Piezoelectric buzzer circuit and piezoelectric buzzer device

Abstract

To provide a technology that can reduce current loss in a piezoelectric buzzer circuit. [Solution] The piezoelectric buzzer circuit according to this technology comprises a piezoelectric buzzer, a discharge resistor, and a first switching element. The piezoelectric buzzer is connected to an input terminal to which the output voltage from a charge pump circuit is input, and periodically repeats charging and discharging. The discharge resistor is connected in parallel to the piezoelectric buzzer and is used to discharge the piezoelectric buzzer. The first switching element is connected in parallel to the piezoelectric buzzer together with the discharge resistor, and switches between an operating state in which the discharge resistor is activated when the piezoelectric buzzer is discharged, and a non-operating state in which the discharge resistor is deactivated when the piezoelectric buzzer is charged.

Description

Technical Field

[0001] This technology relates to technologies such as a piezoelectric buzzer circuit using a piezoelectric buzzer.

Background Art

[0002] Conventionally, a piezoelectric buzzer device including a piezoelectric buzzer composed of a piezoelectric body has been widely known (see, for example, Patent Document 1 below). In a piezoelectric buzzer, when a voltage is applied to the piezoelectric body by an electrical signal, the piezoelectric body is distorted and vibration occurs, and thus any sound can be emitted and reproduced.

[0003] For example, a piezoelectric buzzer device may be composed of a piezoelectric buzzer circuit including a piezoelectric buzzer and a charge pump circuit for supplying power to the piezoelectric buzzer circuit.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In an existing piezoelectric buzzer circuit, there is a problem that its current loss is large.

[0006] [[ID=4^{2}]] In view of the above circumstances, it is an object to provide a technology capable of reducing current loss in a piezoelectric buzzer circuit.

Means for Solving the Problems

[0007] The piezoelectric buzzer circuit in this technology includes a piezoelectric buzzer, a discharge resistor, and a first switching element. The piezoelectric buzzer is connected to an input terminal to which an output voltage from a charge pump circuit is input, and repeatedly charges and discharges periodically. The discharge resistor is connected in parallel to the piezoelectric buzzer and is used to discharge the piezoelectric buzzer. The first switching element is connected in parallel to the piezoelectric buzzer together with the discharge resistor, and switches between an operating state in which the discharge resistor is activated when the piezoelectric buzzer is discharged, and a non-operating state in which the discharge resistor is deactivated when the piezoelectric buzzer is charged.

[0008] In this piezoelectric buzzer circuit, the discharge resistor can be kept inactive during charging of the piezoelectric buzzer, thereby reducing current loss caused by the discharge resistor.

[0009] The piezoelectric buzzer circuit may further include a second switching element connected in series with the piezoelectric buzzer on the opposite side of the input terminal, which switches between charging and discharging the piezoelectric buzzer.

[0010] In the piezoelectric buzzer circuit described above, the first switching element may periodically switch between the operating state and the non-operating state by periodically switching between ON and OFF.

[0011] In the piezoelectric buzzer circuit described above, the first switching element may be configured to activate the discharge resistor when it is ON and to deactivate the discharge resistor when it is OFF.

[0012] In the piezoelectric buzzer circuit described above, the second switching element may periodically switch between ON and OFF to periodically switch the charging and discharging of the piezoelectric buzzer.

[0013] In the piezoelectric buzzer circuit described above, the second switching element may charge the piezoelectric buzzer when it is ON and discharge the piezoelectric buzzer when it is OFF.

[0014] The piezoelectric buzzer circuit may further include an inversion element for inverting the ON and OFF timings of the first switching element and the ON and OFF timings of the second switching element.

[0015] In the piezoelectric buzzer circuit, the first switching element, the second switching element, and the inversion element may each be constituted by a transistor.

[0016] The piezoelectric buzzer device according to the present technology includes a charge pump circuit and a piezoelectric buzzer circuit. The piezoelectric buzzer circuit is connected to an input terminal to which an output voltage from the charge pump circuit is input, and includes a piezoelectric buzzer that periodically repeats charging and discharging, a discharge resistor connected in parallel to the piezoelectric buzzer and used for discharging the piezoelectric buzzer, and a first switching element connected in parallel to the piezoelectric buzzer together with the discharge resistor, which switches between an operating state in which the discharge resistor is operated when the piezoelectric buzzer is discharging and a non-operating state in which the discharge resistor is non-operated when the piezoelectric buzzer is charging.

Advantages of the Invention

[0017] As described above, according to the present technology, it is possible to provide a technology such as a piezoelectric buzzer circuit that can reduce current loss.

Brief Description of the Drawings

[0018] [Figure 1] It is a diagram showing a charge pump circuit according to an embodiment of the present technology. [Figure 2] It is a diagram showing a piezoelectric buzzer circuit according to an embodiment of the present technology. [Figure 3] It is a diagram showing the waveform of the current flowing through the piezoelectric buzzer (upper side) and the waveform of the voltage applied to the piezoelectric buzzer (lower side). [Figure 4] It is a diagram showing the waveform of the output voltage in the charge pump circuit (upper side) and the waveform of the voltage applied to the piezoelectric buzzer (lower side). [Figure 5]It is a diagram showing a piezoelectric buzzer circuit according to a first comparative example. [Figure 6] It is a diagram showing a piezoelectric buzzer circuit according to a second comparative example. [Figure 7] In the piezoelectric buzzer circuit (H-bridge type) according to the second comparative example, it is a diagram showing the waveform of the voltage applied to the piezoelectric buzzer. [Figure 8] In the piezoelectric buzzer circuit (H-bridge type) according to the second comparative example, it is a diagram showing the waveform of the voltage applied to the piezoelectric buzzer (upper side) and the waveform of the current flowing through the piezoelectric buzzer (lower side). [Figure 9] It is a diagram comparing the waveform of the current consumption in the piezoelectric buzzer circuit (H-bridge type) according to the second comparative example (left side) with the waveform of the current consumption in the piezoelectric buzzer circuit according to the present embodiment (right side).

Embodiments for Carrying out the Invention

[0019] Hereinafter, embodiments according to the present technology will be described with reference to the drawings.

[0020] <Overall Configuration and Configuration of Each Part> FIG. 1 is a diagram showing a charge pump circuit 10 according to an embodiment of the present technology. FIG. 2 is a diagram showing a piezoelectric buzzer circuit 20 according to an embodiment of the present technology.

[0021] As shown in FIGS. 1 and 2, the piezoelectric buzzer device according to the present embodiment includes a charge pump circuit 10 and a piezoelectric buzzer circuit 20.

[0022] [Charge Pump Circuit] First, referring to FIG. 1, the configuration of the charge pump circuit 10 will be described. This charge pump circuit 10 generates the voltage required for driving the piezoelectric buzzer B in the piezoelectric buzzer circuit 20 by stepwise boosting and supplies it to the piezoelectric buzzer circuit 20.

[0023] As shown in Figure 1, the charge pump circuit 10 includes five diodes, including the first diode D1 to the fifth diode D5; five capacitors, including the first capacitor to the fifth capacitor C1 to C5; and two transistors, including the first transistor T'1 and the second transistor T'2.

[0024] The first diode D1 through the fifth diode D5 are connected in series from left to right, in the same direction, and the anode side of the first diode is connected to a constant voltage source.

[0025] One end (upper side) of the first capacitor C1 is connected between the first diode D1 and the second diode D2, and the other end (lower side) of the first capacitor C1 is connected to the first path P1. One end (upper side) of the second capacitor C2 is connected between the second diode D2 and the third diode D3, and the other end (lower side) of the second capacitor C2 is connected to the second path P2.

[0026] Furthermore, one end (upper side) of the third capacitor C3 is connected between the third diode D3 and the fourth diode D4, and the other end (lower side) of the third capacitor C3 is connected to the first path P1. One end (upper side) of the fourth capacitor C4 is connected between the fourth diode D4 and the fifth diode D5, and the other end (lower side) of the fourth capacitor is connected to the second path P2.

[0027] Furthermore, one end (upper side) of the fifth capacitor C5 is connected to the cathode side of the fifth diode D5, and the other end (lower side) of the fifth capacitor C5 is connected to ground.

[0028] The capacitances of the first capacitor C1 to the fifth capacitor C5 are, for example, 0.1 μF. Note that the specific values ​​used herein are merely examples and can be changed as appropriate.

[0029] The first path P1 is a path extending from the constant voltage source, and this first path P1 is connected to the other end (bottom side) of the first capacitor C1, the other end (bottom side) of the third capacitor C3, the collector side of the first transistor T'1, and the base side of the second transistor T'2. In the first path P1, a resistor R'1 (for example, 10kΩ) is provided directly below the constant voltage source.

[0030] The second path P2 is a path that branches off from the first path and is connected to the other end (bottom) of the second capacitor C2, the other end (bottom) of the fourth capacitor C2, and the collector side of the second transistor T'2.

[0031] The first transistor T'1 is composed of an npn type transistor. The base of the first transistor T'1 is connected to the microcontroller via a base resistor R'1b (e.g., 4.7kΩ). In other words, a control signal for driving the charge pump circuit 10 is input from the microcontroller to the base of the first transistor T'1. The control signal for driving the charge pump circuit 10 is a rectangular pulse signal. The base of the first transistor T'1 is also connected to ground via a pull-down resistor R'1p (e.g., 47kΩ).

[0032] Furthermore, the collector side of the first transistor T'1 is connected to the first path P1 via a resistor R'2 (for example, 1kΩ), and the emitter side of the first transistor T'1 is connected to ground.

[0033] The second transistor T'2 is constructed using an npn type transistor, similar to the first transistor T'1. The base of the second transistor T'2 is connected to the first path P1 via a base resistor R'1b (e.g., 4.7kΩ). The base of the second transistor T'2 is also connected to ground via a pull-down resistor R'2p (e.g., 47kΩ).

[0034] Furthermore, the collector side of the second transistor T'2 is connected to the second path P2 via a resistor R'3 (for example, 1kΩ), and the emitter side of the second transistor T'2 is connected to ground.

[0035] In this embodiment, the first transistor T'1 and the second transistor T'2 are set to turn ON when the voltage value between their base and emitter is above a predetermined threshold (0.7V to 0.8V) and to turn OFF when the voltage value falls below the threshold.

[0036] The microcontroller includes a control unit such as a CPU (Central Processing Unit), non-volatile memory such as ROM (Read-only memory), volatile memory such as RAM (Random Access Memory), and I / O ports for inputting and outputting signals. The microcontroller generates control signals to drive the charge pump circuit 10 and the piezoelectric buzzer circuit 20, and outputs the generated control signals to the charge pump circuit 10 and the piezoelectric buzzer circuit 20, respectively.

[0037] [Operation of charge pump circuit 10] Next, the operation of the charge pump circuit 10 will be explained. The lower part of Figure 1 shows the first voltage value (signal) φ1 in the first path P1 and the second voltage value (signal) φ2 in the second path P2.

[0038] The first voltage value φ1 and the second voltage value φ2 are each rectangular pulse-shaped signals with opposite phases. These opposite-phase first voltage value φ1 and second voltage value φ2 are realized by the operation of the first transistor T'1 and the second transistor T'2 based on control signals from the microcontroller. In other words, in this embodiment, the first transistor T'1 and the second transistor T'2 can supply the opposite-phase first voltage value φ1 and the second voltage value φ2 to the first path P1 and the second path P2 based on the same control signal.

[0039] First, the voltage values ​​at one end (upper side) of the first capacitor C1 to the fifth capacitor C5 are all Vin (voltage of the constant voltage source). When the first voltage value φ1 is high, the second voltage value φ2 is low, so the first capacitor C2 transfers charge to the second capacitor C3, and the second capacitor C2 maintains a higher voltage value than the first capacitor C1.

[0040] Subsequently, when the first voltage value φ1 becomes low and the second voltage value φ2 becomes high, the second capacitor C2 transfers charge to the third capacitor C3, and the third capacitor C3 maintains a higher voltage value than the second capacitor C2.

[0041] The voltage is then boosted in a similar manner. As a result, the voltage values ​​of each capacitor C1 to C5 are in the following order: voltage of the first capacitor C1 < voltage of the second capacitor C2 < voltage of the third capacitor C3 < voltage of the fourth capacitor C4 < voltage of the fifth capacitor C5. Finally, the voltage value Vout held in the fifth capacitor C5 is output from the output terminal of the charge pump circuit and supplied to the piezoelectric buzzer circuit 10.

[0042] Next, the operation of the first transistor T'1 and the second transistor T'2 will be explained. A control signal from the microcontroller is input to the base side of the first transistor T'1. When the control signal is high level, the first transistor turns ON (base-emitter voltage is above the threshold (0.7V~0.8V)), and at this time, current flows from the first path P1 to ground through resistor R'2, so the first voltage value φ1 of the first path P1 becomes low level.

[0043] When the first voltage value φ1 in the first path P1 is low, the voltage between the base and emitter of the second transistor T'2 falls below the threshold (0.7V to 0.8V). As a result, the second transistor T'2 turns OFF, and this causes the second voltage value φ2 in the second path P2 to become high.

[0044] On the other hand, when the control signal from the microcontroller is low level, the first transistor T'1 turns OFF, and as a result, the first voltage value φ1 in the first path P1 becomes high level.

[0045] When the first voltage value φ1 is at a high level, the second transistor T'2 turns ON (base-emitter voltage is below the threshold (0.7V~0.8V)), which causes the second voltage value φ2 in the second path P2 to become low level.

[0046] In this way, the first transistor T'1 and the second transistor T'2 can make the first voltage value φ1 in the first path P1 and the second voltage value φ2 in the second path P2 into signals with opposite phases, based on the control signal from the microcontroller.

[0047] [Piezoelectric buzzer circuit] Next, with reference to Figure 2, the piezoelectric buzzer circuit 20 according to this embodiment will be described. The piezoelectric buzzer circuit 20 includes a piezoelectric buzzer B, a discharge resistor R1, a current limiting resistor R2, a first transistor T1, a second transistor T2, a third transistor T3, and a fourth transistor.

[0048] Piezoelectric buzzer B is connected to the input terminal, which receives the output voltage from the charge pump circuit 10, via a current-limiting resistor R2. Piezoelectric buzzer B is configured to periodically charge and discharge using the output voltage from the charge pump circuit 10.

[0049] The piezoelectric buzzer B includes, for example, a piezoelectric element and a metal plate provided on the piezoelectric element. The piezoelectric buzzer B vibrates by periodically repeating charging and discharging, thereby emitting and reproducing any sound.

[0050] The current-limiting resistor R2 is interposed between the input terminal, to which the output voltage from the charge pump circuit 10 is input, and the piezoelectric buzzer B. This current-limiting resistor R2 is provided to limit the current to the piezoelectric buzzer B when it is being charged, but it is also used when the piezoelectric buzzer B is being discharged. The resistance value of the current-limiting resistor R2 is, for example, 1 kΩ.

[0051] The first transistor T1 (the second switching element) is connected in series with the piezoelectric buzzer B on the opposite side (downstream side) from the input terminal to which the output voltage from the charge pump circuit 10 is input.

[0052] The first transistor T1 is configured to periodically switch between ON and OFF in response to a control signal for controlling the drive of the piezoelectric buzzer B, thereby enabling periodic switching of charging and discharging of the piezoelectric buzzer B. Specifically, when the first transistor T1 is ON, it charges the piezoelectric buzzer B, and when it is OFF, it discharges the piezoelectric buzzer B.

[0053] The first transistor T1 is an npn type transistor. The base of the first transistor T1 is connected to the microcontroller via a base resistor R1b (e.g., 4.7kΩ) and to ground via a pull-down resistor R1p (e.g., 47kΩ). In other words, the control signal for driving the piezoelectric buzzer circuit 20 is input from the microcontroller to the base of the first transistor T1.

[0054] The control signal for driving the piezoelectric buzzer circuit 20 is a rectangular pulsed signal, such as PCM (Pulse code modulation), PDM (Pulse density modulation), or PWM (Pulse Width Modulation).

[0055] Furthermore, the collector side of the first transistor T1 is connected to the piezoelectric buzzer B, and the emitter side of the first transistor T1 is connected to ground.

[0056] The discharge resistor R1 is connected in parallel to the piezoelectric buzzer B. This discharge resistor R1 is the resistor used for the discharge of the piezoelectric buzzer B. The resistance value of the discharge resistor R1 is, for example, 1 kΩ.

[0057] Here, the resistance value R1 of the discharge resistor and the resistance value R2 of the current limiting resistor are related to the charging and discharging of the piezoelectric buzzer B, and are related to the charging time and discharge time required to fully charge and discharge the piezoelectric buzzer B.

[0058] In this circuit, the time constant is 5RC. buz (C buz :This is the capacitance of the piezoelectric buzzer. Therefore, the minimum time required to fully charge piezoelectric buzzer B is 5R2C buz Therefore, the minimum time required to completely discharge the piezoelectric buzzer is 5(R1+R2)C buz (Note that, as will be explained later, the discharge resistor R1 does not operate during charging, but only during discharge, so the time constant during charging is 5R2C) buz Therefore, the time constant during discharge is 5(R1+R2)C buz (This is the result).

[0059] As can be understood from the explanation here, if the resistance value of the discharge resistor R1 and the resistance value of the current limiting resistor R2 increase, the minimum time required to charge and discharge the piezoelectric buzzer B will increase. Therefore, taking this into consideration, the values ​​of resistance R1 and resistance R2 are set appropriately (in this embodiment, R1=R2=1kΩ).

[0060] As mentioned above, the discharge resistor R1 is used when the piezoelectric buzzer B is discharged. However, if no countermeasures are taken, this discharge resistor R1 will activate when the piezoelectric buzzer B is being charged, resulting in current loss. Therefore, in this embodiment, a second transistor T2 is provided, and this second transistor T2 disconnects the discharge resistor R1 from the charging path when the piezoelectric buzzer B is being charged, preventing the discharge resistor R1 from activating.

[0061] The second transistor T2 (the first switching element) is connected in parallel to the piezoelectric buzzer B together with the discharge resistor R1. This second transistor T2 is configured to switch between an operating state in which the discharge resistor R1 is activated in the discharge path when the piezoelectric buzzer B is discharged, and a non-operating state in which the discharge resistor R1 is disconnected from the charging path and remains inactive when the piezoelectric buzzer B is charged.

[0062] Typically, the second transistor T2 is configured to periodically switch between ON and OFF states in response to a control signal for controlling the operation of the piezoelectric buzzer B, thereby periodically switching the operating and non-operating states of the discharge resistor R1. The second transistor T2 is configured to activate the discharge resistor R1 when it is ON, and to disconnect the discharge resistor R1 and deactivate it when it is OFF.

[0063] Unlike the other transistors, the second transistor T2 is a pnp type transistor. The base of the second transistor T2 is connected to the collector of the fourth transistor T4 via a base resistor R2b (e.g., 4.7kΩ). The base of the second transistor T2 is also connected to the input terminal to which the output voltage from the charge pump circuit 10 is input via a pull-up resistor R2p (e.g., 47kΩ).

[0064] Furthermore, the emitter side of the second transistor T2 is connected to the input terminal to which the output voltage from the charge pump circuit 10 is input, and the collector side of the second transistor T2 is connected to the discharge resistor R1.

[0065] When the first transistor T1 is turned ON, the piezoelectric buzzer B is charged. However, in order to reduce current loss during charging, the discharge resistor R1 needs to be disconnected from the charging path. Therefore, when the piezoelectric buzzer B is being charged, the second transistor T2 is turned OFF, and the discharge resistor R1 is disconnected from the charging path and becomes inoperable.

[0066] On the other hand, when the first transistor T1 is turned OFF, the piezoelectric buzzer B is discharged. At this time, the discharge resistor R1 is used to perform the discharge, so it is necessary to return the discharge resistor R1 to the discharge path. Therefore, when the piezoelectric buzzer B is discharged, the second transistor T2 is turned ON, and the discharge resistor R1 is put into an operating state.

[0067] The first transistor T1 and the second transistor T2 are switched ON / OFF based on the same control signal (PWM, etc.), but in this embodiment, the ON and OFF timings of the first transistor and the ON and OFF timings of the second transistor are opposite to each other.

[0068] Therefore, in this embodiment, a third transistor T3 and a fourth transistor T4 are provided to reverse the ON and OFF timing of the first transistor T1 and the ON and OFF timing of the second transistor T2.

[0069] The third transistor T3 (inverting element), together with the fourth transistor T4, is configured to invert the ON and OFF timing of the first transistor T1 and the ON and OFF timing of the second transistor T2.

[0070] The third transistor T3 is an npn type transistor. The base of the third transistor T3 is connected to the microcontroller via a base resistor R3b (e.g., 4.7kΩ). In other words, the control signal for driving the piezoelectric buzzer circuit 20 is input from the microcontroller to the base of the third transistor T3. The base of the third transistor T3 is also connected to ground via a pull-down resistor R3p (e.g., 47kΩ).

[0071] Furthermore, the collector side of the third transistor T3 is connected to a constant voltage source via a pull-up resistor R3 (for example, 3kΩ), and the collector side of the third transistor T3 is connected to the base side of the fourth transistor T4. The emitter side of the third transistor T3 is connected to ground.

[0072] The fourth transistor T4 (inverting element), together with the third transistor T3, is configured to invert the ON and OFF timing of the first transistor T1 and the ON and OFF timing of the second transistor T2.

[0073] The fourth transistor T4 is an npn type transistor. The base of the fourth transistor T4 is connected to a constant voltage source via a base resistor R4b (e.g., 4.7kΩ) and a pull-up resistor R3, and this base is also connected to the collector side of the third transistor T3 via base resistor R4b. The base of the fourth transistor T4 is connected to ground via a pull-down resistor R4p (e.g., 47kΩ).

[0074] Furthermore, the collector side of the fourth transistor T4 is connected to the base side of the second transistor T2. Also, the emitter side of the fourth transistor T4 is connected to ground.

[0075] In this embodiment, the three transistors, the first transistor T1, the third transistor T3, and the fourth transistor T4, which are npn type transistors, are set to turn ON when the voltage value between the base and emitter is equal to or greater than a first threshold (0.7V to 0.8V), and to turn OFF when it falls below the first threshold.

[0076] On the other hand, in this embodiment, the second transistor, that is, a pnp type transistor, is set to turn ON when the voltage value between the base and emitter falls below a second threshold (-0.7V to -0.8V) (for example, -1.0V), and to turn OFF when the voltage value exceeds the second threshold (for example, 0V).

[0077] In this embodiment, the base resistor and pull-down resistor (or pull-up resistor) of each transistor T1 to T4 have resistance values ​​of 4.7kΩ and 47kΩ, respectively. However, these resistance values ​​can be appropriately selected, for example, to ensure that the base-emitter voltage and base current of the transistor are appropriate (similar to the charge pump circuit 10 described above).

[0078] [Operation of the piezoelectric buzzer circuit 20] Next, the operation of the piezoelectric buzzer circuit 20 will be explained in detail.

[0079] (The voltage value of the control signal is high.) First, let's explain the operation when the voltage value in the control signal (PWM, etc.) from the microcontroller is high level. At this time, the voltage value between the base and emitter of the first transistor T1 becomes equal to or greater than the first threshold (0.7V to 0.8V), so the first transistor T1 turns ON. Similarly, the voltage value between the base and emitter of the third transistor T3 becomes equal to or greater than the first threshold (0.7V to 0.8V), so the third transistor T3 turns ON.

[0080] When the first transistor T1 is turned ON, it conducts, and the current from the output voltage of the charge pump circuit 10 flows to ground through the current limiting resistor R2, the piezoelectric buzzer B, and the first transistor T1. This current charges the piezoelectric buzzer B (like a capacitor).

[0081] When the third transistor T3 is turned ON, it conducts, and the voltage between its collector and emitter becomes 0.2V to 0.3V. As a result, the voltage between the base and emitter of the fourth transistor T4 becomes 0.2V to 0.3V.

[0082] If the voltage between the base and emitter of the fourth transistor T4 is between 0.2V and 0.3V, this voltage is below the first threshold (0.7V to 0.8V), so the fourth transistor T4 is OFF.

[0083] When the fourth transistor T4 is OFF, the voltage at the base of the second transistor T2 is 3.3V, and the voltage between the base and emitter of the second transistor T2 is 0V. When the voltage between the base and emitter of the second transistor T2 is 0V, this voltage is greater than the second threshold (-0.7V to -0.8V), so the second transistor turns OFF.

[0084] When the second transistor T2 is OFF, the discharge resistor R1 is disconnected from the charging path and therefore does not operate. Thus, in this embodiment, when the piezoelectric buzzer B is being charged, the discharge resistor R1 is disconnected from the charging path and does not operate, and therefore the current loss due to the discharge resistor R1 can be reduced.

[0085] (The voltage value of the control signal is low.) Next, we will explain the operation when the voltage value in the control signal (PWM, etc.) from the microcontroller is at a low level. In this case, the voltage value between the base and emitter of the first transistor T1 falls below the first threshold (0.7V to 0.8V), so the first transistor T1 turns OFF. Similarly, the voltage value between the base and emitter of the third transistor T3 falls below the first threshold (0.7V to 0.8V), so the third transistor T3 turns OFF.

[0086] When the first transistor T1 is turned OFF, the current from the input terminal is restricted from flowing to ground via the current limiting resistor R2, piezoelectric buzzer B, and the first transistor T1.

[0087] When the third transistor T3 is OFF, the voltage between the collector and emitter of the third transistor T3 becomes 3.3V. As a result, the voltage between the base and emitter of the fourth transistor T4 becomes 3.3V.

[0088] If the voltage between the base and emitter of the fourth transistor T4 is 3.3V, this voltage exceeds the first threshold (0.7V to 0.8V), so the fourth transistor T4 turns ON.

[0089] When the fourth transistor T4 is ON, the voltage between the base and emitter of the second transistor T2 becomes less than or equal to the second threshold (-0.7V to -0.8V), and the second transistor T2 turns ON.

[0090] When the second transistor is ON, the discharge resistor R1 is returned to the discharge path and the discharge resistor R1 becomes operational. In this embodiment, when the piezoelectric buzzer B is being charged, the discharge resistor R1 is disconnected from the charging path and remains inactive, while when the piezoelectric buzzer B is being discharged, the discharge resistor R1 is returned to the discharge path and the discharge resistor R1 can be properly activated.

[0091] In this case, when the fourth transistor T4 is ON and the second transistor T2 is ON, current flows to ground through the emitter and base of the second transistor T2 and the collector and emitter of the fourth transistor, causing discharge.

[0092] [Current waveform and voltage waveform] Figure 3 shows the waveform of the current flowing through piezoelectric buzzer B (upper side) and the waveform of the voltage applied to piezoelectric buzzer B (lower side).

[0093] When the piezoelectric buzzer circuit is first turned ON, the first transistor T1 is OFF. The time between 0ms and 10ms is the time when the charge pump circuit 10 is OFF, and at 10ms, the charge pump circuit 10 is turned ON.

[0094] Therefore, the applied voltage to piezoelectric buzzer B gradually increases from 10ms, reaching approximately 21V. Then, at 50ms, the piezoelectric buzzer B is activated. In other words, at 50ms, the periodic switching of the first transistor T1 on and off begins, and the periodic switching of the second transistor T2 on and off (in the opposite direction to the first transistor) also begins.

[0095] This initiates the periodic charging and discharging of piezoelectric buzzer B, and starts the output of sound due to the vibration of the piezoelectric buzzer. When piezoelectric buzzer B is charging, the discharge resistor R1 is in a non-operating state, and when piezoelectric buzzer B is discharging, the discharge resistor is in an operating state.

[0096] After 50ms, the waveform of the applied voltage to piezoelectric buzzer B periodically repeats between approximately 20V (charging) and approximately 0V (discharging). Sound is emitted from piezoelectric buzzer B at the timing of the rising and falling edges of the applied voltage waveform.

[0097] Furthermore, after 50ms, the waveform of the current flowing through piezoelectric buzzer B becomes a waveform that periodically repeats between approximately 5.5mA (charging) and 0mA (discharging).

[0098] In this embodiment, the current loss due to the discharge resistance R1 is reduced during charging of the piezoelectric buzzer B, resulting in a low current consumption of approximately 5.5mA in the piezoelectric buzzer B during charging. Therefore, it is possible to efficiently utilize the output voltage from the charge pump circuit 10 (it is only reduced from approximately 21V to approximately 20V).

[0099] [Output voltage waveform and voltage waveform] Figure 4 shows the waveform of the output voltage in the charge pump circuit 10 (upper side) and the waveform of the voltage applied to the piezoelectric buzzer B (lower side).

[0100] As shown in Figure 4, when the boost operation of the charge pump circuit 10 causes the output voltage of the charge pump circuit 10 to rise to approximately 19.6V, this voltage is supplied to the piezoelectric buzzer B. At this time, the output voltage of the charge pump circuit 10 drops sharply to approximately 17.8V.

[0101] Meanwhile, the applied voltage of piezoelectric buzzer B rises sharply from 0V to approximately 18V, then stabilizes to some extent and gradually approaches approximately 20V. Once the applied voltage of piezoelectric buzzer B stabilizes to some extent, the output voltage of the charge pump circuit 10 gradually recovers and rises again to approximately 19.6V.

[0102] The applied voltage of piezoelectric buzzer B reaches approximately 20V while the output voltage of the charge pump circuit 10 is gradually recovering. After that, piezoelectric buzzer B discharges, and the applied voltage of piezoelectric buzzer B becomes approximately 0V. In other words, even while the voltage is decreasing due to the discharge of piezoelectric buzzer B, the output voltage of the charge pump circuit 10 continues to rise.

[0103] When the applied voltage to piezoelectric buzzer B drops to 0V due to discharge, the output voltage of the charge pump circuit 10 recovers to approximately 19.6V, and this voltage is supplied to piezoelectric buzzer B again. Thereafter, the same operation as described above is repeated.

[0104] <Effect, etc.> Next, the operation of this technology will be explained. In this explanation, first, a first comparative example and a second comparative example that are compared with this embodiment will be described.

[0105] [Comparative Example 1] Figure 5 shows a voltage buzzer circuit 30 according to the first comparative example. The piezoelectric buzzer circuit 30 according to the first comparative example shown in Figure 5 is a charge-discharge type piezoelectric buzzer that alternately charges and discharges, similar to this embodiment.

[0106] The piezoelectric buzzer circuit 30 according to this first comparative example has a discharge resistor R1, a current limiting resistor R2, a piezoelectric buzzer B, and a first transistor T1, similar to the piezoelectric buzzer circuit 20 according to this embodiment shown in Figure 2. However, unlike this embodiment, it does not have a second transistor T2, a third transistor T2, a fourth transistor T4, etc.

[0107] In the piezoelectric buzzer circuit 30 of the first comparative example, when the first transistor T1 is turned ON, the piezoelectric buzzer B is charged to +V via the current limiting resistor R2. On the other hand, when the first transistor T1 is turned OFF, the piezoelectric buzzer B discharges via the discharge resistor R1 and the current limiting resistor R2 and becomes 0V.

[0108] In the piezoelectric buzzer circuit 30 of the first comparative example, current flows through the discharge resistor R1 when the piezoelectric buzzer is charged, but this current serves no purpose and results in current loss. Furthermore, this current loss causes a decrease in the output voltage of the charge pump circuit. In other words, there is a problem in that the utilization efficiency of the output voltage by the charge pump circuit is poor.

[0109] [Second Comparative Example] Figure 6 shows a piezoelectric buzzer circuit 40 according to the second comparative example. This piezoelectric buzzer circuit 40 according to the second comparative example is an H-bridge type circuit.

[0110] The piezoelectric buzzer circuit 40 of the second comparative example includes a piezoelectric buzzer B, a resistor R, and four transistors, the first to fourth transistors T"1" to T"4".

[0111] Since the piezoelectric buzzer 40 in this second comparative example is a general H-bridge type circuit, a detailed explanation of its specific configuration will be omitted.

[0112] In the piezoelectric buzzer circuit 40 according to the second comparative example, when the first transistor T"1" and the fourth transistor T"4 are ON, the second transistor T"2" and the third transistor T"3 are OFF. On the other hand, when the second transistor T"2" and the third transistor T"3 are ON, the first transistor T"1" and the fourth transistor T"4 are OFF.

[0113] When the first transistor T"1 and the fourth transistor T"4 are ON, current from the charge pump circuit flows to ground through the first transistor T"1, the piezoelectric buzzer B, the resistor R, and the fourth transistor T"4. At this time, the piezoelectric buzzer B is charged to +V.

[0114] On the other hand, when the second transistor T"2" and the third transistor T"3 are ON, current from the charge pump circuit flows to ground through the second transistor T"2", resistor R, piezoelectric buzzer B, and the third transistor T"3. At this time, piezoelectric buzzer B is charged to -V.

[0115] In the case of the piezoelectric buzzer circuit 40 (H-bridge type) according to the second comparative example, unlike the piezoelectric buzzer circuit 30 (charge / discharge type) according to the first comparative example, the piezoelectric buzzer B is always charged by the output voltage from the charge pump.

[0116] Furthermore, in the case of the piezoelectric buzzer circuit 40 (H-bridge type) according to the second comparative example, power must be constantly supplied to the piezoelectric buzzer B, so there is no time for the output voltage of the charge pump circuit to recover (however, in the piezoelectric buzzer circuit 30 according to the first comparative example and the piezoelectric buzzer circuit 20 (charge / discharge type) according to this embodiment, the output voltage of the charge pump circuit recovers when the piezoelectric buzzer is discharged).

[0117] Therefore, in the case of the piezoelectric buzzer circuit 40 (H-bridge type) according to the second comparative example, the charge pump circuit cannot be properly driven unless a dedicated IC (Integrated Circuit) is used to drive the charge pump circuit. However, such a dedicated IC leads to increased costs.

[0118] In the case of the piezoelectric buzzer circuit 40 (H-bridge type) according to the second comparative example, it is necessary to use additional current to change the voltage of piezoelectric buzzer B from +V to 0, or from -V to 0. Therefore, similar to the piezoelectric buzzer circuit 30 (charge / discharge type: discharge resistor R1 is always operating) according to the first comparative example, there is a problem of low utilization efficiency of the output voltage from the charge pump circuit. This will be explained with reference to Figures 7 and 8.

[0119] Figure 7 shows the waveform of the voltage applied to the piezoelectric buzzer B in the piezoelectric buzzer circuit 40 (H-bridge type) according to the second comparative example.

[0120] As shown in Figure 7, when voltages of 10V and -10V are periodically applied to piezoelectric buzzer B, the voltage waveform of the piezoelectric buzzer fluctuates periodically between 10V and -10V, and the peak-to-peak voltage is 20V.

[0121] Figure 8 shows the waveform of the voltage applied to the piezoelectric buzzer B (upper side) and the waveform of the current flowing through the piezoelectric buzzer B (lower side) in the piezoelectric buzzer circuit 40 (H-bridge type) according to the second comparative example.

[0122] As shown in Figure 8, current flows through piezoelectric buzzer B even when the applied voltage to B drops from 10V to 0V (the same applies when it drops from -10V to 0V), resulting in poor utilization efficiency of the output voltage from the charge pump circuit.

[0123] [This Circumstance] As described above, in this embodiment, when the piezoelectric buzzer B is being charged, the discharge resistor R1 is disconnected from the charging path and remains inactive, while when the piezoelectric buzzer is being discharged, the discharge resistor R1 is returned to the discharge path and can be properly activated. Therefore, in this embodiment, current loss due to the discharge resistor during the charging of the piezoelectric buzzer B can be reduced.

[0124] Therefore, in this embodiment, compared to the piezoelectric buzzer circuit 30 (charge / discharge type: discharge resistor is always operating) according to the first comparative example and the piezoelectric buzzer circuit 40 (H-bridge type) according to the second comparative example, it is possible to make maximum use of the output voltage from the charge pump circuit and provide a high-output piezoelectric buzzer.

[0125] Furthermore, since this embodiment uses a charge / discharge type piezoelectric buzzer circuit 20, it does not require a dedicated IC or the like for driving the charge pump circuit, unlike the piezoelectric buzzer circuit 40 (H-bridge type) in the second comparative example. Therefore, costs can be reduced in this embodiment.

[0126] In this embodiment, the charge pump circuit 10 is driven by a control signal from a microcontroller. However, this microcontroller does not need to be an expensive dedicated IC; its operation can be controlled by a general-purpose microcontroller.

[0127] Furthermore, in this embodiment, relatively inexpensive components can be used for each part of the charge pump circuit 10 and the piezoelectric buzzer circuit 20, thus reducing costs.

[0128] Generally, charge pump circuits have a problem where increasing the output current actually lowers the output voltage. For this reason, the charge pump circuit 10 in this embodiment is also designed to have a low output current. On the other hand, in this embodiment, the current loss due to the discharge resistor R1 can be reduced, so even if the charge pump circuit 10 has a low current, a high-output piezoelectric buzzer circuit 20 can be provided.

[0129] Furthermore, in this embodiment, the total power consumption of the entire circuit can be reduced compared to the piezoelectric buzzer circuit 30 (charge / discharge type: discharge resistor is always active) according to the first comparative example and the piezoelectric buzzer circuit 40 (H-bridge type) according to the second comparative example.

[0130] Figure 9 is a comparison of the current consumption waveform (left) in the piezoelectric buzzer circuit 40 (H-bridge type) according to the second comparative example and the current consumption waveform (right) in the piezoelectric buzzer circuit 20 according to this embodiment.

[0131] As shown in Figure 9, the frequency (left side) of the current consumption waveform in the piezoelectric buzzer circuit 40 (H-bridge type) according to the second comparative example is set to twice the frequency (right side) of the current consumption waveform in the piezoelectric buzzer circuit 10 according to this embodiment. From this, it can be seen that in this embodiment, the total power consumption of the entire circuit can be reduced and sufficient recovery time for the charge pump can be secured compared to the second comparative example.

[0132] <Various variations> In the above explanation, the first transistor T1 was used as an example of a switching element that periodically switches between charging and discharging the piezoelectric buzzer B in the piezoelectric buzzer circuit 20. Furthermore, the second transistor T2 was used as an example of a switching element that periodically switches between operating and non-operating states of the discharge resistor R1 in the piezoelectric buzzer circuit 20.

[0133] On the other hand, instead of the first transistor T1 and the second transistor T2, mechanical switchable first and second switches may be used, respectively. In this case, for example, the ON and OFF timings of the first switch are reversed.

[0134] Here, the ON and OFF frequencies of the first transistor T1 and the second transistor T2 of the piezoelectric buzzer circuit 20 are set to, for example, 2 kHz. The mechanically operated first and second switches only need to be configured to enable ON / OFF switching at this frequency.

[0135] Similarly, instead of the first transistor T'1 and the second transistor T'2 in the charge pump circuit 10, mechanically operated first and second switches may be used, respectively.

[0136] Here, the ON and OFF frequencies of the first transistor T'1 and the second transistor T'2 of the charge pump circuit 10 are set to, for example, 20 kHz. The mechanically operated first and second switches only need to be configured to enable ON / OFF switching at this frequency.

[0137] Furthermore, the piezoelectric buzzer device (circuit) according to this embodiment can be installed in various electronic devices equipped with a buzzer (for example, a multifunction printer). [Explanation of symbols]

[0138] 10... Charge pump circuit 20... Piezoelectric buzzer circuit B... Piezoelectric buzzer R1...Discharge resistance R2...Current limiting resistor T1…First transistor T2... Second transistor T3...Third transistor T4…The fourth transistor

Claims

1. A piezoelectric buzzer is connected to the input terminal to which the output voltage from the charge pump circuit is input, and which periodically repeats charging and discharging. A discharge resistor connected in parallel to the piezoelectric buzzer and used for discharging the piezoelectric buzzer, A first switching element is connected in parallel to the piezoelectric buzzer together with the discharge resistor, and switches between an operating state in which the discharge resistor is activated when the piezoelectric buzzer is discharged, and an operating state in which the discharge resistor is deactivated when the piezoelectric buzzer is charged. A piezoelectric buzzer circuit equipped with the following features.

2. A piezoelectric buzzer circuit according to claim 1, A second switching element connected in series with the piezoelectric buzzer on the opposite side of the input terminal, which switches the charging and discharging of the piezoelectric buzzer. A piezoelectric buzzer circuit further comprising the above.

3. A piezoelectric buzzer circuit according to claim 2, The first switching element periodically switches between the operating state and the non-operating state by periodically switching between ON and OFF. Piezoelectric buzzer circuit.

4. A piezoelectric buzzer circuit according to claim 3, The first switching element operates the discharge resistor when it is ON and deactivates the discharge resistor when it is OFF. Piezoelectric buzzer circuit.

5. A piezoelectric buzzer circuit according to claim 4, The second switching element periodically switches between ON and OFF, thereby periodically switching the charging and discharging of the piezoelectric buzzer. Piezoelectric buzzer circuit.

6. A piezoelectric buzzer circuit according to claim 5, The second switching element charges the piezoelectric buzzer when it is ON and discharges the piezoelectric buzzer when it is OFF. Piezoelectric buzzer circuit.

7. A piezoelectric buzzer circuit according to claim 6, An inversion element for reversing the ON and OFF timing of the first switching element and the ON and OFF timing of the second switching element. It further comprises Piezoelectric buzzer circuit.

8. A piezoelectric buzzer circuit according to claim 7, The first switching element, the second switching element, and the inverting element are each composed of transistors. Piezoelectric buzzer circuit.

9. Charge pump circuit and A piezoelectric buzzer circuit comprising: a piezoelectric buzzer connected to an input terminal to which the output voltage from a charge pump circuit is input and which periodically repeats charging and discharging; a discharge resistor connected in parallel to the piezoelectric buzzer and used for discharging the piezoelectric buzzer; and a first switching element connected in parallel to the piezoelectric buzzer together with the discharge resistor and which switches between an operating state in which the discharge resistor is activated when the piezoelectric buzzer is discharged and a non-operating state in which the discharge resistor is not activated when the piezoelectric buzzer is charged. A piezoelectric buzzer device equipped with the following features.

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