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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a prior art
embodiment, and FIG. 3 is a circuit diagram showing an embodiment of the present invention. 1
to 3 · · · · · · Power amplifier, 5, 6 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·
· · · variable resistor, 10 + 12 + 14 t 16 t 20. 22 · · · · · · · · · · · · · · 11 · · · 15 degrees 17-19, 21.2325 ........... resistance.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a BTL output
circuit. In the audio output circuit, there are cases where it is desired to sound two speakers (for
example, right or left channel signal) for one sound source signal, and to control each volume
independently. Especially car stereo ■ ,! . <G-22 '. In the case of 1 , it is often desirable to
generate the left and right channel sounds on the front and rear speakers and control them with
a four-way parlancer, or left and right balance and front and rear fader volumes. In such a case,
conventionally, as shown in FIG. 1, two power amplifiers are provided with independent volumes
7.8 on the input side, or controlled as shown in FIG. A power type volume 7.8 · is provided in
series with 5 and 6 to control. The amplifiers in FIG. 1 and FIG. 2 are each shown in the BTL
system, but the details are omitted. In the case of FIG. 1, two output circuits (four amplifiers) are
required, and four output lines are also required. In the case of in-vehicle use, the large number
of cables is a major drawback. Also, in the case of FIG. 2, the output circuit is one system (two
amplifiers), but two power type volumes are required, and in the case of a large output, the loss
in the volume is also large, so heat radiation becomes a problem There is a fault. The present
invention does not suffer from the above-mentioned drawbacks, and has a small number of
output terminals (ケ 2), and does not use a power type volume, and independently controls an
output to two speakers using a normal type volume. There is a K that provides a possible circuit
scheme. When configuring a BTL-connected power amplifier that uses two commonly used
power amplifiers with a differential amplifier type in the input stage, the amplifier connected to
the input is a non-inverting amplifier and the other amplifier is the amplifier There is a method of
configuring as an inverting amplifier of gain 1 which receives an output as an input. In the
present invention, two inverting amplifiers are used for one non-inverting amplifier in the above
configuration, and the gain of each of them can be varied up to 1 to 1 or less by four
independent variable resistors. This makes it possible to configure two ETL amplifiers sharing the
input side non-inverting amplifier, the number of output terminals is as large as sixty-one
terminals of the conventional 41fll, and the variable resistance is not a power type but a common
variable resistance . An embodiment of the present invention will be described below with
reference to FIG. In Fig. 3, 1 to 5 are differential input type power amplifiers, 5 and 6 are
speakers, 7 and 8 are variable resistors and resistors, 9 is a signal input terminal, 1D and 14.20
are inputs of each amplifier. Coupling capacitors 11 ° 15.21 and 13, 17.23 are feedback
resistors, 12.16.22 are DC cut capacitors, and 18.24 are gains from point 0 to points B and C at
The feedback resistors 7.19 and 8, 25 are gain adjustment resistors. The same functional units as
in FIGS. 1 and 2 are assigned the same reference numerals. The signal (L channel signal) applied
to the input terminal 9 in such a circuit is the resistors 11 and 13 (hereinafter referred to as R1,.
R11 resistance is the same, and the amplitude is increased by an intermediate degree and output
to point A, so that points H and C are 180 ° different in phase from point A with respect to the
amplitude at point A There is a signal of the ratio Ru + / RIs + Rn / Rn. Usually R □. = RIa, R11 =
R34, and an amplitude twice as high as that obtained between each layer and ground is obtained
between A and B and between A and 0, and is transmitted to the load. However, this is true when
the signal applied to the non-inverting input of the amplifiers 2 and 3 from the dividing point of
the resistors 7 and 7 and the resistors 4 and 19 and the resistors 8 and 25 is very small. Occurs
at points B and 0 as the variable resistors 7 and 8 change and the signal level increases. The
voltage to be output increases in phase with the point A, the current flowing to the load of the
speaker 5.6 decreases, and the output power decreases. According to the present invention
described above, a large output can be obtained with a small number of power amplifiers, and
the number of output terminals can be reduced.
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