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Description / name of invention
Piezoelectric speaker drive circuit
3. Detailed Description of the Invention The present invention relates to a drive circuit of a
piezoelectric speaker. In general, piezoelectric speakers have higher electroacoustic conversion
efficiency than dynamic speakers. For example, to produce the same sound pressure level 90 to
95 d1 □□, the former consumes only 0,01 W of power consumption, while the latter consumes
1 W of electric power. However, even though the piezoelectric speaker requires QOlw, since the
input impedance Z of the speaker is large, the required speaker and the driving type [V need a
rather large one in comparison with the case of the electrodynamic speaker. That is, the main
reason that the piezoelectric type speaker is not adopted for small-sized audio equipment is
mainly that in the case of small size and electrification and ringing, the number of batteries is
small and naturally the voltage is small, so that sufficient sound pressure can not be obtained.
However, in view of the economics of lOO that the power consumption of a piezoelectric speaker
is less than that of an electrodynamic type, we would like to jointly adopt it for small batteries
and drive acoustic equipment. It is the present invention that meets this need. That is, according
to the present invention, by providing an impedance compensation circuit outside the
piezoelectric speaker, it is possible to obtain a sufficient total Q- and 'fi: even if the power supply
voltage is small in the built-in frequency range. The way to use a piezoelectric speaker is open.
The present invention will be described in detail below along with one embodiment shown in the
drawings. The value of the input impedance of the piezoelectric speaker decreases as the
frequency rises, and the value decreases (Fig. 1 curve (21)% frequency characteristic curve (Fig.
Curve (1))), 2 to lOK Hz The same sound pressure level can not be obtained below 2KI-Iz,
although the same sound pressure level can be obtained in the lower half phase. In order to
obtain a flat sound pressure level without raising the voltage even at 2 KHz or less of EndPage: 1,
the impedance should be improved at 2 KF (z or less). In the present invention, as shown in FIG.
2, a coil with tap (I,) and a variable resistor (R) are inserted in parallel to the speaker (SP), and it
is seen as a load of the pull-up type transistor bridge. Become. That is, according to this
compensation circuit, as shown in FIG. 6 curve (2), the impedance of the speaker changes with a
characteristic characterized by IKHz, and therefore the frequency characteristic curve (FIG. 6 (1))
Even at 2 KHz, the sound pressure level is almost flat with 2 KH 2 or more, and the sound
pressure level is improved in the required frequency range. Of course, if the variable resistance
(R) and the pupil of the coil (L) are appropriately set, the sound pressure level can be adjusted
even if the frequency is in the other required frequency range m.
By using a coil and a resistor in parallel with the piezoelectric speaker, the piezoelectric speaker
can be used even with a sufficient sound pressure level even if the power supply voltage is low in
the required frequency range. It is worthwhile to point out that
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the impedance and frequency
characteristic curve of a conventional piezoelectric speaker, and FIG. 2 shows an embodiment of
one drive circuit of the piezoelectric speaker of the present invention. The impedance and the
frequency characteristic curve in the piezoelectric speaker of this invention are shown. SP:
Piezoelectric speaker, 1: sound pressure level, 2: impedance. ,-= IT 'and 〒 agent patent attorney
LL ,,,! :. EndPage: 2
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