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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
speaker driving device equipped with an automatic gain control (hereinafter referred to as AGC).
SUMMARY OF THE INVENTION The present invention is suitable for a speaker drive voltage by
providing a circuit for outputting an AGC output from a collector and changing an amount of
output feedback according to the drive voltage of the speaker in a speaker drive device equipped
with AGC. AGC operation at another level is enabled. 2. Description of the Related Art A
conventional speaker driving apparatus equipped with AGC has performed AGC operation at a
constant level. [Problems to be Solved by the Invention] However, in the above-mentioned prior
art, when used for applications in which the speaker drive voltage changes (for example,
considering a telephone speaker, the telephone can take a large current when it is close to the
central office). The drive voltage of the speaker can also be increased.) The AGC level is
determined so that the output is not distorted when the drive voltage of the speaker is minimum.
In this case, even if the drive voltage of the speaker is high and the sound pressure can be
obtained, the sound pressure at the minimum of the speaker drive voltage can not be changed.
Therefore, the present invention solves such problems, and an object of the present invention is
to provide a speaker drive device that sets an AGC level with an optimal sound pressure at the
drive voltage when the speaker drive voltage changes. Where are you going? [Means for Solving
the Problems] The speaker drive device according to the present invention comprises an
operational amplifier circuit equipped with auto gain control, an inverting amplifier circuit using
the output of the operational amplifier circuit as a human power, and a non-inverting amplifier
circuit. The output of the inverting and non-inverting amplification circuit is connected to the
base of the NPN transistor, the emitter of the NPN transistor is commonly connected to the
negative potential, and the collector of the NPN transistor is connected to the primary example of
the transformer. A speaker driving device serving as a speaker load on the next side is
characterized in that it has a circuit that performs output feedback for auto gain control from the
collector of the NPN transistor and changes the amount of output feedback by the driving voltage
of the speaker. I assume. [Operation] According to the above configuration of the present
invention, since the circuit for changing the output feedback amount by the drive voltage of the
speaker is included in the output feedback for AGC, the AGC level becomes larger when the
speaker drive voltage is increased. Lower, lower. Embodiment FIG. 1 is a diagram showing the
structure of driving a speaker according to an embodiment of the present invention. Coupling
capacitor output for cutting DC component of 1 human power signal becomes input of input
amplifier circuit 2, DC level of input amplifier circuit signal is given by DC bias circuit 3, 4 is AGC
element of human power amplifier circuit The impedance changes according to the external
output level, and the gain of the input amplifier circuit is changed.
The amplifier circuit equipped with AGC is constructed in 2.3.4. The output of the input
amplification circuit passes through the positive and negative amplification circuit 5.6 to drive
the base of the NPN) ranjisk. The reference numeral 9 denotes a transformer of a speaker load,
and a drive voltage 10 of the transformer controls the feedback amount variable circuit 11, and a
feedback input is performed from the collector of the NPN I-transistor. The feedback amount
variable circuit output controls the AGC element 4 through the feedback amplification circuit 13
so as to become the current and voltage passed through the peak detection circuit 12 and the
AGC element. For example, here, when a FET is used as an AGC element, it is a voltage that
controls the impedance of the AGC element, and it is a current that controls the impedance of the
AGC element when the AGC element is a Cds opto-isolator. FIG. 2 is a circuit diagram of a variable
feedback amount in the embodiment of the present invention. The reference numeral 14 is a
returning human power, which in the present invention is a collector output. The reference
numeral 15 denotes a coupling capacitor for cutting the DC component of the feedback human
power, and the reference numeral 16.17 denotes feedback resistors R1 and R2, which provide an
input signal 20 to the peak detection circuit with a resistance division ratio. An N-type MOS
transistor 18 is connected in parallel to the resistor 17. The source potential is connected to an
analog ground formed by the DC bias circuit 19 in common with one end of the resistor 17. The
gate of the N-type MO 9 transistor is a voltage of a transformer drive circuit. The resistance
division potential of R10 is applied. In the above circuit, the analog ground is VAG, the
amplification factor of the N-type MOS transistor is β, the threshold voltage is v7, 1.16 · 17
resistance values R1-R2, and the transformer drive voltage vg is a resistance division ratio output
voltage coefficient Let a be. At this time, the resistance value R7 of the N-type MOS transistor is
expressed by the following equation. According to the above equation (2), when the transformer
drive voltage vE increases, the resistance value of the N-type MOS transistor decreases and the
feedback ratio from the output decreases. Although the N-type MOS transistor is used to change
the feedback amount due to the transformer power supply voltage in this embodiment, another
FET may be used. The same operation is also performed using an AGC element such as a Cds
opto-isolator. In the feedback of the transformer power supply, this embodiment uses only
resistance division, but feedback using an amplification circuit is also conceivable. As described
above, according to the invention, since the output feedback for AGC is performed from the
transformer, an AGC operational amplifier circuit insensitive to hfe variation of the NPN
transistor for driving the transformer can be obtained.
Further, since the feedback variable circuit controlled by the drive voltage of the transformer is
provided, the AGC can be operated at a speaker sound pressure level suitable for the drive
voltage of the transformer. The present invention detects the external power state at that time
when using a speaker at which the power supply voltage changes (telephone etc.), and drives the
speaker to the maximum sound pressure without distortion in that state, and the ability of the
speaker Have the effect of drawing out the Also, since the feedback amount variable circuit in the
embodiment is set after the capacitor coupling, the feedback amount setting circuit can be
formed on the same chip as the circuit such as the human power amplifier circuit and the peak
detection circuit. Effect that can be provided to
Brief description of the drawings
FIG. 1 is a speaker drive configuration diagram in an embodiment of the present invention.
FIG. 2 is a machine quantity variable circuit diagram in the embodiment of the present invention.
2 Φ · · 5.6 φ 9 · · · 10 · ・ 11 11 · · · Manual power amplifier circuit forward, reverse amplifier
circuit Speaker load transformer transformer drive voltage feedback amount variable circuit
Applicants Seiko Epson Corporation LL
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