifying the commercial AC power supply, a smoothing means for smoothing the output of the first rectifying means, a switching means for switching the smoothed output, and the switching means. Control means for controlling the output, and second rectifying means for rectifying the output of the switching means,
A protection device for an electronic device provided with stop means for stopping the control means in response to occurrence of the detection means. The power connection detection device according to claim 1, wherein the detection means includes first and second detection means that simultaneously generate detection signals, respectively.
The AC-DC converting means includes a first rectifying means for rectifying the commercial AC power supply, a smoothing means for smoothing the output of the first rectifying means, a switching means for switching the smoothed output, and the switching means. Control means for controlling the output, and second rectifying means for rectifying the output of the switching means,
An electronic circuit is connected to the output side of the AC-DC conversion means,
A protection means protects the electronic circuit in response to generation of a detection signal of the first detection means,
In response to occurrence of the second detection means, the control means is stopped by the stop means,
An electronic device having a delay unit, wherein the stop unit has a delay unit so that the protection unit operates in response to the generation of the first detection signal, and the stop unit operates in response to the generation of the second detection signal. Protective device.

Images