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DESCRIPTION JP2003250191

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DESCRIPTION JP2003250191
[0001]
The present invention combines a piezoelectric speaker amplifier, which is a low frequency
amplifier, with a step-up DC / DC converter circuit, which is a switching power supply, and in
particular, changes the power supply voltage according to an audio signal. The present invention
relates to a power consumption reduction device for a piezoelectric speaker that can save power
by supplying a minimum necessary amount of power to a piezoelectric speaker amplifier.
[0002]
2. Description of the Related Art Conventionally, as shown in FIG. 2, in this type of device, a stepup DC / DC converter circuit 2 is connected to a battery 1 serving as an input power source, and
a piezoelectric speaker is connected to the step-up DC / DC converter circuit 2. The piezoelectric
speaker 4 is connected to the piezoelectric speaker amplifier 3 while the piezoelectric amplifier 4
is connected. The piezoelectric speaker 4 is a voltage drive element and is proportional to the
voltage of the audio input signal. To increase the volume, the voltage of the audio input signal
applied to the piezoelectric speaker 4 needs to be increased, and the power supply voltage of the
circuit needs to be set higher than the maximum voltage value of the audio signal. The
[0003]
Therefore, since a high voltage output is required from the power supply to obtain the volume,
the loss of the class B amplifier circuit itself requiring the idling current is proportional to the
power supply voltage. The power consumption at no load increases, and the problem is that the
high efficiency conversion characteristics of the piezoelectric speaker can not be utilized.
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[0004]
SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention
provides a battery serving as an input power source as a result of research, a step-up DC / DC
converter circuit connected to the battery, and a step-up DC / DC converter circuit. A
piezoelectric speaker amplifier connected to the piezoelectric speaker, a piezoelectric speaker
connected to the piezoelectric speaker amplifier, an audio input signal source connected to the
piezoelectric speaker amplifier, the piezoelectric speaker amplifier, and a step-up DC / DC
converter circuit And a power saving circuit interposed therebetween.
[0005]
The power consumption reducing device for a piezoelectric speaker according to the present
invention receives an audio signal from an audio input signal source to drive the piezoelectric
speaker and, at the same time, uses + Vcc of the step-up DC / DC converter circuit in a power
saving circuit. The output voltage with -Vcc is changed in proportion to the audio signal level to
be fed back to the DC / DC converter circuit.
[0006]
That is, power is supplied from the battery to the step-up DC / DC converter circuit, boosted by
the step-up DC / DC converter circuit to generate positive and negative power supply outputs,
and power boosted by the step-up DC / DC converter circuit. The output is connected to a
piezoelectric speaker amplifier, and an audio signal is input from an audio input signal source,
whereby the output signal amplified by the piezoelectric speaker amplifier drives the
piezoelectric speaker 4 and the power supply voltage of the piezoelectric speaker amplifier Feed
back the signal amplified by the piezoelectric speaker amplifier from the power saving circuit to
the FB terminal of the step-up type DC / DC converter circuit, thereby changing the power supply
voltage according to the signal voltage. The power consumption of the piezoelectric speaker
amplifier is reduced.
[0007]
The present invention changes the output voltage of + Vcc and -Vcc of the step-up DC / DC
converter circuit according to the voltage of the audio signal, thereby providing a piezoelectric
speaker with the minimum power supply voltage required for audio amplification. It is an object
of the present invention to provide a power consumption reducing device for a piezoelectric
speaker which can operate an amplifier and can realize power saving.
[0008]
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DESCRIPTION OF THE PREFERRED EMBODIMENTS The power consumption reducing device for
a piezoelectric speaker according to the present invention will be described below based on the
drawings of the embodiments.
[0009]
FIG. 1 is a circuit diagram for explaining an outline of an embodiment of a power consumption
reducing device for a piezoelectric speaker according to the present invention, FIG. 2 is a circuit
diagram of a power input device for a piezoelectric speaker according to a conventional example,
and FIG. It is a characteristic view of the power supply voltage-output voltage of the power
consumption reduction device for piezoelectric speakers of the present invention and the power
input device for piezoelectric speakers of the conventional example. FIG. 4 is the power
consumption reduction device of piezoelectric speakers of the present invention and the
piezoelectric of the conventional example. FIG. 5 is a characteristic diagram of power
consumption-output voltage of the power input device for a speaker, and FIG. 5 is a graph
showing a + Vcc output voltage waveform and an audio signal voltage waveform in the power
consumption reducing device for a piezoelectric speaker of the present invention. These are
graphs showing the + Vcc output voltage waveform and the audio | voice signal voltage
waveform of the power supply input device for piezoelectric speakers of a prior art example.
[0010]
The present invention combines the piezoelectric speaker amplifier 3 that is a low frequency
amplifier with the step-up DC / DC converter circuit 2 that is a switching power supply, and in
particular changes the power supply voltage according to the audio signal. The present invention
relates to a power consumption reduction device for a piezoelectric speaker that can save power
by supplying minimum necessary power, and a battery 1 as an input power source and a boost
DC connected to the battery 1. / DC converter circuit 2, piezoelectric speaker amplifier 3
connected to the step-up DC / DC converter circuit 2, piezoelectric speaker 4 connected to the
piezoelectric speaker amplifier 3, and the piezoelectric speaker amplifier 3 Between the voice
input signal source 5 and the amplifier for piezoelectric speaker 3 and the step-up DC / DC
converter circuit 2 And an audio signal is input from the audio input signal source 5 to drive the
piezoelectric speaker 4, and the power saving circuit 6 drives + Vcc of the step-up DC / DC
converter circuit 2. And -Vcc output voltage is changed in proportion to the audio signal level to
be fed back to the DC / DC converter circuit 2.
[0011]
That is, the battery 1 of the power consumption reducing device for a piezoelectric speaker
according to the present invention is not particularly limited as long as the power source
capacity is satisfied, such as alkaline batteries, nickel batteries, nickel hydrogen batteries and
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lithium batteries.
[0012]
Then, as shown in FIG. 1, power is supplied from the battery 1 to the step-up DC / DC converter
circuit 2, and the output voltage of the step-up DC / DC converter circuit 2 is determined by the
values of the voltage dividing resistors R1, R2 and R3. Voltage is applied to the FB terminal of the
step-up DC / DC converter 2.
[0013]
Next, the voltage is controlled to the FB terminal voltage set by the step-up DC / DC converter
circuit 2 and kept at a constant voltage, and the + Vcc output voltage is a value determined by
the values of the voltage dividing resistors R1, R2 and R3. Is set to
[0014]
Furthermore, the -Vcc voltage output is configured to be able to output a negative voltage
proportional to the absolute value output of the + Vcc voltage output of the step-up DC / DC
converter circuit 2. For example, the step-up DC / DC converter circuit 2 The configuration may
be such as a configuration with a transformer and a 2-winding output with the same number of
transformer turns.
[0015]
Next, the + Vcc and −Vcc output voltages of the step-up DC / DC converter circuit 2 are used as
power supply voltages of the error amplifiers IC1, IC2, IC3 and IC4, but when there is no audio
signal output of the audio input signal source 5, By setting the output voltage values of + Vcc and
-Vcc of the step-up DC / DC converter circuit 2 to the lower limit of the operable voltage values
of the error amplifiers IC1, IC2, IC3 and IC4, the error amplifiers IC1, IC2, IC3, It is possible to
minimize the circuit power consumption of the IC 4.
[0016]
Here, when an audio signal is input from the audio input signal source 5 to the non-inverted
input of the error amplifier IC1, it is determined by the resistors R4 and R5 by the non-inverted
amplifier circuit configured by the error amplifier IC1 and the resistors R4 and R5. The audio
signal input from the audio input signal source 5 with amplification degree is to be amplified.
[0017]
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Furthermore, the audio signal output amplified by the error amplifier IC1 is input to the noninverting input of the error amplifier IC2 of the next stage and to the inverting input of the error
amplifier IC3 through the resistor R10, and further amplified by the error amplifiers IC2 and IC3.
The error amplifier IC2 is non-inverted and amplified at an amplification determined by the
resistors R8 and R9, and the error amplifier IC3 is inverted and amplified at an amplification
determined by the resistors R10 and R11.
[0018]
Then, since the outputs of the error amplifiers IC2 and IC3 are reversed in polarity, the outputs
of the error amplifier IC2 are connected to one side of the input terminal of the piezoelectric
speaker 4 through the resistor R12 with the same amplification of the error amplifiers IC2 and
IC3. The output of the error amplifier IC3 is connected to the other input terminal of the input
terminal of the piezoelectric speaker 4 through the resistor R13, whereby an output voltage
twice as high as that of the error amplifiers IC2 and 1C3 can be obtained. It is a thing.
[0019]
Further, the BTL connection can generate a voltage higher than the supply voltage from a low
supply voltage such as a battery drive, and is an advantageous connection method for the
piezoelectric speaker amplifier 3 requiring a high drive voltage. It is.
[0020]
Here, when the output voltage of the error amplifier IC2 increases to the negative voltage side,
the peak voltage value is held as a negative voltage with respect to the GND level in the capacitor
C1 through the resistor R16 and the diode D4.
[0021]
Next, the held voltage is divided by the resistors R14 and R15, and input to the non-inverting
input of the error amplifier IC4 from the connection point of the resistors R14 and R15.
[0022]
The voltage divided by the resistors R14 and R15 input to the error amplifier IC4 is output to the
output of the error amplifier IC4 as the same voltage value as the input, and the output voltage of
the error amplifier IC4 is boosted through the diode D1 and the resistor R3. The voltage
decreases in the direction of decreasing the voltage at the FB terminal of the DC-DC converter 2.
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[0023]
Further, since the step-up DC / DC converter circuit 2 operates to make the FB terminal voltage
constant, control is performed to keep the FB terminal voltage constant by increasing the + Vcc
output voltage.
[0024]
Next, as the + Vcc output voltage increases, the −Vcc output voltage also increases in proportion
to the + Vcc output voltage, and the output voltages of + Vcc and −Vcc change according to the
signal level of the audio input signal source 5 It will be
[0025]
Next, when the output voltage of the error amplifier IC3 increases to the negative voltage side,
the peak voltage is held as a negative voltage with respect to the GND level in the capacitor C1
through the resistor R17 and the diode D5.
[0026]
Here, the voltage held as in the case where the output of the error amplifier IC2 increases to the
negative voltage side is divided by the resistors R14 and R15, and input to the non-inverting
input of the error amplifier IC4 from the connection point of the resistors R14 and R15. Thus,
the output voltages of + Vcc and -Vcc change in accordance with the signal level of the audio
input signal source 5.
[0027]
This means that the output voltages of + Vcc and -Vcc change according to the output voltage
value of the audio input signal source 5, so it is possible to supply the minimum necessary error
amplifier power supply voltage for the signal level. It becomes possible to reduce the loss
generated by the error amplifier.
[0028]
Next, FIG. 3 is a characteristic diagram of power supply voltage-output voltage, and shows the +
Vcc output voltage (power supply voltage) of the present invention and the conventional
example. As an example, the output voltage is 10 Vp-p. In the case of the prior art, the power
supply voltage of +15 V is +7 V according to the power consumption reducing device for a
piezoelectric speaker of the present invention, assuming that the current consumption of the
error amplifiers IC1, 1C2, IC3 and IC4 is 10 mA. Since 10 mA is 0.01 A, a loss of 15 V × 0.01 A
= 0.15 W is obtained in the conventional example, and 7 V × 0.01 A = 0.07 W in the present
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invention, and only the error amplifier is used even at the same volume. Can reduce the power
consumption by 0.08 W.
[0029]
FIG. 4 shows the characteristics of power consumption-output voltage including the step-up DC /
DC converter circuit and amplifier of the present invention and the prior art, and when no signal
(output voltage 0 Vp-p) Then, the power consumption can be reduced to about 1/3 compared to
the present invention and the conventional example.
[0030]
This makes it possible to use the battery 1 used as a power supply for a long time, especially
when using a non-rechargeable battery 1 such as an alkaline battery or a manganese battery, the
cost of the battery is greatly reduced. It can be measured.
[0031]
Since the charge held in the capacitor C1 is discharged through the resistors R14 and R15, the +
Vcc output voltage is lowered to the corresponding + Vcc output voltage when the voltage of the
audio input signal source 5 decreases.
[0032]
Also, the setting of the upper limit value of the + Vcc output voltage is voltage-clamped by the
Zener diode ZD1 and can be set to a value which does not exceed the working voltage of the
error amplifier.
[0033]
Furthermore, FIG. 5 shows the output voltage waveform and the + Vcc output voltage waveform
of the error amplifier IC 2 obtained by amplifying music as the audio signal input source 5 in the
power consumption reducing device for piezoelectric speaker according to the present invention.
It can be confirmed that the + Vcc output voltage is changed according to the signal voltage.
[0034]
6 shows the output voltage waveform and the + Vcc output voltage waveform of the error
amplifier IC2 of the conventional example. Since the constant voltage is maintained, + Vcc when
the voltage of the audio input signal source 5 is lowered. Because the voltage difference with the
output voltage is large, and the loss of the error amplifier can be expressed by (+ Vcc output
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voltage−output voltage) × (consumption current of the error amplifier), the loss in the absence
of a signal becomes larger compared to the present invention It is.
[0035]
The power consumption reducing device for a piezoelectric speaker according to the present
invention changes the output voltage of + Vcc and -Vcc of the step-up DC / DC converter circuit
according to the voltage of the audio signal by the above circuit configuration. By doing this, it is
possible to operate the piezoelectric speaker amplifier with the minimum power supply voltage
required for audio amplification all the time, so it is possible to reduce the power consumption of
the battery, which is revolutionary and practical It is a high invention of
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