JPH02143657A - Ring trip circuit - Google Patents

Abstract

PURPOSE:To make a capacitor being a component of an LPF small in the size and the capacity by transmitting the AC call signal of full wave rectification to a faulty power supply system through a photocoupler, reproducing the waveform with polarity inversion and detecting the DC. CONSTITUTION:An AC voltage across a call signal current detection resistor 2 is rectified in full wave by a diode bridge circuit 4 and a full wave rectified signal flows to the light emitting diode of a photocoupler 5. Thus, the full wave rectifier signal is outputted to a load resistor 6 connecting to the emitter of a transistor (TR) of the coupler 5. A polarity inversion circuit 7 inverts the polarity at every half period at the level of nearly 0V and reproduces a waveform equal to a voltage across the resistor 2. Since the reproduced voltage is attenuated below the detection threshold level of a comparator 9 at an LPF 8, the output of the comparator 9 is unchanged. Thus, the LPF 8 is constituted independently of the circuit at the sending side of the call signal and the capacitor being the component of the LPF 8 is made small in the capacitance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ring trip circuit used in a subscriber circuit of a telephone exchange.

[Conventional technology]

Conventionally, this type of ring trip circuit attenuates the AC component of the voltage across the ring signal current limiting resistor 1, the ring signal current detecting resistor 2, and the ring signal current detecting resistor 2, as shown in FIG. A resistor 16 and a capacitor 17 forming a low-pass filter 8 for extracting components, and a low-pass filter 8
an optical coupling element (photocoupler) 5 that electrically separates the output voltage of and transmits the signal to a power supply system different from the calling signal sending side.
, a load resistor 6 of the photocoupler 5, and a comparator 9 for detecting the output of the photocoupler 5.

As shown in FIG. 4, this circuit includes a telephone 18 equipped with calling signal sending relay contacts 22a, 22b, a hook switch 19, a DC blocking capacitor 20, and a bell coil 21, a calling signal generator 23, a DC power supply 24. 25.

In this configuration, the call signal relay contacts 22a, 22b
is on and the hook switch 19 is off (the telephone 18 is in an on-hook state), the ringing signal current detection resistor 2. Calling signal sending relay contact 22a.

DC blocking capacitor 20. Bell coil 21. A calling signal (16 Hz AC signal) flows through the calling signal sending relay contact 22b and the calling signal current limiting resistor 1, and an alternating current voltage is generated across the calling signal current detecting resistor 2. However, since this AC voltage is attenuated by the low-pass filter 8 composed of a resistor 16 and a capacitor 17, the voltage applied across the light emitting diode of the photocoupler 5 is small. Therefore, since the change in the output voltage of the photocoupler 5 is small, the voltage does not exceed the detection threshold of the comparator 9.
The output of comparator 9 does not change.

Next, when the hook switch 19 is turned on while the ringing signal sending relay contacts 22a and 22b are on (the telephone 18 is in the on-hook state), the ringing signal from the ringing signal voltage generator 23 is generated by alternating current. A composite current of the current and the DC current from the DC power supply 24 is generated by the ringing signal current detection resistor 2. Flows through the calling signal sending relay contact 22a, the hook switch 19, the calling signal sending relay contact 22b, and the calling signal current limiting resistor 1, and a composite voltage of DC voltage and AC voltage is generated across the calling signal current detecting resistor 2. do. The AC voltage component of this composite voltage is attenuated by the low-pass filter 8, but the DC voltage component is applied as is to both ends of the light emitting diode of the photocoupler 5, so the change in the output voltage of the photocoupler 5 becomes large. The voltage exceeds the detection threshold of the comparator 9, and the output of the comparator 9 changes. Therefore, by monitoring the output state of the comparator 9, it is possible to know whether the telephone 18 is off-hook or on-hook.

[Problem that the invention seeks to solve]

In the conventional ring trip circuit described above, since the cutoff frequency of the low-pass filter 8 is low, the low-pass filter 8
The resistor 16 and capacitor 17 that constitute the circuit are large-value elements, and the capacitor 17 requires a bipolar capacitor. In addition, in order to increase the detection output of the photocoupler 5, it is necessary to pass a large amount of direct current to the light emitting diode of the photocoupler 5, and the low-pass filter 8
It is desirable that the value of the resistor 16 constituting the resistor 16 is small.

That is, the conventional ring trip circuit requires a large capacitance capacitor, resulting in large components. Also,
When in the on-hook state, the design must be such that the AC voltage of the output of the low-pass filter 8 is approximately equal to or lower than the forward voltage of the light emitting diode of the photocoupler 5, and the forward voltage of the diode must be Since the variation is large, it is necessary to increase the attenuation amount of the low-pass filter 8 at the calling signal frequency. Therefore, there is a problem that the delay time in the low-pass filter 8 increases, and the off-hook detection time increases.

[Means for solving problems]

The ring trip circuit of the present invention includes a diode bridge circuit that full-wave rectifies an AC calling signal, a photocoupler that outputs a signal proportional to the output of the diode bridge circuit, and a full-wave rectified signal of the output of the photocoupler that converts the full-wave rectified signal into an AC signal. the polarity inversion circuit, a low-pass filter that outputs a DC voltage from the output of the polarity inversion circuit, and a comparator that detects a DC signal from the output of the low-pass filter.

〔Example〕

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

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 shows signal waveforms of each part of this embodiment, and is used to explain operations when the telephone is on-hook and when the telephone is off-hook.

The ring trip circuit of this embodiment includes a ring signal current limiting resistor 1, a ring signal current detecting resistor 2 for exchanging the ring signal current to voltage, a diode bridge circuit 4 for full wave rectification of the voltage across this resistor 2, and a ring trip circuit 4 for full wave rectification of the voltage across this resistor 2. A photocoupler 5 that transmits the rectified current to a power supply system different from the power supply system on the calling signal sending side, a load resistor 6, a limiting resistor 3 that limits the current flowing to the photocoupler 5, and a resistor 3 at both ends of the load resistor 6. A polarity inversion circuit 7 that inverts the polarity of the appearing full-wave rectified signal at approximately 0 (V) every half cycle and reproduces it into an AC signal; a low-pass filter 8 that separates the calling signal from the DC signal; A comparator for detecting DC voltage from the output of the low-pass filter 8, a terminal 10.11 connected to the telephone side, a terminal 12.13 connected to the ringing signal source side, and a ring trip detection output terminal 14. Equipped with

Next, the operation of this embodiment will be explained with reference to FIGS. 1 and 2. Note that the circuit of this embodiment has terminals 10 and 11.
, 12, 13.15 to the telephone set 18., shown in FIG.
It is connected to the calling signal sending relay contacts 22a, 22b, the calling signal voltage generator 25, and the DC power supply 24.25. First, call signal sending relay contacts (22a, 22b in Figure 4)
) is on and the telephone (18) is on-hook, only alternating current flows from the ring signal generator (23) to the telephone (18), and an alternating current voltage is generated across the ring signal current detection resistor 2. However, this voltage is full-wave rectified by the diode bridge circuit 4, and a full-wave rectified signal current flows through the light emitting diode of the photocoupler 5. Therefore, a full-wave rectified signal is output to the load resistor 6 connected to the emitter of the transistor of the photocoupler 5. The polarity inversion circuit 7 inverts the polarity at approximately 0 (V) every half cycle to reproduce a waveform equivalent to the voltage across the calling signal current detection resistor 2. The reproduced voltage is attenuated by the low-pass filter 8 to below the detection threshold of the comparator 9 (around 0 (V), waveform distortion occurs due to the forward voltage drop of the diode of the diode bridge circuit 4 and the photocoupler 5, but the positive and negative (The symmetric DC component is zero), so the output of the comparator 9 does not change.

Next, when the calling signal sending relay contacts (22a, 22b) are in the on state and the telephone (18) is in the off-hook state,
Since the hook switch (19) of the telephone (18) is turned on, both the AC signal from the ring signal voltage generator (23) and the DC current from the DC power supply 24 flow to the telephone (18), and the ring signal current is detected. A DC voltage and an AC voltage are generated across the resistor 2. This voltage is output to the polarity inversion circuit 7 by the same operation as in the off footer state described above. The low-pass filter 8 outputs a DC component, and this voltage is sent to the comparator 9.
Since the detection threshold of is exceeded, the output of the comparator 9 changes.

The on-footer state and off-hook state of the telephone (18) can be determined by the change in the output of the comparator 9.

Note that the polarity inversion circuit 7 and the low-pass filter 8 convert the voltage across the load resistor 6 from an analog signal to a digital signal by analog-to-digital conversion, and reproduce the waveform by alternating the sign bit with 0 (■). However, by adopting a configuration in which direct current is detected using a digital filter, it becomes easier to integrate the device into a semiconductor integrated circuit.

〔Effect of the invention〕

As explained above, according to the present invention, a full-wave rectified AC calling signal is transmitted to a different power supply system using a photocoupler, and the waveform is regenerated by polarity reversal and DC detection is performed, thereby connecting the circuit on the calling signal sending side. Low-pass filters can be constructed independently. As a result, the capacitor constituting the low-pass filter can be designed with a small capacity, and the components can be made smaller. Also,
SCF filters, digital filters, etc. can be used as low-pass filters, and semiconductor integration is easy, and high-order filters can be realized with semiconductor integrated circuits.
A ring trip circuit with short off-hook detection time can be realized.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing waveforms of various parts of the same embodiment, Fig. 3 is a block diagram showing a conventional ring trip circuit, and Fig. 4 is a ring trip circuit. FIG. 3 is a configuration diagram showing the relationship between the computer and peripheral circuits. DESCRIPTION OF SYMBOLS 1... Calling signal current limiting resistor, 2... Calling signal current detecting resistor, 3... Limiting resistor, 4... Diode bridge circuit, 5... Photocoupler, 6... Load resistor,
7... Polarity inversion circuit, 8... Low pass filter, 9
...Comparator. Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] a diode bridge circuit that full-wave rectifies an AC calling signal; a photocoupler that outputs a signal proportional to the output of the diode bridge circuit; and a polarity inversion circuit that regenerates the full-wave rectified signal output from the photocoupler into an AC signal. A ring trip circuit comprising: a low-pass filter that outputs a DC voltage from the output of the polarity inversion circuit; and a comparator that detects a DC signal from the output of the low-pass filter.