WO2011102092A1

WO2011102092A1 - Digital amplifier

Info

Publication number: WO2011102092A1
Application number: PCT/JP2011/000648
Authority: WO
Inventors: 宙菅原; 寿幸佐々木; 茂樹庭山; 佳樹前田; 智臣 ▲高▼野
Original assignee: パナソニック株式会社; ローランド株式会社
Priority date: 2010-02-18
Filing date: 2011-02-04
Publication date: 2011-08-25
Also published as: CN102859868B; CN102859868A; JP2011171967A; JP5430438B2

Abstract

The disclosed amplifier can reduce both overcurrent in output-current and resonance current detection time, minimises output suspension, and is capable of more appropriate current control operations. A digital amplifier has: in the output portion of switch elements (Q1, Q2), an overcurrent detection circuit (19) for detecting overcurrent, which is equal to or exceeds a specified value, in the output current; a phase advance circuit (22) which advances the phase of an overcurrent detection signal; and a resonance current detection circuit (21) which detects resonance current equal to or exceeding a specified value relating to the output current when resonance is generated at an output filter (15). When an abnormal state is detected in the output current on the basis of the overcurrent detection signal or a resonance current detection signal, a drive circuit (12) carries out current limiting operations by turning a drive signal to OFF and stopping the switching operation of the switching elements (Q1, Q2).

Description

Digital amplifier

The present invention relates to a digital amplifier that performs switching operation of a switching element in an output stage to amplify an input signal in class D.

A digital amplifier converts an analog input signal into a digital pulse signal by PWM (Pulse Width Modulation) conversion, and switches the active element (switching element) such as an FET by this digital pulse signal, thereby amplifying power (class D). Amplification). Then, the digital pulse signal after power amplification is passed through a low pass filter of the LC circuit to obtain an analog output signal obtained by power amplification of the source signal.

This type of digital amplifier has a function of protecting an amplifier circuit such as a switching element in the output stage when an overcurrent, resonance, or the like on the load side occurs. For example, when an overcurrent state occurs due to a load short circuit or the like, the output is interrupted by a relay or the like provided in the amplifier output unit to protect the switching element. Also, when there are few speakers connected to the digital amplifier, resonance occurs in the low-pass filter of the amplifier output section at light load (high impedance), and the amplifier circuit may be destroyed due to this resonance phenomenon There is. In order to prevent the destruction of the digital amplifier due to such a resonance phenomenon, a technique for protecting an amplifier circuit by detecting a resonance current at a light load and muting an input signal when an excessive resonance current flows is known. (For example, refer to Patent Document 1).

Japanese Unexamined Patent Publication No. 2007-258903

In the configuration such as the above-mentioned Patent Document 1, if the input signal is muted immediately after the resonance current at the time of light load is detected, when the normal operation is resumed, the operation in the PWM circuit is initialized. There was a problem that it took time to start up a digital amplifier. In this case, output (sound etc.) stops due to muting of the input signal.

Also, in order to protect the circuit of the digital amplifier, a configuration in which a current limiter using an analog circuit that limits the output current of the amplifier circuit is mounted is also conceivable. In such a configuration, a phase delay occurs in the control of the current limiter, and the current limiting operation may not be in time. Further, if the current limiter control is performed in consideration of this control delay, the time when the current limiter control functions is too early or the frequency increases, and there is a problem that the output is easily cut off.

The present invention has been made in view of the above circumstances, and its purpose is to reduce the time for detecting an abnormality in the output current and to protect the amplifier circuit in the event of an abnormality without stopping the output as much as possible. To provide an amplifier.

The present invention is a digital amplifier that amplifies an input signal class D, a switching element that performs a switching operation by a drive signal based on a digital pulse signal of the input signal, a drive circuit that supplies the drive signal to the switching element, An output filter including a low-pass filter connected to the output part of the switching element, and an abnormality that is provided in the output part of the switching element and detects an abnormal state of the output current from the switching element and outputs an abnormal state detection signal A state detection unit, the abnormal state detection unit has a phase advance function for advancing the phase of the abnormal state detection signal, and the drive circuit detects an abnormal state of the output current based on the abnormal state detection signal Digital signal for turning off the drive signal and stopping the switching operation of the switching element when To provide a pump.
With the above configuration, when an abnormal condition is detected, the drive signal from the drive circuit is turned off to stop the switching operation of the switching element, so that the input signal is turned off, the output signal is cut off, etc. Operation is possible. Further, the phase delay of the abnormal state detection signal can be eliminated or reduced by the phase advance function of the abnormal state detection unit. Therefore, it is possible to reduce the time for detecting an abnormality in the output current and protect the amplifier circuit in the event of an abnormality without stopping the output as much as possible.

Further, the present invention is the digital amplifier described above, wherein the abnormal state detection unit detects an overcurrent of a predetermined value or more in the output current from the switching element, and uses the overcurrent detection signal as the abnormal state detection signal. The circuit includes an overcurrent detection circuit for outputting and a phase advance circuit for advancing the phase of the overcurrent detection signal.
With the above configuration, when an overcurrent of a predetermined value or more in the output current from the switching element is detected as an abnormal state of the output current, the drive signal is turned off to stop the switching operation of the switching element and perform current limitation Is possible. In this case, a current limiting operation can be performed at a high speed when an overcurrent occurs, and the amplifier circuit including the switching element can be protected without stopping the output as much as possible.

Further, the present invention is the digital amplifier described above, wherein the abnormal state detection unit detects a resonance current that is equal to or greater than a predetermined value related to an output current when resonance occurs in the output filter, and serves as the abnormal state detection signal. Including those having a resonance current detection circuit that outputs a resonance current detection signal.
With the above configuration, when a resonance current of a predetermined value or more related to the output current when resonance occurs in the output filter as an abnormal state of the output current, the drive signal is turned off and the switching operation of the switching element is stopped. It is possible to limit the current. In this case, a current limiting operation can be performed at high speed when resonance occurs in the output section, and the amplifier circuit including the switching element can be protected without affecting the output in the audible range.

Further, the present invention is the digital amplifier described above, wherein a temperature detection unit that detects a temperature of the switching element or its surroundings, an output blocking unit that blocks the output of the switching element, and the input signal below a predetermined level An input signal mute unit for making a silent state or a minute state of the input signal, and an interlocking control unit for interlocking the output blocking unit and the input signal mute unit, the interlocking control unit having a predetermined value or more by the temperature detection unit In the case where a high temperature state is detected, the output cutoff unit and the input signal mute unit are operated in conjunction with each other.
With the above configuration, when the temperature of the switching element or its surroundings becomes a high temperature state higher than a predetermined value, both the input and output of the switching element are operated by operating the output cutoff unit and the input signal mute unit in conjunction with each other. Can be stopped to protect the switching element. In this case, if the output of the switching element is cut off, the output filter is in a state where no resonance occurs and resonance is likely to occur in the output filter. However, it is possible to prevent resonance in the output filter by muting the input signal. is there.

Further, the present invention is the above digital amplifier, wherein the drive circuit turns off the drive signal when the output current is a predetermined value or more based on the abnormal state detection signal, and performs a switching operation of the switching element. And the current limiting operation of the switching element is performed by repeatedly performing the control to turn on the driving signal and restart the switching operation of the switching element when the output current becomes less than a predetermined value. including.
With the above configuration, the current limiting operation is performed by repeatedly stopping / resuming the switching operation, so that it is possible to protect the amplifier circuit including the switching device without stopping the output as much as possible. It becomes.

The present invention is the above-described digital amplifier, wherein the drive circuit performs a current limiting operation of the switching element when the reference oscillation frequency of the digital pulse signal is one cycle unit or any one cycle unit. In this case, the drive signal is turned on / off at the following timing.
With the above configuration, when an abnormal state such as occurrence of overcurrent or resonance current is detected, real-time current limiting operation is possible at high speed according to the reference oscillation frequency of the digital pulse signal of the input signal. It is possible to protect the amplifier circuit including the switching element without stopping as much as possible.

Further, the present invention is the above digital amplifier, wherein when it is determined that the resonance current detection signal of the resonance current detection circuit is continuously output for a predetermined time and has been continued for the predetermined time, the fact is indicated. It is the structure which has the control part which outputs this signal.
With the above configuration, the system oscillation of the loudspeaker system can be detected and the user of the loudspeaker system can be notified that the system oscillation has occurred, so that the mixer, the digital amplifier, the speaker, or the like is prevented from being broken. It becomes possible.

According to the present invention, it is possible to provide a digital amplifier capable of reducing the time for detecting an abnormality in the output current and protecting the amplifier circuit in the event of an abnormality without stopping the output as much as possible.

1 is a circuit diagram showing a configuration of a digital amplifier according to an embodiment of the present invention. Circuit diagram showing a specific configuration example of a digital amplifier according to the present embodiment Output characteristics diagram showing comparison of thermal design standards for digital and analog amplifiers Operation waveform diagram showing waveforms at the time of amplifier operation by the current limiting circuit of this embodiment (A), (B) is a comparison diagram of output current waveforms depending on the presence or absence of a phase advance circuit in the current limiting circuit of this embodiment. Circuit diagram showing basic configuration of digital amplifier Gain-frequency characteristics diagram of amplifier circuit when resonance occurs in low-pass filter of amplifier output section The flowchart which shows the 1st operation example regarding the circuit protection function of the digital amplifier which concerns on this embodiment. State transition diagram showing a second operation example regarding the circuit protection function of the digital amplifier according to the present embodiment The figure which shows the loudspeaker system using the digital amplifier which concerns on this embodiment The circuit diagram which shows the structure of the digital amplifier which concerns on other embodiment of this invention.

In the following embodiments, as an example of a digital amplifier according to the present invention, a configuration example of a digital amplifier that amplifies an audio signal by using an FET as an output stage switching element and connecting a speaker to a load is shown.

FIG. 1 is a circuit diagram showing a configuration of a digital amplifier according to an embodiment of the present invention. The digital amplifier of this embodiment includes a PWM circuit 11, a drive circuit 12, and switching elements Q1 and Q2. The switching elements Q1 and Q2 are composed of N-channel MOSFETs or the like, and the drain and source are connected in series to constitute a pair of switching elements. The switching elements Q1 and Q2 perform switching operation alternately according to the input of the drive signal to the gate, and amplify the power of the input signal. At this time, the voltage + VB is applied to the drain of the switching element Q1, the voltage −VB is applied to the source of the switching element Q2, and the switching elements Q1 and Q2 are turned on / off according to the gate voltage. The switching element is not limited to the FET, and may be another element capable of switching operation such as a bipolar transistor.

The PWM circuit 11 performs PWM conversion of the input signal and outputs a digital pulse signal having a pulse width corresponding to the input signal level. The drive circuit 12 drives the switching elements Q1 and Q2 based on the digital pulse signal output from the PWM circuit 11, and outputs drive signals to the gates of the switching elements Q1 and Q2, respectively.

An output filter 15 including a low-pass filter including a coil 13 and a capacitor 14 is connected to the output portions of the switching elements Q1 and Q2. A relay 16 that opens and closes an output signal path is connected to the output end of the output filter 15 as an example of an output blocking unit, and a speaker 17 that is a load is connected via the relay 16. The output cut-off unit often uses a relay, but may be other switch means.

The input signal of the analog audio signal is converted into a digital pulse signal by the PWM circuit 11 and input to the drive circuit 12. Based on this digital pulse signal, a drive signal is input from the drive circuit 12 to the gates of the switching elements Q1 and Q2, and the switching elements Q1 and Q2 perform a switching operation by the drive signal. The power-amplified digital pulse signals output from the output units of the switching elements Q1 and Q2 are converted into analog signals by the output filter 15, output as power-amplified analog audio signals, and supplied to the speaker 17. The speaker 17 is driven by this output signal, and sound is emitted.

In addition, a detection resistor 18 is connected in series to the coil 13 of the output filter 15 of the amplifier output unit, and the current flowing through the coil 13 is detected by the voltage across the detection resistor 18 to detect the overcurrent flowing through the load. A detection circuit 19 is provided. Further, a detection resistor 20 is connected in series to the capacitor 14, and a resonance current detection circuit 21 that detects a current flowing through the capacitor 14 by a voltage across the detection resistor 20 and detects a resonance current generated in the output filter 15 is provided. ing.

A phase advance circuit 22 that advances the phase of the overcurrent detection signal is connected to the output terminal of the overcurrent detection circuit 19, and is connected to the drive circuit 12 via the phase advance circuit 22. The output terminal of the resonance current detection circuit 21 is also connected to the drive circuit 12. The overcurrent detection circuit 19 outputs a high-level overcurrent detection signal as an abnormal state detection signal when the overcurrent detection value exceeds a predetermined value. The resonance current detection circuit 21 outputs a high level resonance current detection signal as an abnormal state detection signal when the resonance current detection value is equal to or greater than a predetermined value. Of course, it is possible to configure the overcurrent detection circuit 19 and the phase advance circuit 22 as the same circuit block without using separate circuits. In this case, the voltage across the detection resistor 18 is detected by an operational amplifier (not shown), the phase of the detected waveform is advanced, and then compared with a predetermined value by a comparator (not shown) to detect an overcurrent. The circuit configuration of the resonance current detection circuit 21 other than the phase advance circuit can be realized by the same circuit configuration as that of the overcurrent detection circuit 19 described above.

When the overcurrent detection signal from the overcurrent detection circuit 19 or the resonance current detection signal from the resonance current detection circuit 21 is input, the drive circuit 12 stops operation and is supplied to the switching elements Q1 and Q2. Turn off. As a result, the gate voltages of the switching elements Q1 and Q2 become less than a predetermined value, and both are turned off. The switching elements Q1 and Q2 are alternately turned on / off at a period of a reference oscillation frequency such as 400 kHz during a normal switching operation. On the other hand, when the drive signal is off, both are off, and no output current flows during the off period. The overcurrent detection circuit 19, the phase advance circuit 22, the resonance current detection circuit 21, and the drive circuit 12 constitute a current limit circuit (current limiter) that limits the current of the switching elements Q 1 and Q 2 at the time of abnormality in the present embodiment. Is done.

An input signal mute unit 23 is provided on the input side of the PWM circuit 11. The input signal mute unit 23 includes a mute circuit 24, a bypass circuit 25, and switches 26 and 27 for switching between them, and the mute circuit 24 or the bypass circuit 25 is connected to the input signal path in accordance with an external control signal. Connect to. The mute circuit 24 attenuates the input signal to a predetermined level or less, and has a function of making the input signal silent or minute.

Further, in the vicinity of the switching elements Q1 and Q2, a temperature detection unit 28 for detecting the temperature of the switching elements Q1 and Q2 or its surroundings is provided. The output end of the temperature detection unit 28 is connected to an interlock control unit 29 that controls the relay 16 and the input signal mute unit 23 in an interlocked manner. The interlock control unit 29 outputs a control signal to the relay 16 and the input signal mute unit 23 to operate them in conjunction with each other when the temperature detection value by the temperature detection unit 28 is equal to or greater than a predetermined value. Execute. Thereby, the input / output with respect to the switching elements Q1, Q2 is turned off.

FIG. 2 is a circuit diagram showing a specific configuration example of the digital amplifier according to the present embodiment. FIG. 2 shows an example of a specific configuration of the drive circuit and the phase advance circuit. The drive circuit 31 includes an inverting circuit 32,

photocouplers

33 and 34,

drivers

35 and 36, a switch element 37, and a NOR circuit 38. The LED of one photocoupler 33 is directly connected to the output terminal of the PWM circuit 11, and the LED of the other photocoupler 34 is connected via an inverting circuit 32.

Drivers

35 and 36 are connected to the phototransistors of the

photocouplers

33 and 34, respectively. With such a configuration, one of the

photocouplers

33 and 34 is turned on and the other is turned off based on the digital pulse signal output from the PWM circuit 11, so that the

drivers

35 and 36 are alternately turned on. A level signal is provided. The

drivers

35 and 36 are switched so as to alternately turn on / off the switching elements Q1 and Q2 by alternately supplying drive signals to the switching elements Q1 and Q2 in accordance with input signals from the photocouplers 33 and 34. Make it work. Although a configuration example using a photocoupler, a switch element, and the like is shown here, a configuration in which the drive signal is turned on / off by other switch means may be used.

Further, the other ends of the LEDs of the

photocouplers

33 and 34 are grounded via a switch element 37. An overcurrent detection signal from the overcurrent detection circuit 19 via the phase advance circuit 41 or a resonance current detection signal from the resonance current detection circuit 21 is supplied to the control input terminal of the switch element 37 via the NOR circuit 38. The The switch element 37 is turned on to conduct when a high level is inputted to the control input terminal, and is turned off and opened when a low level is inputted. In this case, when at least one of the overcurrent detection signal and the resonance current detection signal becomes high level, the switch element 37 is turned off, and both the LEDs of the

photocouplers

33 and 34 are turned off. Therefore, when an overcurrent or resonance current exceeding a predetermined value is detected by the overcurrent detection circuit 19 and the resonance current detection circuit 21, the operation of the drive circuit 31 can be stopped and the switching operation of the switching elements Q1 and Q2 can be stopped. .

The phase advance circuit 41 includes a capacitor 42 and a resistor 43 connected in series, and is configured by a CR phase shift circuit that is grounded via a resistor 44. The phase advance circuit 41 advances the overcurrent detection signal by the capacitor 42 and supplies it to the drive circuit 31. The phase advance circuit is not limited to the CR phase shift circuit, and other configurations such as an LC phase shift circuit may be used. This phase advance circuit 41 can eliminate or reduce the phase delay of the overcurrent detection signal that occurs in the system that detects and feeds back the overcurrent of the output current. The phase delay of the overcurrent detection signal is mainly caused by constants, frequency characteristics and the like in the output filter 15 and the overcurrent detection circuit 19, and is about 10 μsec 約, for example. Here, it is more preferable that the phase advance degree in the phase advance circuit is equal to the time that takes into account the delay of the signal in the entire system until the abnormal state of the output current is detected and the drive signal is turned off. Since the resonance current detection circuit 21 has a phase advance function by the capacitor 14 of the output filter 15, it is not necessary to provide a phase advance circuit. By providing the circuit having the phase advance function in this way, the detection time of the overcurrent state can be shortened, and the response characteristic of the circuit protection operation against the overcurrent can be improved.

Here, we explain the thermal design criteria for digital amplifiers. FIG. 3 is an output characteristic diagram showing a comparison of thermal design criteria between a digital amplifier and an analog amplifier. In the graph of FIG. 3, the horizontal axis indicates output, and the vertical axis indicates loss. The digital amplifier has less loss over the entire output range than the analog amplifier, but the loss with respect to the output is almost linear, and the loss increases as the output increases (output current increases). That is, the loss of the digital amplifier is (normal use) << (abnormal). On the other hand, the loss of the analog amplifier is (in normal use) ≈ (in abnormal state), and even if the loss in the abnormal state becomes large, there is no great difference from the normal use. The thermal design standard of the amplifier is generally set based on a loss during normal use, and the heat sink size and the like are determined based on this thermal design standard. In analog amplifiers, if thermal design is performed during normal use, there will be no problem even if the abnormal time is not taken into consideration. However, in the digital amplifier, if the thermal design is not performed with sufficient consideration of the abnormal time, a malfunction such as a failure of the amplifier circuit may occur.

However, since it is not preferable from the viewpoint of designing a digital amplifier to increase the size of the heat sink in consideration of abnormal conditions, a case is assumed here in which a current limiter control is provided to control the current limiter when an overcurrent occurs. . In the present embodiment, the current limiter control is performed by stopping the drive circuit by overcurrent detection and resonance current detection, and a phase advance circuit is added to the overcurrent detection circuit to compensate for the phase delay of the overcurrent detection signal. It has. As a result, when an overcurrent or resonance current occurs in the load of the digital amplifier, the current limiter control reduces the output current abnormality detection time and limits the output current at the time of abnormality without stopping the output as much as possible. It can be performed.

Next, the current limiting operation when an overcurrent occurs will be described in detail. FIG. 4 is an operation waveform diagram showing waveforms during amplifier operation by the current limiting circuit of the present embodiment. In FIG. 4, the current limit value is a current value of a current limiting threshold value based on a predetermined value for detecting an abnormal state in the overcurrent detection circuit 19. When the output current value exceeds the current limit value due to a load abnormality or the like, the operation of the drive circuit 12 is stopped so that no further output current flows. Here, when the output current value exceeds a predetermined value, the drive circuit 12 turns off the drive signal and stops the switching operation of the switching elements Q1 and Q2. Here, in the state where the output current value is equal to or greater than the predetermined value, the operation stop of the drive circuit 12 continues. Thereafter, when the output current value becomes less than the predetermined value, the drive circuit 12 turns on the drive signal and restarts the switching operation of the switching elements Q1 and Q2.

Therefore, when an abnormal state is detected and a current limiting operation is performed, as a current limiter control by the current limiting circuit, the reference oscillation frequency of the digital amplifier (the reference oscillation frequency of the digital pulse signal, the switching frequency of the switching element, for example, 400 kHz) The drive circuit 12 performs on / off control of the drive signal in real time in units of one cycle. Thereby, the switching elements Q1 and Q2 are repeatedly started / stopped (one is on) / stop (both are off). At this time, as shown in the enlarged view in FIG. 4, the output current fluctuates in a sawtooth shape in units of one cycle of the reference oscillation frequency (for example, every cycle T), and the current value is limited to less than a predetermined value. Therefore, it is possible to protect the amplifier circuit including the switching element while continuing the switching operation as much as possible without stopping the output from the switching elements Q1 and Q2. The on / off control of the drive signal is not limited to one cycle unit, but can be performed on / off at an arbitrary timing within one cycle.

5A and 5B are comparison diagrams of output current waveforms according to the presence or absence of a phase advance circuit in the current limiting circuit of the present embodiment. FIG. 5A shows a case where no phase advance circuit is provided, and FIG. Each operation waveform when a phase circuit is provided is shown. When the phase advance circuit of FIG. 5A is not provided, the start of the current limiting operation is delayed due to the phase delay of the overcurrent detection signal. Since the switching elements Q1 and Q2 perform the switching operation based on the reference oscillation frequency (for example, every 2.5 μsec in the case of 400 kHz), if there is a phase delay of the overcurrent detection signal, the switching operation cannot be immediately turned off. Current limit is not possible. In this case, as indicated by the symbol α, the output current exceeds the current limit value for a short period after the occurrence of the overcurrent, and therefore, if the abnormal state continues, the amplifier circuit may be broken. If the current limit value is lowered in consideration of this phase delay, problems such as the output being stopped earlier or the current limiting operation being frequently activated may occur. On the other hand, when the phase advance circuit of FIG. 5B is provided (this embodiment), the overcurrent detection time can be shortened, and the start of the current limiting operation can be prevented from being delayed with respect to the switching operation. Current limit is possible. In this case, as indicated by the symbol β, the current can be reliably limited without the output current becoming equal to or greater than the current limit value from the beginning of the overcurrent.

Next, the current limiting operation when a resonance current is generated will be described in detail. FIG. 6 is a circuit diagram showing the basic configuration of the digital amplifier, and FIG. 7 is a gain-frequency characteristic diagram of the amplifier circuit when resonance occurs in the low-pass filter of the amplifier output section. As a basic configuration, the digital amplifier includes an input signal source 51, an amplifier circuit 52, a low-pass filter 53, and a load 54 such as a speaker. When the load 54 is light load or no load (when the load resistance RL is small), the LC resonance circuit by the coil L of the low-pass filter 53 and the capacitor C may resonate and the amplifier circuit 52 may oscillate. Usually, the resonance frequency fR at which such resonance occurs is a frequency higher than 20 kHz exceeding the audible range based on the constant of the low-pass filter 53. In the present embodiment, when the output current value when the resonance current is generated becomes equal to or greater than a predetermined value, the operation of the drive circuit is stopped and the resonance current is suppressed. In this case, for the overcurrent of the frequency in the audible range, the current limiter by the overcurrent detection is activated and the current is limited, and for the resonance current of the frequency exceeding the audible range, the current limiter by the resonance current detection is activated. Resonant current suppression is performed.

Here, the current limiting operation when the resonance current is generated is limited in real time in the same manner as the current limiting operation when the overcurrent is generated. For this reason, the resonance current can be suppressed without affecting the output in the audible range. Therefore, even when resonance occurs due to a load abnormality, the resonance current can be suppressed without stopping the output as much as possible.

FIG. 8 is a flowchart showing a first operation example regarding the circuit protection function of the digital amplifier according to the present embodiment. In the first operation example, during operation of the digital amplifier, the overcurrent detection of the output stage by the overcurrent detection circuit 19 and the resonance current detection of the output stage by the resonance current detection circuit 21 are performed (S11). Here, the presence / absence of the circuit protection operation of the digital amplifier when the overcurrent / resonance current is generated is switched depending on whether the overcurrent detection value or the resonance current detection value is equal to or greater than a predetermined value (S12). If there is no abnormality in the output current and no overcurrent or resonance current greater than a predetermined value is detected, the operations of S11 to S12 are repeated.

When the overcurrent detection value or the resonance current detection value is equal to or greater than a predetermined value and an abnormal state of the output current is detected, the overcurrent detection signal or the resonance current detection signal becomes high level and the operation of the drive circuit 12 is stopped. The switching elements Q1 and Q2 are both turned off (S13). Thereafter, whether or not the drive circuit 12 resumes operation is switched depending on whether the overcurrent detection value or the resonance current detection value is equal to or greater than a predetermined value (S14). Here, when the overcurrent detection value or the resonance current detection value is equal to or greater than a predetermined value, the operation of the drive circuit 12 is continuously stopped. When the overcurrent detection value and the resonance current detection value are less than the predetermined values, the overcurrent detection signal and the resonance current detection signal become low level, and the operation of the drive circuit 12 restarts, and the switching operation of the switching elements Q1 and Q2 Is resumed (S15).

Further, during the operation of the digital amplifier, the presence or absence of the circuit protection operation of the digital amplifier at an abnormally high temperature is switched depending on whether or not the temperature detection values of the switching elements Q1 and Q2 by the temperature detection unit 28 are equal to or higher than a predetermined value (S16). When the temperature detection values of the switching elements Q1 and Q2 are less than the predetermined value and the temperature is not abnormally high, the operations of S11 to S16 are repeated.

When the abnormal state of the output current continues, the switching elements Q1 and Q2 generate excessive heat and become an abnormally high temperature state, and when the temperature detection value exceeds a predetermined value, the relay controller 16 and the relay 16 and The input signal mute unit 23 operates in conjunction with the relay off and the input signal mute (S17).

When the relay 16 is turned off and the output signal path is interrupted, the load is disconnected and no load is applied, so that resonance is more likely to occur. In this embodiment, since the drive circuit 12 and the switching elements Q1 and Q2 operate intermittently even when resonance occurs and the current is limited, if the resonance state continues, the switching elements Q1 and Q2 become abnormally high temperature. There is a risk of being destroyed. For this reason, the relay 16 and the input signal mute unit 23 are interlocked to perform relay off and input signal mute at the same time, so that both input and output can be turned off to prevent resonance.

In the flowchart of FIG. 8, the temperature detection (S16) of the switching element is provided at the end of the flow, but it may be provided immediately after the start. This is effective because when the switching elements Q1 and Q2 are generating heat due to an initial device failure or the like, the circuit operation can be stopped quickly without detecting abnormal current.

FIG. 9 is a state transition diagram showing a second operation example regarding the circuit protection function of the digital amplifier according to the present embodiment. In the second operation example, during operation of the digital amplifier, the overcurrent detection of the output stage by the overcurrent detection circuit 19, the resonance current detection of the output stage by the resonance current detection circuit 21 (S 21), and the temperature detection unit 28 Temperature detection (S22) of switching elements Q1 and Q2 is performed. If the overcurrent detection value and the resonance current detection value are less than the predetermined value and normal, the overcurrent detection and resonance current detection in S21 are repeated. When the temperature detection value is less than the predetermined value and normal, the temperature detection of S22 is repeated.

When the overcurrent detection value or the resonance current detection value exceeds a predetermined value, the overcurrent detection signal or the resonance current detection signal becomes a high level, the operation of the drive circuit 12 is stopped, and the switching elements Q1 and Q2 are turned off. (S23). Subsequently, overcurrent detection and resonance current detection are performed (S24). Here, when the overcurrent detection value or the resonance current detection value is equal to or greater than the predetermined value, the overcurrent detection and the resonance current detection in S24 are repeated, and the operation stop state of the drive circuit 12 continues. When the overcurrent detection value and the resonance current detection value become normal when they are less than the predetermined values, the overcurrent detection signal and the resonance current detection signal become low level, and the operation of the drive circuit 12 is resumed (S25). Thereafter, returning to the overcurrent detection and resonance current detection of S21, the same operation is repeated.

When the temperature detection value is equal to or greater than the predetermined value, the relay 16 and the input signal mute unit 23 operate in conjunction with each other under the control of the interlock control unit 29, and the relay is turned off and the input signal mute is executed (S26). Subsequently, temperature detection is performed (S27). Here, when the temperature detection value becomes equal to or greater than the predetermined value, the temperature detection in S27 is repeated, and the relay-off and input signal mute states continue. When the detected temperature value is less than the predetermined value and becomes normal, the relay 16 and the input signal mute unit 23 are deactivated in conjunction with the control of the interlock control unit 29, and the relay is turned on and the mute is released (S28). Thereafter, returning to the temperature detection in S22, the same operation is repeated. After the operation of the drive circuit 12 is resumed in S25, the process proceeds to temperature detection in S22. When the temperature detection value becomes equal to or higher than a predetermined value, the relay is turned off and the input signal is muted in S26, and the temperature detection value is less than the predetermined value. In such a case, an operation for shifting to the overcurrent detection and resonance current detection in S21 is also possible.

Next, the case where the digital amplifier according to this embodiment is used in a loudspeaker system will be described with reference to FIGS. FIG. 10 shows a loudspeaker system using the digital amplifier according to this embodiment. In the loudspeaker system, the audio signal collected from the microphone 70 is connected to the mixer 71 via a cable, and the mixer 71 is connected to the digital amplifier 72, and the digital amplifier 72 is connected to the speaker 73. Amplify the signal.

FIG. 11 shows the configuration of a digital amplifier used in this loudspeaker system. In the configuration of FIG. 11, the difference from FIG. 2 is that the output of the resonance current detection circuit 21 is also input to the control unit 80, and the LED 81 is output when the output result of the resonance current detection circuit 21 continues for a predetermined time in the control unit 80. It is having the control part 80 and LED81 so that it can display by.

The digital amplifier 72 of the present invention can detect a resonance current generated in such a loudspeaker system when the number of speakers 73 is small, such as a so-called light load, but the detected frequency is shown in FIG. However, as shown, it is a non-audible frequency band of 20 kHz or more.

Now, in the loudspeaker system including the microphone 70 and the speaker 73, the loudspeaker sound from the speaker 73 is again collected by the microphone 70, and the oscillation frequency generated in the audible frequency band is well known as howling. On the other hand, when the cables of the microphone 70 and the speaker 73 are wired along each other as shown in FIG. 10, the input and output are electrically and magnetically coupled, and positive feedback is applied and oscillation may occur. This is called system oscillation and cannot be heard by the human ear as in howling, so detection is delayed and often causes failure of the mixer 71, the digital amplifier 72, the speaker 73, and the like.

However, according to the resonance current detection circuit 21 of the digital amplifier of the present invention, the band in which system oscillation occurs can also be detected. Therefore, when this resonance current is constantly generated, it is determined that system oscillation has occurred. be able to. Therefore, it is detected by the control unit 80 or a microcomputer (not shown) that the output of the resonance current detection circuit 21 has continued for a predetermined time, and when it continues for a predetermined time, the LED 81 is turned on to confirm that system oscillation has occurred. Users of the loudspeaker system can be notified. Note that the control unit 80 may be configured to include an integration circuit inside and turn on the LED 81 if the integration value is a predetermined value or more.

This allows the user to recognize the occurrence of system oscillation and take appropriate measures before the mixer 71, digital amplifier 72, speaker 73, etc. fail.

Note that the control unit 80 may use a timer or the like because it is only necessary to determine that the output of the resonance current detection circuit 21 has been continuously detected for a predetermined time. The LED 81 may be provided in the digital amplifier, but may be provided in a position where the user can easily see in the loudspeaker system, for example, in the mixer 71, or a light emitter or liquid crystal such as an LED or a warning lamp on the ceiling or wall. A display body such as an organic EL may be provided alone. Furthermore, it is possible to detect system oscillation even when voice signals from various audio sources are amplified instead of the voice signal from the microphone 70.

As described above, in this embodiment, in the circuit that detects the abnormal state of the output current for performing the current limiter control, the detection signal phase-advancing circuit is provided so that the response at the time of detecting the abnormal state is detected early. The time can be shortened, and a fast and reliable current limiting operation can be performed. In this case, since it is not necessary to perform current limiter control assuming a phase delay, when an abnormal state such as an overcurrent occurs, the output can be continued while the current is limited without immediately interrupting the output current. Thereby, for example, when the digital amplifier of the present embodiment is applied to a business broadcast system, an emergency broadcast system, a loudspeaker system, etc., the operation can be continued and the sound can be continuously output until the amplifier circuit completely fails.

Also, a resonance current detection circuit is provided, and the resonance phenomenon of the output filter of the amplifier output section that occurs at the time of light load is detected by the current flowing through the capacitor of the output filter, and the current can be limited by this resonance current detection. For this reason, it is possible to perform an appropriate current limiting operation against an overcurrent caused by a resonance phenomenon of the output unit, and protect the amplifier circuit. That is, in this embodiment, it is possible to deal with both abnormal loads such as when an overcurrent occurs when the load is short-circuited and when a resonance occurs such as when the load is open or when the load is light as the abnormal state.

In the current limiter control in the present embodiment, the operation of the drive circuit is only stopped when an abnormal state is detected, and the previous PWM circuit or the like is operating normally. It doesn't cost. For this reason, when the abnormal state is resolved, the digital amplifier can be quickly started up and output can be started.

In addition, an interlock control unit is provided to detect the temperature of the switching element in the output stage. When the detected temperature exceeds the specified value, the relay of the output unit is turned off and the input signal is muted. I do. As a result, when the temperature becomes abnormally high, both the input and output can be stopped to prevent the switching element from being destroyed. For example, in a state where a current limiting operation is performed by detecting an abnormal state, when the load fluctuates and an overcurrent occurs, the output can be stopped by temperature detection to protect the amplifier circuit.

As described above, according to the present embodiment, the detection time of the overcurrent and the resonance current that cause the destruction of the switching element in the output stage can be shortened, and the stop of the output can be minimized. Can be implemented.

The present invention is intended to be variously modified and applied by those skilled in the art based on the description in the specification and well-known techniques without departing from the spirit and scope of the present invention. Included in the scope for protection. Moreover, you may combine each component in the said embodiment arbitrarily in the range which does not deviate from the meaning of invention.

This application is based on a Japanese patent application filed on Feb. 18, 2010 (Japanese Patent Application No. 2010-033362), the contents of which are incorporated herein by reference.

The present invention has the effect of shortening the time for detecting an abnormality in the output current and protecting the amplifier circuit in the event of an abnormality without stopping the output as much as possible. It is useful as a digital amplifier for performing amplification.

DESCRIPTION OF SYMBOLS 11

PWM circuit

12, 31 Drive circuit 13 Coil 14 Capacitor 15 Output filter 16 Relay 17

Speaker

18, 20 Detection resistance 19 Overcurrent detection circuit 21 Resonance

current detection circuit

22, 41 Phase advance circuit 23 Input signal mute part 24 Mute circuit 25

Bypass Circuit

26, 27 Switch 28 Temperature detection unit 29 Interlocking control unit 32

Inversion circuit

33, 34

Photocoupler

35, 36 Driver 37 Switch element 38 NOR circuit 42

Capacitor

43, 44 Resistance 51 Input signal source 52 Amplifier circuit 53 Low-pass filter 54 Load Q1 , Q2 switching element

Claims

A digital amplifier that amplifies the input signal class D,
A switching element that performs a switching operation by a drive signal based on a digital pulse signal of the input signal;
A drive circuit for supplying the drive signal to the switching element;
An output filter including a low-pass filter connected to the output of the switching element;
An abnormal state detection unit that is provided in an output unit of the switching element and detects an abnormal state of an output current from the switching element and outputs an abnormal state detection signal;
The abnormal state detection unit has a phase advance function to advance the phase of the abnormal state detection signal,
The drive circuit is a digital amplifier that turns off the drive signal and stops the switching operation of the switching element when an abnormal state of the output current is detected based on the abnormal state detection signal.
The digital amplifier according to claim 1,
The abnormal state detection unit detects an overcurrent of a predetermined value or more in the output current from the switching element, and outputs an overcurrent detection signal as the abnormal state detection signal; and the overcurrent detection signal A digital amplifier having a phase advance circuit for advancing the phase.
The digital amplifier according to claim 1,
The abnormal state detection unit detects a resonance current greater than a predetermined value related to an output current when resonance occurs in the output filter, and has a resonance current detection circuit that outputs a resonance current detection signal as the abnormal state detection signal Amplifier.
The digital amplifier according to claim 1,
A temperature detector for detecting the temperature of the switching element or its surroundings;
An output blocking unit for blocking the output of the switching element;
An input signal mute unit for making the input signal a silent state or a minute state below a predetermined level;
An interlock control unit that interlocks the output blocking unit and the input signal mute unit;
The interlock control unit is a digital amplifier that operates the output shut-off unit and the input signal mute unit in conjunction when a high temperature state equal to or higher than a predetermined value is detected by the temperature detection unit.
The digital amplifier according to claim 1,
The drive circuit turns off the drive signal to stop the switching operation of the switching element when the output current is greater than or equal to a predetermined value based on the abnormal state detection signal, and the output current becomes less than the predetermined value. A digital amplifier that performs a current limiting operation of the switching element by repeatedly performing a control of turning on the driving signal and restarting the switching operation of the switching element when the switching signal is turned on.
The digital amplifier according to claim 5,
The drive circuit is a digital amplifier that turns on / off the drive signal at a unit of one cycle of a reference oscillation frequency of the digital pulse signal or at an arbitrary timing within one unit when performing a current limiting operation of the switching element.
The digital amplifier according to claim 3,
A digital amplifier having a control unit that determines that the resonance current detection signal of the resonance current detection circuit is continuously output for a predetermined time and outputs a signal to that effect when the resonance current detection signal has continued for the predetermined time.