JPS5832394B2 - Piezoelectric speaker drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric speaker drive circuit, and more particularly to a piezoelectric speaker drive circuit that reduces power consumption of the piezoelectric speaker.

Conventionally, a piezoelectric speaker is driven by applying a voltage such as C to the piezoelectric speaker by adding signals a and b shown in FIG. 2 to a circuit shown in FIG. 1, for example.

In this case, the signal a is logic "1" (all of the following are also positive logic, logic "1" is "1", and logic "0" is "0").

), the signal S takes the state rOJ, and when the signal a is "0", the signal S takes the state rlJ.

Therefore, when the battery voltage is E, the voltage C across the piezoelectric speaker changes from +E to -E to +E.

At this time, there would be no problem if the piezoelectric speaker was electrically equivalent to a simple resistance, but in reality it is equivalent to a circuit as shown in FIG.

Since the capacitance of the capacitor 10, which is mainly the capacitance between the electrodes, is very large, it becomes equivalent to a capacitor with a slightly large loss at frequencies slightly off the resonance point.

This means that the piezoelectric speaker drive circuit repeatedly charges and discharges the capacitor, and only a small portion of the power consumed by this circuit is related to driving the speaker, with most of the remaining power being consumed by the capacitor. It is consumed in the form of charging and discharging.

Therefore, in such a drive circuit, the efficiency of acoustic output relative to power consumption is extremely low.

This invention was made to improve the above-mentioned drawbacks, and aims to increase efficiency by reducing wasteful power consumption as much as possible.

The present invention will be explained below with reference to the drawings, but for comparison, the operation of a conventional drive circuit will be explained in more detail.

In the circuit shown in Figure 1, "1" is given to the A terminal and "1" is given to the B terminal.
0'' is applied, transistors 2 and 3 are conductive, and the voltage C across the piezoelectric speaker becomes -E (E is the voltage of the battery).

Next, at the moment when the A terminal becomes "0" and the B terminal changes to "1", the voltage C remains at -E because the piezoelectric speaker is almost equivalent to a capacitor.

At this time, consider transistors 1, 2, 3, and 4 as switches,
If a piezoelectric speaker is considered as a capacitor, the state is as shown in FIG.

Therefore, the battery 18 reduces the voltage d across the capacitor 190 to -
An amount of charge must be supplied to change E to +E.

If this charge is q and the capacitance of the capacitor 19 is C, then (q=2CE).

Also, when the signal a changes from "0" to "1", q charges are extracted from the battery 18.

Therefore, according to the conventional drive circuit, the battery 18 must supply 4 CE of charge for one period of the piezoelectric speaker drive signal.

Next, a block diagram of one driving circuit according to the present invention is shown in FIG.

In is an input terminal for an external clock signal, 7 is a control section, 8 is a drive section, and 9 is a piezoelectric speaker.

The drive unit 8 is, for example, a conventionally used circuit as shown in FIG.

However, the signals applied to terminals A and H in FIG. 1 are different from the conventional ones, and are as shown in FIGS. 4 and 5.

The controller 7 creates such a signal.

The drive unit 8 is controlled by the signals a and b generated by the control unit 7.
behaves differently than before.

Since the operation of the drive unit when the signals a and b shown in FIGS. 4 and 5 are applied is almost the same, the operation when the signal of FIG. 4 is applied to the circuit of FIG. 1 will be explained in detail. .

Initially, in the section where the signal a is "1" and the signal a is "0", transistors 2 and 3 are conductive, and the voltage C across the piezoelectric speaker is
is -E.

Next, the signal a remains at "1" and there is a section where the signal becomes "1", and transistors 2 and 4 become conductive.

This state is equivalent to that shown in Fig. 8, and the capacitor 19 is connected to the switch 1.
5 and switch 17.

As a result, the voltage d across the capacitor changes from E to O.

Since the battery is disconnected in this section, there is no charge leakage from the battery 18.

In the next section, signal S remains "1", but signal a becomes "O".
”.

In this state, transistors 1 and 4 are conductive, and the state is equivalent to that shown in FIG.

Therefore, the battery 18 changes the voltage d across the capacitor from O to +E.
Let q′ be the amount of charge required to change it to q
'=supply CE.

Next, the signal A remains at "1" and the signal a becomes "1".

This is almost the same state as in Figure 8, and capacitor 1
9 is a section where switch 15 and switch 1γ are short-circuited.

Finally, the signal a remains at "1" and the signal S becomes "0", returning to the initial state.

In this state, transistors 2 and 3 are conductive.

At this time as well, the battery 18 changes the voltage d across the capacitor from 0 to -
A charge q' is supplied to change the voltage to E.

Therefore, in the above four sections constituting one cycle, the battery capacity is 2 q
A charge of /, that is, a charge of 2CE must be supplied.

Note that the driving force of a piezoelectric speaker is proportional to the applied voltage, so if you shorten the section where both ends of the piezoelectric speaker are shorted, you can obtain a driving force that is almost the same as a conventional drive circuit, and the acoustic output is almost the same. There is no difference.

Furthermore, the configuration of the control section 7 that generates the signals shown in FIGS. 4 and 5 is easy, and as an example, FIG. The signal waveform is shown in FIG.

The circuit shown in FIG. 10 is composed of a 1/10 frequency divider 20 and a D-type flip-flop 21.

When a signal having a frequency 10 times the piezoelectric speaker drive frequency is input to the E terminal, a signal having the speaker drive frequency as shown in FIG. 11f is obtained at the F terminal.

The signal g is a signal obtained by delaying the signal f by one cycle of the signal e (that is, 1/10 of the speaker drive cycle) and inverting the logic thereof, as shown in FIG. 11.

This signal f is connected to terminal A of the circuit in Figure 1, and signal g is connected to terminal B.
You can add it to

As described above, if the drive circuit according to the present invention is used,
Power consumption can be halved without reducing audio output.

Therefore, the efficiency is almost doubled.

Therefore, if the piezoelectric speaker drive circuit according to the present invention is used to drive a piezoelectric speaker built into a battery-operated device (particularly a calculator or watch that uses a CMO8 logic circuit and a liquid crystal display to reduce power consumption), The effects are great, including the ability to extend lifespan.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing part of a piezoelectric speaker drive circuit according to a conventional example and the present invention, FIG. 2 is a drive signal diagram of the conventional example, FIG. 3 is a block diagram of a drive circuit according to the present invention, and FIG. Fig. 5 is a drive signal diagram according to the present invention, Fig. 6 is an equivalent circuit diagram of a piezoelectric speaker, Fig. 7 is an operation explanatory diagram of a conventional example, Fig. 8,
FIG. 9 is an explanatory diagram of the operation of the first drive circuit according to the present invention, and FIG.
1 is a circuit block diagram showing a part of one drive circuit according to the present invention, and FIG. 11 is a signal diagram of the circuit of FIG. 10. 1.2,3,4...MOSFET,5,9...
...Piezoelectric speaker, 6,18...Battery, 7
...control section, 8..., drive section, 10,
11.19... Capacitor, 12...
Inductor, 13... Resistor, 14...
Switch corresponding to FET1, 15...FET
Switch corresponding to 2, 16... Switch corresponding to FET3, 17... Switch corresponding to FET4, 20... Frequency divider, 21...
flip flop.

Claims (1)

[Claims] A drive unit comprising two inverters each having twelve transistors connected in a complementary manner and connected in parallel to a power supply, and a piezoelectric speaker connected between the outputs of the two inverters; In a piezoelectric speaker drive circuit consisting of a control section that generates input signals to two inverters in the piezoelectric speaker, the inverter short-circuits the piezoelectric speaker at the time when the voltage across the piezoelectric speaker is reversed, and discharges the charge remaining in the piezoelectric speaker. A piezoelectric speaker drive circuit characterized in that two signals outputted from the control section to the inverter are rectangular waves having sections where they are at the same level so as to cause discharge. 2. In the piezoelectric speaker 1 drive circuit according to claim 1, the two outputs from the control section are rectangular wave signals having the same period, the same duty ratio, and different phases. drive circuit. 3. The piezoelectric speaker drive circuit according to claim 1, wherein the two outputs from the control section are rectangular wave signals having the same period and different duty ratios.