US3666998A

US3666998A - Relay input circuit

Info

Publication number: US3666998A
Application number: US112530A
Authority: US
Inventors: Wayne H Wielebski
Original assignee: Allen Bradley Co LLC
Current assignee: Allen Bradley Co LLC
Priority date: 1971-02-04
Filing date: 1971-02-04
Publication date: 1972-05-30
Anticipated expiration: 1989-05-30
Also published as: CA941498A

Abstract

A relay coil is divided into two series connected sections and a dissipation resistor is connected in series with one lead of both sections to improve the drop out response of the relay. The dissipation resistor is shunted by a transistor the base of which is connected through coupling resistors to the other leads of the coil sections. The transistor operates as a switch to short circuit the dissipation resistor when power is applied to the relay coil to retain the pick up response of the relay. An alternative embodiment has a single coil section and coupling resistor. The dissipation resistor is connected to one lead of the coil section and the coupling resistor connects the transistor base to the other lead.

Description

United States Patent [151 3,666,998 51 May 30, 1972 Wielebski [54] RELAY INPUT CIRCUIT [72] Inventor: Wayne H. Wielebskl, Milwaukee, Wis.

(73] Assignee: Allen-Bradley Company, Milwaukee, Wis.

22 Filed: Feb. 4, 1971 211 App]. No.: 112,530

[52] U.S. Cl. ..317/123, 317/D1G/4, 317/1555, 3l7/D1G. 6

[51] Int. Cl. ..HOlh 47/04 [58] Field of Search... ...317/D1G. 4, DIG. 6, 123, 148.5 R,

[56] References Cited UNITED STATES PATENTS 3,582,718 6/1971 Spellman ..3l7/148.5 R

3,356,910 12/1967 Bushnell ...3l7/148.5 R

3,172,020 3/1965 Spinelli et a1. ..317/D1G. 6

Primary Examiner-L. T. Hix Assistant Examiner-Ham E. Moose, Jr. Attorney-Arthur H. Seidel and Barry E. Sammons ABSTRACT sistor. The dissipation resistor is connected to one lead of thecoil section and the coupling resistor connects the transistor base to the other lead. I

8 Claims, 2 Drawing Figures I Patented May 30, 1972 5 fi I I 1 I a 1 1 I 1 1 l 1 i||||||||l||1|1 Tl 4" m W n U M fi 3 9 q 4. W 2 M H w M J n W w w H M M 2 7/0 D H M w m A A m N n N n u H A M M Z m u l l l I l I l I I l I ll r /J I- INVENTOR WAYNE H-WIELEBSK ATTORNEY RELAY INPUT CIRCUIT BACKGROUND OF THE INVENTION The field of the invention is input circuits for d-c relays connectable to a-c power sources. Prior relay input circuits generally contain one relay coil connected to a standard fullwave bridge rectifier comprised of four diodes. When the relay is deactuated, its drop out response is determined by the rate at whichthe energy stored in the coils magnetic field is dissipated. The faster the field collapses, the shorter the response time of the switches controlled by the relay. In prior input circuits the relay coil is shunted by the very low resistance path formed by the forward biased diodes of the rectifier circuit. To improve the drop out response of the relay therefore, an energy-dissipating device, such as a resistor or a zener diode, is commonly added in series with the relay coil. Although such devices improve the drop outresponse by rapidly dissipatingthe energy stored in the coils magnetic field, their series connection with the coil slows the pick up response of the relay. Thus, in an effort to improve the drop out response of the relay, the elapsed time between actuation of the relay and response from the switches is increased. In prior art input circuits the value of the energy dissipating 'device is chosen by compromising both the pick up and drop out responses. g

'. SUMMARY OF THE INVENTION The relay input circuit of the present invention includes an energy dissipating device connected to one lead of the relay coil, andan electronic switch connected in shunt relationship with the energy dissipation device and having acontrol element connected to the other lead of the relay coil. The electronic switch is operable to shunt the energy dissipation device when power is applied to the relay coil, and operable to open, or drop out of the circuit, when the power is removed from the relay coil. v

An inherent characteristic of an inductor is its resistance to the change in current flow through'it. Thus when the power supplied to the relay coil through the rectifier circuit is disconnected, the coils magnetic fi'eld begins to collapse and it begins to generate a current. This is accompanied by a change in the voltage polarity of the relay coil which is sensed, by the electronic switch. The electronic switch responds by opening thus injecting the dissipation device into the circuit to absorb theenergy in the collapsing magnetic field. v

The circuit of the present invention is particularly applicable to sealed contact relays such as that disclosed in my U.S. Pat. No. 3,605,049 entitled Sealed Contact Relay where a pair of relay coils generate magnetic flux to operate a plurality of reed switches. To operate the reed switches, direct current is supplied to the coils, and therefore, when operating the relay from an a-c power source, a rectifier circuit is included which provides a low resistance path for the deactuated coils.

A general object of the invention is to improve the drop out response of a relay by inserting an energy dissipation device in series with the relay coil without slowing the relays pick up response. A transistor is connected to shunt the energy dissipation device when power is applied to the relay, and to drop out, or open, when the relay is deactuated.

Another object of the invention is to-provide a means of adjusting the drop out response of the relay without affecting its pick up response. Because the electronic switch shunts the energy dissipation device when the relay is actuated, the impedance of the input circuit to the relay coil is low regardless of the value of the energy dissipation device. The dissipation device can be a resistorwhich the user can easily install to provide the drop out response he desires.

Still another object of the invention is to provide an inexpensive, compact and reliable circuit for improving the drop out response of a relay.

The foregoing and other objects and advantages of the invention will appear from the following description. In the description reference is made to the accompanying drawing which forms a hereof, and in which there is shown by way of illustration and not of limitation preferred embodiments of the invention. Such embodiments do not represent the full scope of the invention, but rather the invention may be employed in many different embodiments, and reference is made to the claims herein for interpreting the breadth of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electrical schematic diagram of a preferred em- DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. 1, an electrical circuit for a sealed contact relay is designated by the dashed line 1. An a-c power source 2 in series with a switch 3 is connected across input terminals 4 and 5 of the relay 1. A relay coil divided into a first coil section 6 and a second coil section 7 has one lead of the first coil section 6 connected to the input terminal 4 and its other lead connected through a common point 8 to one lead of the second coil section 7. The other lead of the second coil section 7 is connected to the input terminal 5. Both coil sections 6 and 7 are wound on the magnetic core of the relay such that the fluxes generated by them when current flows through them to the common point 8 is additive. This is designated in standard fashion in FIG. 1 by the dots adjacent the leads of the coil sections 6 and 7.

One lead of a power dissipation resistor 9 is connected to the common point 8 and its other lead is connected to the anodes of a first rectifier diode 10 and a second rectifier diode 11. The cathode of the first diode 10 is connected to the input terminal 4, and the cathode of the second diode 11 is connected to the input terminal 5. They collector of an NPN of a second switching transistor 12 is connected to the common point 8 v and the dissipation resistor 9. The emitter of the transistor 12 is connected to the other lead of the dissipation resistor 9 and the anodes of the diodes l0 and 11. The base of the transistor 12 is connected to the input terminal 4 through a first coupling resistor 13 and to the input terminal 5 through a second coupling resistor 14. g 1

When the switch 3 is closed, positive current, flows altemately into terminal 4 through the first coil section 6, through the second rectifier diode l1 and out terminal 5; then into terminal 5, through the second coil section 7, through the first rectifier diode 10 and out terminal 4. The pick up response of the relay is determined by the elapsed time between actuation of the switch 3 and a response by the 'reed switches controlled by the'magnetic field generated by coils 6 and 7. To decrease this time interval, or in other words increase ,the pick up response, the electrical resistance of the two current paths outlined above is kept to a minimum.

The switching transistor 12 is an electronic switch which closes to shunt or short out the dissipation resistor 9 when the switch 3 is closed. As long as power is supplied through the switch 3, base current flows through either

coupling resistor

13 or 14 causing the switching transistor 12 to saturate, or turn on. The values of the

coupling resistors

13 and 14 are chosen both to protect the switching transistor 12 and provide suflicient base current to saturate the transistor 12 when power is applied to the relay 1.

When the switch 3 is opened, the magnetic field generated by the coil sections 6 and 7 begins to collapse, generating a current into the common point 8. At this point the input terminals 4 and 5 swing negative with respect to the common point 8 and the base emitter junction of the transistor 12 becomes reverse biased. The transistor 12 drops out of saturation and turns off. The current flowing into the common point 8 thus flows through the dissipation resistor 9, to the rectifier diodes 10 and 11, and back to the coil sections 6 and 7. The

is rapidly dissipated as heat in the dissipation resistor 9.

Other dissipation devices such as a zener diode can be sub- PNPtransistor can be substituted for the switching transistor 12. v

The embodiment shown in FIG. 2 is an adaptation of the above 'circuit to a single coil relay. Such a relay circuit is designated in H6. 2 by the dashed lines 15. It has two input terminalsl6 and 17 connected to an a-c power source 18 through aswitch 19. Four rectifier diodes 20 23 are connected to the

input terminals

16 and 17 in a standard full-wave bridge rectifier configuration. The cathodes of the

diodes

20 and 2! connect together and to one lead of a dissipation resistorv 24. The other lead of the resistor 24 connects to one lead of the relay. coil 25, the other lead of which is connected to the anodes of the

diodes

22 and 23 at a common point 26. The emitter of a PNP switching transistor 27 is connected to the lead of the dissipation resistor 24 connected to the

diodes

20 and 21, and its collector is connected to the other leadof the dissipation resistor 24 connected to the relay coil 25. The base of the switching transistor 27 is connected to the common point 26 through a coupling resistor 28.

'When the a-c power source 18 is connected to the input termina'ls l6 and 17 by closing the switch 19, positive current flows alternatively through the

diodes

20 and 21 downward through the relay coil 25 and alternately through the

diodes

23 and 22. This'current flow holds the voltage at the common point 26 negative with respect to the voltage on the emitter of the switching transistor 27. Asa result, thebase emitter junction of the switching transistor 27 is forward biased and the transistor 27 is'saturated, or turned on. Thus, when the power is supplied to the relay, the dissipation resistor 24 is effectively shunted or short circuited by the switching transistor 27 allowing a rapid buildup of current flow through the relay coil 25. When the switch 19 is openedthe magnetic field of the relay coil 25 begins to collapse and generate a current through the diodes 20 23. This current flows in two loops. One through the

diodes

20 and 22, and the other through

diodes

21 and 23. As a result of this collapsing field, the common point 26 is driven .positive with respect to the emitter of switching transistor 27; This reverse biases the emitter base junction and turns the switching transistor 27 off. As a result, the resistor 24 is inserted into the circuit with the relay coil 25, and dissipates the energy stored in the magnetic field.

As with the circuit in FIG. 1, other devices can be substituted for the resistor 24 and the transistor 27. Additionally, the series connection of the dissipation resistor 24 and relay coil 25 can be reversed allowing the use of an NPN switching transistor 27 .-ln such an arrangement the coupling resistor 28 is connected to the cathodes of the

diodes

20 and 21 rather than common point 26. Other arrangements are possible if two dissipation resistors and two switching transistors are used. The essential feature of the invention is a series connection of the energydissipation device to one lead of the relay coil and shunting the dissipation device by an electronic switching device having a control element connected to the other lead of the relay coil. The invention thus makes use of the polarity change occurring across the relay coil to insert an energy dissipation device into the circuit.

What is claimed is:

1. An input circuit for a direct current relay coil the com device with its control element connected to the other lead of said relay coil, wherein said electronic switch is operable in response to the voltage drop developed across said relay coil when energizedby saida-c power source to short circuit said energy dissipation device and responsive to the polarity reversal in the voltage drop across said relay coil to open when the relay coil is deenergized thereby inserting said energy dissipation device into the circuit defined by said relay coil and said rectifier circuit.

2. The input circuit as recited in claim 1, wherein said elec tronic switch is a transistor with its collector connected to one lead of said dissipation device and its emitter connected to the other lead of said dissipation device and its base is the control element.

3. The input circuit as recited in claim 2, wherein a coupling resistor is connected between the transistor base and the other lead of the relay 'coil.

4. The input circuit as recited in claim gy dissipation device is a resistor.

5'. An input circuit for a direct current relay coil having'first and second coil sections, each section having one lead con- 3, wherein said enernected to a'common point, the other lead of the-first section being connected to a first input terminal and the other lead of the second section being connected to a second input terminal, the combination comprising:

two rectifiers connected in series second input terminals; an energy dissipation device connected between the common point and the connection point of the two rectifiers; and an electronic switch having a control element, said-switch connected in shunt relation to. said energy dissipation device with its control element connected to the first and second input terminals, wherein said electronic switch is operable to short circuit said energy dissipation device when a power source is applied to said input terminals and to open when'said power source is removed from said input terminals. I 6. The input circuit as recited in claim 5, wherein said electronic switch is a transistor with its collector and emitter connected to the energy dissipation device and its base connected to the input terminals. v

7. The input circuit as recited in claim 6, wherein a first between the first and coupling resistor connects the transistor base to the first input

Claims

1. An input circuit for a direct current relay coil the combination comprising: an energy dissipation device having one lead connected to one lead of the relay coil; a full wave bridge rectifier circuit having a pair of input terminals adapted for connection to an a-c power source and a pair of output terminals, one of said output terminals connected to the other relay coil lead and the other of said output terminals connected to the other lead of said energy dissipation device; and an electronic switch having a control element, said switch connected in shunt relation to said energy dissipation device with its control element connected to the other lead of said relay coil, wherein said electronic switch is operable in response to the voltage drop developed across said relay coil when energized by said a-c power source to short circuit said energy dissipation device and responsive to the polarity reversal in the voltage drop across said relay coil to open when the relay coil is deenergized thereby inserting said energy dissipation device into the circuit defined by said relay coil and said rectifier circuit.

2. The input circuit as recited in claim 1, wherein said electronic switch is a transistor with its collector connected to one lead of said dissipation device and its emitter connected to the other lead of said dissipation device and its base is the control element.

3. The input circuit as recited in claim 2, wherein a coupling resistor is connected between the transistor base and the other lead of the relay coil.

4. The input circuit as recited in claim 3, wherein said energy dissipation device is a resistor.

5. An input circuit for a direct current relay coil having first and second coil sections, each section having one lead connected to a common point, the other lead of the first section being connected to a first input terminal and the other lead of the second section being connected to a second input terminal, the combination comprising: two rectifiers connected in series between the first and second input terminals; an energy dissipation device connected between the common point and the connection point of the two rectifiers; and an electronic switch having a control element, said switch connected in shunt relation to said energy dissipation device with its control element connected to the first and second input terminals, wherein said electronic switch is operable to short circuit said energy dissipation device when a power source is applied to said input terminals and to open when said power source is removed from said input terminals.

6. The input circuit as recited in claim 5, wherein said electronic switch is a transistor with its collector and emitter connected to the energy dissipation device and its base connected to the input terminals.

7. The input circuit as recited in claim 6, wherein a first coupling resiStor connects the transistor base to the first input terminal and a second coupling resistor connects the transistor base to the second input terminal.

8. The input circuit as recited in claim 7, wherein the energy dissipation device is a resistor and the rectifiers are diodes.