JPS5840678Y2 - phone call circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a communication circuit for a telephone, and particularly to a communication circuit most suitable for public telephones where line current changes significantly.

For example, in a dial call using a public telephone, a billing signal is sent from the station equipment to the telephone when the called party answers or every time one call time elapses.

Although there are various signal formats for this signal, for example, a DC polarity reversal signal that reverses the polarity of the line current from the station equipment is used.

However, before and after this polarity reversal signal, the call loop current is temporarily cut off, so the current in the handset is cut off, and if a carbon-type handset is used, the audio output is lost and the sound is temporarily cut off. This causes an inconvenience.

In order to eliminate such inconveniences, a circuit as shown in FIG. 1 has been conventionally used.

In the same figure, Ll and Ll are terminals connected to the office line, and as shown in Figure 2a, during a call, normally the terminal L1 is ten-polarity, and the terminal Ll is ten-polar.
The terminal is unipolar, and when the called party answers or the unit call time has elapsed, terminal L1 changes to unipolar, Ll changes to decapolarity, and after a predetermined period of time, the polarity changes again: Ll is depolar, Ll is depolar. Connected to restore polarity.

A coin storage relay (not shown) in the switching circuit SWC is actuated by the polarity change of this call loop current to store coins.

The switching circuit SWC has a hook switch contact, a response monitoring relay, an incoming call relay, a coin storage relay, their contacts, a coin detection relay contact, a diode, etc., and is used to form and disconnect a call loop.

D1 to D4 are connected by diodes in a bridge configuration as shown in the figure to form a full wave rectifier circuit.

A full-wave rectifier circuit in the form of diodes D1-D4 is connected between the lines via a blocking wire CHI to prevent speech signals (voice signals) between the lines from being bypassed, and a full-wave rectifier circuit in the form of diodes D1-D4 is cathode side and diode D
A smoothing capacitor C is connected between the anode side of 2 and D4.
2 are connected.

At both ends of the capacitor C2 there is a blocking wire CH2 for blocking AC.
A transmitter T is connected via.

CI and C3 are capacitors for bypassing call signals, ■N
D is a guide ring.

If the loop current sent from the station equipment is ten-polar on the terminal L1 side and unipolar on the Ll side, as shown in Figure 2a,
The next loop is formed.

In this way, current flows in the same direction through the transmitter T, rectified by the full-wave rectifier circuit composed of diodes D1 to D4.

The waveform of the current flowing through the transmitter T in the circuit shown in FIG. 1 without the smoothing capacitor C2 is shown in FIG. 2.

As shown in this figure, the current flowing through the transmitter T is interrupted before and after the polarity change signal.

The transmitter T is a carbon-type transmitter, and in this type of transmitter, the current flowing through the carbon is changed by voice to send a communication signal between lines, so the current flowing through the transmitter T is During this period, the call signal will also be interrupted.

However, since the capacitor C2 is provided in this circuit, the charge stored in the capacitor C2 is discharged in the next loop when the line current is zero immediately before the polarity inversion signal shown in FIG.

By appropriately selecting a time constant determined by the capacitance of the capacitor C2 and the resistance of the transmitter T, changes in the current flowing through the transmitter T can be smoothed to the extent that it does not interfere with conversation.

Next, capacitor C2 is charged again while a constant loop current with polarity reversal is flowing, and when the line current is zero immediately after the polarity reversal current ends as shown in Figure 2, the charge in capacitor C2 is discharged in the same loop as above. The current flowing through the transmitter T is the second
It is smoothed as shown in Figure C.

In this way, in the conventional circuit shown in Fig. 1, the current flowing through the transmitter T is rectified by a full-wave rectifier circuit composed of diodes D1 to D4, so that even if a current with reversed polarity comes, the transmitter In addition to allowing a loop current to flow in a constant direction through T, a capacitor C2 is provided to charge this capacitor C2 when a constant loop current is flowing, and when the loop current decreases or is momentarily interrupted, a capacitor C2 is charged. By causing a discharge current of 1 to 1 to flow through the transmitter T so that a current of a constant value or higher is always supplied to the transmitter T, the communication signal from the transmitter T is prevented from being interrupted.

However, in such a conventional circuit, the resistance value of the transmitter T is usually several tens of ohms, and the resistance value of the transmitter T as the discharge loop resistance of the capacitor C2 is small, so the above purpose cannot be sufficiently achieved. To achieve this, it is necessary to use a capacitor C2 with an extremely large capacitance of about 2000 μF.

In addition, in order to prevent the audio current from being bypassed through this capacitor C2, it is necessary to use a blocking wire CH2 that has a large inductance and can superimpose direct current.
Furthermore, since the blocking wire CHI is also connected between the lines, it is necessary to use a device that can superimpose direct current with an extremely large inductance, for example, one with an inductance of 3H or more with a direct current superposition of 70 mA.

Since extremely large and heavy capacitors and blocking wires must be used, they cannot be incorporated into a printed circuit board unit that incorporates a telephone circuit, for example, and must be mounted separately, which takes up a lot of space in the device. However, it has disadvantages such as increased size and therefore higher cost.

The present invention has been developed in view of the above circumstances, and provides a telephone communication circuit that prevents the communication signal from being affected by changes in the communication loop current, and further enables miniaturization and cost reduction of the device. This is the 9th point.

The present invention does not provide the current rectified and smoothed by a rectifier, a flow wire, and a capacitor directly to the transmitter as in the conventional circuit described above, but instead passes the communication signal to be sent through an amplifier circuit to the transmission input terminal of the communication circuit. At the same time, as a power supply for this amplifier circuit, the loop current is passed through a full-wave rectifier circuit that converts the loop current into a current of the same polarity from both ends of a communication signal bypass capacitor inserted in series in the communication circuit, and further consists of a capacitor and a Zener diode. The gist of this is to provide a smoothed voltage through a current smoothing circuit.

The present invention will be explained below with reference to an embodiment shown in FIG.

In the figure, Ll and L2 are terminals connected to a communication line from the station equipment, and SWC is a switching circuit.

A full-wave rectifier circuit composed of diodes D1 to D4 is connected in series to the communication loop as shown.

A capacitor C4 connected in parallel with this connection point is for bypassing the speech signal.

Cathode side of diodes D1 and D3 and diode D2
A smoothing capacitor C is connected between the anode side of D4 and the anode side of D4.
5 and a constant voltage diode D5 for voltage setting are connected as a current smoothing circuit).

The anode side of the constant voltage diode D5 is connected to the diode D2.
Connected to the anode side of D4.

AMP is an amplifier circuit, and both ends of the capacitor C5 are connected to a power input terminal of the amplifier circuit AMP.

A transmitter T is connected to the input terminal of the amplifier circuit AMP.

TF is an output transformer provided on the output side of the amplifier circuit AMP, and R1 is a resistor, and the speech signal from the transmitter T that has been amplified by the amplifier circuit AMP is taken out to the resistor R1 via the output transformer TF and transmitted. It is applied to input terminals T1 and T2.

IND is a guide ring. Note that the transmitter T may be of the form of an electromagnetic transmitter, a carbon transmitter, or the like.

When using a carbon-type transmitter, a circuit (not shown) that applies a DC bias to the carbon-type transmitter is added to the amplifier circuit AMP.
is provided to allow DC bias current to flow.

Furthermore, as shown in FIG.
A similar call signal may be input via the transformer TS as shown in the figure.

Alternatively, the output transformer TF may be built in the amplifier circuit AMP, or the output transformer TF may not be used, and the amplifier circuit AMP and the transmitting input terminals T1 and T2 are separated in terms of DC by a capacitor. Only the call signal may be applied to the transmission input terminals T1 and T2 (1/).

In the circuit shown in FIG. 3 of this embodiment, if the loop current sent from the station equipment is as shown in FIG. A group is formed.

As shown in Figure 2, a diode D is connected to the power supply terminal of the amplifier circuit AMP.
A full-wave rectifier circuit composed of circuits 1 to D4 rectifies the currents and supplies currents of the same polarity.

However, as shown in FIG. 2a, when the loop current is interrupted when the polarity reversal signal arrives, the charge charged in the capacitor c5 is discharged, and the power is applied to the power supply terminal of the width amplification circuit AMP and flows to the amplification circuit AMP. The current never stops.

Also, during this time, the full-wave rectifier circuits D1-D4 are non-conductive, so that an alternating current signal of a small level of 1 or less, such as a telephone call signal, cannot pass through the rectifier circuits D1-D4.

In this state, the capacitor C4 bypasses the full-wave rectifier circuits D1 to D4 and transmits the communication signal to the office line through the switching circuit SWC without distortion.

Next, capacitor C5 is charged while the polarity reversal current is flowing, and when the loop current is interrupted immediately after the polarity reversal signal ends as shown in Figure 2a, the discharge current of capacitor C5 is similarly charged to the amplifier circuit AMP. It flows and never stops.

In this way, in the circuit of this embodiment, the full-wave rectifier circuit composed of diodes D1 to D4 converts the loop current into a current of the same polarity, and by charging and discharging the capacitor C5,
A constant current is always supplied to the power supply terminal of the amplifier circuit AMP even if a polarity reversal signal is received during a call.

Therefore, the amplifying circuit AMP always performs the amplifying action without interruption even if a polarity reversal signal is received during a call, and the condenser C
4 bypasses the call signal, so the call signal from the transmitter T is amplified without interruption and transmitted to the office line without distortion.

Furthermore, if the power supply voltage is above a certain value, the amplifier circuit AMP
The amplification degree does not change due to fluctuations in the power supply voltage,
In particular, if the amplifier circuit includes an automatic gain control circuit, the change in amplification degree is even smaller, so even if there is some voltage fluctuation due to discharge of the capacitor C5, the output of the amplifier circuit AMP will not change.

Note that the constant voltage diode D5 sets the power supply voltage of the amplifier circuit AMP to further reduce fluctuations in the output of the speech signal of the amplifier circuit AMP, and also suppresses surge voltages superimposed on the speech line and surges generated within the switching circuit SWC. It protects the amplifier circuit AMP and capacitor C5 from voltage.

In this way, according to the circuit of this embodiment, when a polarity reversal signal is used as a billing signal, it is possible to prevent call interference due to this polarity reversal signal, as in the conventional circuit shown in FIG. The above-mentioned influence due to DC current fluctuations on the transmitter, which could not be achieved, can be removed, and the amplifier circuit AMP is efficient.
Since the impedance seen from the transmitter can be set to 400Ω, which is eight times larger than the approximately 50Q of the transmitter T shown in Fig. 1, the discharge loop resistance of the capacitor C5 becomes large. circuit capacitor C
It can be made much smaller than 2.

Specifically speaking, the capacitor C2 in the conventional circuit has a capacity of 200
When the transmitter T is removed at 0 μF, the maximum voltage of the station equipment is 60
Since V is directly applied to capacitor C2, an extremely large capacitor with a withstand voltage of 60 V or more is required.In contrast, in this embodiment, the zener voltage of voltage regulator diode D5 of about 4 V is sufficient, and the withstand voltage of capacitor C5 can be set to about 10 V. The capacitance can be reduced to about 250 μF for the reasons mentioned above.

Further, since the configuration is not such that the communication signal bypasses the capacitor C5, the blocking wire CH2 in the conventional circuit can also be omitted.

Furthermore, since the current smoothing circuit is not connected between the lines as in the conventional circuit, the blocking wire CHI of the conventional circuit can also be omitted.

Further, in the conventional circuit, C1 and C3 are required as capacitors for bypassing the speech signal, but in the circuit of this embodiment, the speech signal can be bypassed using only the capacitor C4.

In this way, there is no need for a blocking wire, only one capacitor is required for bypassing the call signal, and the smoothing capacitor C5 can also be made extremely small in size, so it can be used, for example, in a printed circuit board unit with a built-in telephone circuit. Capacitor C5 can be incorporated, making it possible to significantly downsize the device and reduce costs.

Note that the output transformer TF can also be made small because it only needs to transmit speech signals, and the amplifier circuit AMP can also be made into an IC, so the overall size can be significantly reduced.

Furthermore, since the speech signal is sent through the amplifier circuit AMP, it is also possible to set the output level characteristics and frequency characteristics of the input signal of the amplifier circuit AMP to appropriate values.

In addition, in telephones that store coins using an AC or DC signal with a return path to ground as a billing signal sent from an exchange, the terminal of the transmitter T is artificially grounded using a wire or the like to ground the billing signal. However, in this embodiment, an electromagnetic type transmitter is used for the transmitter T, and the transmitter T''/1.
If the output of these communication signals is input to the amplifier AMP via a transformer whose primary side and secondary side are DC-separated, the transmitter T is separated from the communication circuit. Such fraud can be prevented.

Also, if a differential microphone is used for the transmitter T, noise can be prevented.

In addition, the input terminal of the amplifier circuit AMP is not limited to the transmitter T, but as shown in Fig. 4.5, signals such as a coin reminder sound, coin money, coin storage money, before coin return, etc., and an AC signal of a push button dial, etc. can be input. When the speech signal Sig is applied, the signal can be transmitted with a small speech signal Sig because of the amplification effect of the amplifier circuit AMP.

In the above explanation, a public telephone was used as an example of a telephone, but the present invention can also be applied to a general telephone.

[Brief explanation of the drawing]

FIG. 1 shows a conventional example of a telephone circuit that receives a polarity-changing current signal during a call. FIG. 2a shows a loop current waveform diagram, FIG. 2b shows a current waveform diagram flowing through the transmitter T without the capacitor C2, and FIG. 2C shows a current waveform diagram flowing through the transmitter T when the capacitor C2 is attached. Fig. 3 is a circuit diagram showing an embodiment of the present invention, and Fig. 4.5 is a circuit diagram showing an embodiment of the present invention in which a call signal other than the transmitter T is applied to the input terminal of the amplifier. It is. Ll, L2...terminal, D1-D4...
Diode, D5... Constant voltage diode, C4
, C5... Capacitor, AMP... Amplifier circuit, T... Transmitter, TF... Output transformer, R1... Load resistance. .

Claims (1)

[Scope of utility model registration request] A full-wave rectifier circuit that generates a voltage across a call signal bypass capacitor inserted in series in the call circuit using the loop current of the call circuit, receives the voltage, and outputs a current of the same polarity; a current smoothing circuit that smoothes the output current of the circuit; an amplifier circuit that uses the output voltage of the current smoothing circuit as a power supply voltage, amplifies a speech signal to be sent, and applies the output signal to a transmission input terminal of the speech circuit; A telephone call circuit for a telephone, comprising: separating the loop current from the call signal input to the amplifier circuit to prevent call interference due to changes in the loop current.