JP3882579B2 - Switching amplifier device and protection circuit control method for switching amplifier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an audio power amplifier device that amplifies an audio signal for driving a speaker, and in particular, switching that directly powers a switching means with a signal modulated by a PWM (Pulse Width Modulation) method and performs power supply amplification. The present invention relates to an amplifier device and a switching amplifier protection circuit control method.
[0002]
[Prior art]
Conventionally, various types of power amplifier devices that amplify audio signals for driving speakers have been commercialized. As a method of a power amplifier device for amplifying the audio signal, a so-called digital power amplifier device for amplifying the audio signal by directly switching the power source with a signal obtained by modulating the input digital audio signal has been developed. ing. In the case of this digital power amplifier device, for example, based on the input digital audio signal, a pulse wave modulated (PWM) PWM wave (hereinafter referred to as a PWM signal) is generated and stabilized by this PWM signal. The switched power supply is switched at high speed, the switched power supply is supplied to a filter, and an audio signal component is extracted to obtain a speaker drive signal.
[0003]
The PWM signal is a signal that is pulse-width modulated in accordance with the waveform level of the analog audio signal. The PWM signal controls on / off of switching means (power switch) that switches the power source.
[0004]
Then, the power source switched by the PWM signal by the switching means is supplied to the low-pass filter, and the high frequency component is cut and the audio signal band component is extracted, so that the output of the speaker corresponding to the power source voltage is used for driving the speaker. An amplified signal is obtained.
[0005]
[Problems to be solved by the invention]
By the way, in the case of such a digital power amplifier device, some kind of protection circuit is necessary for the switching means for obtaining the amplified signal for driving the speaker. That is, for example, when the speaker connection terminal is short-circuited with some metal object, or when some noise is mixed in the power supply supplied to the switching means or static electricity is generated, these effects are directly applied to the switching means. Therefore, it is necessary to provide a protection circuit so that the operation of the switching means is stopped when these abnormalities occur.
[0006]
However, when this protection circuit is activated, the amplifier operation of the input audio signal is completely stopped, resulting in a so-called silent state. In the conventional digital power amplifier device, in order to recover from the silent state, if there is a reset button, the user needs to operate the reset button. If there is no reset button, the power amplifier device It was necessary to perform the operation to turn on the power again.
[0007]
As described above, in the case of the conventional digital power amplifier device, unless the user manually operates, it is impossible to return from the state in which the protection circuit is activated, and there is a troublesome problem.
[0008]
In addition, when viewed from the user, the input audio signal is a silent signal waveform, so the speaker output is silent, or the power amplifier device protection circuit is activated. In addition, it is difficult to quickly determine whether the output of the speaker is in a silent state, and it is usually impossible to determine the appearance of the speaker to some extent, and it is difficult for the user to quickly deal with it.
[0009]
In addition, in the case of the protection circuit of the conventional digital amplifier device as described above, once it is activated, it takes time to restore it, so that the protection circuit is not required to be activated as much as possible. Was necessary. Specifically, for example, a large shield case is installed inside the amplifier device, or a noise countermeasure capacitor or diode is added to the circuit to reduce the influence of external noise. For this reason, there has been a problem of increasing the manufacturing cost of the digital amplifier device.
[0010]
The present invention has been made in view of such a situation, and an object of the present invention is to automatically restore the protection circuit of an amplifier device using a switching element.
[0011]
[Means for Solving the Problems]
The present invention provides a switching means that obtains a pulse signal for driving a speaker based on an input audio signal waveform, and performs a protection operation by stopping the switching operation of the switching means when an abnormality in the input or output of the switching means is detected. A protection means , a filter means for smoothing the pulse signal output from the switching means, a determination means for comparing the output voltage of the filter means with a predetermined threshold value to determine that the pulse signal is stopped, and a determination means. When the pulse signal is considered to be in a stopped state, the detecting means for detecting that the switching operation of the switching means is stopped, and the protection means when the detecting means detects that the operation of the switching means is stopped Reset the protection operation and resume the output of the pulse signal by the switching means. It is obtained by a means.
[0012]
According to the present invention, when the protection means is activated, the control means automatically performs an operation of resetting the protection operation, and the output of the speaker driving pulse signal by the switching means is resumed.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
[0014]
FIG. 1 is a diagram illustrating an overall configuration of a digital power amplifier device 10 of the present example. For the sake of simplicity, FIG. 1 shows only one channel processing configuration, but in actuality, it is configured to process audio signals of a plurality of channels such as two channels.
[0015]
The digital power amplifier device 10 of this example supplies a digital audio signal obtained from an external audio signal source (not shown) to the terminal 11 to the gain control unit 12, performs gain adjustment, and the gain is adjusted. The digital audio signal is converted into 1-bit digital audio data by the digital sigma converter 13, and the converted 1-bit digital audio data is supplied to the signal processing unit 14 to drive the switching element. A PWM signal is generated.
[0016]
The PWM signal generated by the signal processing unit 14 is supplied to the switching amplification unit 15, and the stabilized DC power supplied from the power supply circuit 18 is controlled on / off based on the PWM signal, and the audio signal is supplied to the power supply. Superimpose components. The switching amplification unit 15 of this example is configured by an integrated circuit, and, for example, a field effect transistor is used as a switching element included in the switching amplification unit 15. The signal switched by the switching amplifier 15 is supplied to a low-pass filter (LPF) 16 to remove the high-frequency component generated by the switching and extract only the audio signal component, and the extracted audio signal component is extracted from the speaker. A drive signal is supplied to the speaker device 1 connected to the speaker connection terminal 17, and audio (sound) is output from the speaker device 1 at a predetermined volume.
[0017]
Note that the switching element always performs a switching operation except when a protection circuit 15a described later is in operation. For example, a pulse signal having a constant frequency is output even in a silent state. is there. By removing the high-frequency component corresponding to the switching frequency in the low-pass filter 16, only the audio signal component is supplied to the speaker device side. For example, a pulse signal of about 250 KHz is generated by the switching element, and the signal component of about 250 KHz is removed by the low-pass filter 16 so that an audio signal component in a so-called audible band (for example, up to about several tens of kHz) is obtained. The signal is output from the speaker connection terminal 17.
[0018]
The digital power amplifier device 10 further includes an operation unit 19 including various operation keys and a volume knob for volume adjustment. The CPU 20 determines the operation status of the operation unit 19 and the CPU 20 adjusts the volume. Various controls such as these are performed.
[0019]
Here, the switching amplifier 15 of this example incorporates a protection circuit 15a. The protection circuit 15a detects an abnormality in the power supply input from the power supply circuit 18 to the switching amplification unit 15, an abnormality in the input PWM signal, an abnormality in the output switched by the switching element (such as a short circuit), and when the abnormality is detected, The switching operation of the switching elements of all the channels is stopped, and the output from the switching amplifier 15, that is, the output of the speaker drive signal from the speaker connection terminal 17 is stopped.
[0020]
The protection circuit 15a is configured to reset the protection operation when the protection operation is executed by a reset signal supplied from the CPU 20.
[0021]
The CPU 20 is configured to determine the output of the switching amplifier 15 in order to determine whether the protection circuit 15a is activated and the switching operation of the switching element is stopped. That is, the output of any one channel switching element in the switching amplifier 15 is smoothed by the low-pass filter 21, and the output of the low-pass filter 21 is supplied to the analog / digital converter 22 of the CPU 20. The data converted into the data corresponding to the above is determined in the CPU 20 based on the data converted by the analog / digital converter 22 and a reset signal is output to the protection circuit 15a based on the determined data. The output of the reset signal here means that the low level signal “L” is temporarily supplied to the protection circuit 15a as the reset signal, and the high level signal “H” is sent from the CPU 20 to the protection circuit 15a except at the time of reset. To supply. The determination process for outputting the reset signal will be described later.
[0022]
The low-pass filter 21 is a filter having different characteristics from the low-pass filter 16 provided on the speaker connection terminal 16 side. In other words, the filter is configured to have different voltage values when the switching element in the switching amplifier 15 performs a switching operation and when the switching element does not perform the switching operation. Specifically, for example, a low-pass filter having a cutoff frequency of about 3 Hz is used to convert the pulse signal modulated by the PWM signal into a direct current.
[0023]
FIG. 2 is a diagram showing in more detail the configuration related to the protection operation of the digital amplifier device 10 of this example. In FIG. 2, the switching amplification unit 15 is shown as a configuration for processing a 2-channel signal, and includes a left-channel switching element 15L and a right-channel switching element 15R. Output signals switched by the switching elements 15L and 15R for the respective channels are supplied to the speaker connection terminals 17L and 17R via the low-pass filters 16L and 16R for the respective channels. The low-pass filters 16L and 16R are filters that remove high-frequency components generated by switching. The speaker devices 1L and 1R for each channel are connected to the speaker connection terminals 17L and 17R for the left and right channels.
[0024]
Here, in this example, a signal obtained at one pole of the output of the switching element 15R of one channel (right channel in FIG. 2) is supplied to the analog / digital converter 22 in the CPU 20 via the low-pass filter 21. It is comprised so that it may do. As already described, the low-pass filter 21 is a filter having a cutoff frequency of about 3 Hz. Here, for example, the resistor R1 and the diode D1 are connected in series, and one end of the resistor R2, one end of the capacitor C1, and the cathode of the diode D2 are connected between the diode D1 and the input of the converter 22. The other end of the resistor R2, the other end of the capacitor C1, and the anode of the diode D2 are respectively connected to the ground side and configured as a low-pass filter.
[0025]
By passing through the low-pass filter 21 having such a configuration, when the switching element normally performs a switching operation, the output of the low-pass filter 21 is set to a voltage of 0.8 V or more. When the switching operation by the element is stopped, the voltage is close to 0V, less than 0.8V. That is, when the switching element normally performs a switching operation, for example, as shown in FIG. 3A, a pulse signal of about 250 kHz is output from the switching element. Although the pulse signal waveform varies depending on the audio signal waveform, the basic frequency of the pulse signal is the same even in the case of a silent audio signal. In this example, the pulse signal is passed through the low-pass filter 21 so that the voltage becomes 0.8 V or more. On the other hand, when the switching element stops the switching operation, the voltage becomes a constant voltage such as 0 V as shown in FIG. 3B.
[0026]
The CPU 20 determines whether or not the output of the analog / digital converter 22 is 0.8 V or higher data.
[0027]
Next, control processing based on the output data of the analog / digital converter 22 in the CPU 20 will be described with reference to the flowchart of FIG.
[0028]
When the CPU 20 proceeds from the main routine (step S10) to a subroutine for starting the operation state determination process of the protection circuit (step S11), the CPU 20 reads the output data of the analog / digital converter 22 and outputs the output voltage of the low-pass filter 21. The value is determined and stored (step S12). Then, it is determined whether or not the voltage value determined at this time is less than 0.8 V (step S13). If it is not less than 0.8V (that is, 0.8V or more), this subroutine is terminated (step S16), and the process returns to the main routine of step S10. Thereafter, the process proceeds to a subroutine for determining the operation state of the protection circuit in step S11 at a cycle of about 10 ms.
[0029]
When it is determined in step S13 that the voltage value is less than 0.8V, it is determined whether or not the voltage value determined and stored in the previous subroutine is less than 0.8V (step S14). Here, when the previously determined voltage value is 0.8 V or more, the process proceeds to step S16 to end the subroutine, and returns to the main routine of step S10. If it is determined in step S14 that the voltage is less than 0.8 V, the process proceeds to step S15, where the reset signal is set to the low level signal “L” for 10 ms, and then returned to the high level signal “H”. Thereafter, the process proceeds to step S16, and this subroutine is terminated.
[0030]
Since the low level signal “L” for 10 ms in step S15 is supplied as a reset signal to the protection circuit 15a, the protection circuit 15a is reset, and the switching operation is stopped by the operation of the protection circuit 15a. The switching operation of the switching elements 15L and 15R is restored, and the audio output from the connected speaker device is resumed.
[0031]
When the CPU 20 performs the control operation in this way, when it is detected twice continuously at intervals of about 10 ms that the output voltage of the low-pass filter 21 is less than 0.8 V, the protection in the switching amplifier 15 is protected. It is determined that the circuit 15a is activated and the switching operation is stopped, a reset signal is supplied to the protection circuit 15a, the protection operation by the protection circuit 15a is reset, and the switching operation in the switching amplifier 15 is performed. Resumed. Therefore, when the protection circuit is activated due to a temporary factor such as power supply noise, it automatically returns about 10 ms after the activation. Therefore, the audio output from the speaker device when the protection circuit is activated is temporarily interrupted for a short time, and the user does not need to operate the reset button or turn the power of the amplifier device on again. .
[0032]
In addition, when the protection circuit is activated in this way, it is automatically restored after a lapse of a short time, so that the amplifier device can tolerate a temporary output stop for a short time. In addition, it is not necessary to spend so much cost on noise countermeasures such as a shield plate and a capacitor, and the manufacturing cost of the amplifier device can be reduced.
[0033]
Further, in the case of this example, as shown in steps S13 and S14 in the flowchart of FIG. 4, the voltage of the switching output is judged twice continuously at an interval of 10 ms. The influence can be avoided and the operation of the protection circuit can be reliably detected.
[0034]
In the example shown in the flowchart of FIG. 4, the reset signal is supplied to the protection circuit when the switching output is in a stopped state twice consecutively. However, after the reset signal is supplied, the reset signal is further continuously supplied. When the protection circuit is activated, the reset signal may not be supplied. The flowchart of FIG. 5 is a diagram illustrating a processing example in this case.
[0035]
The operation of the flowchart of FIG. 5 will be described. When the CPU 20 proceeds from the main routine (step S10) to a subroutine for starting the operation state determination process of the protection circuit (step S11), the output data of the analog / digital converter 22 is output. Is read and the output voltage value of the low-pass filter 21 is determined and stored (step S12). Then, it is determined whether or not the voltage value determined at this time is less than 0.8 V (step S13). If it is not less than 0.8V (that is, 0.8V or more), this subroutine is terminated (step S16), and the process returns to the main routine of step S10. Thereafter, the process proceeds to a subroutine for determining the operation state of the protection circuit in step S11 at a cycle of about 10 ms.
[0036]
When it is determined in step S13 that the voltage value is less than 0.8V, it is determined whether or not the voltage value determined and stored in the previous subroutine is less than 0.8V (step S14). Here, when the previously determined voltage value is 0.8 V or more, the process proceeds to step S16 to end the subroutine, and returns to the main routine of step S10. Up to this point, the processing is the same as that shown in the flowchart of FIG.
[0037]
If it is determined in step S14 that the voltage is less than 0.8V, the process proceeds to step S17, and it is determined whether or not the determined voltage value is less than 0.8V continuously for 10 times or more. If it is determined in this determination that the determined voltage value is less than 0.8 V for 10 times or more, the process proceeds to step S16 to end this subroutine, and returns to the main routine in step S10. Not performed. If it is determined in step S17 that the determined voltage value is continuously less than 0.8 V is less than 10, the process proceeds to step S15, and the reset signal is set to the low level signal “L” for 10 ms. Then, the process of returning to the high level signal “H” is performed, and then the process proceeds to step S16 to end this subroutine.
[0038]
If the reset operation is performed and the protection operation by the protection circuit is reset by performing the processing as shown in the flowchart of FIG. 5, if the protection operation is performed again immediately after that, the protection operation is reset. Is not executed, the protection circuit is activated, and the switching operation remains stopped.
[0039]
If the protection operation is performed immediately after resetting in this way, it is assumed that the cause of the activation of the protection circuit has not been removed. In this case, the cause of the activation of the protection circuit (for example, the speaker connection terminal When the user depresses the reset button or turns the power on again after removing the short circuit or the like, the operation of the protection circuit can be restored as in the conventional case.
[0040]
In the above-described embodiment, a PWM signal that is pulse-width modulated based on 1-bit digital audio data is generated to control the switching of the power switch. However, the PDM (Pulse Duration Modulation) method is used. The present invention can also be applied to various types of switching amplifier devices in which switching is controlled by other pulse-modulated signals such as those to obtain an amplified signal.
[0041]
Further, in the above-described embodiment, although configured as a single amplifier device that drives a connected speaker device based on an input audio signal, an audio signal source such as a playback device, a speaker device, and the like are integrated. Of course, the present invention can also be applied to an amplifier section of an audio device.
[0042]
In the above-described embodiment, the low-pass filter (corresponding to the low-pass filter 16 in FIG. 1) that removes high-frequency components generated by switching is provided between the switching amplification unit and the speaker connection terminal. When a similar low-pass filter is connected to the connected speaker device side, or when high frequency removal is not necessary due to the characteristics of the speaker device, the output low-pass filter may be omitted.
[0043]
【The invention's effect】
According to the present invention, the operation of automatically resetting the protection operation is executed even if the protection means is activated. Therefore, when the protection means is activated by an input of temporary noise, etc., the user can be silent automatically for a short period of time during which the protection means is activated. Thus, it is possible to effectively prevent the protection means from operating due to power noise or the like and continuing the silent state.
[0044]
In this case, the detection means comprises a filter means for smoothing the pulse signal output from the switching means and a determination means for determining the output voltage of the filter means, and the determination means detects a voltage without a pulse signal. In this case, it is possible to easily detect that the switching operation is stopped by detecting that the switching operation is stopped.
[0045]
The pulse signal for driving the speaker output from the switching means is removed from the high frequency component by a filter means different from the filter means provided in the detection means and is supplied to the speaker. The characteristics can be set optimally, and the switching operation can be detected and the output for supplying the speaker can be satisfactorily performed.
[0046]
In addition, when the detection means detects that the switching operation has been stopped for a predetermined number of times, the control means resets the protection operation by the protection means, so that the state in which the protection operation is performed continues. The operation of resetting after reliably detecting is performed.
[0047]
Further, when resetting is performed when it is detected that the switching operation has been stopped for a predetermined number of times in this way, the detection means detects that the switching operation has further stopped immediately after the reset. Since the reset is not performed at the time of detection, when the factor for operating the protection means continues, the reset operation is not executed, and the protection function functions effectively.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an example of an overall configuration according to an embodiment of the present invention.
FIG. 2 is a configuration diagram showing an example of a configuration of a portion related to a protection operation according to an embodiment of the present invention.
FIG. 3 is a waveform diagram illustrating an example of an output waveform of a switching amplifier.
FIG. 4 is a flowchart showing an example of a return operation according to an embodiment of the present invention.
FIG. 5 is a flowchart showing an example of a return operation according to another embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,1L, 1R ... Speaker apparatus, 10 ... Digital power amplifier apparatus, 11 ... Input terminal, 12 ... Gain control part, 13 ... Digital sigma conversion part, 14 ... Signal processing part, 15 ... Switching amplification part, 15L, 15R ... Switching element, 16, 16L, 16R ... low pass filter, 17, 17L, 17R ... output terminal, 18 ... power supply circuit, 19 ... operation unit, 20 ... central control unit (CPU), 21 ... low pass filter, 22 ... analog / digital converter

Claims (5)

Switching means for obtaining a speaker driving pulse signal based on the input audio signal waveform;
Protection means for stopping the switching operation of the switching means and performing a protection operation when an abnormality in the input or output of the switching means is detected;
Filter means for smoothing the pulse signal output by the switching means;
Determining means for comparing the output voltage of the filter means with a predetermined threshold value to determine that the pulse signal is stopped;
Detecting means for detecting that the switching operation of the switching means is stopped when the pulse signal is regarded as being stopped by the determining means;
When the detecting means detects that the operation of the switching means is stopped, by resetting the protection operation by the protection means, switching amplifier and control means for resuming the output of the pulse signal by said switching means apparatus. The switching amplifier device according to claim 1 ,
The speaker driving pulse signal output from the switching unit is supplied to the speaker after removing a high frequency component by a filter unit different from the filter unit included in the detection unit.
A switching amplifier device characterized by that . The switching amplifier device according to claim 1,
When the detection means detects that the switching operation has been stopped for a predetermined number of times, the control means does not reset the protection operation by the protection means
A switching amplifier device characterized by that . The switching amplifier device according to claim 1 ,
The control means does not reset when the detection means detects that the switching operation is further stopped immediately after the reset.
A switching amplifier device characterized by that . A switching step for obtaining a pulse signal for driving the speaker based on the input audio signal waveform;
A protection step for stopping the switching operation of the switching step and performing a protection operation when an abnormality in the input or output of the switching step is detected;
A filter step for smoothing the pulse signal output by the switching step;
A determination step of comparing the output voltage of the filter step with a predetermined threshold value to determine that the pulse signal is stopped;
A detection step for detecting that the switching operation of the switching means is stopped when the pulse signal is regarded as being stopped by the determination step;
When the detecting step detects that the switching step is stopped, by resetting the protection operation by the protection step, to resume the output of the pulse signal by said switching step
A switching amplifier protection circuit control method.

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