JP2005269291A - Acoustic apparatus with headphone output jack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simplify the circuit constitution by omitting an audio amplifier circuit for the headphone output only. <P>SOLUTION: The acoustic apparatus comprises BTL type output amplifiers 10, 11 to which AC voltages of audio signals superposed on a DC voltage bias are inputted. The output of either the amplifier 10 or 11 is connected to a headphone output jack 2 through a DC voltage cutoff means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an audio device including a speaker and a headphone output jack.

The audio amplifier can be classified into an SE (single end) type and a BTL (bridged transformerless) type depending on the audio output format, and both are input with an AC voltage that is an audio signal superimposed on a DC voltage bias. As is well known, the bias is a higher voltage than the audio signal.
As shown in FIG. 3, the SE type has a configuration in which the output of the amplifier (10) is connected to the positive electrode of the speaker (3) and the negative electrode of the speaker (3) is grounded (see, for example, Patent Document 1). On the other hand, as shown in FIG. 4, the BTL type is one of the two amplifiers (10) and (11) that is normally rotated, the other input is inverted, and the respective outputs are input to the speaker (3). It is the structure to do. The speaker (3) is input with a normal phase signal and a reverse phase signal, the voltage amplitude is doubled, and ideally the output power is quadrupled, so that the characteristics are improved compared to the SE type. Such BTL type audio amplifiers are widely used in car audios and the like whose power supply voltage is limited to about 12V.

Many of such acoustic devices have a headphone jack. However, as shown in FIG. 6, when this headphone output circuit is configured in the BTL type in the same manner as the SE type, since the BTL output has a DC voltage bias, the DC voltage is applied to the headphone jack (2). Is transmitted. For this reason, when the user inserts the plug (4) into the jack (2), there is a risk of electric shock. In order to avoid this danger, as shown in FIG. 5, the BTL type audio amplifier was used exclusively for the output of the speaker (3), and the headphone output was output by providing a separate audio amplification circuit (6).
JP-A-9-107256

In the configuration shown in FIG. 5, the headphone output sound amplifying circuit (6) is required, so that the circuit board (not shown) on which the sound amplifying circuit (6) is mounted is enlarged. Further, since the audio amplifier circuit (6) for headphone output is necessary, the cost increases and the number of parts of the audio equipment increases.
An object of the present invention is to simplify a circuit configuration by omitting an audio amplifier circuit dedicated for headphone output.

  The acoustic device includes a BTL type output amplifier (10) (11) in which an AC voltage that is an audio signal is superimposed on a bias of a DC voltage, and one output of the amplifier (10) (11) is connected to a DC voltage. It is connected to the headphone output jack (2) through the voltage cutoff means.

  The outputs of the amplifiers (10) and (11) are transmitted to the headphone output jack (2) after the bias, which is a DC voltage, is cut off by a DC voltage blocking means, specifically, a capacitor. Accordingly, only an audio signal having a weak voltage is transmitted to the headphone output jack (2), and there is no possibility of electric shock when the user inserts the plug (4) into the headphone output jack (2). As a result, it is possible to omit the audio amplifier circuit (6) dedicated to headphone output, which has been necessary in the past, and to simplify the circuit configuration. Moreover, an increase in cost and an increase in the number of parts of the audio equipment can be suppressed.

Hereinafter, an example of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the circuit configuration of the acoustic apparatus of this example. For convenience of illustration, only the Lch connection configuration is shown, but Rch has the same circuit configuration as the Lch.
The acoustic device includes an amplifier circuit (1) that amplifies Lch and Rch signals, a headphone jack (2) in which a headphone plug (4) is fitted, and a speaker (3). Each of the Lch and Rch signals is a signal in which an AC voltage, which is an audio signal, is superimposed on a DC voltage bias, and the BTL output amplifier (10) (11) causes the voltage amplitude to be twice that of the input signal. And output from the amplifier circuit (1).
When the plug (4) is inserted, the headphone jack (2) is pushed by the plug (4) to bend and deform in a direction away from the plug (4). And a second contact piece (21) that is in electrical contact with the plug (4).
The Lch inversion signal is supplied to the speaker (3) as it is. The Lch normal rotation signal is supplied to the speaker (3) at the contact A via the first contact piece (20) of the jack (2). The Lch forward signal is supplied to the second contact piece (21) of the jack (2) via the capacitor (5).

  As shown in FIG. 2, when the user inserts a headphone plug (4) between the first and second contact pieces (20) and (21) of the jack (2), the first contact piece (20) is removed. When pushed by the tip of the plug (4), it is bent away from the plug (4), as indicated by the alternate long and short dash line. The first contact piece (20) is separated from the contact point A, and the signal supply to the speaker (3) is cut off. Since the audio output from the speaker (3) stops and the normal rotation signal of Lch is supplied to the second contact piece (21), the normal rotation signal flows to the plug (4), and the user uses headphones (see FIG. You can listen to the voice only.

  In this case, since the Lch normal rotation signal is supplied via the capacitor (5), the DC voltage as the bias is cut off, and only the audio signal as the weak voltage is transmitted to the plug (4). Therefore, there is no possibility of electric shock when the user inserts the plug (4) into the headphone output jack (2). As a result, it is possible to omit the audio amplifier circuit (6) dedicated to headphone output, which has been necessary in the past, and to simplify the circuit configuration. Moreover, an increase in cost and an increase in the number of parts of the audio equipment can be suppressed.

The applicant assumes a television receiver as the audio equipment. However, it goes without saying that the above configuration can also be applied to other audio equipment such as car audio equipment and cassette recorders with CD.
The headphone output jack (2) may be replaced with an earphone output jack. In this case, any one signal of Lch and Rch may be transmitted to the earphone output jack.

  The above description of the embodiments is for explaining the present invention, and should not be construed as limiting the invention described in the claims or reducing the scope thereof. In addition, the configuration of each part of the present invention is not limited to the above embodiment, and various modifications can be made within the technical scope described in the claims.

It is a block diagram which shows the circuit structure of the audio equipment of this example. It is a figure which shows the operation | movement which inserts a plug into a jack. It is a figure which shows SE type | mold audio amplifier. It is a figure which shows a BTL type | mold audio amplifier. It is a block diagram of the conventional audio equipment. It is a block diagram at the time of comprising the output circuit for conventional headphones with BTL type similarly to SE type | mold.

Explanation of symbols

(2) Jack
(3) Speaker
(4) Plug
(5) Capacitor
(10) BTL output amplifier
(11) BTL output amplifier

Claims (3)

A BTL type output amplifier (10) (11) is provided, in which an AC voltage as an audio signal is superimposed on a DC voltage bias, and one output of the amplifier (10) (11) is connected to a DC voltage blocking means. Via the headphone output jack (2). A BTL type output amplifier (10) (11) is provided, in which an AC voltage as an audio signal is superimposed on a DC voltage bias, and one output of the amplifier (10) (11) is connected to a DC voltage blocking means. An audio device characterized by being connected to an earphone output jack. The acoustic device according to claim 1 or 2, wherein the DC voltage blocking means is a capacitor (5).

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