US3737732A

US3737732A - Time delay relay

Info

Publication number: US3737732A
Application number: US00176144A
Authority: US
Inventors: H Suemasa; K Honda; K Yoda; T Hanahara
Original assignee: Matsushita Electric Works Ltd
Current assignee: Panasonic Electric Works Co Ltd
Priority date: 1970-09-01
Filing date: 1971-08-30
Publication date: 1973-06-05
Anticipated expiration: 1990-06-05
Also published as: DE2143591A1; DE2143591C3; DE2143591B2

Abstract

A time delay relay of the type in which a semiconductor switching element is made conductive after a predetermined time by a RC time constant circuit so as to actuate a relay connected in series with the semiconductor switching element with respect to a power source. The RC time constant circuit is connected to the semiconductor switching element through a transistor element and, among leakage current of the semiconductor switching element, the current flowing through resistor of the RC time constant circuit is restrained to be low utilizing amplifying action of the transistor element, thereby enabling a delaying action for a long time period.

Description

United States Patent 1191 Suemasa et al. 1 June 5, 1973 [541 TIME DELAY RELAY 3,349,284 10/1967 Roberts ..317/14s.s B 3,474,293 10/1969 Siwbo et al. ..317/33 so Inventors: Hideo Suemasa, Neyagawa; Kazuyoshi Honda, Kadoma; Kenichi Yoda, Moriguchif Toru Hanahara, Hirakata all of Japan Matsushita Electric Works, Ltd., Osaka, Japan Filed: Aug. 30, 1971 Appl. No.: 176,144

Assignee:

Foreign Application Priority Data Sept. 1, 1970 Japan ..45/76800 Man-30, 1971 Japan ..46/l8962 US. Cl. "317/1418, 3l7/l42 R, 3l7/l48.5 B

'Int. Cl. ..H0lh 47/18 Field of Search ..3l7/l4l S, 142 R, 317/1485 B, 33 SC 7/l963 Herr. ..317/l41S Primary Examiner-J. D. Miller Assistant ExaminerHarry E. Moose, Jr. Attorney-Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.

[5 7] ABSTRACT A time delay relay of the type in which a semiconductor switching element is made conductive after a predetermined time by a RC time constant circuit so' as to actuate a relay connected in series with the semiconductor switching element with respect to a power source. The RC time constant circuit is connected to the semiconductor switching element through a transistor element and, among leakage current of the semiconductor switching element, the cur rent flowing through resistor of the RC time constant circuit is restrained to be low utilizingamplifying action of the transistor element, thereby enabling a delaying action for a long time period.

4 Claims, 8 Drawing Figures VPATENTEDJUN 51m 3,737,732

SHLEI 1 OF 3 CURRENT (I l I vs VOLTAGE)! I 9- (P |oR ART) D| D2 R I INVENTORS ATTORNEYJ' TIME DELAY RELAY DISCLOSURE OF THE INVENTION This invention relates to a time delay relay enabling a long delaying action. Such time delay relay that the relay therein is actuated by the voltage of a time constant circuit comprising a capacitor and resistor detected by such .a switching element having a negative resistance characteristic as, for example, a silicon unilateralswitch, a silicon bilateral switch, a silicon synmetric switch of the like is well known. Such kind of relay is featured in that its operation includes snap action and the relay can be self-retained without using relay contacts.

FIG. 1 shows a voltage-current characteristic of the above mentioned switching element, in which the element is completely turned on when voltage across the switching element is gradually increased and reaches the switching voltageVs and, if a current greater than holding current I, is caused to continue flowing thereafter, the switching element holds its conductive state. In this case, forward voltage drop of the switching element is V,. This switching element is not brought into .conduction unless a current of the magnitude I,

(switching current or break over current) is caused to flow there through just before firing thereof.

FIG. 2 shows an example of the relay circuit utilizing the above mentioned switching element. In this drawing, Q is a switching element, X is a relay coil, D and D, are diodes, R, is a resistor, R, and C, are time limiting resistor and capacitor, respectively, and E and E, are DC. power sources. E, has a voltage higher than the firing voltage V, of the switching element and the time limiting resistor R, and capacitor C, are connected in series therewith. The resistor R,, diode D and the switching element Q are connected in paralled to said capacitor C,. The relay coil X, the diode D and the element Q are connected in parallel to the power source E (which is of lower voltage than V,).

Upon application of power supply voltage, the voltage V across the time limit capacitor C, is gradually increased. When the voltage V, reaches the firing voltage V, of the switching element Q, the element turns ON and thereby the relay X is actuated. At the same time, the charge on the capacitor C, is discharged through the resistor R diode D and switching element Q.

' In the relay of such circuit as above, there arise the following problems:

a. In case the leakage current I, just before firing of the switching element is large, such current will flow into the time limit resistor R, causing a larger voltage drop to occur. This results in' that the voltage V across the capacitor C, will not'be raised up to desired value and thus the switching element will not be conducted. This may cause failure of operation. On this account, the time limit resistor R, cannot be made large in value and, consequently, the long delaying operation cannot be expected and the switching element utilizable is limited to an element that has a very small value of l,.

b. The switching element Q is to be maintained in its conductive state by a continuous current mainly from the power supply voltage 'E, and larger than the holding current I,,. In case many ripples are included in the power supply voltage E the currentflow may happen to be lowered below the holding current 1,, and the switching element Q may become non-conductive,

causing the relay to be turned OFF.

c. If the power supply is interrupted at a time (FIG. 4) shorter than the normal delaying time t, by any reason during time limiting operation (the condition in which the capacitor C, is being charged and the voltage V, of the time limiting capacitor C, cannot be decreased through discharging below the sum of the forward voltage drop of the diode D, and the forward voltage drop V, of the switching element, and subsequent delaying time is similarly influenced by this.

e. Such relationship that the voltage of source E, voltage V, of element Q voltage of source E, is required, and two source voltages are also necessary. Furthermore, driving voltage of the relay cannot be made larger.

According to the present invention, the above men tioned problems in the time delaying relay can be solved by detecting the voltage rise at the time constant circuit by a switching element having a negative resistance characteristic inserted through a transistor.

It is a principal object of the present invention to provide a'relay capable of actuating with a long delay time.

Another object of the invention is to provide a relay capable of actuating even with large leakage current of the switchingelement.

A further object of the invention is to provide a relay in which the'timing capacitor discharges rapidly its charge even if the power supply is interrupted during the delay timing, and no adverse effect on the next timing operation will be caused.

It is a further object of the invention to provide a relay capable of normally operating even with a power supply voltage containing many ripples.

The present invention will be explained in connection with embodiments thereof with reference to the accompanying drawings, in which:

FIG. 1 shows a characteristic of a switching element;

FIG. 2 is a circuit of a conventional time delay relay;

FIG. 3 is an embodiment of the time delay relay circuit according to the present invention;

FIG. 4 and 5 show operational characteristics;

FIG. 6 shows an equivalent circuit of the switching element; and

FIG. 7 is another embodiment of-the present invention. Referring to FIG. 3 showing an embodiment of the present invention, a time constant circuit comprising a timing resistor R, and a timing capacitor C, is con-' nected in parallel with a DC. power supply E. The

junction point between said resistor R, and capacitor C, t

is connected to the base of a first transistor T,. The transistor T, has a collector connected to the positive side of the power supply through a resistor R, and also to the negative side of the power supply through another resistor R The emitter of the transistor T is conthree terminals which has a negative resistance characteristic. The cathode of the element Q is connected to the-negative side of the power supply. A capacitor C, is connected between the gate of the switching element Q and the base of the transistor T Operation of this circuit is as follows.

Upon application of the power supply voltage, the timing capacitor C, begins to charge and, when voltage V, across the capacitor C, reaches the firing voltage V of the switching element Q, the latter detects this through the base and the emitter of the respective transistors T, and T so asto be conducted. Thus, base cur rent will flow and the transistors T, and T thereby the transistors are made to be conductive so as to drive the relay X.

The features of the present circuit is as follows:

a. Even in case of a large leakage current I, of the switching element Q, only the base current divided by an actual amplification factor will flow on account of amplifying action of the transistor (the current flowing through the timing resistor corresponds to the base current), and thus most of the leakage current I, will flow through the delay coil X while little current will flow through the timing resistor R,. As a result, thecurrent I,, will produce no voltage drop across the timing resistor R, and, therefore, the voltage V across the timing capacitor C, will fully rise sufficiently higher and thus there occurs no failure in the relaying operation. It is, therefore, possible to select a large value for the timing resistor R, and a long time delaying can be achieved.

b. In the case of a large ripple current, the conduction of the switching element Q is maintained by means of discharging charge of the capacitor C1 even when the current flowing through the switching element Q is lowered below the holding current 1,. Accordingly, the switching element Q does not become non-conductive not only at the time when the supply voltage contains large ripple but also in case of halfwave rectified supply voltage or full-wave rectified supply voltage; This is also applicable to the case of momentary OFF state of the power source.

c. In case the power supply is interrupted during the timing operation, that is, at the time t, shorter than the normal delay time t,, adverse biasing between the base and the collector of the transistor T is released and P-N junction is established between such base and collector of the transistor. Thus the charge on the timing capacitor C, is discharged through the base, the collector of the transistor T, and the resistor R This discharging is shown by a broken line in FIG. 5. The resistor R has no effect on normal time delaying operation and provides a compensation for withstand voltage of the transistor T,. r

d. In case the power supply is cut off after the timing operation, that is, at the time point 1,, residual charges left in the timing capacitor C, will completely discharge through the resistor R,, R, and R as shown by a solid line in FIG. 5. If the discharging path does not consist of only pure resistance components, such complete discharging cannot be expected. Accordingly, the next delaying operation will be quite normal and an excellent repeating time characteristic can be obtained.

e. If withstand voltage of the transistors T, and T is selected to be sufficiently large, the power supply voltage can be made large irrespective of the voltage V, of the element Q.

' f. Even if a surge appears in the power supply line during the timing operation, any erroneous operation can be prevented by the capacitor C,.

g. The transistors T, and T are connected in the form of two stages and a large base current for the relay driving transistor T is taken out of the. resistor R, without directly passing the current through the timing resistor R,. This causes a very large coil current for the relay X to flow. This allows uses of a relay having a large coil capacity and a timing resistor whose value is very large. Even in this case, the transistors T, and T can be maintained in complete conductive state.

FIG. 6A shows an equivalent circuit of the switching element having negative resistive characteristic, and FIG. 6B shows terminals thereof.

FIG. 7 shows another embodiment of the present invention, in which polarities of the transistors are reversed and also the polarity of the switching element Q is reversed. The capacitor C, is connected between the gate and the anode of the switching element Q. Operation of the circuit is similar to that of the circuit shown' in FIG. 3.

What is claimed is:

1. A time delay relay comprising a first series circuit including a timing resistor and a timing capacitor, a second series circuit including a pair of resistors con nected in parallel with said first series circuit, a DC source connected across each of said series circuits, a first transistor element having its base connected between said timing resistor and said timing capacitor and its collector connected between the two resistors in said second series circuit, and a second transistor element having its base connected to-the emitter of said first transistor element, a relay winding connected between the collector of said second transistor element and the resistor end of said first series circuit, and a semiconductor switching element connected between the emitter of said second transistor element and the capacitor end of said first series circuit.

2. A time delay relay as defined in claim 1 wherein a discharging resistor is connected between the collector of said first transistor element and the capacitor end of said first series circuit, so that a discharging by-pass for residual charges of the timing capacitor is formed through the base and emitter of the first transistor element and said discharging resistor when the timing operation is interrupted before completion of the timing period.

3. A time delay relay according to claim 1, in which said semiconductor switching element is a three terminal semiconductor switching element, and a capacitor for maintaining conduction of the switching element is connected between the gate electrode of said semiconductor switching element and the base of the transistor element.

4. A time delay relay according to claim 1 in which said semiconductor switching element is a three terminal semiconductor switching element, and a capacitor for maintaining conduction of the switching element is connected between the gate electrode and the anode electrode of the switching element.

Claims

1. A time delay relay comprising a first series circuit including a timing resistor and a timing capacitor, a second series circuit including a pair of resistors connected in parallel with said first series circuit, a D.C. source connected across each of said series circuits, a first transistor element having its base connected between said timing resistor and said timing capacitor and its collector connected between the two resistors in said second series circuit, and a second transistor element having its base connected to the emitter of said first transistor element, a relay winding connected between the collector of said second transistor element and the resistor end of said first series circuit, and a semiconductor switching element connected between the emitter of said second transistor element and the capacitor end of said first series circuit.