US3783368A

US3783368A - Process and circuit for the approximately continuous control by means of an electric on-off control

Info

Publication number: US3783368A
Application number: US00240543A
Authority: US
Inventors: P Dosch; D Dorsch
Original assignee: Heberlein and Co AG
Current assignee: Heberlein and Co AG
Priority date: 1972-04-03
Filing date: 1972-04-03
Publication date: 1974-01-01
Anticipated expiration: 1991-01-01

Abstract

Continuous control of an on-off-type A-C powered regulating system incorporating a thyristor switch is obtained by varying the switch activation threshold voltage repetitively at a rate the period of which is several times greater than the period of the supply voltage.

Description

O Umted States Patent 1 1 1111 3,783,368

Dosch et al. Jan. 1, 1974 PROCESS AND CIRCUIT FOR THE 3,493,846 2/1970 Tyley 321/16 APPROXIMATELY CONTINUOUS 3,243,689 3/1966 Perrins 323/22 SC 3,340,460 9/1967 Clarke et al. 323/22 SC CONTROL BY MEANS AN ELECTRIC 3,579,096 5/ 1971' Buchanan, Jr. 323/22 SC ON-OFF CONTROL 3,582,763 6/1971 Huber 323/22 sc x [75] Inventors: Peter Dosch, Jona; Dieter Dorsch,

Ebnat-Kappel, both of Switzerland Primary Examiner-Gerald Goldberg [73] Assrgnee: l-leberlem & Co. AG., Wattw1l, 1n

the Canton of St. Gall, Switzerland Attorney Joseph Fltzpamck et [22] Filed: Apr. 3, 1972 [21] App]. No.: 240,543

[5 7] ABSTRACT [52] US. Cl 321/18, 323/22 SC, 323/38,

307/2 3 Continuous control of an on-off-type A-C powered 51 1111. c1 ..r102m 7/20, G05f 1/64 regulating System incorporating a thyristor Switch is [58] Field of Search 307/252 .1, 252 N, Obtained y y n the switch activation threshold 307 2 3 2 4; 321 1 13; 323 22 5 31 33 voltage repetitively at a rate the period of which is several times greater than the period of the supply [56] References Cited Voltage- UNITED STATES PATENTS 3,185,912 5/1965 Smith et al 321/18 16 Claims, 3 Drawing Figures YVIVA PROCESS AND CIRCUIT FOR THE APPROXIMATELY CONTINUOUS CONTROL 'BY MEANS OF AN ELECTRIC ON-OFF CONTROL The present invention relates to the substantially continuous control of an A-C powered electrical regulator system; and more particularly it concerns an electric on-off control which incorporates an electric switch activated by control impulses. The control impulses are themselves controlled in amplitude by the action of a sensor which responds to' conditions affected by the regulator system. Each control pulse whose amplitude lies above a predetermined threshold value, serves to activate the electrical switch for the particular half wave of the A-C power in which the particular control pulse is produced. Control processes are known in which a thyristor operated by alternating voltage receives control impulses, the amplitude of which is so-determined by the sensor of the control circuit that ignition of the thyristor and current flow through the controlled member, to which current is fed by the thyristor, occurs only if a control deviation from a predetermined norm occurs. In spite of the advantage which this process offers, particularly because of the possibility of contact less control of the thyristor by the sensor, it has proved desirable to convert the on-off control with its swing-over tendency and dead times into an approximately continuous control while maintaining the impulse control of the thyristor operated as a switch.

According to the present invention, this problem is resolved in a simple way by periodically shifting or oscillating between a minimum and maximum value, the threshold value at which activation of the switch takes place.

By varying the switch activator threshold value in this manner, as the control deviation becomes smaller, a correspondingly smaller number of the control pulses whose amplitudes are influenced by the sensor, produces ignition of the thyristor; so that the energy content of the controlled electric variable values is continuously controlled without thereby essentially increasing circuit complexity and without permitting the appearance of the highfrequency disturbances of a phase-out control.

According to the present invention, quite generally, the comparison of the control voltage amplitude with a periodically varying voltage amplitude is important, this periodically varying voltage being used advantageously for threshold value activation of the switch. It is, however, not important in practical application whether impulses lying regularly either above or below the threshold value are used for activation of the switch. It is also within the scope of the invention to I allow the threshold value to rise periodically and gradually from minimum to maximum or to reduce the same gradually from maximum to minimum;

The process of the present invention can be realized in a particularly simple manner by means of a system which includes a control circuit for delivering control pulses to the switch. One of the inputs of the control circuit is connected to receive signals from the sensor while the other input is fed with periodically alternating voltage by a generator, for example a sawtooth generator. The control circuit also includes means for producing switch activating pulses only when sensor impulses of a certain minimum amplitude are produced, the limit value of those impulses being determined by the momentary value of the generator voltage. The switch itself preferably comprises a thyristor having its control electrode connected with the output of the control circuit.

In a system as described above, a trigger circuit for switch activating pulse production may be coupled to the control curcuit in a manner such that the coupling between the control circuit and the trigger circuit is determined by the sensor as a function of control deviation. In such an arrangement, the periodically varying threshold value can be obtained in a particularly simple manner if the control circuit is an amplifier, preferably a transistor amplifier for the periodically oscillating voltage supply of which the sawtooth generator is provided. A good control constancy, even under variations in supply voltage, can be obtained according to the present invention by connecting the trigger circuit and the sawtooth generator with the same voltage source so that, while the supply voltage diminishes simultaneously with the trigger pulses, such a reduction of the sawtooth voltage occurs that the impulse diminution is compensated by the threshold value increase of the transistor amplifier.

The present invention, therefore, assures in a most simple way, a continuous control without swing-over and dead periods, the new combination and subcombinations of the described features being particularly advantageous.

There has thus been outlined rather broadly the more important features of the invention in order that the detail description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several purposes of the invention. It is important, therefore, that the claims be regarded as including such equivalent construction as do not depart from the spirit and scope of the invention.

A specific embodiment of the invention has been chosen for purposes of illustration and description, and is shown in the accompanying drawings, forming a part of the specification wherein:

FIG. 1 shows a block diagram ent invention,

FIG. 2 shows a diagram of the essential voltage and current curves; and

FIG. 3 shows a detailed diagram of an arrangement with the features of the present invention.

According to FIG. 1, a bridge rectifier 2 is connected with a voltage source (not shown) via a resistor l which serves as a control member. The bridge rectifier 2 furnishes operating voltages for a sawtooth generator 3, an impulse producer 4 and a control circuit 5. The output of the bridge rectifier 2 is also bridged by thyristor 6 so that, upon ignition of the thyristor, the resistor I receives a current of corresponding intensity.

The impulse producer 4 delivers, at the beginning of each half wave of the voltage source, impulses to the control circuit 5. The amplitudes of the impulses are controlled by a sensor 7, which senses conditions relating to the operation of the control member 1. Thus, for

of a circuit of the presexample, where the control member 1 is a heater, the sensor 7 may be a temperature sensing element. If the pulses controlled by the sensor 7 lie above a certain threshold value, the control circuit 5 delivers ignition impulses to the thyristor 6. The magnitude of the threshold voltage is determined by the momentary output voltage of the sawtooth generator 3. This threshold value increases while the generator voltageincreases so that, for example, impulses of small amplitude effect ignition of the thyristor 6 at the beginning of the sawtooth whereas they are suppressed while the generator voltage increases. These associations are shown in FIG. 2 as a function of time. In FIG. 2 U 8 represents the output voltage of the rectifier bridge circuit 2, U E represents (at various points taken at random along the solid portion of the abscissa) the voltage impulses produced by the impulse producer 4 and modified by the sensor 7, U represents the sawtooth voltage output of the generator 3 and I represents the current flow through the resistor 1. As can further be seen in FIG. 2, the number of current half waves flowing through resistor l continuously diminishes as the control impulses become smaller, i.e., as the control deviation diminshes, whereby nearly continuous control is obtained.

FIG. 3 shows a circuit diagram of an arrangement in which the impulse imparter 4 is formed by a Schmitt trigger consisting of complementary transistor 10 and 11 as well as Zener diode 12.

Resistors

20, 21, 22 serve to produce pretension whereas a condenser 23 assures voltage supply during zero passages of supply voltages. The output pulses produced by the Schmitt trigger are fed to an input resistor 25 of the control circuit 5 through a primary winding 13a and a secondary winding 13b of a transformer 13. The coupling factor of transformer 13 is controllable by the sensor 7. The sawtooth generator 3 contains, as time-determining member, a condenser 14 and a four-layer diode 15 which thus control the base voltage of a transistor 16 via a series resistor combination 24, so that a periodical sawtooth impulse is delivered to the collector of a transistor 17 in the control circuit 5. This periodical increase of collector potential effects sinking of the output signal through a resistor 26 at a constant input signal. As a result, the ignition impulses delivered to the thyristor 6 through a transistor 18, used as a neutral stage via a potentiometer l9, diminish below the threshold value necessary for ignition. A condenser 27 assures the voltage supply of the control circuit 5 after ignition of the Schmitt trigger.

Having thus described the invention with particular reference to the preferred form thereof, it will be obvious to those skilled in the art to which the invention pertains, after understanding the invention, that various changes and modifications may be made therein without departing from the spirit and scope of the invention, as defined by the claims appended thereto.

What is claimed is:

l. A method of obtaining continuous control of an A-C powered electrical circuit in which a switch is provided to control A-C current flow through a control element in response to trigger voltages above a threshold voltage level, said method comprising the steps of connecting said control element in series with an A-C source and the input nodes of a full wave rectifier bridge, and connecting said switch in series with the output nodes of said bridge, generating trigger voltages having amplitudes which vary in proportion to a sensed deviation of said control element, varying said threshold level between a minimum and maximum level at a constant rate the period of which is several times greater than the period of applied A-C voltage variation, and applying only said trigger voltages which are larger than said threshold level to said switch.

2. A method according to claim 1, wherein said threshold level is varied according to a sawtooth pattern.

3. A method according to claim 1, wherein said trigger voltages are generated upon each reversal of voltage direction produced by applied A-C electricl power.

4. A method according to claim 1, wherein said step of applying only said trigger voltages which are larger than said threshold level to said switch is performed by electrically summing the trigger voltages and a generator voltage which varies alternately at a rate the period of which is several times greater than the period of applied A-C voltage variation.

5. A system for obtaining continuous control of an A-C powered electrical circuit in which a switch is provided to control current flow through a control element in response to trigger voltages above a threshold voltage level, said system comprising a full wave rectifier bridge having a pair of input nodes and a pair of output nodes, and having said control element connected in series with an A-C source across said input nodes and said switch connected across said output nodes, means for generating trigger voltages having amplitudes which vary in proportion to a sensed deviation of said control element, means for generating a threshold voltage which varies between a minimum and maximum level at a constant rate the period of which is several times greater than the period of applied A-C voltage variations, and comparison means connected to said trigger voltage and threshold voltage generating means for applying only said trigger voltages which are larger than said threshold level to said switch.

6. A system according to claim 5, wherein said means for generating said threshold voltage comprises a sawtooth voltage generator.

7. A system according to claim 5, wherein said means for generating trigger voltages comprises an impulse generator operative to generate a voltage impulse in response to each reversal of applied A-C electrical power.

8. A system according to claim 7, wherein said means for generating trigger voltages further comprises means for controlling the amplitude of each voltage impulse in response to a sensed deviation of said control element.

9. A system according to claim 5, wherein said switch is a thyristor having a control electrode coupled to said comparison means.

10. A system according to claim 5, wherein said means for generating trigger voltages comprises an impulse generator operative to generate a voltage impulse in response to each reversal of applied A-C electrical power, and variable coupling means for coupling said voltage impulses to said comparison means.

11. A system according to claim 5, wherein said comparison means comprises a transistor amplifier connected such that its voltage supply is received from said threshold voltage generating means and its signal input is received from said trigger voltage generating means.

12. A system according to claim 5, further comprising a voltage supply conncted in common to said means for generating trigger voltages and said threshold voltage generating means so that, upon variations in said common voltage supply, mutually compensating voltage changes occur in said means for generating trigger voltages and in said threshold voltage generating means.

13. A method according to claim 1, wherein said step of generating trigger voltages having amplitudes which vary in proportion to a sensed deviation of said control element is performed by generating a trigger pulse upon each reversal of voltage direction of said A-C power, applying said trigger pulses to the primary of a transformer, and producing the said trigger voltages at the secondary of the transformer by varying the coupling between the transformer primary and secondary of the transformer'in proportion to a sensed deviation of said control element.

14. A method according to claim 13 further comprising the step of supplying power for generating said tn'gger voltages and threshold voltage from a common power supply. 82

15. A system for continuously controlling the quantity of A-C power applied to a control element comprising: a full wave rectifier bridge having a pair of A-C inputs and a pair of D-C outputs; a control element for connection in series with said A-C inputs across an A-C source; an electronic switch having a pair of principal conducting electrodes and a control electrode, and

having its principal conducting electrodes connected across said D-C outputs; means for generating trigger voltages at twice the frequency of said A-C source, said trigger voltages having amplitudes which vary in proportion to a sensed deviation of said control element; means for generating a threshold voltage which varies between a minimum and maximum level at a constant rate the period of of which is several times greater than the period of applied A-C voltage variations; and comparison means connected to said trigger voltage and threshold voltage generating means for applying only said trigger voltages which are larger than said threshold level to said control electrode for actuating said switch to provide an A-C current path through said control element.

16. A system as set forth in claim 19, wherein said means for generating trigger voltages comprises an impulse generator connected across said D-C outputs and being operative to generate a voltage impulse in response to each reversal of applied A-C electrical power, and variable coupling means for coupling said voltage impulses to said comparison means, and wherein said comparison means comprises a transistor amplifier connected such that its voltage supply is received from said threshold voltage generating means,

generating means.

UNITED STATES PATENT OFFICE CERTIFICATE OF- CORRECTION Patent NO. ,368 Dated January 1 1974 Inventor) DOS CH and DIETER DORSCH It is certified that error appears in the above-identified patent and that saidLetters Patent are hereby corrected as shown below:

Front page, below "[21] Appl No. 240,543", insert [30] Foreign Application Priority Data A ril's, 1971 Switzerland 4959/71 Column 1, line 45, change "phase-out" to phase-cut Column 2, line 8, change "curcuit" to circuit line 32, change "tail" to tailed-.

Column 3, line 3, change "pulses" to impulses line 27, change "transistor" to transistors line 56, change "thereto" to hereto Column 4, line 12, change "electricl" to electrical line 67, change "conncted" to connected Column 5, line-21, delete "82". Column 6, line 8, delete "of" (second occurrence);

line 16, change claim 19," to claim 15,

Signed and sealed this 2nd day of July 1974 (SEAL) Attest:

EDWARD M. FLE TCHER,JR. C-MARSHALL DANN Attesting Officer Commissioner of Patents FORM (10.69) I USCOMM-DC wave-p09

Claims

1. A method of obtaining continuous control of an A-C powered electrical circuit in which a switch is provided to control A-C current flow through a control element in response to trigger voltages above a threshold voltage level, said method comprising the steps of connecting said control element in series with an AC source and the input nodes of a full wave rectifier bridge, and connecting said switch in series with the output nodes of said bridge, generating trigger voltages having amplitudes which vary in proportion to a sensed deviation of said control element, varying said threshold level between a minimum and maximum level at a constant rate the period of which is several times greater than the period of applied A-C voltage variation, and applying only said trigger voltages which are larger than said threshold level to said switch.

12. A system according to claim 5, further comprising a voltage supply connected in common to said means for generating trigger voltages and said threshold voltage generating means so that, upon variations in said common voltage supply, mutually compensating voltage changes occur in said means for generating trigger voltages and in said threshold voltage generating means.

13. A method according to claim 1, wherein said step of generating trigger voltages having amplitudes which vary in proportion to a sensed deviation of said control element is performed by generating a trigger pulse upon each reversal of voltage direction of said A-C power, applying said trigger pulses to the primary of a transformer, and producing the said trigger voltages at the secondary of the transformer by varying the coupling between the transformer primary and secondary of the transformer in proportion to a sensed deviation of said control element.

14. A method according to claim 13 further comprising the step of supplying power for generating said trigger voltages and threshold voltage from a common power supply.

15. A system for continuously controlling the quantity of A-C power applied to a control element comprising: a full wave rectifier bridge having a pair of A-C inputs and a pair of D-C outputs; a control element for connection in series with said A-C inputs across an A-C source; an electronic switch having a paiR of principal conducting electrodes and a control electrode, and having its principal conducting electrodes connected across said D-C outputs; means for generating trigger voltages at twice the frequency of said A-C source, said trigger voltages having amplitudes which vary in proportion to a sensed deviation of said control element; means for generating a threshold voltage which varies between a minimum and maximum level at a constant rate the period of which is several times greater than the period of applied A-C voltage variations; and comparison means connected to said trigger voltage and threshold voltage generating means for applying only said trigger voltages which are larger than said threshold level to said control electrode for actuating said switch to provide an A-C current path through said control element.

16. A system as set forth in claim 19, wherein said means for generating trigger voltages comprises an impulse generator connected across said D-C outputs and being operative to generate a voltage impulse in response to each reversal of applied A-C electrical power, and variable coupling means for coupling said voltage impulses to said comparison means, and wherein said comparison means comprises a transistor amplifier connected such that its voltage supply is received from said threshold voltage generating means, and its signal input is received from said trigger voltage generating means.