US3321674A - Apparatus for supplying pulses of constant width to a load device - Google Patents

Description

y 23, 1967 M. FELCHECK ETAL APPARATUS FOR SUPPLYING PULSES OF CONSTANT WIDTH TO A LOAD DEVICE I Filed July 14, 1964 INVENTQRS MARVIN- FELCHECK N. NARASIMHA MURTHY' United States Patent 3,321,674 APPARATUS FOR SUPPLYING PULSES 0F CON- STANT WIDTH TO A LOAD DEVICE Marvin Felcheck, Bayside, N.Y., and Nanjundiah N.

Murthy, Norwalk, Conn., assignors to American Machine & Foundry Company, a corporation of New Jersey Filed July 14, 1964, Ser. No. 382,553 5 Claims. (Cl. 317148.5)

This invention relates to circuits for providing an electrical pulse of predetermined duration, or a succession of pulses each of predetermined duration, to a load device and, more particularly, to such systems capable of operating from an unregulated voltage source.

In the design and construction of various automatic sysbems, including computers, automatic machine tools and the like, it is frequently desirable to use electromagnetic relays of various types which require pulses of a particular, predetermined duration for proper operation. Circuits have been designed to provide such fixed-width pulses, but these circuits have generally required the use of power sources which are closely regulated so that the time constants on which pulse duration depends do not vary.

Relays in general are designed to operate within a specified range of voltages. Usually, a minimum energizing voltage or current is specified below which the device will not dependably function, and a maximum may also be specified above which the device may overheat or be otherwise damaged. Within this range, the pulse duration should be constant for proper operation of relays of the type referred to.

It is therefore an object of this invention to provide a circuit by which successive pulses of fixed duration can be supplied to a load device.

Another object is to provide a circuit by which successive pulses of constant duration can be supplied to a load regardless of significant variations in source voltage.

A further object is to provide such a device in which the source voltage may vary over a range limited only by the characterstics of the load device, and within which range the load device will be provided with pulses each of constant, predetermined duration.

The invention employs a single power transfer element controlled by start and stop impulses, the start impulses being provided by external means, and the stop impulses being provided by a timing circuit. The timing circuit operation is also initiated by the start impulse, and is effective to supply the stop pulse a predetermined time later than the next preceding start pulse, in a manner substantially independent of supply voltage variation. The timing circuit employs a multi-element semiconductor device, such as a silicon controlled switch or a silicon controlled rectifier, which is responsive to two voltages to provide the stop pulse. One of the two voltages varies directly with changes in supply voltage, and the other varies inversely with changes in supply voltage. These two effects tend to cancel, holding the time delay constant.

In order that the manner in which the foregoing and other objects are attained in accordance with the invention can be understood in detail, a particularly advantageous embodiment of the invention will be described with reference to the accompanying drawings, which form a part of this specification, and wherein:

FIG. 1 is a schematic diagram showing one advantageous embodiment of the invention; and

FIGS. 2A-D illustrate waveforms occurring at various points in the circuit of FIG. 1.

Referring now to the drawings, it will be seen that an electromagnetic relay, indicated generally at 1, is shown as the load device to be energized, one terminal of the relay coil being'connected to ground and the other terminal being connected to the cathode of a silicon controlled switch (SCS) 2, and also to the cathode of a semiconductor diode 7. The cathode gate of the SCS is connected to a start input pulse terminal 3, and the anode of the SCS is connected to a positive D.C. supply terminal 4. The anode gate of the SCS is connected to one terminal of a resistor 14 and also to one terminal of capacitor 15. The other terminal of capacitor 15 is connected to resistor 5 and the cathode of a second SCS 6. The other terminal of resistor 5 is connected to ground. The other terminal of resistor 14 is connected to positive D.C. supply terminal 4. The anode of SCS 6 is connected to one terminal of a resistor S, and also to the anode of diode 7, the cathode of a second diode 9, and to one terminal of a capacitance 10. The other terminal of capacitance 10 and the anode of diode 9 are connected to ground. The other terminal of resistor 8 is connected to positive D.C. supply terminal 4. The anode gate of SCS 6 is connected to one terminal of each of two resistors 11 and 12, the other terminal of resistor 11 being connected to positive D.C. supply terminal 4, and the other terminal of resistor 12 being connected to ground.

No connection is made to the cathode gate of SCS 6. It will be obvious to those skilled in the art that a unijunction transistor (UJT) could be employed in place of the SCS 6, the SCS being advantageous because of its superior switching characterstics.

Before operation of the subject circuit commences, SCS 2 and SCS 6 are both in their nonconductive states, and the capacitance 10 is held at a state of essentially Zero charge by the clamping action of diode 7 through the relatively low D.C. resistor of the load 1. Capacitor 15 is charged via resistors 14 and 5 with the polarity shown. Operation is initiated by the application of a start pulse to terminal 3, the start pulse being of positive polarity and of relatively short duration. The start pulse is shown at FIG. 2A, the assumption being made at this point that the maximum amplitude of the start pulse applied is just suflicient to cause SCS 2 to go into its high conduction state, the sequence of operation initiatingwhen the start pulse reaches that peak.

When SCS 2 begins to conduct, power will be supplied immediately to relay 1, the current flowing through the circuit formed by positive D.C. supply terminal 4, SCS 2, and the coil of relay 1 to ground being limited almost exclusively by the impedance of relay 1, the impedance of SCS 2 being substantially zero when that device is in its high conduction state. The voltage at junction 13, and therefore at the cathode of diode 7, will then increase nearly to the level of the positive D.C. source, this action being illustrated in FIG. 2C at the leading edge 20 of the pulse shown therein. Diode 7 will then be rendered nonconductive, and capacitor 10 will commence charging through the circuit from the positive D.C. supply terminal 4 through resistor 8 and capacitor 10 to ground. Capacitor 10 will charge in a period of time determined by the product of the values of resistor 8 and capacitor 10, this charge being represented by the curved portion 9 of FIG. 2B.

The voltage divider network formed by resistors 11 and 12 acts to hold the anode gate of SCS 6 at a relatively constant voltage level, assuming that the positive D.C. supply voltage remains constant, this reference voltage level being shown at FIG. 2B by the dotted line 16. When the charge across capacitance 10 increases to such a value that the voltage at the junction of resistor 8 and capacitance -10, this junction also being connected to the anode of SCS 6, reaches a level above that at which the anode gate of SCS 6 is held as indicated by line 16 of 3 FIG. 2B, SCS 6 will go into its highly conductive state, thereby discharging capacitor 10 very rapidly as indicated by portion 17 of the Waveform diagram of FIG. 2B. The voltage across C at this instant is indicated as V High current will then flow from DC. supply terminal 4, and through the circuit including resistor 8, SCS 6, and resistor 5 to ground, and also from capacitor 10, discharging through SCS 6 and resistor 5 to ground. This positive pulse passes through capacitor 15, thereby raising the voltage level at the anode gate of SCS 2 above the voltage at the anode of SCS 2 by an amount V for a short period of time, as shown in FIG. 2D. This short duration high voltage pulse will act to turn SCS 2 off, thereby terminating the current supply to the load device 1, as indicated by portion 18 of the Waveform diagram of FIG. 2C.

Diode 9 is inserted to absorb any inductive kickback from the load device, thereby preventing capacitor 10 from accumulating a negative charge.

As briefly described above, the duration of the pulse supplied to relay 1, represented by the space between portions 14 and 18 of the waveform diagram of FIG. 2C, is essentially independent of variations in the DC. supply voltage over a considerable range, including the intended operating voltage range for the relay 1. It will be clear that the period of time required for capacitor 10 to charge to a level sufiicient to initiate the turn-ofi pulse by placing SCS 6 in its conductive state will change with variation in the DO. supply voltage. That is, as the D.C. supply voltage provided to terminal 4 decreases, the time required for the voltage to traverse waveform portion 15, FIG. 2B, and to reach a predetermined voltage level will increase. However, it will also be seen that, by the action of the voltage divider circuit including resistors 11 and 12, as the voltage .at DC. supply terminal decreases, the voltage reference level at the anode gate of SCS 6 similarly decreases, thereby effectively lowering the dotted line 1 6 in FIG. 2B, i.e., the voltage necessary to cause SCS 6 to conduct. These two changes tend to counteract each other, and effectively mantain constant the period of time between the initiation of the charging cycle of capacitor 10 and its discharge. The time period between the waveform portions of FIG. 2C indicated at 14 and 18, and representing the width of the pulse supplied to the load device, therefore remains essentially constant.

As the DC. voltage supplied to terminal 4 is decreased, a point will be reached below which the system will not operate, simply because sufficient potentials will not be present to cause the silicon controlled switches to go into their conductive states. However, it will further be seen that proper silicon controlled switches and the resistors 8, 11 and 12 and capacitor 10 can be selected by one skilled in the art for any nominal value of DC. voltage as required by the particular relay used which will permit continued reliable operation without the need for special regulation of the DC. voltage supply. In general, electromagnetic relays are characterized by maximum and minimum current requirements, and also by a pulse width requirement, the pulse Width requirement being especially applicable to the more complex relay devices such as stepping switches and the like. Thus, given a relay having particular characteristics, to apply the subject invention the designer need only select the proper ones of commercially available silicon controlled switches and a nominal middle value of DC. supply voltage. The circuit will then provide the desired reliability in pulse duration over considerable variation of the supply voltage from the middle value selected, obviating the need for a regulated power supply.

Though one particularly advantageous embodiment of the invention has been chosen for illustrative purposes, it will be clear that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.

4 What is claimed is: 1. In apparatus for providing pulses of constant duration to a relay, the combination of a terminal to which unregulated positive DC voltage can be supplied, first circuit means having a first control terminal, a

second control terminal, and an output terminal,

said circuit means being operative to provide at said output terminal of said first circuit means an electrical pulse of a duration dependent upon the time between application of a start pulse to said first control terminal and a stop pulse to said second control terminal; capacitive circuit means; charging circuit means; means for preventing operation of said charging circuit means until a start pulse is applied to said first control terminal of said first circuit means; second circuit means operative to provide a reference voltage proportional to said positive D.C. supply voltage; and means responsive to charging of said capacitive circuit means to a predetermined voltage level and to said reference voltage provided by said second circuit means for supplying a stop pulse to said second control terminal,

said last mentioned means being operative to provide said stop pulse at a fixed time later than the next preceding start pulse when said D.C. supply voltage is within a predetermined range. 2. In an apparatus for supplying a pulse of predetermined duration to a relay device to energize the same, the combination of first switching means having an ON state and an OFF state and including a first control terminal to which a command pulse can be supplied, a second control terminal to which a stop pulse can be supplied, and an output terminal to which the relay device to be energized can be connected, said first switching means being operative to convert to its ON state in response to a command pulse supplied to said first control terminal and to convert to its OFF state upon application of a stop pulse to said second control terminal; and timing circuit means comprising second switching means, a capacitor, charging circuit means connected to said capacitor,

and clamping circuit means connected to prevent charging of said capacitor by said charging circuit means until a command pulse has been supplied to said first control terminal of said first switching means, said second switching means being connected to discharge said capacitor at a predetermined time after supply of the command pulse to said first control terminal of said first switching means, said timing circuit means being connected to supply a stop pulse to said second control terminal of said first switching means upon such discharge. 3. In a device of the type described, the combination of an electromagnetic relay device; first controlled asymmetrically conductive circuit means having a conductive state and a nonconductive state, said first controlled asymmetrically conductive circuit means 'being connected to energize said electromagnetic relay device when conductive; second controlled asymmetrically conductive circuit means having a conductive state and a nonconductive state;

first circuit means operative to render said first controlled asymmetrically conductive circuit means nonconductive when said second controlled asymmetrically conductive circuit means conducts; capacitive circuit means connected to be charged when said first controlled asymmetrically conductive circuit means is conductive; second circuit means for providing a reference voltage for said second controlled asymmetrically conductive circuit means; and third circuit means for impressing the voltage level at said capacitive circuit means on said second controlled asymmetrically conductive circuit means,

said second controlled asymmetrically conductive circuit means being operative to conduct when said volt-age level of said capacitor circuit means exceeds said reference voltage level provided by said second circuit means. 4. A relay energizing circuit comprising the combination of a first semiconductor switching device having a conductive state and a nonconductive state, and including an anode, a cathode, a first control electrode and a second control electrode; v an input terminal to which successive start pulses can be supplied,

said input terminal being connected to said first control electrode of said first semiconductor switching device, said first semiconductor switching device being rendered conductive when each of said pulses is applied to said first control electrode thereof; a second semiconductor switching device having a conductive state and a nonconductive state, and including an anode, a cathode and a control electrode; first circuit means connecting said cathode of said second semiconductor switching device to said second control electrode of said first semiconductor switching device, said first circuit means being operative to render said first semiconductor switching device nonconductive when said second semiconductor switching device is conductive; a supply terminal connectable to a source of positive DC. voltage; voltage divider means connected to said supply terminal for providing a reference voltage which is a substantially constant proportion of the voltage at said supply terminal,

said voltage divider means being connected to said control electrode of said second semiconductor switching device; a capacitor; a charging circuitfor said capacitor; second circuit means connecting said anode of said second semiconductor switching device to said capacitor and said charging circuit and operative to impress the voltage level of said capacitor on said anode of said second semiconductor switching device; first asymmetrically conductive circuit means connected to said cathode of said first semiconductor switching device and to said capacitor,

said first asymmetrically conductive circuit means being operative to hold said capacitor in a state of substantially no charge when said first semiconductor switching means is in a nonconductive state, and to electrically isolate said capacitor from said first semiconductor switching device when said first semiconductor switching device is in a conductive state;

a circuit portion for connecting a relay in series in the anode-cathode circuit of said first semiconductor switching device;

said capacitor being operative to accumulate a charge when said first semiconductor switching device is in a conductive state; and

said second semiconductor switching device being rendered conductive when said capacitor accumulates a charge sufiicient to raise the voltage level of said anode of said second semiconductor switching device above said relatively constant voltage level at said control electrode of said second semiconductor switching device.

5. In a device of the type described, the combination of an electromagnetic relay energizable by an electrical pulse of predetermined width and within a predetermined range of magnitude;

a first semiconductor switching device connected in series circuit relationship with said relay, and having a first control electrode to which a start command pulse can be applied, and

a second control electrode to which a stop comcommand pulse can be applied,

said first semiconductor switching device being operative to convert to a condition of substantially zero impedance when a start command pulse is applied to said first control electrode;

a terminal connectable to a source of variable D.C.

' voltage predetermined range of magnitude for supplying voltage to the series circuit of said relay and said first semiconductor switching device;

a second semiconductor switching device having an anode, a cathode and a control electrode;

a voltage divider circuit for providing a reference voltage to said control electrode of said second semiconductor switching device,

said reference voltage being a substantially fixed proportion of the voltage at said terminal and which varies in direct proportion to said voltage;

a capacitor; and

a charging circuit connected for charging said capacitor to the level of said reference voltage in a period of time substantially equal to the width of said electrical pulse when said voltage supplied to said terminal is within said predetermined range of magnitude.

References Cited by the Examiner UNITED STATES PATENTS 7/1965 Orsino 317l48.5 9/1966 Schreiner 307-88.5

Claims (1)

1. IN APPARATUS FOR PROVIDING PULSES OF CONSTANT DURATION TO A RELAY, THE COMBINATION OF A TERMINAL TO WHICH UNREGULATED POSITIVE D.C. VOLTAGE CAN BE SUPPLIED, FIRST CIRCUIT MEANS HAVING A FIRST CONTROL TERMINAL, A SECOND CONTROL TERMINAL, AND AN OUTPUT TERMINAL, SAID CIRCUIT MEANS BEING OPERATIVE TO PROVIDE AT SAID OUTPUT TERMINAL OF SAID FIRST CIRCUIT MEANS AN ELECTRICAL PULSE OF A DURATION DEPENDENT UPON THE TIME BETWEEN APPLICATION OF A START PULSE TO SAID FIRST CONTROL TERMINAL AND A STOP PULSE TO SAID SECOND CONTROL TERMINAL; CAPACITIVE CIRCUIT MEANS; CHARGING CIRCUIT MEANS; MEANS FOR PREVENTING OPERATION OF SAID CHARGING CIRCUIT MEANS UNTIL A START PULSE IS APPLIED TO SAID FIRST CONTROL TERMINAL OF SAID FIRST CIRCUIT MEANS; SECOND CIRCUIT MEANS OPERATIVE TO PROVIDE A REFERENCE VOLTAGE PROPORTIONAL TO SAID POSITIVE D.C. SUPPLY VOLTAGE; AND MEANS RESPONSIVE TO CHARGING OF SAID CAPACITIVE CIRCUIT MEANS TO A PREDETERMINED VOLTAGE LEVEL AND TO SAID REFERENCE VOLTAGE PROVIDED BY SAID SECOND CIRCUIT MEANS FOR SUPPLYING A STOP PULSE TO SAID SECOND CONTROL TERMINAL, SAID LAST MENTIONED MEANS BEING OPERATIVE TO PROVIDE SAID STOP PULSE AT A FIXED TIME LATER THAN THE NEXT PRECEDING START PULSE WHEN SAID D.C. SUPPLY VOLTAGE IS WITHIN A PREDETERMINED RANGE.

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