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JPS61102827

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DESCRIPTION JPS61102827
[0001]
The present invention relates to an output switching circuit of a radio receiver capable of
switching between stereo reproduction by headphones and monaural reproduction by speakers.
2. Description of the Related Art Configuration of the Conventional Example and its Problems In
recent years, the demand for radio receivers capable of stereo reproduction by headphones has
been increasing. On the other hand, there is also a strong demand for monaural reproduction
radio receivers using speakers, and radio receivers having both of the characteristics of switching
circuits of output amplifiers are put on the market. The output switching circuit of the
conventional radio receiver will be described below. FIG. 1 shows an output switching circuit of a
conventional radio receiver. Reference numeral 1 denotes an input end to which the L channel
output of the radio section is applied, 2 denotes an input end to which the R channel output is
applied, and 3 and 4 denote switches for switching between headphones and speakers, which
switch the output from the radio section. Reference numeral 5 denotes a headphone output DO
cut output capacitor, and 6, 7 ░ 8 a headphone antenna choke coil, which are connected to the
headphone jack 9. Reference numeral 1Q denotes an output capacitor for DC cut, and five
speakers are landed on the speaker 11. The operation of the radio reception type output
switching circuit configured as described above will be described below. First, in the case of
stereo reproduction with headphones, the L channel output from the radio section The R channel
output is the first switching terminal of the switching switches 3 and 4 from the middle terminals
a and d of the headphone and speaker switching switch 3.4. Input to the stereo output amplifier
19 as an input signal through e. A signal extracted from the stereo output amplifier 19 is
transmitted to the headphone jack 9 through the headphone antenna choke coil 7. Therefore, by
inserting a headphone plug into the jack 9, it is taken out as a stereo output. Here, the side
connected to the headphone jack 9 of the headphone antenna choke coil / I / 8 is connected with
a large FM input, so that the cord of the stereo headphone is used as an FM antenna. Next, in the
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case of monaural reproduction by a speaker, the L channel output surface of the radio section
and the R channel output become a monaural signal through the second changeover terminals c
and b of the changeover switches 3 and 4 and enter the output amplifier 20 as an input signal.
The signal taken out of the output amplifier 20 is transmitted to the speaker through the DC cut
output capacitor 10 and becomes an audio signal. However, in the above-described configuration,
two power amplifiers are required, so the number of parts is large and the cost is high.
SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional
problems, and provides an output switching circuit of a radio receiver capable of enabling stereo
reproduction by headphones and monaural reproduction by speakers by one stereo output
amplifier. The purpose is to The present invention is characterized in that switching between
headphones and speakers, BTL connection of a stereo output amplifier, and monauralization of a
stereo signal are simultaneously switched by means of changeover switches provided on the
input side and output side of the stereo output amplifier. It is said that. DESCRIPTION OF THE
PREFERRED EMBODIMENT FIG. 2 shows an output switching circuit of a radio receiver according
to an embodiment of the present invention. In FIG. 1, the same reference numerals indicate
similar components. In FIG. 2, 12, 13 and 17.18 are headphone and speaker changeover
switches, 1 <DC force of negative feedback section, 7) capacitor, 16 is a resistor for determining
the amount of negative feedback, and 16 is for BTL operation. It is a feedback resistor. The
operation of the output switching circuit of the radio receiver according to this embodiment
configured as described above will be described below. First, in the case of stereo reproduction
with headphones, the L channel output face of the radio section is R channel output, which is
connected to the intermediate terminal a of the headphone and speaker changeover switch 12.13
and the first changeover terminal e, respectively. The channel output directly enters the stereo
output amplifier 19 as an input signal through the middle terminal d of the changeover switch
13 via the L terminal. The signal taken out from the stereo output amplifier 19 is connected to
the middle terminal g of the changeover switch 17.18, respectively, and is connected to the first
switch terminal of the changeover switch 17.18 via the k. It is transmitted to the headphone jack
9 through 1/617 and taken out as a stereo output. Next, in the case of monaural reproduction by
a speaker, the R channel output toward the L channel output of the radio section becomes a
monaural signal through the second switching terminal C to the intermediate terminal of the
switching unit 12 and to the L channel of the stereo output amplifier 19 Enter as an input signal.
The signal taken out from the L channel of the stereo output amplifier 19 passes through the
middle terminal g of the changeover switch 17 and the second switching terminal 1 and the
negative feedback in the R channel of the stereo output amplifier 19 by the BTL operation
feedback resistor 16. The DC cut capacitor 14 of the part and the resistor 16 which determines
the negative feedback amount are fed back to the connected part. At this time, since the R
channel input of the stereo output amplifier 19 is grounded through the intermediate terminal d
of the changeover switch 13 and the second switching terminal, the R channel of the stereo
output amplifier 19 has a phase opposite to that of the L channel. To amplify.
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Then, the signal taken from the R channel of the stereo output amplifier 19 is sent to the middle
terminal of the changeover switch 18 and the second changeover terminal t! Are connected to
the speaker 11. Here, since one of the Heuss coils of the speaker 11 is connected to the L
channel / 1 / earth force of the stereo output amplifier 19, the speaker 11 is BTL driven by the
stereo output amplifier 19. As described above, according to the present embodiment, by
providing four selector switches and feedback resistors at the input and output of the stereo
output amplifier 19, switching between headphones and speakers, BTL connection of the stereo
output amplifier 19, and stereo signal Monaural can be switched simultaneously. Although the L
channel output of the stereo output amplifier 19 is fed back to the negative feedback portion of
the R channel in this embodiment, the R channel output may be fed back to the negative
feedback portion of the L channel. Needless to say. Effect of the Invention The present invention
simultaneously switches the headphone and the speaker, the BTL connection of the stereo output
amplification + 47i, and the monauralization of the stereo signal by providing four switches and a
resistor at the input and output of the stereo output amplifier. In addition, by making the output
amplifier into one system, it is possible to realize an excellent output switching circuit of a radio
receiver which can obtain the effects of reducing the number of parts and the cost.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is an output switching circuit diagram of a conventional radio receiver, and FIG. 2 is an
output switching circuit diagram of a radio receiver according to one embodiment of the present
invention.
12.13,17.18 ...... changeover switch, 5 ии DC cut for the output capacitor, 6,7.8 ... headphone
antenna for Nayokukoiru, 9 ... headphone Shack, 11 ...? Speaker ? ? ? ? ? ? ? ? ? DC
cutting capacitor for negative feedback part ? ? ? ? ? ? ? ? Resistor to determine the
amount of negative feedback ? ? ? ? ? ? ? ? Feedback resistance for BTL operation, ? ?
?Stereo output amplifier.
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