JPH0242265B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a telephone set called a speaker horn, which uses a speaker to amplify a received signal.

Conventional configurations and their problems In telephones that are generally called speaker horns,
As shown in FIG. 1, the reception signal appearing at the handset connection terminals b ₁ and b ₂ of the telephone line network 1 connected to the telephone lines L ₁ and L ₂ is taken out via a transformer 2, and is connected to a separately provided power supply. Amplifier 4 driven by 3
The signal is amplified and applied to the speaker 5. However, this type of device requires a separate transformer 2 and power source 3, which increases the size of the telephone as a whole, and the signal from the transmitter 6 is transmitted through a hybrid transformer T, resistor R ₁ ,
R ₂ , R ₃ , R ₄ , R ₅ , capacitor C ₁ , C ₂ , varistor
Although the sidetone prevention circuit consisting of V ₁ , V _{2 ,} etc. is configured so that it does not appear significantly on the receiver connection terminals b ₁ , b ₂ , once the receiver connection terminals b ₁ ,
When a signal from the transmitter 6 appears at b ₂ , it is greatly amplified by the transformer 2 and amplifier 4 and applied to the speaker 5, so that a louder transmitted sound than the speaker 5 appears. There was a problem that a large sidetone prevention effect could not be obtained.

Purpose of the Invention The present invention eliminates the above-mentioned conventional drawbacks, and provides an excellent telephone that has a simple configuration, can be downsized, and can obtain a sufficient sidetone prevention effect. The purpose is to

Structure of the Invention The present invention connects a constant voltage element in series to a telephone transmitter, configures a constant voltage power supply circuit with this constant voltage element, and uses the output of this constant voltage power supply circuit to connect a constant voltage element to a telephone line. In addition to obtaining a power source for an amplifier circuit that amplifies a received signal, the transmitter is configured to mute the amplifier at the time of transmitting using the voltage appearing at both ends of the transmitter.

DESCRIPTION OF EMBODIMENTS FIG. 2 is an electrical wiring diagram of an embodiment of the telephone according to the present invention. In the figure, L ₁ and L ₂ are connection terminals connected to a telephone line, and 10 is a hybrid transformer T ₁ and a resistor. R ₁₁ , R ₁₂ , R ₁₃ , R ₁₄ , capacitor
A telephone line network consisting of C ₁₁ , C ₁₂ , C ₁₃ , C ₁₄ , and a varistor V ₁₁ , the input end of which is connected to the middle tap of the third winding l ₃ of the hybrid transformer T ₁ constituting the telephone network 10 is a resistor R. ₁₄ , an amplifier circuit connected through _R27 , 12 a speaker connected to the output terminal of the amplifier circuit 11 through a capacitor _C19 , 13 transistors _TR1 , _TR2 , _TR3 , and resistors _R15 to This muting circuit consists of R ₂₆ and capacitors C ₁₅ to C ₁₈ and detects the voltage across the transmitter 14 and applies muting to the amplifier 11 when transmitting a voice.

A parallel circuit consisting of a constant voltage element ZD such as a Zener diode and a capacitor _C11 is connected in series to the transmitter 14, and the power supply for the amplifier 11 and the muting circuit 13 is connected to the constant voltage element ZD and the capacitor.
The voltage is obtained by a constant voltage circuit made of _C11 . Furthermore, the hybrid transformer T ₁ is composed of three windings l ₁ , l 2 , l ₃ , first, second, and _third , and a capacitor is connected to the intermediate tap of the third winding l ₃ .
C ₁₄ is connected, and the receiver signal is input to the amplifier 11 with stable impedance.

In the above embodiment, when the connection terminals L ₁ and L ₂ are connected to the telephone line, the normal 48V DC voltage applied to the telephone line itself is directly applied to the connection terminals L _{1 and} L 2 .
Since it is applied to _L2 , a substantially constant DC voltage appears at both ends of the constant voltage element ZD regardless of whether a call is being sent or received. And this DC voltage is the amplifier 1
1. Since the voltage is applied as the power supply voltage of the muting circuit 13, the amplifier 11 and the muting circuit 13 can be made operable without using a separate power supply.

Now, suppose that an incoming call signal is input from the telephone line, and this is transmitted from the connection terminals L ₁ and L ₂ to the telephone circuit network 10.
The signal is applied to the amplifier 11 via the speaker 12, and is amplified by the speaker 12.

On the other hand, when a signal is output from the transmitter 14, the muting circuit 13 operates accordingly. That is, when a signal is output from the transmitter 14, the voltage across the signal changes, is amplified by the transistor _TR1 , and is applied to the transistor _TR2 through the capacitor _C17 and the resistor _R20 . Therefore, if the level of the signal output from the transmitter 14 is above a certain value, the transistor TR ₂ is repeatedly turned on and off, and the capacitor C ₁₈ is charged with a constant voltage. Therefore, transistor TR ₃ is a capacitor
It is turned on by the charging voltage of _C18 , and mutating is applied to the amplifier 11. That is,
When a signal is output from the transmitter 14, muting is applied to the amplifier 11 to prevent the signal from the transmitter 14 from being applied to the speaker 12. Therefore, according to the above embodiment, even if the telephone circuit network 10 is configured relatively simply, it is possible to effectively obtain the sidetone prevention effect.

Effects of the Invention As is clear from the above embodiments, the present invention is configured such that the power for the amplifier and muting circuit is obtained by a constant voltage power supply circuit comprising a constant voltage element connected in series to the transmitter. Therefore, there is an advantage that no separate transformer, battery, etc. are required, and the telephone as a whole can be made considerably smaller. According to the present invention, the voltage across the transmitter is detected during transmission, and muting is applied to the amplifier circuit that amplifies the received signal. This has the advantage that it is possible to almost completely prevent the sound from appearing significantly on the speaker, and that a sufficient sidetone prevention effect can be obtained even if the telephone circuit network is configured relatively simply.

[Brief explanation of the drawing]

FIG. 1 is an electrical wiring diagram of a conventional telephone, and FIG. 2 is an electrical wiring diagram of an embodiment of the telephone of the present invention. 10...Telephone circuit network, 11...Amplifier, 12...
... Speaker, 13 ... Muting circuit, 14
...Telephone, ZD... Constant voltage element, L ₁ , L ₂ ... Telephone line connection terminal.

Claims (1)

[Claims] 1. A constant voltage power supply circuit consisting of a constant voltage element that is connected in series to a transmitter connected to a telephone line and outputs a predetermined constant voltage, and the output from this constant voltage power supply circuit is used as a power source, and the above telephone line an amplifier circuit that amplifies the received signal from the speaker and drives the speaker;
A telephone comprising a muting circuit that detects the voltage appearing across the transmitter during transmission and applies muting to the amplifier circuit.