AU620087B2

AU620087B2 - Relay driving circuit using a thyrister

Info

Publication number: AU620087B2
Application number: AU33843/89A
Authority: AU
Inventors: Takeo Anzai
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 1988-04-28
Filing date: 1989-04-28
Publication date: 1992-02-13
Anticipated expiration: 2009-04-28
Also published as: GB8909610D0; AU3384389A; JPH01279533A; GB2218284B; JPH0587930B2; GB2218284A

Description

TO: THE COMMISSIONER OUR REF: 94306 S&F CODE: 59060 OF PATENTS 5845/2 1 620087 S F Ref: 94306 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int Class Complete Specification Lodged: Accepted: Published: Priority: Related Art:

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Name and Address of Applicant: S Address for Service: NEC Corporation 33-1, Shiba Minato-ku Tokyo 108

JAPAN

Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: Relay Driving Circuit Using a Thyrister The following statement is a full description of this invention, including the best method of performing it known to me/us 5845/3

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o e4 4, The basic application(s) referred to in paragraph 2 of this Declaration was/were the first application(s) made in a Convention country in respect of the invention-.() the subject of the application.

Declared at Tokyo, Japan this 29th day of March, 1989.

NEC CORPORATION SFP4 To: The Commissioner of Patents Signature of Declarant(s) 11/81 Susumu Uchihara General Manager, Patents Division .I I 1 _II L l circuit and, more particularly, to a relay driving circuit for switching over a relay contact in association with a DC voltage which is received over a transmission line.

A relay is extensively used with various kinds of apparatuses as a switch. For example, in a communication S. system having a central station and a remote station which o. are interconnected by a transmission line, an electro- S 10 magnetic switch is built in for switching over the line 0 from a communication terminal to test equipment in 00 00 for a line testing purpose. In general, a circuit for a o 0o 0 driving such a relay is made up of an electromagnetic relay, a Zener diode connected in parallel with a relay 000 S..ot coil adapted to energize the relay for the purpose of bypassing an overcurrent, and a coil connected in series communication frequency band.

The prior art relay driving circuit has a problem left unsolved, as follows. When the DC resistance of the line exceeds a certain upper limit due to an excessive line length or a small wire diameter, for example, the current which flows through the relay coil upon the drvn uharlyi aeu fa lcrmgei -2arrival of the DC voltage over the line fails to reach the working current of the electromagnetic relay. This makes it impossible to switch the line from the communication terminal to the test equipment.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a relay driving circuit which raises the allowable upper limit of DC resistance of a communication line.

According to one aspect of the present invention there is disclosed a relay driving circuit for selectively connecting communication terminal means and test equipment means to a communication line comprising: 00 40 relay contact means associated with an electromagnetic relay for 0 selectively connecting said communication line to said communication 0000 terminal means and said test equipment means; 0 drive coil means connected to said communication line via a choke 0109 So o0 15 coil means for driving said relay contact means, said chokr coil means 00oo preventing an AC signal from flowing through said drive coil means; control means connected to said drive coil means for controlling a supply of current to said drive coil means; capacitor means connected to said drive coil means to be charged by 20 a DC signal which comes in over said communication line; o 0means for producing a control voltage for said control means from a 0 00 04 voltage charged in said capacitor means; and switch means coupled between said capacitor means and said drive coil means for discharging said capacitor means through said drive coil S 25 means to increase the supply of current through said drive coil means.

o, According to another aspecL of the present invention there is S disclosed a relay driving circuit comprising: relay contact means of an electromagnetic relay for selectively switching over first and second equipment; drive coil means for driving said relay contact means; control means connected to said drive coil means for controlling a supply of current to said drive coil means; capacitor means to be charged by a DC signal which drives said drive coil means; means for producing a control voltage for said control means from a voltage charged in said capacitor means; and switch means coupled between said capacitor means and said drive mg/0587y 0I PM4 -2acoil means for discharging said capacitor means through said drive coil means to increase the supply of current through said drive coil means.

According to a still further aspect of the present invention there is disclosed an apparatus for supplying working current from a communication line to an electromagnetic relay comprising: a capacitor having a first electrode connected to receive current from the communication line; a relay coil for switching the electromagnetic relay and having a first electrode connected to receive current from the communication line and the first electrode of the capacitor and having a second electrode; a control circuit connected to the second electrode of the relay coll to draw current through the relay coil responsive to a turn-on voltage; 4, a control voltage generator connected between the first electrode 15 of the capacitor and the control circuit to supply the turn-on voltage to the control circuit when the capacitor has received enough current from Sthe communication line to charge the capacitor to the predetermined voltage value; and a switching circuit operatively connected to the capacitor for discharging the capacitor through the relay coil to thereby increase the current through the relay coil.

According to a still further aspect of the present invention there is disclosed an apparatus for supplying working current from a communication line to an electromagnetic relay comprising: a capacitor having a first electrode connected to receive current from the communication line; a relay coil for switching the electromagnetic relay and having a first electrode connected to receive current from the communication line and the first electrode of the capacitor and having a second electrode; a control circuit connected to the second electrode of the relay coil to draw current through the relay coil responsive to a turn-on voltage; a control voltage generator connected between the first electrode of the capacitor and the control circuit to supply the turn-on voltage to the control circuit when the capacitor has received enough current from the communication line to charge the capacitor to the predetermined voltage value; and 4?a diode and a resistor connected in parallel with the diode, the i -2bdiode having an anode connected to the first electrode of the capacitor and a cathode connected to the first electrode of the relay coll, wherein current from the communication line flows through the resistor to the capacitor and current from the capacitor flows through the diode and the resistor to the relay coil.

00 0 o 0 0000 0000 0 00 oo 0 0 0 0o g o0 00 Q 0 00000 /0587y 0N0 0, 0 g!0587y F 6-

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3 The above and other objects, features and advantages of the present invention will become more apparent fromthe following detailed description when taken with the drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the figure, a central station 40 and a communication terminal 20 and test equipment 30 are interconnected by a communication line 4. The communication terminal and the test equipment 30 are selectively connected to o aQ0 o' 10 the line. 4 by a contact 2 of an electromagnetic relay.

SA

The electromagnetic relay has a drive coil or relay coil 0 1 connecting to the line 4 via a choke coil 3. The choke 0 0 o0 o 0 0Q000 coil 3 prevents a signal current from flowing through the 9 0 relay coil 1 when communications are under way. A Zener 15 diode 4 is connected in parallel with the relay coil 1 0 o 0"a*o for the purpose of bypassing an overcurrent. A thyristor is connected in series in a forward direction on a current path which'extends through the relay coil 1.

A capacitor 7 and a parallel connection of a diode and a resistor 6 are connected in series with the junction of the coils 3 and 1. Resistors 8 and 9 are connected to the capacitor 7 so as to feed a voltage developing across the capacitor 7 to the gate of the thyristor The relay driving circuit having the above

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rrrac 00 *1 o o 000 O 0 0 00 00 00 B 0 *0 8 04 t 00 0 ae o 0 0 0*00 on S00 00 0 0 II 000w a (09 4 construction will be operated as follows. First will be described the case of the small DC resistance of the line.

When a communication is held over the line 4, the impedance of the choke coil 3 is high so that no current flows through the relay. In this condition, the contact 2 of the electromagnetic relay connects the communication terminal 20 to the line 4. When a DC voltage comes in over the line 4 for testing the line 4, a charging current is applied to the capacitor 7 via the resistor 6 because both the diode 5 and the thyristor 10 remain turned off at first. As the voltage across the capacitor 7 is increased by the charging voltage to a certain level, the thyristor 10 is turned on so that a current begins to flow through the relay coil 1. Since it is assumed 15 that the DC resistance of the line 4 is small, the current through the relay coil 1 becomes greater than the working current of the relay coil 1 which is a minimum currenL to energige the relay coil and, hence, the relay coil 1 switches over the contact 2.

Meanwhile, when the DC resistance of the line 4 is great, the voltage across the capacitor 7 is also sequentially increased by the DC voltage from the line 4, and as soon as the voltage across the capacitor 7 reaches the predetermined value, the thyristor 10 is turned on to cause a current to flow through the relay coil 1.

These operations are the same as those in the case of .LI1' t i :z i a 0 0 6 0 0B 0 0 060 0 0 0 0o 0 6 o 0 0 0 S06 0 6 0 0 0 0 0 6O o y a the small DC resistance. However, since the resistance of the line 4 is great as mentioned above, the current through the relay coil 1 is smaller than the working current which is necessary to excite the relay coil 1 and, therefore, it fails to energize the relay coil 1.

Thereafter, as the voltage across the capacitor 7 is further increased by the charging current, it exceeds the voltage appearing on the junction of the coils 1 and 3 in due course. Then, the diode 5 is turned on to cause a current to flow from the capacitor 7 to the relay coil 1. By adequately selecting the capacitance of the capacitor 7, it is possible to allow the discharge current of the capacitor 7 to exceed the working current of the electromagnetic relay. Hence, when the relay 15 coil 1 is excited by the discharge current from the capacitor 7, the contact 2 of the relay is actuated to connect the test equipment 30 to the communication line 4.

As the voltage across the capacitor 7. is lowered after the discharge, only a current which is associated with the DC voltage coming in over the line 4 is allowed to flow through the relay coil 1. Although this current is smaller than the working current of the relay, the contact 2 is capable of maintaining the test equipment in connection to the line 4 only if the current through the relay coil 1 is greater than the holding current of the relay, be-'ause the relay has already worked.

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j.llli. I S6 Concerning an oridinary electromagnetic relay, the holding current is less than one half of the working current. Hence, upon the arrival of a DC current over the line 4, a cur'rent greater than the working current of the relay is fed to the relay coil 1 by the charging and discharging of the capacitor 7 so as to cause the test equipment 30 into connection with the line 4 via the contact 2. Then, the test equipment 30 can be held in connection with the line 4 only if the current flowing through the relay coil 1 in association with the DC 4o c0 Svoltage which has been lowered on the line 4 is greater 0o 0I than the holding current. The illustrative embodiment, 4 00 4 therefore, accommodates a higher upper limit of line 4 4 DC resistance than the prior art, broadening the o 9 applicable range of a relay driving circuit.

In summary, it will be seen that the present invention provides a relay driving circuit which operates an electromagnetic relay by a current which is generated by the charging and discharging of a capacitor upon the arrival of a DC voltage over a communication line, thereby 0°0, successfully coping with a higher upper limit of line 4° DC resistance than the upper limit heretofore accommodated.

Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the sope thereof.

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Claims

1. A relay driving circuit for selectively connecting communication terminal means and test equipment means to a communication line comprising: relay contact means associated with an electromagnetic relay for selectively connecting said communication line to said communication terminal means and said test equipment means; drive coil means connected to said communication line via a choke coil means for driving said relay contact means, said choke coil means preventing an AC signal from flowing through said drive coil means; control means connected to said drive coil means for o controlling a supply of current to said drive coil means; too@ ,capacitor means connected to said drive coil means to be L charged by a DC signal which comes in over said communication line; 15 means for producing a control voltage for said control means k from a voltage charged in said capacitor means; and switch means coupled between said capacitor means and said drive coil means for discharging said capacitor means through said drive coil means to increase the supply of current through said drive coil means.

2. A relay driving circuit comprising: relay contact means of an electromagnetic relay for selectively switching over first and second equipment; drive coil means for driving said relay contact means; control means connected to said drive coil means for controlling a supply of current to said drive coil means; capacitor means to be charged by a DC signal which drives said drive coil means; means for producing a control voltage for said control means from a voltage charged in said capacitor means; and switch means coupled between said capacitor means and said drive coil means for discharging said capacitor means through said drive coil means to increase the supply of current through said drive coil means.

3. An apparatus for supplying working current from a communication line to an electromagnetic relay comprising: amgi'0587y -8- a capacitor having a first electrode connected to receive current from the communication line; a relay coil for switching tte electromagnetic relay and having a first electrode connected to receive curreot from the communication line and the first electrode of the capacitor and having a second electrode; a control circuit connected to the second electrode of the relay coil to draw current through the relay coil responsive to a turn-on voltage; a control voltage generator connected between the first electrode of the capacitor and the control circuit to supply the turn-on o o voltage to the control circuit when the capacitor has received enough current from the communication line to charge the capacitor to the 0oo predetermined voltage value; and 0oo 15 a switching circuit operatively connected to the capacitor for a 0 discharging the capacitor through the relay coil to thereby increase the current through the relay coil.

4. An apparatus for supplying working current from a communication line to an electromagnetic relay comprising: a capacitor having a first electrode connected to receive current from the communication line; a relay coil for switching the electromagnetic relay and having a first electrode connected to receive current from the communication line and the first electrode of the capacitor and having a second electrode; a control circuit connected to the secon6 electrode of the relay coil to draw current through the relay coil responsive to a turn-on voltage; a control voltage generator connected between the first electrode of the capacitor and the control circuit to supply the turn-on voltage to the control circuit when the capacitor has received enough current from the communication line to charge the capacitor to the predetermined voltage value; and a diode and a resistor connected in parallel with the diode, the diode having an anode connected to the first electrode of the capacitor and a cathode connected to the first electrode of the relay amg/0587y r K K I -9- coil, wherein current from the communication line flows through the resistor to the capacitor and current from the capacitor flows through the diode and the resistor to the relay coil. A relay driving circuit substantially as described with reference to the accompanying drawing. DATED this TWENTY FIRST day of NOVEMBER 1991 NEC Corporation Patent Attorneys for the Applicant SPRUSON FERGUSON 0a 04 oO oo 0 06 00 00 0E 00 0 0O 0 6 0 0 4 t i t t 1/0587y