JPH0821975B2 - Ring trip circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ring trip circuit using a photocoupler used in a subscriber circuit of a telephone exchange.

[Conventional technology]

As shown in the circuit diagram of FIG. 3, a conventional photocoupler or a ring trip circuit is used, as shown in the circuit diagram of FIG. 3, the ringing signal current limiting resistor 1, the ringing signal current detecting resistor 2, and the AC component of the voltage across the ringing signal current detecting resistor 2. A resistor 16 and a capacitor 17 that constitute a low-pass filter 8 that attenuates
A photocoupler 5 that electrically separates the output voltage of the low-pass filter 8 and transmits a signal to a power supply system different from the calling signal sending side, a load resistor 6 of the photocoupler 5, and a photocoupler 5.
And a comparator 9 for detecting the output of.

In this ring trip circuit, as shown in the connection diagram of the peripheral circuit in FIG. 4, terminals 10, 11 are connected to hooks switch 19, DC blocking capacitor 20, bell coil 21 via calling signal transmission relay contacts 22a, 22b. , And terminals 12, 13 are connected to a ringing signal generator 23 and a DC power supply 24.

The operation of this ring trip circuit is as follows: First, when the ringing signal transmission relay contacts 22a, 22b are on and the hook switch 19 is off (in the on-hook state as the telephone 18), the ringing signal current is The ringing signal (16) via the ringing current detection resistor 2, ringing signal sending relay contact 22a, DC blocking capacitor 20, bell coil 21, ringing signal sending relay contact 22b and ringing signal current limiting resistor 1
(AC signal of Hz) flows, and an AC voltage is generated across the calling signal current detection resistor 2. But resistor 16 and capacitor
Since this AC voltage is attenuated by the low-pass filter 8 constituted by 17, the voltage applied across the diode of the photocoupler 5 is small, and the change in the output voltage of the photocoupler 5 is also small, so that the comparator 9 Since the voltage does not exceed the threshold value, the output of the comparator 9 does not change.

Next, when the hook switch 19 is turned on while the call signal transmission relay contacts 22a and 22b are turned on (the telephone
(When in the off-hook state as 18) The combined current of the ringing signal AC current from the ringing signal voltage generator 23 and the DC current from the DC power supply 24 is called the ringing signal current detection resistor 2, ringing signal sending relay contact 22a, and hook switch 19 Signal transmission relay contact 22b
And the ringing signal current limiting resistor 1, and a combined voltage of the DC voltage and the AC voltage is generated across the ringing signal current detecting resistor 2. By passing this voltage through the low-pass filter 8, the AC voltage is attenuated, but the DC voltage is directly applied to both ends of the diode of the photocoupler 5, so that the change in the output voltage of the photocoupler 5 becomes large.
The voltage exceeds the threshold value of the comparator 9, and the output of the comparator 9 changes. Therefore, by monitoring the output state of the comparator, the on-hook and off-hook states of the telephone 18 can be known.

[Problems to be Solved by the Invention]

In the conventional ring trip circuit described above, since the cutoff frequency of the low pass filter 8 is low, the resistance 16 and the capacitor 17 which form the low pass filter have large values, and the capacitor 17 requires a non-polarized capacitor. And Further, in order to increase the detection output of the photocoupler 5, it is necessary to flow a large amount of direct current flowing through the diode of the photocoupler 5, and it is desirable that the value of the resistor 16 forming the low pass filter 8 is small. That is, in the conventional ring trip circuit, there is a problem that the parts are upsized because a large capacity capacitor is required.

Further, in the on-hook state, it is necessary to design the AC voltage of the output of the low-pass filter 8 to be substantially equal to or lower than the forward voltage of the diode of the photocoupler 5, and the forward voltage of the diode includes the temperature characteristic. Since the variation is large, it is necessary to increase the amount of attenuation of the low pass filter 8 at the ringing signal frequency. Therefore, there is a problem that the delay time in the low-pass filter 8 becomes long and the off-hook detection time becomes long.

[Means for solving the problem]

The ring trip circuit of the present invention is a ring trip circuit for detecting a direct current signal superimposed on an alternating current signal used in a subscriber response detection circuit of a telephone exchange, and an input for detecting a direct current signal superimposed on the alternating current signal. Two photocouplers whose terminals are reversely connected to each other, and an adder circuit which adds the outputs of the photocouplers and outputs a full-wave rectified waveform,
A polarity reversing circuit for reversing the polarity of the waveform of the output of the adder circuit other than around O volt alternately into positive and negative polarities to reproduce an input signal waveform in which a direct current signal is superimposed on an alternating current signal input to the two photocouplers; A low-pass filter for extracting a DC component from the output of the polarity reversing circuit, and a comparator for detecting the DC signal superimposed on the AC signal by comparing the DC component extracted by the low-pass filter with a reference threshold value. With.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 shows the signal waveforms of the respective parts shown in FIG. 1, and is a waveform diagram for explaining the operation of this embodiment when the telephone is on-hook and when the telephone is off-hook. First, the configuration of this embodiment will be described with reference to FIG.

In this embodiment, a ringing signal current limiting resistor 1, a ringing signal current detecting resistor 2 for converting a ringing signal current into a voltage, a voltage across the ringing signal current detecting resistor 2 is different from a power source system on the ringing signal sending side. Photocoupler 4,5 to transfer current to
A limiting resistor 3 that limits the current flowing through the photocouplers 4,5; an adder circuit 6 that receives and adds the outputs of the photocouplers 4,5 and outputs a full-wave rectified waveform; Polarity inverting circuit 7 for reproducing an input signal waveform in which a DC signal is superimposed on an AC signal input to two photocouplers by alternately inverting the polarity of the waveform of the wave rectified waveform into positive and negative polarities, and an AC signal. A low-pass filter 8 for separating the ringing signal from the inside and a DC, a comparator 9 for detecting a DC voltage from the output of the low-pass filter 8, terminals 10 and 11 connected to the telephone side, and a ringing signal. Terminal 1 connected to the source side
2, 13 and a ring trip detection output terminal 14.

Next, the operation will be described with reference to FIGS. 1 and 2.

Similar to the conventional circuit, the circuit of the embodiment of the present invention includes the telephone 18 and the call signal transmission relay contacts 22a and 22b shown in FIG.
It shall be connected to the call signal generator 23 and the DC power supply 24.

First, when the call signal transmission relay contacts 22a and 22b are in the ON state and the telephone 18 is in the on-hook state, only the AC current flows from the call signal generator 23 to the telephone 18, and the AC voltage is applied across the call signal current detection resistor 2. Occurs, photo coupler 4,
Signals of each polarity are transmitted from 5 to another power supply system. The outputs of the photocouplers 4 and 5 are added by the adder circuit 6, and the full-wave rectified waveform of the voltage generated across the calling signal current detection resistor 2 is output. The polarity reversing circuit 7 alternately inverts the waveforms other than around O volt into positive and negative polarities to reproduce a waveform equivalent to the voltage across the ringing signal current detection resistor 2. This reproduction voltage is attenuated by the low-pass filter 8 below the detection threshold value of the comparator 9. Further, in this process, the waveform distortion occurs due to the forward voltage characteristics of the diodes of the photocouplers 4 and 5, but since they are symmetrical in the positive and negative directions, the DC components cancel each other out to 0, and the output of the comparator 9 becomes It does not change.

Next, when the call signal transmission relay contacts 22a and 22b are in the on state and the telephone 18 is in the off-hook state, when the hook switch 18 of the telephone 18 is turned on, the telephone 18 is connected to the ring signal generator.
An AC signal from 23 and a DC current from a DC power supply 24 flow, and a combined voltage of the DC voltage and the AC voltage is generated across the calling signal current detection resistor 12. This voltage is output to the polarity reversing circuit 7 by the same operation as in the on-hook state described above, and a DC component is output from the low pass filter 8. Since this DC voltage exceeds the detection threshold value of the comparator 9, comparison is performed. Bowl 9
Output changes. Due to the change in the output of the comparator 9,
The off-hook state of the telephone 18 can be detected.

The polarity reversing circuit 7 and the low-pass filter 8 convert the output voltage of the adding circuit 6 from an analog signal to a digital signal by A / D conversion, and alternately change the sign bit by OV. It is also possible to easily form a semiconductor integrated circuit by reproducing the waveform and detecting the direct current with a digital filter.

〔The invention's effect〕

As described above, according to the present invention, a photocoupler transmits a signal to a different power supply system, and by inverting the polarity, a waveform in which a DC signal is superimposed on an AC signal is reproduced and DC detection is performed. Since the low-pass filter can be formed in the above, the capacitor forming the low-pass filter can be counted with a small capacity, which has the effect of miniaturizing the components.

In addition, SCF filters, digital filters, etc. can be used as low-pass filters, and semiconductor integration is easy, and higher-order filters can be realized in semiconductor integrated circuits, so a ring trip circuit with a short off-hook detection time can be realized. There is also an effect.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing waveforms of respective parts of the embodiment of the present invention, and FIG. 3 is a circuit diagram of a conventional ring trip circuit. FIG. 4 is a connection diagram showing the relationship between the ring trip circuit and the peripheral circuits. 1 ... Call signal current limiting resistor, 2 ... Call signal current detecting resistor, 3 ... Limiting resistor, 4,5 ... Photo coupler, 6 ... Adding circuit, 7 ... Polarity inverting circuit, 8 ... Low pass filter, 9 ... Comparator , 10,11,12,13,14,15 ... Terminal, 16 ... Resistor, 17,20 ... Capacitor, 18 ... Telephone, 19 ... Hook switch, 21 ... Bell coil, 22a, 22b ... Call signal sending relay contact, 23 ... Ring signal generator, 24, 25 ... DC power supply.

Claims (1)

[Claims] 1. A ring trip circuit for detecting a direct current signal superimposed on an alternating current signal used in a subscriber response detection circuit of a telephone exchange, wherein input terminals are mutually reversed for detecting the direct current signal superimposed on said alternating current signal. Two connected photocouplers, an adder circuit for adding the outputs of the photocoupler to output a full-wave rectified waveform, and a waveform of the output of the adder circuit other than around 0 volt are alternately inverted in polarity. A polarity inverting circuit for reproducing an input signal waveform in which a DC signal is superimposed on an AC signal input to the two photocouplers, a low pass filter for extracting a DC component from the output of the polarity inverting circuit, and the low pass filter And a comparator configured to compare the extracted DC component with a reference threshold value to detect the DC signal superimposed on the AC signal. .