JP2003304123A - Audio amplifier and its abnormality detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for detecting the operation abnormality of an audio amplifier during the operation of the amplifier. <P>SOLUTION: This audio amplifier is provided with a power amplifier circuit 19, an output signal discriminating means 25 for discriminating whether or not the voltage V0 of the output signal of the amplifier circuit 19 exceeds a prescribed threshold, a time measuring means 27 for measuring time length Tsc when the voltage V0 continuously exceeds a threshold by using the output of the output signal discriminating means 25, and a comparing means 28 for comparing the time length Tsc with the preliminarily set threshold. When the time Tsc measured in a status than an audio signal is inputted to the power amplifier circuit 19 exceeds the prescribed time length, a switch 21 is controlled to stop any output from the power amplifier circuit 19 to a speaker 23. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio amplifier, an audio amplifier abnormality detecting means, and an audio amplifier abnormality detecting method. More particularly, the present invention relates to an audio amplifier for monitoring an abnormality of the audio amplifier even during operation and the abnormality detecting method. Regarding the method.

[0002]

2. Description of the Related Art An audio amplifier is mainly composed of a preamplifier and a power amplifier circuit which amplifies the output of the preamplifier and gives it to a speaker. The preamplifier and the power amplifier circuit are usually provided with two channels for stereo reproduction, or circuits with more channels than that. In the following description, a circuit for one channel will be described for ease of description. Although the actual circuit configuration of the power amplification circuit is various, in a power amplification circuit driven by a single power source such as a vehicle audio device, the BTL (Ba
Many lanced transformer less type circuits are adopted, and in other power amplifier circuits driven by bipolar power sources for home use etc., SEPP circuit (Single Ended P
ush-PullCircuit) is often adopted.

In the BTL circuit, two signals of in-phase and anti-phase are generated from the output of the preamplifier, and the two signals are converted into two signals.
Two power amplifier circuits amplify the two signals and give two audio signals with opposite phases to the speaker as audio output for one channel. When the audio amplifier is operating normally, the operation reference voltage of each of the signals output from the two power amplifier circuits is approximately 1/2 of the power supply voltage Vcc. The DC component of the voltage applied between the two terminals of the speaker is almost zero, and only the AC component corresponding to the audio signal is applied to the speaker. On the other hand, in the case of the SEPP circuit, when the middle point of the plus and minus power supplies is connected to the ground line and the normal operation is performed, the average value of the output voltage (operation reference voltage) is almost zero, and Same as voltage. The DC component of the output audio signal is almost zero, and only the AC component corresponding to the audio signal is given to the speaker.

However, in both the BTL circuit and the SEPP circuit, when there is some abnormality in the audio amplifier, especially in the power amplifier circuit, a large DC voltage is applied to the speaker or an excessive AC voltage is applied, and the speaker is May be destroyed. The main cause of such a problem is an offset voltage applied to the power amplifier circuit, a short circuit of an output semiconductor such as a transistor or FET, and the like.

One proposal for avoiding these problems is disclosed in Japanese Patent Laid-Open No. 2000-174571. According to the technique disclosed in the publication, in order to prevent the speaker from being damaged, in the BTL amplifying device having two power amplifiers having a BTL configuration for driving the speaker, the above-mentioned 2
A DC offset detection device is configured by a detection unit that detects the differential voltage of the power amplifier outputs, and a determination unit that determines whether the differential voltage detected by the differential voltage detection unit is greater than a predetermined value. The DC offset detection device is operated during a period when no signal is input to the power amplifier, and when the difference voltage is equal to or higher than a predetermined value, the signal output from the power amplification circuit to the speaker is stopped.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
According to the method disclosed in Japanese Patent No. 174571, the abnormality of the audio amplifier is detected only when the audio signal is not input to the amplifier and is in a no signal state. For this reason, the audio amplifier abnormality detection processing is limited to the state where the audio signal to be reproduced is not input to the power amplification circuit, such as when the power of the audio amplifier is turned on or when the signal source is switched. Done. However, an abnormal state of the audio amplifier may occur while the audio signal is being output from the power amplification circuit, and in such a case, the abnormality is detected after a considerable time has elapsed from the occurrence of the abnormality, There was a problem that the speaker could not be protected immediately after the abnormality occurred.

The present invention has been made to solve the above problems, and one of the objects thereof is to provide a method and apparatus for detecting an abnormal operation of an audio amplifier in a signaled state, that is, while the amplifier is operating. Another object of the present invention is to provide an audio amplifier which detects an abnormal operation at an early stage and prevents the speaker from being destroyed.

[0008]

The present invention has been made in view of the above problems, and a first aspect of the present invention is a power amplifier circuit and the voltage of an output signal of the power amplifier circuit exceeds a predetermined threshold value. An output signal discriminating unit that discriminates whether or not there is a signal and an output of the output signal discriminating unit are used to measure the length of time during which the voltage of the output signal of the power amplification circuit continuously exceeds the threshold value. An audio amplifier, comprising: time measuring means, so as to stop the output of the power amplification circuit when the time measured by the time measuring means exceeds a predetermined time length.

According to a second aspect of the present invention, a preamplifier, a power amplifier circuit to which the output of the preamplifier is given via a capacitor, and a signal state indicating whether or not the voltage of the output signal of the power amplifier circuit exceeds a predetermined threshold value. And a second discriminating means for discriminating whether or not the voltage of the output signal of the preamplifier exceeds a predetermined threshold different from the threshold, and the output of the second discriminating means is negative. Then, when the output of the first discriminating means is affirmative, the output of the power amplifier circuit is stopped.

According to a third aspect of the present invention, when the voltage of the output signal of the power amplifier circuit and the power amplifier circuit in the signal state is higher than a first threshold value which is higher than the operation reference voltage of the power amplifier circuit by a predetermined value. First comparing means for outputting an output signal having a predetermined amplitude, and second voltage for which the voltage of the output signal of the power amplification circuit in the signal state is lower than the operation reference voltage by the predetermined value.
Second comparing means for outputting an output signal of the predetermined amplitude when the value is lower than the threshold value of, the difference between the integrated value of the output of the first comparing means and the integrated value of the output of the second comparing means is within a predetermined range. The audio amplifier is configured to stop the output of the power amplifier circuit when it is not inside.

A fourth aspect of the present invention uses an output signal discriminating means for discriminating whether or not the voltage of the output signal of the power amplifying circuit exceeds a predetermined threshold value in a signaled state, and the output of the output signal discriminating means. The output signal voltage of the power amplifier circuit comprises a time measuring means for measuring a time length continuously exceeding a threshold value, when the time measured by the time measuring means exceeds a predetermined time length, An audio amplifier abnormality detection device for determining that an audio amplifier including the power amplification circuit is abnormal.

According to a fifth aspect of the present invention, there is provided a first discriminating means for discriminating whether or not the voltage of the output signal of the power amplifier circuit, to which the output of the preamplifier is given via the capacitor, exceeds a predetermined threshold value in the signaled state, A second discriminating means for discriminating whether or not the voltage of the output signal of the preamplifier exceeds a predetermined threshold value different from the threshold value, the output of the second discriminating means is negative, and the output of the first discriminating means is If yes,
The audio amplifier abnormality detecting device is configured to determine that an audio amplifier including the preamplifier and the power amplifier circuit is abnormal.

According to a sixth aspect of the invention, when the voltage of the output signal of the power amplification circuit in the signal state is higher than a first threshold value which is higher than the operation reference voltage of the power amplification circuit by a predetermined value, an output signal of a predetermined amplitude. And a voltage of the output signal of the power amplifier circuit in the signal state, which is lower than a second threshold value lower than the operation reference voltage by the predetermined value, outputs the output signal of the predetermined amplitude. A second comparison means,
Abnormality detection device for audio amplifier, which determines that the audio amplifier including the power amplification circuit is abnormal when the difference between the integrated value at the time t1 and the integrated value at the time t2 is not within a predetermined range. Is.

According to a seventh aspect of the present invention, there is provided an output signal determination step of determining whether or not the voltage of the output signal of the power amplification circuit exceeds a predetermined threshold value in a signaled state, and a determination result of the output signal determination step. And a time measuring step for measuring a time length in which the voltage of the output signal of the power amplifier circuit continuously exceeds the threshold value, and the time measured in the time measuring step exceeds a predetermined time length. In this case, the audio amplifier abnormality detection method is configured to determine that the audio amplifier including the power amplification circuit is abnormal.

An eighth aspect of the invention is a first determining step of determining in a signaled state whether or not the voltage of the output signal of the power amplifier circuit, to which the output of the preamplifier is given via a capacitor, exceeds a predetermined threshold value, and A second determination step of determining whether or not the voltage of the output signal of the preamplifier has exceeded a predetermined threshold value different from the threshold value, the determination result of the second determination step is negative, and the first determination step Is a method for detecting an abnormality in an audio amplifier, which determines that the audio amplifier including the preamplifier and the power amplifier circuit is abnormal when the determination result in step 1 is affirmative.

According to a ninth aspect of the present invention, an output signal determining step of determining whether or not the voltage of the output signal of the power amplifier circuit exceeds a predetermined threshold value in a signaled state, and a process of the output signal determining step for a predetermined time. If the affirmative appearance is repeated a predetermined number of times or if the affirmation is equal to or more than a predetermined rate, the audio amplifier including the power amplification circuit is abnormal. This is a method for detecting an abnormality in an audio amplifier, which is determined to be

A tenth aspect of the present invention is an output signal having a predetermined amplitude when the voltage of the output signal of the power amplification circuit in the signal state is higher than a first threshold value which is higher than the operation reference voltage of the power amplification circuit by a predetermined value. A first comparing step of outputting Sx and an output signal Sy of the predetermined amplitude when the voltage of the output signal of the power amplifier circuit in the signal state is lower than a second threshold value lower by the predetermined value than the operation reference voltage. And a second comparison step for outputting the output signal Sx and the difference between the integrated value of the output signal Sx and the integrated value of the output signal Sy are not within a predetermined range, the audio amplifier including the power amplifier circuit is abnormal. This is a method for detecting abnormality in an audio amplifier, which is determined to exist.

An eleventh aspect of the present invention is the power amplifier circuit according to the seventh aspect or the ninth aspect, wherein the power amplifier circuit is abnormal when it is determined that the audio amplifier including the power amplifier circuit is abnormal. Is a method for detecting an abnormality in an audio amplifier, in which the amplitude of an input signal to the audio amplifier is reduced to determine again whether or not the audio amplifier including the power amplification circuit is abnormal.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. In the audio amplifier of the present invention, it is determined whether or not there is an abnormality in the operation of the amplifier while the audio signal is being input to the power amplification circuit, and if it is determined that there is abnormality, the output of the power amplification circuit is output to the speaker. Control not to give. The audio signal is basically an AC signal, and the output signal of the power amplifier circuit is an AC signal centered on the operation reference voltage in most cases, and its average value is almost the same as the operation reference voltage. There is no bias toward the plus side or minus side.

By utilizing the property of the audio signal, in the operation abnormality determination of the audio amplifier according to the present invention, the output signal of the power amplifier circuit is observed in a state where the audio signal is included, and the voltage of the output signal is predetermined. Basically, it is determined to be abnormal if the time exceeds the threshold and the time when the threshold is continuously exceeded is longer than a predetermined time. In the following description, the state in which the audio signal is being input to the power amplifier circuit is also referred to as a signal presence state.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of an audio amplifier of the present invention. The audio amplifier of the present invention normally handles audio signals of two or more channels, but only one channel is described in the present specification and the drawings for ease of explanation. In the audio amplifier 10 shown in FIG. 1, the audio signal to be reproduced is given to the preamplifier 13 via the capacitor 11. The preamplifier 13 includes a tone control circuit and an electronic volume, but is not shown. The preamplifier 13 is provided to the power amplification circuit 19 via the capacitor 15. The bias voltage VB is applied to the input side of the power amplifier circuit 19 via the resistor 17.

The power amplification circuit 19 is one of the two output circuits forming the BTL circuit, or
It is a SEPP circuit. As described above, the BTL circuit is driven by a single power supply, and the average voltage (operation reference voltage) of the audio signal output from the power amplification circuit 19 is approximately ½ of the power supply voltage. The SEPP circuit is driven by both positive and negative power supplies, and the average voltage (operation reference voltage) of the audio signal output from the power amplification circuit 19 is substantially equal to the voltage of the ground line to which the midpoint of both power supplies is connected. Here, the voltage of the ground line is 0 volt.

The output of the power amplifier circuit 19 is given to the speaker 23 via the switch 21 and the output signal discriminating means 25. The discriminating means 50 is composed of an output signal discriminating means 25, a time measuring means 27 and a comparing means 28. The preamplifier 13 sends an audio signal to the power amplifying circuit 19 to determine whether the output signal of the power amplifying circuit 19 is abnormal. In the input state (signaled state), the determination process is always performed. The output signal discrimination means 25 is, for example, a comparator using a differential amplifier, and the power amplification circuit 1
When the voltage V0 of the output signal of 9 exceeds the predetermined upper threshold value V2 or becomes lower than the predetermined lower threshold value V1, the H level signal is output, and otherwise the L level signal is output.

The time measuring means 27 is an output signal discriminating means 25.
When H is output from H, the time at which H is output continuously is measured by using a timer, and the value Tsc is compared by the comparing means 2.
Give to eight. The comparing means 28 compares the time Tsc given from the time measuring means 27 with a predetermined time length Tth. When Tsc is larger than Tth, it is determined that the operation of the audio amplifier 10 is abnormal, and the micro Output an H level signal to the processor (MPU) 29,
In other cases, it is determined that the operation of the audio amplifier 10 is normal, and the L level signal is output to the MPU 29.

When the high-level signal (hereinafter also referred to as H-level signal) is output from the comparison means 28, the MPU 29 gives a control signal to the switch 21 to open the switch 21, and outputs from the power amplification circuit 19 to the speaker 23. Stop the supply. Therefore, when the output voltage V0 of the power amplification circuit 19 as viewed from the ground line continuously exceeds the predetermined threshold range for a time longer than the time Tth, it is determined that the audio amplifier is abnormal, The speaker 23 is protected by opening the switch 21.

FIG. 2 is a diagram for explaining the timing and threshold value of the time measurement in the present invention, and assists in explaining the operation of the discriminating means 50. In FIG. 2, Vs is an operation reference voltage of the power amplification circuit 19 and is a voltage from the ground line. The Vs is usually approximately 1 of the single power supply voltage Vcc.
/ 2 or approximately zero for both positive and negative power supplies. V2 is the upper threshold and V1 is the lower threshold.
Normally, (V2-Vs) and (Vs-V1) are set equal.

The output signal discrimination means 25 is the power amplifier circuit 1
When the output voltage V0 of 9 becomes higher than V2 (from time t1 to t2) or lower than V1 (from time t3 to t4), H is output to the time measuring means 27. The time measuring means 27 measures the time (t2-t1) or the time (t4-t3) with a timer, and the time length Tsc
Is given to the comparison means 28. The comparison means 28 compares the time length Tsc with the time threshold value Tth. Then, when the time Tsc in which the output voltage V0 is not within the range between the upper threshold value V2 and the lower threshold value V1 is larger than the time threshold value Tth, it is determined that the audio amplifier is abnormal, and the MPU 29 is set to H level.
Output level signal. The above-mentioned observation is continued by the determination means 50 until H is output from the comparison means 28.

The time threshold Tth compared with the time Tsc in the comparison means 28 is not fixed,
It may be changed according to the setting value of the volume in the preamplifier 13, the setting state of the tone control, the type of the signal source device, etc. By doing so, the abnormality of the amplifier can be detected more accurately. Also, M
It is convenient for the operator to provide a display device connected to the PU 29 to display the progress of the abnormality detection of the amplifier and the abnormality detection result. Further, while the operator is changing the volume and sound quality settings of the preamplifier, in order to reduce misjudgment, the above-mentioned discrimination means 50 may not discriminate the amplifier abnormality. The same applies to the second and subsequent embodiments described below.

FIG. 3 is a block diagram showing a second embodiment of the audio amplifier of the present invention. 3 and FIG. 1 have the same function,
Elements having the same action are denoted by the same reference numerals, and the description thereof will be omitted. The main difference between FIG. 3 and FIG. 1 is that in the audio amplifier 20 shown in FIG. 3, the output of the power amplifier circuit 19 is given to the first discriminating means 31, the output of the preamplifier 13 is given to the second discriminating means 33, and The point is that the inverter 35 and the AND gate 37 are provided. First discriminating means 31
Compares the voltage V0 of the output signal of the power amplifier circuit 19 with a predetermined upper threshold value V2 and lower predetermined threshold value V1, and the power amplifier circuit 1
It is temporarily determined whether or not the operation of 9 is abnormal, and when it is temporarily determined to be abnormal, an H level signal is given to the AND gate 37. The temporary discrimination by the first discriminating means 31 is repeatedly performed at predetermined time intervals, and the threshold voltage to be set is the same as V1 and V2 shown in FIG.

The second discriminating means 33 observes the voltage of the output signal of the preamplifier 13 and tentatively discriminates whether or not the operation of the preamplifier 13 is abnormal. When it is tentatively discriminated as abnormal, the H level signal is ANDed. Give to the gate 37. That is,
The second discriminating means 33 compares the voltage of the output signal of the preamplifier 13 with a predetermined upper threshold value V2p and lower predetermined threshold value V1p,
It is temporarily determined whether or not the operation of the preamplifier 13 is abnormal, and when it is temporarily determined that the operation is abnormal, H is set to the inverter 35.
Give to. Although the temporary determination by the second determination means 33 is repeatedly performed at a predetermined time interval, the temporary determination by the first determination means 31 and the temporary determination by the second determination means 33 are synchronously performed at the same timing.

In the output signal of the preamplifier 13, the expected average value (operation reference voltage) is Vsp, and the upper threshold value is V2.
If p and the lower threshold are V1p, (V2p-Vsp) is set to (V2-Vs) * M / Gm. Here, Gm
Is the voltage gain of the power amplifier circuit 19, for example, 26d
b. Further, M is a positive number less than 1, and is 0.7, for example. Similarly, (Vsp-V1p) is (Vs-
V1) × M / Gm. The M is a coefficient for reducing the risk of erroneous determination that the power amplifier circuit is abnormal due to the variation of Gm and the content of the audio signal.

The output of the second discriminating means 33 is the inverter 35.
Flipped over. The AND gate 37 has a first discrimination means 31.
And the output of the inverter 35 are applied, and the output is given to the MPU 29. As a result, when the first determining unit 31 tentatively determines that the amplifier is abnormal and the second determining unit 33 tentatively determines that the preamplifier 13 is not abnormal, it is finally determined that the amplifier is abnormal. , MP
H is output to U29. Therefore, for example, when the volume control volume is raised too high, it is highly likely that both the first determination unit 31 and the second determination unit 33 are abnormal, but in that case, the amplifier is not abnormal. Finally, the AND gate 37 outputs Low.
A level signal (hereinafter, also referred to as an L level signal) is output. In this way, the switch 21 is prevented from being opened frequently.

FIG. 4 is a diagram showing an abnormality detecting method in the third embodiment of the audio amplifier of the present invention. FIG. 8 is a block diagram showing a third embodiment of the audio amplifier of the present invention. Elements having the same functions and functions in FIGS. 8 and 1 are designated by the same reference numerals, and the description thereof will be omitted. In FIG. 8, the counting means 6 is used instead of the time measuring means 27 and the comparing means 28 shown in FIG.
1 is provided, and the output signal determining means 25 and the totalizing means 61 constitute the determining means 60. The major difference between the first embodiment described with reference to FIG. 1 and this third embodiment is that the output signal discriminating means 25 makes provisional discrimination as to whether or not the amplifier is abnormal.
Is obtained by sampling every predetermined time, and using the sampling results thus obtained a plurality of times, the summing means 61 determines whether or not the amplifier is abnormal, and finally makes a determination. The tentative discrimination by the output signal discriminating means 25 is performed at intervals of 5 ms, for example, and the aggregating means 61 discriminates using, for example, 12 sampling values. The detection of the operation abnormality by the determination unit 60 is continuously performed until the abnormality is detected.

FIG. 4 shows an example in which the number of samplings of the temporary discrimination before the final discrimination by the totaling means 61 is set to 12. FIG. 4A shows an example of the case of finally determining that an abnormality has occurred when it is temporarily determined that the abnormality has occurred 5 times or more in the 12 times of the provisional determination. The level signal is output. (B) of the figure is
In the above-described 12 times of temporary discrimination, an example of finally determining that the amplifier is abnormal when the abnormal determination is made 6 times or more out of 7 consecutive temporary determinations An H level signal is output at time t5.

(C) in the figure shows the case where the amplifier is finally judged to be abnormal when the temporary judgment of "abnormality" which occurs four or more times consecutively occurs twice in the above-mentioned 12 times of temporary judgment. , An H level signal is output at time t6. Figure 4
According to the third embodiment shown in FIG. 6, even if the determination as to whether or not the audio amplifier is abnormal is performed in a short time, whether or not the amplifier is abnormal is determined according to the timing of sampling and the content of the audio signal. It is possible to prevent the discrimination from being different.

FIG. 5 is a diagram showing an abnormality detecting process in the third embodiment of the audio amplifier of the present invention. In FIG. 5, initialization is performed by setting the number of repetitions Rep = 1 in step S11, and in step S13, whether the voltage V0 of the output signal of the power amplifier circuit currently exceeds a predetermined threshold value,
Sampling and checking are performed, and it is temporarily determined whether or not the amplifier is abnormal, and the process proceeds to step S15. In step S15,
If an abnormality is detected in the temporary determination (if the abnormality is temporarily determined), the process proceeds to step S17, and otherwise, the process proceeds to step S25. In step S17, in the provisional determination, if the abnormality is detected a predetermined number of times consecutively (if it is provisionally determined to be abnormal), the process proceeds to step S21, and otherwise, the process proceeds to step S19.

In step S19, if the abnormality occurrence rate (provisionally determined to be abnormal) exceeds a predetermined value, step S2
1, and otherwise proceeds to step S25. In step S21, it is finally determined that the amplifier is abnormal, and the process proceeds to step S23. In step S23, the output of the power amplifier circuit is stopped and this flow is ended. Step S2
In step 5, it is determined whether or not the number of repeats Rep has exceeded 12 times. If yes, the process proceeds to step S11, and if not, the process proceeds to step S27. In step S27, the value of Rep is incremented, the process proceeds to step S13, and a process of repeating provisional determination as to whether or not the amplifier is abnormal is performed. It should be noted that in the process of step S19, it may be determined whether or not the abnormality occurrence rate (proportion tentatively determined to be abnormal) is greater than or equal to a predetermined value. Further, in the process of step S19, as shown in FIG. , "Abnormality" that occurs consecutively more than a predetermined number of times
It may be possible to determine whether the provisional determination has been performed a predetermined number of times or more. Further, the processing from step S11 is executed at predetermined time intervals even while the audio signal is being output from the power amplifier circuit.

FIG. 6 is a block diagram showing a fourth embodiment of the audio amplifier of the present invention. 6 and 3 have the same function,
Elements having the same action are denoted by the same reference numerals, and the description thereof will be omitted. In the audio amplifier 30 shown in FIG. 6, the output V0 of the power amplification circuit 19 is given to the first comparing means 41 and the second comparing means 43, and the first comparing means 41 and the second comparing means 4 are provided.
The outputs of 3 are the first integration circuit 45 and the second integration circuit 4 respectively.
7 to the differential amplifier 49.

The voltage V0 of the output signal of the power amplification circuit 19
However, while the voltage is higher than the threshold value V2, which is higher than the operation reference voltage Vs of the power amplification circuit by a predetermined value, the first comparison means 41 outputs an H level signal having a predetermined amplitude to the first integration circuit 45.
While the voltage V0 of the output signal of the power amplification circuit 19 is lower than the threshold value V1 which is lower than the operation reference voltage Vs by the predetermined value, the second comparison means 43 outputs the H level signal of the predetermined amplitude to the second integration circuit. Output to 47. The first comparing means 41 and the second comparing means 43 are composed of, for example, comparators using differential amplifiers.

The first comparing means 41 outputs the H level to the first integrating circuit 45 while the output voltage V0 of the power amplifier circuit 19 exceeds the upper threshold value V2 shown in FIG. 2 to the upper side, and the second comparing means 41. 43, the output voltage V0 of the power amplifier circuit 19 is shown in FIG.
The H level is output to the second integrating circuit 47 while the lower threshold value V1 shown in (1) is exceeded. However, in the fourth embodiment, V2 and V1 are set so that the potential differences (V2-Vs) and (Vs-V1) between the operation reference voltage Vs and the respective threshold values V2 and V1 are equal.

The outputs of the first comparing means 41 and the second comparing means 43 are respectively integrated by the first integrating circuit 45 and the second integrating circuit 47, and the integrated results are given to the differential amplifier 49.
In the differential amplifier 49, the difference between the output of the first integrating circuit 45 and the output of the second integrating circuit 47 is calculated and given to the in-phase input line of the differential amplifier 51 and the anti-phase input line of the differential amplifier 53. The positive side threshold Vtp is applied to the negative phase input line of the differential amplifier 51, and the negative side threshold V is applied to the same phase input line of the differential amplifier 53.
tm is applied.

When the differential signal output from the differential amplifier 49 is higher than the + side threshold value Vtp, the differential amplifier 51 outputs the H level to the OR gate 55, and the differential signal output from the differential amplifier 49 is the-side. When it is lower than the threshold value Vtm, the differential amplifier 53 outputs the H level to the OR gate 55. The outputs of the differential amplifier 51 and the differential amplifier 53 are applied to the OR gate 55, and the output of the OR gate 55 is applied to the MPU 29.

As described above, when the output voltage of the differential amplifier 49 is not within the predetermined range (between Vtp and Vtm), the H level signal signal notifying the abnormality is given from the OR gate 55 to the MPU 29. , MPU29 is switch 2
1 is opened to protect the speaker 23. When the audio amplifier 30 is an amplifier driven by both positive and negative power supplies, Vtp and Vtm have the same value with different signs, and the absolute value of the voltage of the differential signal output from the differential amplifier 49 is larger than Vtp. Audio amplifier 30
Is determined to be abnormal, the MPU 29 opens the switch 21 to protect the speaker 23.

If the output signal of the power amplifier circuit 19 is a normal audio signal, the time when the voltage V0 is above the operation reference voltage Vs is substantially the same as the time when it is below the operation reference voltage Vs.
Further, the time when the voltage V0 is higher than the upper threshold value V2 and the time when the voltage V0 is lower than the lower threshold value V1 are substantially the same. In other words, the time when the voltage V0 becomes higher than the upper threshold value V2,
If the time when the value is lower than the lower threshold V1 is significantly different, there is a high possibility that the operation of the audio amplifier 30 is abnormal, and it is determined that the amplifier is abnormal and an H level signal is given to the MPU 29. The fourth embodiment utilizes the property of the AC signal described above.

FIG. 7 is a diagram showing an abnormality detecting process in the fifth embodiment of the audio amplifier of the invention. In the fifth embodiment, when the operation of the audio amplifier is once determined to be abnormal in the first embodiment shown in FIG. 1 or the third embodiment shown in FIG. 8, the volume control volume of the preamplifier 13 is turned down. By reducing the amplitude of the audio signal output from the preamplifier 13 to the power amplification circuit 19 to some extent, determining again whether the amplifier is abnormal, and making the final determination the result of this redetermination. In addition, the sound of the speaker is often prevented from being interrupted. For example, it is possible to prevent misjudgment caused by the input signal to the power amplification circuit 19 being too large.

In FIG. 7, when an abnormality of the audio amplifier is detected in step S31, the process proceeds to step S33. In step S33, the volume is reduced and the amplitude of the input signal of the power amplification circuit is reduced to proceed to step S35. In step S35, it is determined again whether or not the audio amplifier is abnormal, and the process proceeds to step S37. Step S
At 37, if an abnormality is detected in the re-determination, the process proceeds to step S39, and if not detected, the process proceeds to step S31. In step S39, it is finally determined that the audio amplifier is abnormal, and the process proceeds to step S41. In step S41, the output of the power amplification circuit 19 is stopped and this flow is ended.

In the process of step S33, the gain Gp of the preamplifier 13 including the volume adjusting volume and the sound quality adjuster is set as follows regardless of the setting by the operator. That is, Smax is the maximum amplitude (peak to peak value) of the signal input to the preamplifier 13, M is a positive number smaller than 1, Gv is the gain of the power amplification circuit 19, and Vw is the upper level with respect to the output signal of the power amplification circuit 19. If the difference between the threshold V2 and the lower threshold V1 (V2-V1), Gp = Vw
It sets as xM / (Smax * Gv). Set the value of M to 1
The reason for making it smaller is to prevent the amplifier abnormality from being frequently detected due to variations in the gain of the power amplifier circuit and the contents of the audio signal, and is set to 0.7, for example.

As described above in detail, according to the embodiment to which the present invention is applied, the audio amplifier is kept in the operating state (the state where the audio signal is input to the power amplifier circuit). Since the abnormality is detected, the operation of the power amplification circuit can be stopped in a short time after the abnormality of the audio amplifier occurs, or the output from the power amplification circuit to the speaker can be stopped by a switch etc. Can be protected.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of an audio amplifier of the present invention.

FIG. 2 is a diagram illustrating timing and thresholds for time measurement in the present invention.

FIG. 3 is a block diagram showing a second embodiment of the audio amplifier according to the present invention.

FIG. 4 is a diagram showing an abnormality detection method in a third embodiment of the audio amplifier of the present invention.

FIG. 5 is a diagram showing anomaly detection processing in a third embodiment of the audio amplifier of the present invention.

FIG. 6 is a block diagram showing a fourth embodiment of the audio amplifier according to the present invention.

FIG. 7 is a diagram showing anomaly detection processing in a fifth embodiment of the audio amplifier of the present invention.

FIG. 8 is a block diagram showing a third embodiment of the audio amplifier of the present invention.

[Explanation of symbols]

11, 15 capacitors 13 preamplifier 19 Power amplifier circuit 21 switch 23 speakers 25 Output signal discrimination means 27 hour measuring means 28 Comparison means 29 Microprocessor (MPU) 31 First discriminating means 33 Second discriminating means 35 inverter 37 AND gate 41 First Comparison Means 43 Second Comparison Means 45 First integrating circuit 47 Second integrating circuit 49, 51, 53 differential amplifier 50, 60 Discriminating means 61 Aggregation means 55 OR gate

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kasei Mio             1-14-6 Dogenzaka, Shibuya-ku, Tokyo Stocks             Company Kenwood (72) Inventor Takeshi Naito             1-14-6 Dogenzaka, Shibuya-ku, Tokyo Stocks             Company Kenwood F term (reference) 5J091 AA02 AA41 AA53 CA56 FA18                       FP02 GP02 GP04 HA25 HA32                       HA38 KA00 KA02 KA04 KA17                       KA31 KA33 KA62 SA05 TA01                       TA06 TA07                 5J500 AA02 AA41 AA53 AC56 AF18                       AH25 AH32 AH38 AK00 AK02                       AK04 AK17 AK31 AK33 AK62                       AS05 AT01 AT06 AT07 PF02                       PG02 PG04

Claims (11)

[Claims] 1. A power amplifier circuit, an output signal discriminating means for discriminating whether or not a voltage of an output signal of the power amplifier circuit exceeds a predetermined threshold value in a signaled state, and an output of the output signal discriminating means. Using a time measuring means for measuring the length of time that the voltage of the output signal of the power amplification circuit has continuously exceeded the threshold value, and the time measured by the time measuring means exceeds a predetermined time length. An audio amplifier characterized in that the output of the power amplifier circuit is stopped. 2. A preamplifier, a power amplifier circuit to which an output of the preamplifier is given via a capacitor, and a judgment as to whether or not a voltage of an output signal of the power amplifier circuit exceeds a predetermined threshold value in a signal state. 1 determination means and second determination means for determining whether or not the voltage of the output signal of the preamplifier exceeds a predetermined threshold value different from the threshold value, the output of the second determination means is negative, and the second (1) An audio amplifier characterized by stopping the output of the power amplifier circuit when the output of the discriminating means is affirmative. 3. A power amplifier circuit and a predetermined amplitude when a voltage of an output signal of the power amplifier circuit in a signal state is higher than a first threshold value higher by a predetermined value than an operation reference voltage of the power amplifier circuit. When the voltage of the output signal of the power amplifier circuit in the signal state and the first comparing means for outputting an output signal is lower than a second threshold value lower than the operation reference voltage by the predetermined value, the output signal of the predetermined amplitude. Output of the power amplifier circuit when the difference between the integrated value of the output of the first comparing means and the integrated value of the output of the second comparing means is not within a predetermined range. Audio amplifier characterized by stopping. 4. An output signal discriminating means for discriminating whether or not the voltage of the output signal of the power amplifying circuit exceeds a predetermined threshold in a signaled state, and the output of the output signal discriminating means for amplifying the power. And a time measuring means for measuring a time length in which the voltage of the output signal of the circuit continuously exceeds the threshold value, and when the time measured by the time measuring means exceeds a predetermined time length, the power amplification circuit An audio amplifier abnormality detection device, characterized in that it determines that the audio amplifier including is abnormal. 5. A first discriminating means for discriminating whether or not the voltage of the output signal of the power amplifier circuit, to which the output of the preamplifier is given via the capacitor, exceeds a predetermined threshold value, and the output signal of the preamplifier. And a second discriminating means for discriminating whether or not the voltage exceeds a predetermined threshold different from the threshold, the output of the second discriminating means being negative and the output of the first discriminating means being positive. In addition, an abnormality detecting device for an audio amplifier, characterized in that it is determined that an audio amplifier including the preamplifier and the power amplifier circuit is abnormal. 6. A first output signal having a predetermined amplitude when the voltage of the output signal of the power amplification circuit in the signal state is higher than a first threshold value higher than the operation reference voltage of the power amplification circuit by a predetermined value. Comparing means and second comparing means for outputting the output signal of the predetermined amplitude when the voltage of the output signal of the power amplifier circuit in the signal state is lower than the second threshold value which is lower than the operation reference voltage by the predetermined value. When the difference between the integrated value at the time t1 and the integrated value at the time t2 is not within a predetermined range, the audio amplifier including the power amplification circuit is determined to be abnormal. Audio amplifier abnormality detection device. 7. An output signal determination step of determining whether or not the voltage of the output signal of the power amplification circuit exceeds a predetermined threshold value in a signaled state, and the determination result of the output signal determination step, The voltage of the output signal of the power amplifier circuit has a time measuring step for measuring the length of time continuously exceeding the threshold value, when the time measured in the time measuring step exceeds a predetermined time length, the A method for detecting abnormality of an audio amplifier, which comprises determining that an audio amplifier including a power amplifier circuit is abnormal. 8. A first discrimination step of discriminating whether or not the voltage of the output signal of the power amplifier circuit, to which the output of the preamplifier is given through a capacitor, exceeds a predetermined threshold value in a signaled state, and the output signal of the preamplifier. And a second determination step of determining whether or not the voltage has exceeded a predetermined threshold value different from the threshold value, the determination result of the second determination step is negative, and the first
An abnormality detecting method for an audio amplifier, comprising determining that the audio amplifier including the preamplifier and the power amplifier circuit is abnormal when the determination result of the determining step is affirmative. 9. An output signal determination step of determining whether or not the voltage of the output signal of the power amplifier circuit exceeds a predetermined threshold value in a signaled state, and the processing of the output signal determination step is repeated at predetermined time intervals. If the affirmative appearance occurs a predetermined number of times in succession, or if the affirmation is equal to or more than a predetermined rate, it is determined that the audio amplifier including the power amplification circuit is abnormal. A method for detecting an abnormality in an audio amplifier, which comprises: 10. An output signal Sx having a predetermined amplitude is output when the voltage of the output signal of the power amplification circuit in the signal state is higher than a first threshold value which is higher than the operation reference voltage of the power amplification circuit by a predetermined value. 1 comparison step and a second output of the output signal Sy of the predetermined amplitude when the voltage of the output signal of the power amplifier circuit in the signal state is lower than a second threshold value lower than the operation reference voltage by the predetermined value. A comparing step, and when the difference between the integrated value of the output signal Sx and the integrated value of the output signal Sy is not within a predetermined range, it is determined that the audio amplifier including the power amplifier circuit is abnormal. A method for detecting abnormality of an audio amplifier, which is characterized in that 11. The method for detecting abnormality of an audio amplifier according to claim 7 or 9, when the audio amplifier including the power amplifier circuit is determined to be abnormal, the amplitude of the input signal to the power amplifier circuit. To determine again whether or not the audio amplifier including the power amplifier circuit is abnormal, and a method for detecting abnormality in an audio amplifier.