JPH06121037A - Call signal generating circuit - Google Patents

Abstract

PURPOSE:To efficiently generate a call signal having a sine wave with a small- sized and light-weight constitution by providing a DC/DC boosting converter and an analog output amplifier which is driven by the output power of the converter and amplifies the output of a sine wave generator. CONSTITUTION:This circuit, is provided with a DC/DC step-up converter 11 or an AC/DC step-up converter, a sine wave generator 12, and an analog output amplifier 13 which is driven by the output power of the converter and amplifies the output of the sine wave generator 12. The analog output amplifier 13 can be constituted so that an FET is used as the output element. The analog output amplifier 13 may be provided with an output current limiting circuit with time constant which immediately limits the current to a first certain current value or smaller in the case of the output current value larger than the first certain current value and limits the output current to a second certain current value with a desired time constant in the case of the output current value which is equal to or smaller than the first certain current value but exceeds the second certain current value lower than the first certain current value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to circuits for generating ringing signals for use in exchanges or key telephone systems.

[0002]

2. Description of the Related Art In a switching system or a key telephone system, it is necessary to send a ringing signal in order to ring an expropriated single telephone. The call signal is typically p-p200.
A signal of about 16 Hz at V is used. on the other hand,
The voltage supplied from the system is generally -48V or +2
Since it is 4V, it is necessary to boost the voltage by some method in order to create a p-p200V ringing signal from the system power supply. Further, it is desirable that the ringing signal be as close to a sine wave as possible rather than a square wave or step wave. The ringing signal needs to be free of harmonics in order to reduce radio emission, and if the ringing signal is a square wave or staircase, it will not ring well or the ringing tone will not be heard in the computerized single telephone. Often small, the ringing signal is ideally a sine wave in order to ring the incoming call efficiently.

Circuits that have been generally used as call signal circuits are shown in FIGS. 9 and 10. In FIG. 9, 1 is 16
Hz sine wave oscillator, 2 and 3 are drive amplifiers, 4 and 5 are output transistors, and 6 is an output transformer. Although the bias circuits of the transistors 4 and 5 are omitted here, the transistors 4 and 5 and the output transformer 6 constitute a class B push-pull output amplifier. Electric power obtained on the primary side of the transformer 6 is boosted to a required voltage using the transformer 6 to generate a sine wave ringing signal. In this circuit, the circuit on the primary side of the transformer 6 efficiently generates a sine wave. The circuit excluding the transformer 6 can be configured to be relatively small and lightweight.

Further, in the conventional circuit of FIG. 10, 7 is a DC / DC converter for inputting the power supply of the system to generate + 100V and -100V, 8 and 9 are output switching transistors, and 10 is a control circuit for the transistors 8 and 9. Is. The control circuit 10 alternately turns on / off the transistors 8 and 9 at a cycle of 16 Hz. Considering the efficiency of this circuit, the DC / DC converter 7
Since the input power is switched at an oscillating frequency of several tens of kHz or more, a small and lightweight transformer can be used, and power conversion can be performed with high efficiency. Further, the transistors 8 and 9 are completely turned on and off.
Since it is FF, the power consumed here is extremely small. Therefore, the efficiency of this circuit is high, and it can be realized in a small size and a light weight.

[0005]

In the conventional example of FIG. 9, it is necessary for the transformer 6 to have a large number of windings in order to obtain a sufficiently large impedance for a very low frequency of 16 Hz. For this reason, the winding and the transformer core become large in size and heavy in weight. Further, as the number of windings increases, the DC resistance increases, and the efficiency of the transformer 6 decreases. In order to prevent this, it is necessary to increase the thickness of the winding, which would increase the size and weight of the transformer. As described above, the size and weight of the transformer 6 are contradictory to the improvement in efficiency. Since the transformer 6 is large, heavy, and has high DC resistance, the efficiency is low. The entire circuit of FIG. 9 can obtain a sinusoidal ringing signal, but has the drawbacks of large size, heavy weight, and low efficiency because of the presence of the output transformer 6 described above.

On the other hand, considering the output waveform in the circuit of FIG. 10, the output of the DC / DC converter 7 is switched by the transformers 8 and 9, so that the output is a square wave. As mentioned above, the ringing signal should be as close as possible to a sine wave instead of a square wave or staircase wave.
This circuit is small and lightweight, but has the disadvantage that the output is a square wave.

The present invention eliminates the above-mentioned drawbacks of the conventional circuit and provides a ringing signal generating circuit which is highly efficient, small in size, and lightweight and can generate a ringing signal of a sine wave.

[0008]

To achieve this object, a ringing signal generating circuit according to the present invention comprises a DC / DC boost converter or an AC / DC boost converter, a sine wave generator, and an output of the converter. An analog output amplifier that is driven by a power supply and amplifies the output of the sine wave generator is provided. Further, the analog output amplifier can be configured to use a FET as an output element. Further, when the output current value exceeds the first constant current value, the analog output amplifier immediately limits the current to the first constant current value or less, and if the output current value is equal to or less than the first current value, And a configuration including an output current limiting circuit with a time constant for limiting the output current to a second constant current value with a desired time constant when a second constant current value lower than the first constant current value is exceeded. You can also do it.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first configuration example of the present invention. Here, 11 is a DC / DC converter, 12 is a 16 Hz oscillator, and 13 is an output amplifier that uses the output voltage of the DC / DC converter as a driving power supply. This circuit uses -48V DC /
The DC converter boosts the voltage to + 100V and -100V, and the output amplifier uses the output voltage as a drive power source for 16Hz,
A sine wave of p-p200V is output as a calling signal. First, considering the efficiency of the circuit, it is the "DC / DC converter 11" and the "output amplifier 13" that mainly cause power loss in the circuit of FIG. First,
When the "output amplifier 13" in FIG. 1 is examined, it is generally known that when a sine wave is output using the power supply voltage to the limit, for example, if the load is a resistive load, the efficiency is theoretically 78%. Therefore, the circuit can be configured to be relatively small and lightweight. Next, the "DC / DC converter 11"
Since switching is performed at an oscillating frequency of several tens of kHz or more, a small and lightweight transformer can be used, so that the entire DC / DC converter can be made compact and lightweight, and power conversion efficiency is high.

FIG. 2 shows another embodiment of the present invention. Figure 2
22 is -48V to 100V (100V to 1
00 VG) isolated DC / DC converter for boosting voltage, 2
3 is an intermediate potential generating circuit for generating an intermediate potential of 100V-100VG, 24 is a 16 Hz oscillator, 25 and 26 are D
Output amplifiers that use the output voltage of the C / DC converter as a power source, and 27 to 32 are resistors. This example is an example of push-pull output instead of single-ended output. When the output load is comparatively heavy, the push-pull output is used to reduce the allowable power loss in one amplifier by half.

Considering the output amplifiers necessary for constructing a large-capacity calling signal generating circuit using the above-described embodiments. For example, when several tens of telephones are to ring simultaneously, when a push-pull circuit as shown in FIG. 2 is used, an output amplifier having a power supply voltage of about 100 V and an output current of several hundred milliamperes must be used. I won't. Figure 3
Fig. 1 shows an example of an output amplifier that uses a bipolar transistor as an output element, which is conventionally used. Here, 33 and 34 are input transistors, 35 is a drive transistor, 36 and 37 are output transistors, 38 and 39 are diodes, and 40 to 44 are resistors. This amplifier has the following disadvantages in order to be used as an output amplifier of a large-capacity calling signal generation circuit. The operating range for high voltage and large current is narrow. The bipolar transistor has a secondary breakdown phenomenon as a characteristic thereof. For this reason, the safe operating area that can be used at high voltage and large current is limited, and there is a risk of damage if the safe operating area is exceeded. Large reactive power when no load is applied. High-voltage, large-current bipolar transistors generally have a current amplification factor h _fe of 2
It is as low as 0-30. In order to have an output current of several hundred mA at the maximum, a drive current of several tens of mA must be passed through the transistor. In FIG. 3, when the resistance value of the resistor 44 is set to a low value so that a current of several tens of mA is passed, the reactive voltage of several tens of mA must be continuously passed through the amplifier even if there is no load because the power supply voltage of this amplifier is high. Disappeared
A few watts of power is wasted and the efficiency of the entire circuit decreases. As described above, when the conventional output amplifier circuit is used to form the large-capacity calling signal generating circuit according to the first aspect of the present invention, there is a drawback that the efficiency of the circuit decreases.

An output used in the embodiment of the second invention of the present application (circuit of FIG. 2) capable of eliminating the above-mentioned drawbacks and realizing a large-capacity ringing signal generation circuit for generating a sinusoidal ringing signal with high efficiency. A specific example of the amplifier (25, 26) is shown in FIG.
Here, 45 and 46 are input transistors, 47 is a driving transistor, 48 and 49 are output FETs, 50 is several diodes, and 51 to 55 are resistors. Since the output element of this circuit is a FET, it has the following advantages as compared with FIG. Wide operating range for high voltage and large current. Unlike the bipolar transistor, there is no secondary breakdown phenomenon, so the safe operating area is wide. There is little reactive power when there is no load. Unlike the bipolar transistors, the FETs 48 and 49 are high-impedance voltage-driven elements and have extremely low power for control. A resistor 55 corresponding to the resistor 44 may be extremely high, and the reactive power without load can be set to several hundred mW.

Further, it may be configured as shown in FIG. Here, 56 and 57 are input transistors, 58 is an output-combined drive FET, 59 is an output FET, 60 is a diode, and 61 to 65 are resistors. In FIG. 5, FE
Since T is a voltage drive element with a high input impedance, it is possible to eliminate one stage of drive transistor.
In this amplifier, the FET 58 corresponding to the drive transistor 35 in FIG.

FIG. 6 shows an embodiment of a calling signal generating circuit using the amplifier having the configuration example of FIG. Here, 66 is -48V
To 100V (100V to 100VG) boosted insulation type DC / DC converter, 67 is 100V to 100VG
16H is an intermediate potential generation circuit for generating an intermediate potential of
z oscillators, 69 and 70 are output amplifiers using the output voltage of the DC / DC converter shown in FIG. 6 as a power source and FETs as output elements, and 71 to 76 are resistors.

The embodiments of FIGS. 2 and 4 to 6 can output a sinusoidal ringing signal, realize a high-capacity ringing signal generation circuit with low reactive power and high efficiency.

Next, let us consider a case where a single telephone (hereinafter referred to as "telephone") connected to the end of a large-capacity ringing signal generating circuit forms a DC circuit (off-hook). FIG. 7 shows a system diagram when the exchange or the key telephone system sends a call signal to the telephone. When the telephone does not form a DC circuit (on-hook), no direct current flows, but when the telephone is off-hook, a direct current of several tens of mA flows per single telephone. The period in which the direct current of several tens mA flows is several hundred mS at the longest because each interface circuit that accommodates the telephone has a detection circuit for detecting whether or not the direct current has flowed. However, since the ringing signal generating circuit is connected not only to the telephone set which has been off-hooked for several 100 mS, but also to the other telephones at the same time, it is also connected to the telephone set which has been on-hooked. The ringing signal must continue to be supplied. Therefore, the call signal generation circuit is 16Hz
It is necessary to have the ability to superimpose the alternating current on the direct current and to flow.

Here, in the present invention, since the output is directly connected to the output amplifier, the output amplifier itself is
It must be able to supply a direct current in addition to the 6 Hz alternating current. However, since the ringing signal is distributed inside the exchange and the key telephone system and is also connected to the outside thereof, there is a risk that the ringing signal is short-circuited with the ground or the power supply. Even in that case, an output current protection circuit is necessary so that the ringing signal generation circuit is not destroyed or burned out. The problem is the set value of the protection current of the output current protection circuit. If the set value is increased, it is necessary to design the allowable power loss of the output element in the output amplifier to be large.
The output element of the amplifier and its heat sink need to be large, and the calling signal generation circuit as a whole becomes large.

For example, consider a large-scale call signal generation circuit that supplies call signals to 24 telephones at the same time.
At this time, the chances that three or more phones will be off-hook at the same time are extremely small in terms of traffic, so it is not considered.
Assuming that the set value of the protection current of the output current protection circuit is the maximum value of AC + DC in which two units are in the off-hook state and the remaining 22 units are in the on-hook state, the current value becomes extremely large. The wiring of the calling signal is short-circuited due to some accident,
In order to prevent the ringing signal generation circuit from being damaged or burned out even when this large protection current value is maintained, an extremely large capacity output element and heat sink are required, and the ringing signal generation circuit is large. become.

Therefore, an embodiment of the third invention of the present application will be described which realizes a highly efficient sinusoidal ringing signal and realizes a small-sized and lightweight large-capacity ringing signal generating circuit. The point of this embodiment is to add an output current control circuit with a time constant to the output amplifier of the embodiment of FIGS.

As before, let us consider a ringing signal generating circuit of a scale that supplies ringing signals to, for example, 24 telephones at the same time. This time too, it is practically rare for three or more phones to hook up at the same time, so we will not consider it.
The current control circuit with a time constant limits the current immediately when more than the current (first current value) when two of the 24 cars go off-hook (the first current value). When two of the 24 cars remain off-hook (first current value), the current is gradually limited to a second current value lower than the first current value. This second current value is smaller than when one unit is off hooked. No current limit is applied when all 24 phones are on hook. If a current control circuit with such a time constant is used, for example, 2 out of 24
Compared with the case of using a current control circuit without a time constant that allows the current to flow continuously when hooked, the allowable power loss of the output amplifier is a fraction. Therefore, the volume of the output element of the output amplifier and the heat radiating plate thereof can be further reduced, and a compact and lightweight large-capacity calling signal generation circuit can be realized.

FIG. 8 shows a configuration example of an output amplifier having an output current limiting circuit with a time constant. Here, 101 and 102 are input transistors, 103 is an output-combined drive FET, and 10
4 is an output FET, 105 and 106 are output current control transistors, 107 and 108 are capacitors, and 109 to 123.
Is a resistor and 124 is a diode. Output FET 10
The output current control of No. 3 will be described. Resistor 113 is several Ω
The resistors 114 to 117 are resistors of several K to several tens of KΩ. Therefore, most of the output current of the FET 103 flows through the resistor 113, and the voltage appearing across the resistor 113 is proportional to the output current of the FET 103. Since the resistor 116 has a value about 10 times that of the resistor 115, the capacitor 107
At, a voltage proportional to the average output current of the FET 103 appears. Base-emitter voltage V of transistor 105
_{When be} becomes equal to or higher than V _F , the transistor 105 starts to be turned on, and the gate-source potential of the FET 103 is lowered, so that the output current of the FET 103 is limited. When a current more than the current when two of the 24 devices go off hook is about to flow, the transistor 105 immediately starts to turn on through the resistor 114 to control the output current. When two of the 24 units remain off-hook, the average current of the FET 103 increases, so that the voltage across the capacitor 107 gradually increases, and the transistor 105 gradually increases the limiting current value through the resistors 116 and 114. Lower. When all 24 telephones are on hook, the instantaneous current is not large and the average current is small, so the resistance 11
The transistor 105 does not start to turn on via 4 or 116, and the output current of the FET 103 is not limited. The output current limiting characteristic of the FET 104 is also the same.

In the entire diagram of the large-capacity calling signal generating circuit according to this embodiment, the amplifier 69 in FIG. 6 may be replaced with the amplifier shown in FIG. In FIG. 6, the amplifier 69
Since the current output from the amplifier always returns to the amplifier 70, it is not necessary for both the amplifiers 69 and 70 to be the output current limiting circuit with the time constant. Only the amplifier 69 has the output current limiting circuit with the time constant. It will be good.

[0023]

As described above, according to the first invention of the present application, the analog output amplifier is used to output a sine wave, thereby suppressing radio wave radiation and transmitting an efficient ringing signal to a single telephone for expropriation. can do. Also, DC
By using the / DC converter, it is possible to construct a compact and lightweight ringing signal generating circuit that consumes less power and reduces heat generation. Further, the second invention enables a large capacity. Further, according to the third aspect of the invention, it is possible to configure a calling signal generating circuit which has a large capacity and is small and lightweight. As described above, the present invention greatly contributes to power saving, size reduction and weight reduction of exchanges and button telephone systems.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

FIG. 3 is a circuit diagram showing an example of an output amplifier used in the present invention.

FIG. 4 is a circuit diagram showing an example of an output amplifier used in the present invention.

FIG. 5 is a circuit diagram showing an example of an output amplifier used in the present invention.

FIG. 6 is a circuit diagram showing another embodiment of the present invention.

FIG. 7 is a system diagram showing an example of an exchange or a key telephone system to which the present invention is applied.

FIG. 8 is a circuit diagram showing another embodiment of the present invention.

FIG. 9 is a circuit diagram showing an example of a conventional call signal generation circuit.

FIG. 10 is a circuit diagram showing an example of a conventional call signal generation circuit.

[Explanation of symbols]

1 16 Hz sine wave oscillator 2, 3 drive amplifier 4, 5 output transistor 6 output transformer 7 DC / DC converter 8, 9 output switching transistor 10 control circuit for transistors 8 and 9 11 DC / DC converter 12 16 Hz oscillator 13 output amplifier 22 DC / DC converter 23 Intermediate potential generation circuit 24 16 Hz oscillator 25,26 DC / DC converter 27,28,29,30,31,32 Resistor 33,34 Input transistor 35 Drive transistor 36,37 Output transistor 38,39 Diode 40, 41, 42, 43, 44 resistor 45, 46 input transistor 47 drive transistor 48, 49 output FET 50 diode 51, 52, 53, 54, 55 resistor 56, 57 input transistor 58 output dual drive FET 60 diode 61,62,63,64,65 resistor 66 DC / DC converter 67 intermediate potential generation circuit 68 16Hz oscillator 69,70 output amplifier 71,72,73,74,75,76 resistor 101,102 input transistor 103 Output-combined drive FET 104 Output FET 105, 106 Output current control transistor 107, 108 Capacitor 109, 110, 111, 112, 113, 114, 1
15, 116, 117, 118, 119, 120, 12
1,122,123 Resistor 124 Diode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuneharu Kimeda 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. A DC / DC boost converter or AC / D
A call signal generation circuit comprising a C boost converter, a sine wave generator, and an analog output amplifier driven by an output power source of the converter to amplify the output of the sine wave generator. 2. The ringing signal generating circuit according to claim 1, wherein the analog output amplifier uses a FET as an output element. 3. The analog output amplifier, when the output current value thereof exceeds a first constant current value, immediately outputs the first first current value.
Current is limited to a predetermined constant current value or less, and when the second constant current value lower than the first constant current value but lower than the first constant current value is exceeded, the output current is changed with a desired time constant. 3. The call signal generating circuit according to claim 1, further comprising an output current limiting circuit with a time constant for limiting the current to the second constant current value.