JPH0315874B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ring trip circuit. 1st
The figure shows the entire circuit in which a conventional ring trip circuit LT and a ring trip circuit are connected. This circuit consists of telephone TEL, battery V _BB , sound source CR, and resistor R ₀
~ _R10 , capacitor C, Zener diode (C
It consists of a constant voltage diode) D, a comparator COM, relay contacts rl ₁ , rl ₂ , rl ₃ and lines L0 and L1 (represented by line resistances RL0 and RL1 in the figure).

When sending a call signal, relay contact rl ₀ closes to the sound source CR side. At this time, the signal current is sent to the line via resistor R1, and is sent to line RL0, telephone TEL, line
It returns to the circuit again via RL1 and flows to battery V _BB (-48V) and ground via resistor R0. In a telephone TEL, this current causes the bell to ring.

On the other hand, when sending a silent signal, connect contact rl ₀ to the earth side. At this time, earth air is sent to the telephone via the above-mentioned path. In either case, the DC current from the earth to -48V via R1, RL0, TEL, and R0 flows only during off-hook, and does not flow during off-hook.

The ring trip circuit LT is configured to detect this direct current. That is, during off-hook, the input to the low-pass filter COM is determined by R ₆ to _{R 10} .
Since it is connected to ±5V, VA-VB>0, and the output is at H level. On the other hand, when off-hook, R1
A DC potential difference is generated between both ends of the circuit, which is connected to the input of the comparator COM by _R2 to _R5 , and by setting VA-VB<0, the output becomes L level and off-hook is detected.

Capacitor C, together with R ₂ and R ₃ , forms a low-pass filter, allowing direct current to pass through but attenuating the calling signal. For example, the total line resistance is RL0 + RL1 = 0 to 1500Ω, and the telephone impedance Z _T (on-hook 2KΩ, off-hook 220Ω)
Then, the detection voltage at R ₁ is at maximum when on-hook: V _cR ×R ₁ /R ₀ +R ₁ +Z _T =83×
√2×470/470+470+2000=18.8Vop...(1) Off-hook minimum: V _BB ×R ₁ /R ₀ +R ₁ +Z _T = 43 × 4
70/470+470+1500+220=7.6V...(2)

That is, with the voltage across _R1 , AC should not detect 18.8Vop, and DC should detect 7.6V. The alternating current is therefore attenuated by R ₂ , R ₃ and C.

According to the above explanation, the larger the time constant of the low-pass filter, the better. That is, the larger the time constant, the smaller the alternating current component that occurs in VA-VB, and by reducing the margin V1 shown in FIG. 2 or the reverse bias _V0 that occurs at ±5V,
The margin V2 can be increased.

Here, FIG. 2 will be explained. ~ is a comparator
The waveform of the COM differential input VB-VA is shown. ~
shows the transient response when the ring trip circuit LT is off-hook when the silent signal is sent and the ring trip circuit LT is further disconnected by the contacts rl ₁ and rl ₂ . When on-hook, biased by ±5V, VB-VA
= -V0. At the same time as off-hook, the signal shifts in the direction of VB-VA>0 according to the time constant of the filter, and reaches a certain level. indicates the longest line, and V ₂ is the operating margin. On the other hand, , indicates the case where the line is the shortest. 1 shows the case where the Zener diode D is not provided, and 1 shows the situation where the DC input level is clamped by the Zener diode D. , are the comparator outputs for the input waveforms, respectively, and VB
-VA>0, H level corresponding to VB-VA<0,
It is at L level. On the other hand, indicates the input when sending a calling signal during off-hook. VB−VA=−
AC waveforms are superimposed around V0, and _V1 is the operating margin.

As shown in FIG. 2, td ₁ and td ₂ are the response time and recovery time. As described above, the margin increases as the filter time constant increases, but td ₁ and td ₂ also increase, which is undesirable because it increases restrictions on the operation of the switching system. The Zener diode D shown in FIG. 1 is inserted in order to shorten the recovery time and alleviate the limitations. Its operation is as described above,
The effect is to reduce td ₂ to td ₂ ′.

The above ring trip circuit has the following drawbacks. Zener diode D clamps the terminal voltage to the Zener voltage (for example, 5V) in the reverse direction, but in the forward direction it clamps to 0.7V like a normal diode.
Clamp to a certain degree. On the other hand, in conventional ring trip circuits, a filter time constant of about 0.17ms is used. In this case, the 16Hz ringing signal will be attenuated by approximately _25dB . Therefore, when the calling signal is at its maximum, an AC signal of 18.8×0.056=1.06V is applied across the diode. The 1.06Vop AC signal is clamped to 0.7V by the Zener diode only at the peak in the direction of VA-VB<0, resulting in a waveform that is asymmetrical to the positive page. In other words, it will have a DC component in the direction of VA-VB>0, and V ₁ in Figure 2 will become smaller.
The on-hook margin becomes smaller.

An object of the present invention is to provide a ring trip circuit with a large operating margin.

The gist of the present invention is that the diode is connected in series with the Zener diode in the opposite direction. below,
The present invention will be explained in detail with reference to the drawings.

FIG. 3 is a diagram showing an embodiment of the ring trip circuit LT of the present invention and the overall configuration in which the ring trip circuit is connected. ring trip circuit
LT consists of resistors _R1 to _R10 , a capacitor C, a diode _D1 , a Zener diode _D0 , and a comparator COM. Outside, telephone TEL, lines L0, L1,
Resistance R0, contacts rl ₀ , rl ₁ , rl ₂ , sound source CR, battery V _BB
Consists of. The feature of this embodiment is that a diode D1 is provided in series with the Zener diode D0 in the opposite direction.

According to this embodiment, in the direction of VB-VA>0,
The clamp voltage will be the sum of the Zener voltage and the forward voltage of diode D1, but VB-VA
In the <0 direction, there is no clamping for voltages up to the reverse breakdown voltage of the diode D1. Therefore, the drawbacks mentioned in the conventional example are completely eliminated.

On the other hand, VB-VA due to the addition of diode D1
The increase in clamp voltage in the direction of >0 can be compensated for by selecting a diode with a small Zener voltage, so that the response time recovery time is comparable to that of the conventional circuit.

According to the present invention described above, a ring trip circuit with a large margin can be easily realized by simply adding one diode.

[Brief explanation of drawings]

FIG. 1 is a diagram of a conventional example, FIG. 2 is a waveform diagram, and FIG. 3 is a diagram of an embodiment of the present invention. LT...Ring trip circuit, COM...Comparator, D1...Diode, D0...Zener diode.

Claims (1)

[Scope of Claims] 1. A resistor-capacitor type low-pass filter connected in parallel to a path connecting a mutually selected sound source or ground air and a telephone to capture a DC voltage generated by a DC current flowing during off-hook. Input the voltage across the capacitor of the filter,
a comparator for detecting on-hook or off-hook of the telephone by determining the input voltage, and a constant voltage diode connected in series with the forward direction with respect to the DC voltage, and a constant voltage diode with the reverse direction with respect to the DC voltage. is provided in parallel with the capacitor of the filter, and only the voltage across the voltage regulator diode in the opposite direction is clamped to a constant voltage higher than the voltage at which the comparator determines that the input voltage is off-hook, and the comparator A ring trip circuit characterized by an input to the ring trip circuit.