JP7616116B2 - Vehicle approach notification device - Google Patents

Description

The present invention relates to a vehicle approach notification device that notifies a driver of an approaching vehicle by outputting a warning sound from a speaker mounted on the vehicle.

Conventionally, vehicle approach notification devices have been used to notify the surrounding area of approaching vehicles by outputting a warning sound from a speaker mounted on the vehicle, thereby alerting those around to the approach of quiet vehicles such as electric cars and hybrid cars.

This vehicle approach notification device has the problem that a "pop noise" such as a "pop" or "pop" occurs when the vehicle's activation switch (ignition switch or start switch) is turned on, reducing its marketability. In response to this problem, Patent Document 1 proposes a configuration that can reduce pop noise without adding a circuit that switches the output of a power amplifier (hereinafter referred to as AMP). Specifically, a capacitor is provided between the connection point of multiple resistors that generate the reference voltage and the ground terminal to delay the rise time of the reference voltage when power supply to the power supply terminal begins. Then, the sound signal is raised to the same level as the reference voltage so that the change in the potential difference between the reference voltage and the voltage of the sound signal when power supply to the power supply terminal begins is within a predetermined range.

JP 2013-203209 A

In recent years, there has been a shift in vehicle approach notification devices from switch-on control, which operates when the start switch is turned on, to battery-operated control, which operates based on a direct power supply from the battery. For example, there is a demand to reduce vehicle costs, and there is a demand to integrate a buzzer into the vehicle approach notification device and use it to sound the vehicle's answerback buzzer, in which case battery-operated control is used. As a result, it has become necessary to control the AMP power supply on and off in order to reduce the current consumption of the AMP as a dark current specification for the vehicle.

However, in the control of repeatedly turning the AMP power on and off, depending on the timing of turning the AMP power on, a charging current flows through the AC coupling capacitor connected between the AMP output and the speaker input in the vehicle approach notification device. This timing causes pop noise, which reduces the product's value.

Note that the example given here is of a vehicle approach notification device that is battery-powered and has a buzzer integrated into it, but even if the buzzer is not integrated, the same problems as above will occur if the device is battery-powered.

In view of the above, the present invention aims to provide a vehicle approach notification device that can reduce pop noise when controlled by battery power.

In order to achieve the above object, the present invention provides a vehicle approach notification device that notifies a driver of an approaching vehicle by outputting a notification sound from a sound generator (2) mounted on a vehicle, the device comprising:
A control unit (10) that outputs a sound generation signal based on a sound generation request;
a reference voltage generating circuit (13) that generates a reference voltage (Vref) by dividing a positive power supply voltage (Vin) input based on a power supply voltage (V) using a plurality of resistors (13a, 13b);
an AMP (14) that operates based on the input of a negative power supply voltage in addition to a positive power supply voltage, and outputs a signal obtained by amplifying the potential difference between a reference voltage and the voltage of a sound generation signal;
a coupling capacitor (15) provided between the output of the AMP and an output terminal (Vout) to which a sound generator is connected;
a bypass capacitor (17) arranged between a portion of the AMP to which a positive power supply voltage is input and a portion to which a negative power supply voltage is input;
and a discharge resistor (20) connected in parallel to the bypass capacitor.

In this way, a discharge resistor is provided that is connected in parallel to the bypass capacitor of the AMP. This allows the bypass capacitor to be quickly discharged via a path that runs from the bypass capacitor through the discharge resistor, making it possible to provide a vehicle approach notification device that can reduce pop noise when the device is battery-powered.

In the invention described in claim 2, a capacitor (16) is connected between the non-inverting input terminal (IN+) of the AMP and the part to which the negative power supply voltage is input, which delays the rise time of the reference voltage when power supply based on the power supply voltage starts.

In this way, when a capacitor is provided between the non-inverting input terminal (IN+) of the AMP and the part to which the negative power supply voltage is input, there is a limit to the discharge, especially in the path through the reference voltage generating circuit. In such a configuration, it is particularly preferable to provide a discharge resistor.

In the third aspect of the present invention, the discharge resistor is provided in each of the plurality of parallel connection circuits that are connected in parallel to the bypass capacitor and the reference voltage generating circuit .

In this way, a configuration can be provided in which a plurality of parallel connection circuits are connected in parallel to the bypass capacitor and the reference voltage generating circuit , and each of the plurality of parallel connection circuits is provided with a discharge resistor. In this case, the resistance values of the discharge resistors provided in the plurality of parallel connection circuits can be the same, but if they are made different as described in claim 4, the freedom of selection of the resistance value increases, making it easy to make adjustments to satisfy the instantaneous interruption characteristics.

The invention described in claim 5 has a switch (12) that is controlled by the control unit to be turned on and off when a sound generation request is input and is turned off when the sound generation request is released.

In this way, the vehicle approach notification device is equipped with a switch, and the control unit can turn the switch on and off to control battery operation.

In the invention described in claim 6, the control unit raises the voltage of the sound signal so that the change in the potential difference between the reference voltage and the voltage of the sound signal at the start of power supply based on the power supply voltage falls within a predetermined range.

This controls the voltage of the sound signal to eliminate the potential difference between the reference voltage and the voltage of the sound signal. In this way, during the transition period immediately after the power is turned on, the charging current of the coupling capacitor can be controlled to a frequency change outside the lowest audible range, suppressing pop noise. However, even when such control is performed, if a discharge resistor is not provided, when the power is turned on and then turned off, the AMP is shut down, and an imaginary short circuit can no longer be created, a potential difference between the voltage of the inverting input terminal (IN-) and the voltage of the non-inverting input terminal (IN+) of the AMP will continue for a long time. For this reason, it is preferable to provide a discharge resistor.

The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below.

1 is a diagram showing a schematic configuration of a vehicle approach notification device according to a first embodiment; 13 is a time chart showing a case where a discharge resistor is not provided in parallel with the bypass capacitor. 11 is a time chart showing a case where a discharge resistor is provided in parallel with a bypass capacitor.

The following describes embodiments of the present invention with reference to the drawings. In the following embodiments, parts that are identical or equivalent to each other are denoted by the same reference numerals.

First Embodiment
The circuit configuration of a vehicle approach notification device according to one embodiment of the present invention is shown in Fig. 1. This vehicle approach notification device 1 notifies surrounding pedestrians of the approach of a vehicle by outputting a notification sound from a speaker 2 mounted on the vehicle. In addition, the vehicle approach notification device 1 of this embodiment has an answer back function, that is, a function of notifying a user by emitting a sound when an operation to unlock or lock a door provided on the vehicle is performed using an electronic key (not shown) that the operation has been performed.

The vehicle approach notification device 1 includes a control unit 10, a low-pass filter (hereinafter referred to as LPF) 11, a switch 12, a reference voltage generating circuit 13, an AMP 14, a coupling capacitor 15, and various capacitors 16 to 19. In addition, the vehicle approach notification device 1 of this embodiment includes a resistor 20.

The control unit 10 is battery-controlled, that is, driven based on a direct power supply from the battery Batt regardless of whether the vehicle start switch is on or off. The control unit 10 is configured with a microcomputer equipped with a CPU, ROM, RAM, I/O, etc., and is configured with a sound signal output unit 10a that outputs a sound signal to cause the speaker 2 to produce sound and outputs the output sound signal to the LPF 11. When a sound production request is transmitted through a communication line 3 such as CAN (Controller Area Network) communication, the control unit 10 goes into a wake-up state, turns on the switch 12, and outputs a sound production signal to cause the speaker 2 to produce sound in accordance with the content of the sound production request. When the sound production request is released, the control unit 10 switches off the switch 12 and switches to a sleep state.

Specifically, when the vehicle starts to move and is traveling at a low speed, the control unit 10 outputs a sound signal corresponding to the traveling state of the vehicle in order to sound the approaching vehicle warning sound based on a sound sound request transmitted according to the traveling state of the vehicle.

Examples of the sound request transmitted according to the vehicle's running state include a vehicle speed signal itself corresponding to the vehicle speed output by a vehicle speed sensor (not shown), or an approaching sound request signal issued when the vehicle speed indicated by the vehicle speed signal is equal to or lower than a predetermined speed. The control unit 10 inputs the vehicle speed signal through the communication line 3, and outputs a sound signal when the vehicle speed indicated by the vehicle speed signal is equal to or lower than a predetermined speed, or when the approaching sound request signal is transmitted. For example, the microcomputer constituting the control unit 10 is provided with a CPU, a memory that stores sound data for vehicle approaching sound such as a pseudo engine sound or a pseudo motor sound, or a digital-to-analog converter (hereinafter referred to as DAC) in addition to a sound control program. When the control unit 10 is configured to have a memory that stores sound data, the sound data for the vehicle approaching sound is read out at each predetermined sampling period corresponding to the input vehicle speed signal or approaching sound request signal, and output as a sound signal. When the control unit 10 is configured to have a DAC, the input vehicle speed signal or approaching sound request signal is converted into a corresponding digital signal by the DAC, and output as a sound signal.

As an example, when the control unit 10 is configured to include a memory that stores sound generation data, the memory stores a table of pitch increase amount and sound volume associated with the vehicle speed. For example, the table may be configured to increase the pitch increase amount or sound volume as the vehicle speed increases. When the CPU determines that the vehicle is traveling at a low speed, that is, when the vehicle speed indicated by the vehicle speed signal is below a predetermined speed, the CPU calculates the pitch increase amount and sound volume corresponding to the vehicle speed based on the table stored in the memory. In addition, the control unit 10 outputs a sound generation signal having an output waveform that corresponds to the calculated sound volume for each sampling period corresponding to the calculated pitch increase amount. With this configuration, the pitch and sound volume can be varied according to the vehicle speed. In addition, since the approach notification sound request signal is also a request corresponding to the vehicle speed, it can be treated in the same way as the vehicle speed signal, such as by calculating the pitch increase amount and sound volume corresponding to the request.

Here, we have taken the example of the control unit 10 outputting a sound signal according to the vehicle speed as the vehicle driving state, but it is also possible to generate a sound signal according to other vehicle driving states, such as the accelerator pedal depression. It is also possible to generate a start signal that takes into account both the vehicle speed and the accelerator pedal depression. For example, the higher the vehicle speed, the greater the amount of pitch increase, and the greater the accelerator pedal depression, the louder the volume. Then, sound data is read for each sampling period corresponding to the calculated amount of pitch increase, and a transmission signal with a waveform magnitude corresponding to the calculated volume can be output.

When a user uses an electronic key to unlock or lock the vehicle doors, an answerback sound request is transmitted to the control unit 10 via the communication line 3, and the control unit 10 outputs a sound signal to sound the answerback sound based on the sound request. For example, when an electronic key is used to unlock or lock a door, a sound request is output to the communication line 3 from an electronic control device (hereinafter referred to as ECU) that controls the door, such as a body ECU. This sound request is transmitted from the communication line 3 to the control unit 10, which then outputs a sound signal.

The answerback pronunciation request includes, for example, information regarding the instruction to pronounce the sound, the volume, and the number of times the sound is to be played. This answerback pronunciation request can be handled in the same way as a request to pronounce a vehicle approach warning sound by providing the control unit 10 with a memory or DAC that stores pronunciation data for the answerback voice.

The LPF 11 corresponds to a filter section, and removes high-frequency components such as harmonics contained in the sound signal and passes low-frequency components. For example, the LPF 11 is configured with an RC circuit using a built-in capacitor and resistor (not shown), and stores a voltage corresponding to the output of the sound signal output section 10a in the capacitor and outputs it to the AMP 14.

The switch 12 is turned on and off based on a control signal from the control unit 10; it is turned on when a sound generation request is issued and the control unit 10 is in a wake-up state, and it is turned off when the sound generation request is released and the control unit 10 switches to a sleep state. When the switch 12 is turned on, a power supply voltage V, for example the voltage of a battery Batt, is applied to the power supply terminal Vt, and a positive power supply voltage Vin is applied to the AMP 14, causing the AMP 14 to operate.

The reference voltage generating circuit 13 has a first resistor 13a and a second resistor 13b, and generates a reference voltage Vref by dividing the power supply voltage V applied to the power supply terminal Vt, here the voltage of the battery Batt, by the first resistor 13a and the second resistor 13b. The reference voltage Vref is input to the non-inverting input terminal IN+ of the AMP 14, and is set to a neutral voltage, here an intermediate voltage level of the positive power supply voltage Vin of the AMP 14. For example, by setting the first resistor 13a and the second resistor 13b to the same resistance value, the reference voltage generating circuit 13 generates the reference voltage Vref at a voltage value that is 1/2 the power supply voltage V.

AMP14 is configured as a differential amplifier that amplifies the potential difference between a reference voltage Vref applied to the non-inverting input terminal IN+ and the voltage applied to the inverting input terminal IN-. AMP14 operates based on the power supply voltage V applied from the power supply terminal Vt, and generates an output corresponding to the voltage applied to the inverting input terminal IN- as a speaker output. The sound pressure generated by the speaker 2 is determined by the magnitude of the output of AMP14, for example the magnitude of the output current, that is, the amplitude, and the magnitude of the output of AMP14 is determined by the output waveform of the LPF 11 corresponding to the sound signal output from the control unit 10. For this reason, the output of AMP14 can be changed based on the sound signal output from the control unit 10 corresponding to the vehicle speed etc. transmitted through the communication line 3, making it possible to adjust the sound generated by the speaker 2.

The coupling capacitor 15 provides AC coupling between the AMP 14 and the speaker 2, cutting out the DC components contained in the output signal of the AMP 14 and allowing only the AC components to pass. This coupling capacitor 15 provides AC coupling between the AMP 14 and the speaker 2.

The capacitor 16 is connected between the non-inverting input terminal IN+ of the AMP 14 and the ground potential point, and is charged when the switch 12 is switched from off to on and power supply based on the power supply voltage V is started (hereinafter referred to as power supply start time). The capacitance of the capacitor 16 is provided so that the rise time of the reference voltage Vref at the start of power supply is longer than the value corresponding to a frequency sufficiently lower than the speaker resonance frequency _f0 . As a result, immediately after the vehicle approach notification device 1 is turned on, when the voltage of the non-inverting input terminal IN+ of the AMP 14 is raised to a neutral potential, that is, an intermediate voltage level of the maximum amplitude maximum value of the sound signal, the rising curve is raised outside the minimum audible range. For example, the capacitance of the capacitor 16 is set so that the rise time of the reference voltage is 20 Hz or less, in other words, the half cycle is 25 ms or less, so as to be outside the minimum audible range.

Capacitor 17 is a bypass capacitor for AMP 14 that is placed between the part where the positive power supply voltage Vin is input to AMP 14 and the part where the negative power supply voltage is input. This capacitor 16 allows AC components such as noise to flow to the ground potential point, stabilizing the positive power supply voltage Vin of amplifier 14.

Capacitors 18 and 19 are placed on either side of LPF 11, that is, between control unit 10 and LPF 11, and between LPF 11 and AMP 14, respectively. These capacitors 18 and 19 are coupling capacitors for matching the voltage of the sound signal input from control unit 10 with the drive voltage of AMP 14. For example, when control unit 10 is driven by a 5V power supply, the sound signal is output based on an intermediate potential of 2.5V as a reference and input to LPF 11. For this reason, capacitors 18 and 19 are provided to match the voltage of the output of LPF 11 with the battery voltage, for example, the input voltage to AMP 14, which has a drive voltage of 12V.

Resistor 20 is a discharge resistor arranged between the part of AMP 14 to which the positive power supply voltage Vin is applied and the part to which the negative power supply voltage is applied, in this case between the power supply line to which the positive power supply voltage Vin is applied and the ground potential point. Resistor 20 is connected in parallel to capacitor 17 and reference voltage generating circuit 13, and has a smaller resistance value than first resistor 13a and second resistor 13b. When driving of vehicle approach notification device 1 is stopped, resistor 20 discharges capacitor 17 more quickly to lower reference voltage Vref, thereby shortening the time during which AMP 14 is shut down and imaginary short cannot occur. This reduces pop noise, as described below.

The speaker 2 is a sound generator that outputs a vehicle approach warning sound or an answerback sound in response to a signal input from the AMP 14 via the coupling capacitor 15.

Next, we will explain the operation of the vehicle approach notification device 1 configured as described above.

First, when a sound generation request is input to the vehicle approach notification device 1 through the communication line 3, the control unit 10, which was in a sleep state, switches to a wake-up state and turns on the switch 12. As a result, a positive power supply voltage Vin is applied to the AMP 14 based on the power supply voltage V, and the power supply voltage V is divided by the first resistor 13a and the second resistor 13b to generate a reference voltage Vref, which is input to the non-inverting input terminal IN+ of the AMP 14.

In addition, a sound signal is output from the sound signal output unit 10a of the control unit 10 based on a sound request input through the communication line 3. This sound signal passes through the LPF 11, extracting only the low-frequency components, which are input to the inverting input terminal IN- of the AMP 14. The AMP 14 then amplifies the potential difference between the reference voltage Vref applied to the non-inverting input terminal IN+ and the voltage applied to the inverting input terminal IN-, and outputs a corresponding signal as a speaker output. This speaker output is transmitted to the speaker 2 via the coupling capacitor 15, and outputs a vehicle approaching notification sound or an answerback sound according to the input signal.

In this way, a vehicle approach notification sound or answerback sound can be generated in response to a sound request input through communication line 3.

In the vehicle approach notification device 1 of this embodiment, a resistor 20 is placed between the part of the AMP 14 to which the positive power supply voltage Vin is applied and the part to which the negative power supply voltage is applied, so that pop noise can be reduced. The reason for this will be explained.

First, based on the capacity of the capacitor 16, immediately after the vehicle approach notification device 1 is powered on, when the reference voltage Vref, which is the voltage at the non-inverting input terminal IN- of the AMP 14, is raised to a neutral potential, that is, the intermediate voltage level of the maximum amplitude maximum value of the sound signal, the rising curve is set to rise outside the minimum audible range. Furthermore, in order to create a silent state, when the control unit 10 raises the sound signal to a neutral potential, the sound signal is output so that it matches the rising curve of the transient period of the voltage at the non-inverting input terminal IN+ of the AMP 14. This controls so that the potential difference between the voltage of the sound signal and the reference voltage Vref, that is, the potential difference between the voltage at the inverting input terminal IN- and the voltage at the non-inverting input terminal IN+, is eliminated.

By doing this, during the transitional period immediately after the power is turned on, the charging current of the coupling capacitor 15, which is the transient current at this time, can be controlled to a frequency change outside the lowest audible range, and as a result, the pop noise can be reduced to an inaudible level.

However, in the past, when the power was turned on and then turned off, and the AMP 14 was shut down and an imaginary short was no longer possible, a state in which a potential difference occurred between the voltage of the inverting input terminal IN- and the voltage of the non-inverting input terminal IN+ continued for a long time. For example, the state in which the potential difference occurred continued for more than one minute. When the power was turned on again in such a state in which a potential difference occurred, the potential difference between the voltage of the inverting input terminal IN- and the voltage of the non-inverting input terminal IN+ was amplified by the AMP 14. This transient voltage caused a transient current, which became a charging current, to flow into the coupling capacitor 15 arranged between the output of the AMP 14 and the speaker 2. This transient current was output to the speaker 2 via the coupling capacitor 15, causing pop noise.

This will be described in detail with reference to the time charts shown in Figures 2 and 3. Figure 2 is a time chart for a case where the switch 12 in Figure 1 is not provided, and where the resistor 20 serving as a discharge resistor is not provided in parallel with the capacitor 17 in a case where switch-on driving is performed when the start switch is on. Figure 3 is a time chart for a case where the resistor 20 serving as a discharge resistor is provided in parallel with the capacitor 17 as a configuration of this embodiment. Figures 2 and 3 show a state where a sound signal based on a sound request is not output from the control unit 10, but when a sound signal is output, the voltage value at the output terminal Vout of the vehicle approach notification device 1 is set to a value corresponding to that.

As shown in Figure 2, when the start-up switch is on and a positive power supply voltage Vin is applied to AMP14, an imaginary short is created, so the potential difference between the voltage at the inverting input terminal IN- and the voltage at the non-inverting input terminal IN+ is nearly zero. In this state, even if the start-up switch is switched from on to off at time T1, the potential difference between the voltage at the inverting input terminal IN- and the voltage at the non-inverting input terminal IN+ is nearly zero, so almost no voltage is generated at the output terminal Vout even when amplified by AMP14.

After this, when the start switch is turned off and the application of the power supply voltage V is released, the voltage at the inverting input terminal IN- and the voltage at the non-inverting input terminal IN+ both drop. At this time, because capacitor 17 is charged to the power supply voltage V, here the positive power supply voltage Vin, the rate at which the voltage at the inverting input terminal IN- and the voltage at the non-inverting input terminal IN+ drop slows. Discharge occurs through a path that passes through first resistor 13a and second resistor 13b, but because capacitor 16 is also charged, there is a limit to how much discharge can be achieved through this path. Specifically, the presence of capacitor 16 makes it difficult for the charge at the non-inverting input terminal IN+ to escape, and discharging only occurs slowly.

For this reason, when the imaginary short is deactivated at time T2 when the voltages at the inverting input terminal IN- and the non-inverting input terminal IN+ have not yet dropped sufficiently, the potential difference between the voltages at the inverting input terminal IN- and the non-inverting input terminal IN+ increases, as shown by the hatching in the diagram. Then, in this state, when the start-up switch is switched from off to on again at time T3, the potential difference between the voltages at the inverting input terminal IN- and the non-inverting input terminal IN+ is amplified, and a large voltage is generated from the output terminal Vout based on this. This is what causes the pop noise.

In contrast, the vehicle approach notification device 1 of this embodiment is provided with a resistor 20 in parallel with the capacitor 17. Therefore, the capacitor 17 can be quickly discharged through a path from the capacitor 17 through the resistor 20. That is, as shown in FIG. 3, when the drive of the vehicle approach notification device 1 is stopped, the switch 12 is switched from on to off at time T1, and then the AMP 14 is shut down at time T2 and an imaginary short cannot be created, the capacitor 17 can be discharged more quickly to lower the positive power supply voltage Vin. This allows the voltage of the inverting input terminal IN- and the voltage of the non-inverting input terminal IN+ to be lowered more quickly, and the time when the AMP 14 is shut down and the imaginary short is deactivated can be shortened. For example, the time it takes for the positive power supply voltage Vin to drop to the voltage at which the AMP 14 is shut down from time T1 to time T2 in FIG. 3 is about 0.8 seconds, and the time it takes for the positive power supply voltage Vin and the voltage of the inverting input terminal IN- to reach 0 V from time T2 is about 0.3 seconds. These times vary depending on the capacitance of the capacitor 17 and the resistance value of the resistor 20, but can be made sufficiently short compared to when the resistor 20 is not provided. Even when the resistor 20 is provided, there is still a slight potential difference between the voltage of the inverting input terminal IN- and the voltage of the non-inverting input terminal IN+ after the AMP 14 is shut down, but the magnitude of this potential difference can be reduced.

Therefore, even if the power supply of AMP 14 is repeatedly turned on and off, the time during which pop noise may occur can be shortened. At the timing of time T3 in FIG. 3, the positive power supply voltage Vin and the voltages of the non-inverting input terminal IN+ and the inverting input terminal IN- are in a zero state. This makes it possible to suppress the occurrence of pop noise. Even if a sound request is issued again during that short period of time, such as when the start switch is turned on, the potential difference between the voltage of the inverting input terminal IN- and the voltage of the non-inverting input terminal IN+ is small, so that pop noise can be reduced. Therefore, when the vehicle approach notification device 1 is battery-driven, it is possible to provide a device that can reduce pop noise. In other words, when the control unit 10 controls the application of the positive power supply voltage Vin to AMP 14 to be turned on and off, the capacitor 17 is discharged through a path that passes through the resistor 20 when the voltage is off, thereby reducing pop noise.

As described above, the vehicle approach notification device 1 of this embodiment is equipped with a resistor 20 connected in parallel to the capacitor 17. This allows the capacitor 17 to be quickly discharged through the path from the capacitor 17 through the resistor 20, and provides a vehicle approach notification device 1 that can reduce pop noise when the device is battery-powered.

Other Embodiments
Although the present disclosure has been described based on the above-described embodiment, it is not limited to the embodiment, and includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, and other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure.

For example, in the above embodiment, a structure having only one resistor 20 in parallel with the capacitor 17 is exemplified, but a plurality of parallel connection circuits connected in parallel with the capacitor 17 may be provided, and each of the plurality of parallel connection circuits may be provided with a resistor 20. In this case, the resistance value of the resistor 20 provided in each parallel connection circuit may be equal or different. The resistance value of the resistor 20 is preferably smaller than the first resistor 13a and the second resistor 13b in order to discharge the capacitor 17 in a short time. However, it is desirable to set the resistance value so as to satisfy the instantaneous interruption characteristics of the circuit from the viewpoint of the rated power of the element. Even if the resistance values of the resistors 20 provided in each parallel connection circuit are equal, it is possible to satisfy the instantaneous interruption characteristics, but if the resistance values are different, the freedom of selection of the resistance value increases, and adjustment to satisfy the instantaneous interruption characteristics can be easily performed.

In the above embodiment, immediately after the power is turned on, that is, when the application of the power supply voltage V from the power supply terminal Vt starts, the sound signal is raised to a neutral potential so as to match the rising curve of the voltage of the non-inverting input terminal IN+ during the transient period. However, it is not necessary to raise the sound signal to a neutral potential so as to match the rising curve of the voltage of the non-inverting input terminal IN+ during the transient period immediately after the power is turned on from the power supply terminal Vt. In short, it is sufficient to raise the voltage of the sound signal to a voltage level equivalent to the transient period of the voltage of the non-inverting input terminal IN+ so that the change in the potential difference between the reference voltage Vref, which is the voltage of the non-inverting input terminal IN+ immediately after the power is turned on, and the voltage of the sound signal is within a range in which pop noise does not occur.

In addition, in the above embodiment, the first resistor 13a and the second resistor 13b are provided to divide the positive power supply voltage Vin to generate the reference voltage Vref, but the number of resistors is arbitrary as long as the reference voltage Vref is generated by voltage division using multiple resistors. Also, an example has been shown in which the first resistor 13a and the second resistor 13b have the same resistance value, thereby generating the reference voltage Vref at a voltage value of 1/2 the power supply voltage V, which is an intermediate voltage level of the positive power supply voltage Vin in this case, but it does not necessarily have to be 1/2.

In addition, in the above embodiment, the power supply voltage V applied to the power supply terminal Vt is the positive power supply voltage Vin of the AMP14, but the power supply voltage V may be reduced by a certain amount to be the positive power supply voltage Vin.

In addition, in the above embodiment, the part of AMP14 that is the negative power supply voltage is connected to a ground potential point, but this does not have to be a ground potential point, and it can be a reference potential point that is a predetermined voltage lower than the positive power supply voltage Vin.

The present invention is not limited to the above-described embodiments, and can be modified as appropriate within the scope of the claims. In addition, in each of the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential, except when expressly stated as essential or when it is considered to be clearly essential in principle. In addition, in each of the above-described embodiments, when the numbers, values, amounts, ranges, etc. of the components of the embodiments are mentioned, they are not limited to the specific numbers, except when expressly stated as essential or when it is clearly limited to a specific number in principle.

1... Vehicle approach notification device, 2... Speaker, 3... Communication line, 10... Control unit, 10a... Sound signal output unit, 11... LPF, 12... Switch, 13... Reference voltage generation circuit, 14... AMP, 15... Coupling capacitor, 16-19... Capacitors, 20... Resistor

Claims (6)

A vehicle approach notification device that notifies a vehicle of its approach by outputting a notification sound from a sound generator (2) mounted on the vehicle,
A control unit (10) that outputs a sound generation signal based on a sound generation request;
a reference voltage generating circuit (13) that generates a reference voltage (Vref) by dividing a positive power supply voltage (Vin) input based on a power supply voltage (V) using a plurality of resistors (13a, 13b);
a power amplifier (14) that operates based on the input of a negative power supply voltage in addition to the positive power supply voltage and outputs a signal obtained by amplifying a potential difference between the reference voltage and a voltage of the sound generation signal;
a coupling capacitor (15) provided between the output of the power amplifier and an output terminal (Vout) to which the sound generator is connected;
a bypass capacitor (17) arranged between a portion of the power amplifier to which a positive power supply voltage is input and a portion of the power amplifier to which a negative power supply voltage is input;
and a discharge resistor (20) connected in parallel to the bypass capacitor. The vehicle approach notification device according to claim 1, wherein a capacitor (16) is connected between the non-inverting input terminal (IN+) of the power amplifier and a portion to which a negative power supply voltage is input, the capacitor (16) delaying the rise time of the reference voltage when power supply based on the power supply voltage starts. 3. The vehicle approach notification device according to claim 1, wherein the discharge resistor is provided in each of a plurality of parallel connection circuits connected in parallel to the bypass capacitor and the reference voltage generating circuit . The vehicle approach notification device according to claim 3, wherein the resistance values of the discharge resistors provided in each of the multiple parallel connection circuits are different. The vehicle approach notification device according to any one of claims 1 to 4, further comprising a switch (12) that is controlled by the control unit to be turned on or off when the sound generation request is input and turned off when the sound generation request is cancelled. The vehicle approach notification device according to any one of claims 1 to 5, wherein the control unit raises the voltage of the sound signal so that the change in the potential difference between the reference voltage and the voltage of the sound signal at the start of power supply based on the power supply voltage is within a predetermined range.

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