DE2319552A1 - POWER SOURCE FOR HAND WELDING - Google Patents

Description

PATENT LAWYERS

. DR. IUR. 'D I P i _.- 1N Θ.

VOLKER BUSSE DIETRICH BUSSE

45 OSNABRÜCK, April 17, 1973

MOSERSTRASSE 2Ο / 24 VB / bottle

Company Kjellberg-Esab GmbH 2319552

'565 SOLINGEN, Beethovenstrasse 135-139

• Power source for manual welding

The present invention relates to a power source intended for hand welding with covered electrodes with sharply decreasing voltage-current characteristics, consisting of a three-phase transformer with a low magnetic level Scattering (low reactance), a three-phase rectifier connected to its secondary winding with controlled Valves, an ignition angle sensor for generating ignition pulses that control the valves, their phase position through the size of a supplied to the ignition angle sensor, consisting of a direct current or a direct voltage Control signal is determined, and a control signal generating control signal generator, which means for producing a constant, adjustable first component (basic component) of the control signal and means including a link for taking the actual welding current value, for the production of a second component that acts against the basic component and is proportional to the welding current of the control signal.

309844/0475

The fact that the current source has a sharply falling characteristic is to be understood here as meaning that the short-circuit current / arc current ratio must not exceed 1.5.

The valves of the three-phase rectifier do not all need to be controlled. As is known, a controlled one is sufficient Provide valve in each of the phase branches. ^.

In a power source of the type specified above described in U.S. Patent No. 3,530,359, the adjustable basic component of the control signal obtained by the combination of two subcomponents, each of which can be set individually. There are an adjusting member for one of the subcomponents and two adjusting members independent of one another and from said adjusting member intended for the second sub-component. One of these setting members is also used to set the slope of the characteristic curve the current source by adjusting the ratio between said second component of the control signal and the Actual welding current value. If the, welder a certain If you want to set the welding current and a certain inclination of the characteristic curve, he must therefore use three different setting elements operate, which is practically awkward. The welder therefore tends to close the characteristic curve with a constant incline work and only adjust the amperage, but this reduces the welding properties, at least in certain ways Will cause sharing of the current range of the power source. ·

3 0 9 8 4 4 / 0475-

The invention is based on the knowledge that man-bet Adjustment of the working current the best on average Welding properties with a certain inclination (steepness) of the static and / or dynamic ones corresponding to this setting Receives characteristic curve of the power source, d. H. that it is possible to establish a certain, favorable correlation between the current intensity setting and the static and / or dynamic characteristic curve of the power source. The invention is thus in the first Spaces based on a design of the power source that allows such a correlation to be maintained automatically

A first embodiment of the invention is characterized in that that the control signal generator also comprises means for introducing a third component of the control signal, which is the actual value is equal to the welding voltage multiplied by a second proportionality factor, as well as a term for setting the ratio between the second and the first proportionality factor, which member is coupled to the member for adjusting the basic component, thus between that by the basic component certain current setting and the slope of the (static) characteristic curve a certain correlation automatically is maintained.

A second embodiment of the invention is featured in that the control signal generator comprises the following means in addition to the means specified at the beginning:

3 Oi: 8 ί / i / CU 75

a. Means for introducing a third component of the control signal which multiplies the actual value of the welding voltage is equal with a second constant of proportionality,

b. a series connection of a capacitor and a resistor, which series connection the welding voltage or a voltage reflecting the changes in the welding voltage is hung up,

c. Means for producing a fourth component of the control signal, which of the voltage occurring between the ends of the resistor multiplied by a third proportionality factor is the same and which interacts with the basic component when the capacitor is discharged, and

d. a member for setting the ratio between the third and the first proportionality factor, which member is coupled to the element for adjusting the basic component, so that between that determined by the basic component Current setting and the slope (steepness) of the dynamic characteristic curve of the current source a certain correlation automatically is maintained.

A preferred embodiment of the invention combines the characteristics of the two forms of execution given above, so that both the steepness of the static characteristic and the size the grant that occurs temporarily in the event of a short circuit Sum static short-circuit current is automatically in the desired Weis · ® change with the setting of · Stroasfcärfc © »

309 844/04

- 5 -
2319552 1 a circuit diagram of an embodiment of FIG , T at a three-phase network can be connected and to its the Invention will now be explained in more detail with reference to the accompanying drawings Invention, Secondary winding a rectifier 2 with controlled valves be explained. Show it: la
Ib one modification of the circuit diagram of FIG. 1, Fig. 2a - e Diagrams showing the with the device according to Fig.l illustrate available characteristics, Fig.
and 3 a circuit diagram of a second embodiment Fig. the invention, 4th a voltage-current diagram showing the effect Fig. as the power source of Fig. 3 illustrates, 5 a circuit diagram of a third embodiment Fig. the invention, 6th a voltage-current diagram showing the effect Fig. way of the power source of Fig. 5 illustrates, 6a a corresponding voltage-current diagram for a Fig. modified design of the power source of FIG. 5, 7th a circuit diagram for one of the ignition angle sensors Fig. Power source of FIGS. 5, and 8th Stress-time diagrams for stresses which are in Fig. certain points of the circuit diagram of FIG step. Fig. in Fig. 1 shown welding power source consists of a turn Current transformer 1 with low reactance, its primary terminals R, S the

44/0475

closed is. A welding circuit connected to the output terminals of the rectifier contains an inductor 3 in series with a welding electrode 4 and the workpiece 5. A freewheeling diode 6 is connected between the end of the inductor winding connected to the rectifier and the other welding current conductor. The rectifier 2 is controlled by an ignition angle transmitter 7, which sends a series of ignition pulses to the ignition electrodes of the controlled valves in a known manner. The phase positions of the said pulses, which are synchronized with the mains voltage, are controlled by a control signal which is fed to the ignition angle transmitter by an amplifier device 8. A summing circuit consisting of four resistors 9, 10, 11, 12 is arranged at the input of the amplifier device. The resistor 12 is connected to a slide or some other adjustable tap 13a of a potentiometer 13 connected to a constant voltage source Ik. The resistor 12 is thus traversed by a constant current, the size of which can be adjusted by means of the potentiometer tap 13a. The resistor 9 is connected to one end of the shunt resistor 15 connected to a welding current conductor and a current proportional to the welding current flows through it. The resistor 11 is by means of a switch

16 to one or the other of the two adjustable taps 17a, 17b of a potentiometer connected to the welding voltage

17 can be connected and a current proportional to the welding voltage flows through it. The ones labeled "P" Points of the circuit diagram are interrelated by not shown The means are galvanically connected and set the zero potential of the

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Control signal transmitter. The currents flowing in resistors 9, 11, 12 are algebraically summed. The polarities are chosen such that the S "currents in resistors 9 and 11 counteract the current in resistor 12. In the present case The negative polarity became the trap for the constant component of the control signal which can be set by means of the potentiometer 13 selected, since the amplifier device 8 is assumed to be inverting or pole-reversing, d. H. an output voltage whose polarity is opposite to that of the input voltage. '

The fourth resistor 10 of the summing circuit can be connected by means of the switch 10 to one or the other of the two adjustable taps 19a, 19b of a potentiometer 19, which is connected to a voltage that varies with the charging or discharging current of a capacitor 20 by a circuit described below . The capacitor is connected in series with a resistor 21 to the welding voltage. In the steady state, the capacitor branch is de-energized, so that the taps 19a, 19b are de-energized and the resistor 10 is de-energized. In the steady state, the input voltage of the amplifier device 8 and thus also its output voltage consist of a constant component minus the sum of a component proportional to the sum of the current and a component proportional to the voltage. The control signal composed in this way is fed to the ignition angle transmitter 7 and determines the phase position of the sin impulses transmitted to the rectifier 2 and synchronized with dsr iJ ^ taspiuiiiung & n. Bear coupling of the force and tension described by oils

308844/047?

the rectifier receives a falling static characteristic, the position of which depends on the setting of the potentiometer taps 13a and 17a or 17b, in such a way that the setting the potentiometer tap 13a determines the size of the short-circuit current, while the setting of the tap 17a or 17b of the potentiometer 17 determines the steepness of the characteristic.

According to the invention, the three taps or slides 13a, 17a, 19a coupled to one another by means of a member, so that each setting of the tap 13a has a specific setting each corresponds to the taps 17a, 19a. When the switch 16 is in the is the lower position shown, thus for each short-circuit current determined by the position of the tap 13a a certain, slope or steepness of the static characteristic curve determined by the position of the tap 17a. In the embodiment according to FIG. 1, the steepness of the characteristic curve decreases as the current setting increases in the entire setting range (provided that switch 16 is in the lower position shown). How on Junten explained with reference to FIG. 3, but it will sometimes be useful to initially use the

to
Decrease / let the slope of the characteristic curve decrease, but from a certain current level a constant slope or even an increasing slope at the highest current settings must be provided. FIGS. La and lb show examples of devices for bringing about such a change in the slope. These figures each show a modification of that part of the circuit according to FIG. 1, which lies between points r, s and t. In the embodiment according to Fig. La, the tension-sensitive

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At the end of the potentiometer 17, a contact sleeve 23, which is part of the contact path of the slide 17a. The relationship the welding voltage-dependent one set by means of the slide 17a The component of the control signal for the welding voltage thus initially increases with the current setting, but remains constant when the slide 17a enters the part of the contact path formed by the contact sleeve 23 .. In the execution according to Pig. Ib connects to the live end of the potentiometer 17 a contact sleeve 24 to which in turn a second potentiometer 17 is connected, the distal end of which is at zero potential. The slide 17a is here along the entire length from the potentiometers 17 and 17 'and the one in between Contact sleeve 24 formed potentiometer unit movable. When the slide 13a of the potentiometer 13 in the direction of low is displaced after high current settings, the slide coupled to the slide 13a by means of the member 22 moves 17a first along the potentiometer 17, the relationship between the voltage-dependent component of the control signal and the welding voltage is increased, thereafter along the contact sleeve 24, said ratio remaining constant, and finally along the potentiometer 17 '* where the ratio is decreased again. The steepness of the characteristic curve of the power source will thus initially decrease, then remain constant in a certain current setting range and at the increase again at the highest current settings.

The potentiometer 19 is connected to the series resistor 21 of the capacitor 20 by means of a switch 108. In the lower

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In the position of the switch, a rectifier bridge 18l is switched on between the resistor 21 and the potentiometer 19. It is first assumed that the switch 180 is in the position shown and that the welding voltage across the series circuit of the capacitor 20 and the resistor 21 suddenly drops, e.g. B. as a result of a short circuit between the welding electrode k and the workpiece 5 · Through the resistor 21 an .Ent lade current will flow in the direction indicated by the arrow to the left of the resistor 21. The upper end of the resistor 21 and thus also of the potentiometer 19 thus get a negative potential during the duration of the discharge of the capacitor 20. Through the movable tap 19a of the potentiometer 19 and the resistor 10, a component is fed to the control signal which corresponds to that of the Setting the tap 13a cooperates corresponding basic component. In the event of a sudden increase in the welding voltage, a transient, additional control signal component that is opposite to the basic component is formed in a corresponding manner. The device described thus results in a transient control signal component both with a sudden increase and with a sudden decrease in the welding voltage, which, while it is present, reduces the static slope set by means of the potentiometer 17. In the event of a short circuit between the electrode and the workpiece, a transient addition to the short circuit current strength determined by the static characteristic is obtained, which facilitates the ignition of the arc. On the other hand, the transient control signal component that occurs when the short circuit is cleared causes the arc current intensity to begin with

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is smaller than the static working current strength corresponding to the intersection of the static characteristic and the arc characteristic In many cases, this transient reduction in the operating current did not have a noticeably harmful effect, but it did has no useful purpose and must be viewed as undesirable. To eliminate this disadvantage, the circuit of Fig. 1 is with two alternative means of preventing the transient drop-down of the arc current. One of these means consists of a synchronizing valve 183, which is switched on in parallel with the potentiometer 19 by means of a switch 182 can and is polarized so that the generated by a charging current through the resistor 21 (which flows in the opposite direction to the arrow) Voltage acts in the forward direction of valve I83. The valve I83 thus switches off in the event of a sudden increase in the welding voltage a short circuit of the potentiometer 19, so that the transient control signal component is suppressed-d. When climbing of the welding voltage, the power source will follow the static characteristic curve, while in the event of a short circuit, the the desired transient supplement to the static short-circuit current gets. The rectifier bridge I8I which is the second of the above said alternative means and which is switched on by the fact that the switch I80 in the lower position causes a pole reversal of the voltage supplied to the potentiometer 19 in the event that a charging current flows through the resistor flows. The potential caused by a change in the welding voltage at the upper end of the potentiometer 19 is thus always negative, regardless of whether the change in question is an increase or a decrease. It follows that the sudden

3 0 3 8 44/04 7 5

Voltage drop occurring transient control signal components such as earlier a transient decrease in the steepness of the characteristic curve brings about, while the transient control signal component that occurs in the event of a sudden increase in voltage is the opposite brings about a transient increase in the steepness of the characteristic curve. It follows that after a short circuit has been removed between the electrode and the workpiece, the control signal generator creates an arc current intensity for the duration of the transient component which is greater than the one corresponding to the intersection of the static characteristic and the arc characteristic Amperage is. This effect makes it easier for the arc to burn for a few moments after it has been ignited.

The resistor 21 is connected in series with a Zener diode

184 and a rectifier diode 85 connected in parallel. the the latter is polarized in such a way that it blocks voltages caused by a charging current through resistor 21 caused. Opposite voltages in the other direction, corresponding to the discharge of the capacitor 20, the diode is

185 permeable, so that the entire voltage is applied to the Zener diode .184. The same serves as a voltage limiter to prevent the voltage occurring at the resistor 21 in the event of a short circuit between the electrode and the workpiece from exceeding a predetermined amount. The amount in question is considerably lower than the idling thus voltage of the current source _s afoei ³ is slightly above the normal range dss Bogenspanmmgen "The arrangement Üewlrkt limiting dss maximum amount that transiently en voltage ₃ which the Pofcenfcloriie'cer 19 b®i a course

3 0 984_4 / 0475 _____________

Circuit between the electrode and the workpiece is supplied, and thus also a limitation of the corresponding transient component of the control signal. This limitation is desirable for the following reason. The proportional ratio of the transient control signal component set by means of the tap 19a or 19b is dimensioned such that in the event of short-circuits during welding, ie in the event of a sudden drop in the welding voltage from the arc voltage to zero, an appropriate, transient increase in the short-circuit current intensity is obtained. In the event of a short circuit from the de-energized state, i.e. when the arc is ignited for the first time or after an accidental extinguishing during welding, a significantly larger voltage jump occurs (from the open circuit voltage to zero) and thus a larger discharge current through the resistor 21 . Without the zener diode 18 ¹ I, this high discharge current would bring about a corresponding increase in the transient control signal component and thus also a transient increase in the short-circuit current intensity to an undesirably high amount.

The diagrams of FIGS. 2a to 2e are intended to illustrate the operation of the Illustrate the device according to Fig. 1 or la and Ib. Fig. 2a emphasizes that switch 16 is in the down position. The static characteristic curves 190 have an increasing Short-circuit currents decreasing steepness. The line 191 is the characteristic curve of the power source when it is fully controlled Rectifier valves and has a slight inclination, which is caused by the inevitable voltage drops in the transformer 1 and caused in rectifier 2. Fig. 192 is a through

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Fast arc characteristic for covered hand welding electrodes.

FIG. 2b schematically shows a family of characteristic curves which are obtained with the schema variant according to FIG. La. With low currents, as in FIG. 2a, there is a decreasing slope with an increased current setting. For higher current settings at which the slide 17a touches the contact lens, there are characteristic curves 193 ^with constant steepness.

FIG. 2c schematically shows a family of characteristic curves which are obtained with the schema variant according to FIG. Ib. The characteristic curves here initially show an increase in the current setting decreasing slope (19 * 0 on, then in a certain Current setting range (corresponding to the movement of the slide 17a along the contact sleeve 24) a constant slope (194-195) and in the upper part of the current setting range an increasing slope when setting higher currents (196) corresponding to the movement of the slide 1.7a along the potentiometer 17 ''

In the cases described above in connection with FIg * 2a to c the switch, 18 can either assume its lower position shown, the proportional relationship between the transient The control signal component and the entire ..voltage occurring at the resistor are automatically adjusted with the current setting changes, or take its upper position in which said Ratio a constant, from the position of the tap

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19b has a certain value.

In FIG. 2d, in addition to some static characteristic curves 197 and an arc characteristic curve 198, the dynamic characteristic curves occurring during short circuits during visual welding, which correspond to the translent component of the control signal occurring during short circuit, are shown with dashed lines. It was assumed that the switch 18 is in the lower position, so that the proportional ratio of the transient component is increased when higher currents are set, and that the switch 16 is in the upper position, in which the characteristic curves have a constant, have a steepness determined by the tap Ub ».

. The left-2e in Fig together ni ⁵ "- ^ ner static characteristic dynamic characteristics ΊΟΊ shown 199 Π 02 ■ ^;.... ·· 5 m with a device according to Fig 1 in the case srhaltöii- when the Sehalter upper in the The position is until the switch 182 is open. It is assumed that the arc is burning with a current and a voltage which are determined by the intersection point A of the static characteristic curve and the arc characteristic curve 200, and that a sudden short circuit has occurred einenfeetrag I ". _s at which the sum of by the

Ov

static characteristic curve of seared Ku ^ sschlussati-oines and the through

j represents the transients control signal kciiipone?; "* received from the tap 19s, vsiage at tr-ansiU- O ^ · S ^ -uaauaöhrisses . The

er.ts'srer-hsr.-de dynaniis she ¥ .ύ:.:> ^: λί: Λ,?. . is designated as 201 . . 202 loading j ζεί-Glinst i: e entsprecliends ύ: / ΐ ': "" ΊΪ2 ~ - ~ <Zemilinie ie in the picked "3 U ö G ^ 4/0 4> ΰ

a short circuit (assuming that the duration of the short circuit was sufficient to remove the transient component of the Short-circuit current to decay). The transient component of the control signal that occurs when the voltage rises rapidly temporarily sets an operating current that is lower than that of operating point A.

Following the static characteristic curve 203, a corresponding Illustrates operation in the event that switch 182 is closed. At the moment of a short circuit, a dynamic characteristic curve and a corresponding power supply, which match those of the case just described are identical. The removal of the short circuit does not, however, cause a transient component of the control signal, because the rectifier valve 183 now causes a voltage to appear on the potentiometer 19 prevented.

Following the static characteristic curve 204, the basic appearance of the dynamic characteristic curve 205 or 206 that occurs at the moment of the short circuit or when the short circuit state is canceled is shown in the event that the switch 180 assumes its lower position. Due to the already explained effect of the rectifier bridge I8l vLrd, the transient components of the control signal both in the event of a short circuit and in the removal of the short circuit act in such a direction that the current intensity is higher than that indicated by the static characteristic.

309844/0475

The dynamic characteristic curves 208, 209 connected to the static characteristic curve 207 are intended to illustrate the effect of the zener diode 184. 208 is the one when shorting out a burning one The dynamic characteristic curve that occurs during the arc, while 209 the dynamic characteristic curve that occurs in the event of a short circuit from the de-energized state Characteristic is. The transient component of the control signal occurring in the latter case is not proportional to the whole open circuit voltage, because the one lying across the resistor 21 Voltage cannot be higher than the critical voltage of the Zener diode. The one in the event of a short circuit from the de-energized state occurring transient addition d to the static short-circuit current is thus only slightly larger than the allowance that occurs when a burning arc is short-circuited.

The practical welding power sources of the invention are not like the many in Pig. I switches 16, 18, 181, 182, equipped, which are some of the options available to illustrate the structure of the control system of the power source according to the invention. The manufacturer goes from somebody certain combination of, e.g. B. a circuit which the lower position of the switch l6 under the upper position of the switch l8, or the lower position of both switches, or the upper position of switch 16 and the lower position of switch 18, and measures the constants of the chosen circuit in the best way.

The time constant of the transient component of the control signal

should be at least 0.1 sec., preferably at least 0.2 sec. 309844/0475

be. A time constant of about .0.5 seconds is necessary for most of the practical cases useful and suitable.

The one in Pig. 3 schematically illustrated embodiment of the Invention comprises a three-phase transformer 26, on whose secondary winding a main rectifier 27 and an auxiliary rectifier 28 are connected. The main rectifier is with controlled valves. The auxiliary rectifier 28 consists only from diodes (not controlled valves). The two rectifiers are connected to the same welding circuit, the auxiliary rectifier being connected in series with a resistor which controls the short-circuit current of the auxiliary rectifier limited to a low amount. The welding circuit includes an inductor 30. Between the connection of the inductor with the power source and the other welding current conductor is a free-wheeling diode 31. The rectifier 27 is controlled by an ignition angle sensor 32, which is controlled by one of the control signal generated by the amplifier device 33 is controlled. The input circuit of amplifier 33 is designed as a summing circuit formed, which four resistors 34, 35, 36, 37 contains. The resistor 37 is connected to an acceptance element 38 for the actual value of the welding current, e.g. B. one in a welding current conductor switched on shunt resistor, and thus conducts a current proportional to the welding current. The resistor 36 is connected to a slide or some other adjustable tap 39 on the constant voltage source 4l lying potentiometer 40 connected. The resistance is to the adjustable tap 42 of a potentiometer 43

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closed, at which one changes with the welding voltage Voltage is, which is supplied by a comparison circuit 44. The one existing between the welding current conductors Welding voltage and the constant voltage of the to a constant voltage source 46 connected potentiometers 45 are each for itself introduced into the comparison circuit 44, which is designed so that it is applied to the output conductor 47 a voltage sets which is proportional to the difference between the welding voltage and a constant voltage V, the voltage V is equal to the voltage supplied by potentiometer 45 is or has a certain relationship with it. The voltage delivered to conductor 47 is fed to a potentiometer 48 fed, whose tap 49 to the potentiometer already mentioned 43 is connected. Between the conductor 47 and the tap 49 of the potentiometer 48, a capacitor 48 is switched on, the task of which corresponds to that of the capacitor 17 of the device according to FIG.

Generate the currents flowing through the three resistors 35, 36, 37 a corresponding input voltage of the amplifier 33. As can be seen from the above, this contains voltage the following (static) components:

a. A constant, adjustable by means of the potentiometer 40 Component.

b. A constant component in the same direction as component a, adjustable by means of potentiometers 48 and 43.

c. A welding voltage with the changing, the component a counteracting component, wherein the proportion ratio

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between this component and the welding voltage can be adjusted by means of the potentiometers 48 and 43.

d. A component that changes with the welding current and counteracts component a (which is the 'current pickup element is removed).

The sum of the two adjustable components a and b_ represents represents the constant basic component or reference component of the control signal and thus corresponds to that control signal component the device according to FIG. 1 is generated by the potentiometer 13 and the resistor 12. The operation of the device corresponds essentially to the working mode of the device according to FIG. 1 in the case when the switches I6, 18, 18o and 182 assume the positions shown in FIG.

The series connection of the capacitor 50 and the between the tap 49 and the zero potential connection Part of the resistor 48 generated transient component of the control signal is through the potentiometer 43 in the same ratio as the static component is reduced. At low Current settings, the transient component thus transmitted has proven to be too small. The one at the input of the amplifier device 33 arranged summing circuit therefore contains a fourth resistor 34, which through a capacitor with the Output conductor 47 of the comparison circuit 44 directly connected is, the capacitor in series with a charging or discharging resistor 53 lies. A supplementary transient component is thus generated by this circuit, the size of which depends on the

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Resistance of the resistor 3 ¹ J depends.

It has been found that the best welding properties are obtained when the steepness of the characteristic is within a certain range Way is selected depending on the arc current strength, in such a way that the ratio of short-circuit current strength / Arc current strength and thus also the relative current increase arising in the event of a short circuit, at least in the medium-high area Currents is approximately constant. Excellent results can be achieved with such a correlation of the steepness of the characteristic curve the current setting that the ratio of (static) short-circuit current strength / arc current strength in the entire current range is between 1.1 and 1.2, which is achieved by a corresponding mutual adjustment of the potentiometers 40 and 4 3. It is assumed that the arc voltage increases with the arc current in accordance with the internationally accepted The average arc characteristic changes, which in the current range 0 to 600 A results in a linear increase in the arc voltage from 20 to 40 volts.

At high current settings, there may be some reduction in the short-circuit current / arc current ratio be admissible and appropriate, inter alia. for the purpose of avoiding overloading of the rectifier valves.

Fig. 4 shows as an example a group of controlled according to the invention Characteristic curves as well as the characteristic curve of the power source with fully modulated valves and the characteristic curve 25 of the auxiliary

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rectifier ^ 28. The curves 55 to 58 show one at As the current setting increases, the slope decreases, while in the area of the characteristic curves 58 to 60 at the upper end of the current setting range a constant slope is maintained.

It can u. It may be useful to check the steepness of the characteristics on the the upper end of the current range can even be increased slightly with the current setting. In the area of small welding currents, in particular with welding currents less than 50 amperes, it will sometimes be advisable to use a higher ratio of short-circuit amperage / arc amperage than to be provided in the area of medium-high welding currents.

The lying through the series circuit of the capacitor 50 and between the tap 49 and the zero potential portion dei resistor 48, transient voltage generated is reduced by the potentiometer 43 in the same ratio as the static voltage component. At the lower end of the current setting range, the transient control signal component thus generated and the resulting transient current increase in the event of a short circuit become too small. A supplementary transient control signal component is introduced by resistor 34 which is part of the summing circuit at the input end of amplifier device 33. Resistor 34 is connected to output conductor 47 of comparison circuit 44 through a circuit which includes capacitor 52 in series with resistor 53.

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At low welding currents, there is the main rectifier Delivered current from relatively short pulses, which are separated by currentless pauses. The one from the auxiliary rectifier 28 in series with the resistor 29 supplied low current bridges the aforementioned currentless pauses, which occurs at low Welding currents result in improved arc stability. In the embodiment of FIG. 3, the auxiliary rectifier is connected to the same transformer winding as the main rectifier 27. It is also possible to use the auxiliary rectifier to be connected to a particular winding of the transformer 26 or to a particular transformer, which resp. which preferably has a higher sectarian tension than the den Has main rectifier supply winding.

If the Stromrückkopp mentation f act -cr of the device of FIG. 3 is to be measured, entxedei ^j i ^ ;. Auxiliary rectifier 28 switched off or a load fies SehssiS ^ Ifeichriehters can be provided.

The welding power source of FIG. 5 has a main transformer which, in addition to a primary winding 65 and a secondary winding 66, has a tertiary or auxiliary winding 67 which does not transmit welding power but only generates a three-phase voltage required for the control device. A main rectifier connected to the secondary winding is composed of three diodes 68 ιιηύ three thyristors 69 s. Three further diodes 70 together with the diodes 68 represent an auxiliary rectifier. One output conductor 77 of the

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The rectifier is connected to the welding electrode 71. The other output conductor 76 of the main rectifier is connected to the ■ Workpiece 74 through a shunt resistor 72 and a welding inductor 73 connected. The shunt resistor 72 represents the current actual value removal element The auxiliary rectifier is connected to the welding circuit in series with the current limiting resistor 75 connected. A freewheeling diode 78 is between the welding current conductors 76, 77 switched on.

The three thyristors 69 are each controlled by an ignition angle transmitter 79, 80, 81 by the ignition angle transmitter each with the control electrode a thyristor 69 through an ignition pulse conductor 82, 83, 84 (which is only partially shown in the figure) are. The circuit diagram of the ignition angle sensors is based on FIG. 7 emerged.

The auxiliary equipment required for the operation of the control device or operating voltages are generated by a single-phase transformer 87, the secondary winding of which has a center tap is provided. The secondary voltage is rectified by the rectifier bridge 88. The rectified voltage becomes by means of one made up of capacitors 89 and resistors 90 Filter smoothed and stabilized by means of two Zener diodes 91, which are connected in series between the positive operating voltage conductor 93 and the negative operating voltage conductor 94 are. The conductor connecting the Zener diodes is connected to the center tap 85 and to the zero potential terminal 92.

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The positive terminal of the main rectifier is connected to the zero potential conductor 92 connected by a conductor 95. The voltage of the other terminal of the main rectifier, which in relation to the zero potential conductor 92 is negative is fed to a conductor 97 through a smoothing filter 96. The head 97 is with connected to one end of a resistor 98, the other end of which is connected to the input of an operational amplifier 99. A second resistor 100 connects said input to the constant positive voltage of the operating voltage conductor 93. The voltage fed to the input of the operational amplifier is thus proportional to a current, which corresponds to the quotient the constant voltage of the conductor 93 and the resistance of the resistor 100, minus the quotient of the welding voltage of conductor 97 and the resistance of resistor 98 is equal. The operational amplifier 99 is provided with a feedback branch which consists of the parallel connection of a resistor 101 and a diode 102. If the input voltage is zero, the output voltage is also zero. With positive The operational amplifier supplies a negative input voltage Output voltage, which is proportional to the input voltage. With negative input voltages (i.e. when the welding voltage dependent Component of the input voltage is greater than the constant component), the output voltage is the Operational amplifier zero because diode 102 prevents a positive output voltage from occurring. If no The operational amplifier supplies the proportionality constant, V denotes the welding voltage and V a constant voltage an output voltage VV = K (V "- V), if V is less than V

au s s r s r

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and an output voltage V _ ,, _ - O when V is equal to or greater than V. The output voltage is fed to a potentiometer 103 connected between the output of the operational amplifier 99 and the zero potential conductor 92. The tap 104 of the potentiometer is connected to a second potentiometer, which is connected between said tap and the zero potential conductor 92 and consists of the series connection of the two resistors 105 and 106. The resistor 105 is a photosensitive resistor which is exposed to the light radiation of a photodiode 105a. An increase in the light radiation received by the resistor 105 causes a decrease in the resistance of the resistor 105. The potentiometers 103 and 105-106 correspond to the potentiometers 48 and 43, respectively, in FIG. 3. The connection of the resistors 105 and 106 is to one end of a resistor 10? connected, the other end of which is connected to the input conductor 108 of an amplifier device 109, which corresponds to the amplifier device 33 of FIG.

A capacitor 110, the function of which is identical to that of the capacitor 50 in FIG. 3, is connected between the output conductor of the operational amplifier 99 and the potentiometer tap 104. A second capacitor 111 in series with a resistor 112 is connected between the output conductor of the operational amplifier 99 and the zero potential conductor 92. The connection of the capacitor 111 to the resistor 112 is to the input filter 108 of the amplifier device 109 through a resistor 113 νβ ^ μηαεη. The task of the circuit composed of members 111, 112, 113 is identical

3098-44 / 0475.

table with that of the corresponding circuit 52, 53, J> of FIG. 3.

A potentiometer 114 is connected between the zero potential conductor and the negative operating voltage conductor 9 **. The adjustable negative voltage of the tap 115 is applied to the series connection of the photodiode 105a and a resistor 116 and also applied to one end of a resistor 117, the other end to the input conductor 108 of the amplifier device 109 is connected.

The small voltage drop in resistor 72 caused by the welding current is calculated by means of one of the resistors 178 and The filter existing on the capacitor 179 is smoothed and through a resistor 118 to the input of a with a feedback Resistance 119 provided operational amplifier supplied. The output voltage of this amplifier, which is positive in With respect to the zero potential conductor 92 and is proportional to the welding current, one end of a resistor 149 is supplied, the other end of which is connected to the input conductor 108 of the Amplifier device 109 is connected.

The control signal, which is fed to the input conductor of the amplifier device 109 through the summing circuit composed of the resistors 113, 107, 117, IkS , is thus composed of the following static components:

a. a constant, negative component, which can be adjusted by means of the potentiometer 103,

'30984 47 0475

b. a component supplied by the operational amplifier 99 and the potentiometers 103 and 105-106, which is equal to zero as long as the welding voltage is higher than a certain amount V, and which is _{negative for welding voltages V "s} which are less than V , assumes a proportional value to the difference V - V;

c. a positive component supplied by operational amplifier 120 which is proportional to the welding current.

The amplifier device 109 contains an operational amplifier 121 and one consisting of three branches connected in parallel Feedback loop. The first branch contains a resistor 122, the second branch the series connection of a resistor 123 and a capacitor 124, and the third branch a diode 125, which is polarized in such a way that it prevents the occurrence of negative output voltages prevented. The operational amplifier 121 as well as the other operational amplifiers 99 and 120 are pole-reversing, d. H. they generate an output voltage whose polarity is opposite to that of the input voltage *

The output of the amplifier device 109 is of the Transfer conductor 126 to each of the three ignition angle sensors 79, 80, 8l. The ones required for the operation of the ignition angle sensors Operating voltages are supplied to the ignition angle sensors through the conductors 127, 128 and 129, which with the operating voltage conductors 93, 94 or the zero potential conductor 92 are connected. Also required for the operation of the ignition angle sensor pulsating voltage is applied to the auxiliary winding 67 of the

3 0 9-8 Λ 4 '/ (U 7 5

Main transformer connected rectifier device generated. This rectifier device consists of three branches connected in parallel with one another, each of which consists of the series connection of two rectifier valves 130, 131 and a resistor 132. The output terminals of the auxiliary winding 67 are each connected to the connection of the two rectifier valves of a branch. The connection of the three resistors is connected to the negative operating voltage conductor 3 * \ . The positive voltages at the three resistors, which are variable in relation to this conductor, are each fed to one of the three ignition angle sensors 79, 80, 81 through a conductor 133, 13 ^, 135. The circuit and the mode of operation of the ignition angle sensors are described in more detail in connection with Mg. 7 and 3. For the time being, it only needs to be mentioned that the phase position of the ignition pulses generated by the ignition angle sensors is controlled as a function of the size of the control signal fed through the conductor 126 in such a way that the thyristors remain non-conductive as long as the control signal remains zero, and that when a control voltage occurs, the thyristors are in the conductive state for a period that increases with the magnitude of the control voltage.

In Fig. 6, which shows a group of characteristics corresponding to different For representing settings of the potentiometer 114, the same designations are used as in FIG. 4. Any of the controlled Characteristic curves 55-60 contain, besides the inclined part, a vertical part 55a-60a, which extends between the voltage V

and the characteristic curve 5 ^ of the fully controlled current source . 3Ω 9 8 A4 / (U 7 "5"

given maximum voltage. This vertical part is created by the above-described mode of operation of the amplifier 99, the output voltage of which remains higher than V zero for all welding voltages, so that only the current feedback is effective in this voltage range. The voltage V is expediently ^{chosen within the range 2} JO to 50 volts.

When choosing the correlation between the steepness of the characteristic curve and the current setting, those in connection with FIG. 4 the rules and points of view presented must be taken into account. For reasons explained there, the steepness of the characteristic should be increasing current settings up to a certain current strength decrease, but are kept almost constant at the highest current settings (characteristic curves 58-60). At the device According to FIG. 5, this correlation was established by such an adaptation of the characteristic curve of the photodiode 105a and the light-sensitive Resistor 105 achieves that the resistance of the resistor 105 with increasing voltage of the unit Tap 115 of the potentiometer. 114 only up to a certain point Limit drops and remains essentially constant as the voltage increases further.

In connection with FIG. 4 it was mentioned that the constant voltage V can optionally be chosen so that the line V = V intersects the arc characteristic. In the case of the device according to FIG. 5, however, this is not expedient, since the operating point should lie in the inclined part of the characteristic curve. However, it is still possible to detect the difference between the arc voltage and 3US8LL / 0475

of the voltage V _x , by making the setting of the voltage V variable with the current setting in such a way that the voltage V increases with the current setting. Pig. 6a illustrates this possibility, which can be realized, for example, by making the resistor 100 adjustable and arranging such a coupling between its setting element and the setting of the potentiometer 114 that the resistance of the resistor 100 decreases as the potentiometer voltage increases.

In describing the mode of operation of the amplifier device 109 it was assumed that its second input conductor 136 constantly has the potential of the zero potential conductor 92. However, the device according to FIG. 5 contains a special bias circuit, which gives the input conductor 136 a negative bias as long as the welding rectifier is not loaded. The amplifier 109 then sends no signal, see above that the thyristors of the main rectifier remain non-conductive. The purpose of this arrangement is to prevent an excessive current rise when shorting out of the open circuit condition .

The bias circuit includes two transistors 137, 138. The emitters 139, 140 of the transistors are connected to the zero potential conductor 92. The collectors l4l, 142 are to the negative operating voltage conductor 94 by one resistor each 143 or 144 connected. The collector l4l of a transistor 137 is with the base of the other transistor 138 through one

Resistor l45 connected. The base of the transistor 137 is connected to the connection point P1 of two resistors. 146.1 ¹ I? connected, one of which is connected to the positive operating voltage conductor 93, while the other is connected to that conductor 97 which is connected to the negative output voltage of the welding rectifier with respect to the zero potential conductor 92. The resistors 146, 1 * 17 are dimensioned in such a way that the point P1 has a negative polarity with respect to the zero potential conductor 92 as long as the conductor 97 has a high voltage (the open circuit voltage), but assumes a positive polarity with respect to the zero potential conductor, as soon as the output voltage of the welding rectifier becomes lower than a predetermined voltage. The collector 142 of the transistor 138 is connected to the input conductor 136 of the amplifier 121 through a resistor 148. A resistor 150 also connects the input conductor I36 to the zero potential conductor 92.

The circuit described operates in the following manner. As long as the conductor 97 has the open circuit voltage and the point Pl thus has a negative potential, the transistor 137 is conductive and transistor 138 non-conductive. Denf entrance manager 136 a negative potential is supplied under these conditions, which is a through the potentiometer arrangement 144, 148, 150 represents a certain fraction of the negative operating voltage. The output voltage of the amplifier 109 is zero, so that the Thyristors remain non-conductive. When the output voltage of the welding rectifier decreases so much that the point Pl becomes a positive Gets potential, the transistor 137 becomes non-conductive,

3Q984 & / Q475

while transistor 138 becomes conductive and, the input conductor 136 of the amplifier 121 is connected to the zero potential conductor 92 through the resistor 148.

From the above explanation it can be seen that the auxiliary rectifier consisting of the diodes 70 together with the diodes 68 of the Current source according to FIG. 5 also has an additional task, namely the one with completely non-conductive thyristors Maintain open circuit voltage, which operates the circuit just described.

FIG. 7 shows the circuit diagram of the ignition angle transmitter 79 from FIG. 5. The following conductors discussed earlier are shown again in FIG. 7: The one connected to the positive operating voltage conductor Conductor 127; the conductor 129 connected to the zero potential conductor; to the negative operating voltage connected conductors 128; the conductor 133 for supplying the line voltage occurring at one of the resistors 132 synchronous voltage pulses; conductor 126 which conducts the control signal of amplifier device 109; and the one to the Ignition electrode connected to one of the thyristors of the main rectifier Ladder 82.

The DC voltage pulses transmitted by the conductor 133 become a voltage divider consisting of two resistors 151, 152 fed. The base of a transistor 153, whose emitter through the conductor 128 to the negative operating voltage

3098 4 4/0475

- .de:

is closed. The collector of the transistor 153 is connected to the on / "positive operating voltage conductor 127 through an RC-Net2, which consists of a capacitor 15 ¹ J, the charging resistor 155, 156, 157, a discharge resistor 158 and two diodes 159, 160. The desired charging time constant is set by means of the resistor 155. The connection point P2 of the resistor 156, the capacitor 154 and the diode 159 is connected to the base of a transistor 152 and also to the conductor 129, which is at zero potential, by a diode 161 polarized in such a way that it only allowed the occurrence of a positive potential at point P2. The purpose of this diode is to protect the transistor 162 from overvoltages. A transistor 163 acts together with the transistor 162 in the manner of a differential amplifier. The control signal of the operational amplifier 121 (FIG. 5) is fed to the base of transistor I63 through conductor 126 and resistor 164. Transistors I62, I63 are denoted by e A common emitter resistor I65 is provided. The collector of transistor I63 is connected through resistor 146 and conductor 127 to the positive operating voltage conductor and is also directly connected to the base of a transistor

167, the emitter of which is connected to conductor 127. The transistor I67 represents the first stage of a pulse amplifier, its second and third stage from the transistor

168 and 169, respectively. The collector of the transistor

169 becomes a certain through the resistors 170, 171 a voltage divider 172, 173 certain proportion of the negative Operating voltage supplied. The one to the ignition electrode of one of the Thyristors 69 connected conductor 82 is to the collector

.3 09844/0475

of the transistor 169 is connected by the series connection of two resistors 17 ¹ *, 170, the resistor 170 being connected in parallel with a capacitor 175.

The diagrams in FIG. 8 illustrate the working cycle of the ignition angle sensor. Diagram a shows the voltage pulses supplied through the conductor. Diagram 3 shows the voltage at transistor 153 at point P3. Diagram £ shows the voltage at point P2 (the solid line 176) and that transmitted through conductor 126 Control voltage of the operational amplifier 121 (the dashed line 177). The diagram d shows the voltage in the connection point P4 of the resistors 170, 171. The diagram <e shows the ignition pulses transmitted through the conductor 82.

During the duration of the voltage pulse supplied by the conductor 133 (Pig. 8a), the transistor 153 is conductive, so that the potential of the point P3 is negative (FIG. 8b). A charging current flows from the positive operating voltage conductor through the conductor 127, the resistor 157, the capacitor 15 ¹ J, the resistors 156, 155, the transistor 153 and the conductor after the negative operating voltage conductor 9 ¹ J. Charging the capacitor 15 ¹ * causes the potential of point P2 to drop (curve 176 in FIG. 8c). The steep voltage drop marked r at the beginning of the charging process is caused by the voltage dividing effect of the resistors 155-156 and 157. The charging of the capacitor continues until the point P2 has reached the potential of the neutral conductor. The potential then remains

309844/0475

constant (curve segment s). When the voltage pulse of the conductor 133 ceases, the transistor 153 becomes non-conductive. The capacitor 15 ¹ I discharges through the resistor 158 in series with the diodes 159, l6o. The resistance of the Ent LadewiderStandes 158 is much smaller than the resistance of the charging resistors 155, 156, 157. The discharge is therefore fast (section u). Point P2 as well as point P3 are now again at the potential of the positive operating voltage conductor (curve section v). The transistor 162 is conductive as long as its emitter voltage is greater than the emitter voltage of the transistor I63 corresponding to the control voltage of the conductor 126. If the latter emitter voltage is predominantly, the transistor I63 is turned on and turns off transistor 162. This process occurs in the cutting ^ι point of the curve 176 and the line 177 in Fig. 8c. The resulting pulse is amplified in the three stages of the pulse amplifier. When the transistor I69 of the last amplifier stage becomes conductive, the point P 4 assumes a positive potential (FIG. 8d). This creates a current surge through the capacitor 175 and a corresponding current surge through the conductor 82 (FIG. 8e). The ignition current is interrupted when the point P2, when the capacitor 154 discharges, reaches such a high positive potential that the emitter voltage of the transistor 162 becomes predominant again and the transistor I63 becomes non-conductive. This takes place at the intersection of the charging line u (FIG. 8c) and the line 177. As a result, the transistor 169 also becomes non-conductive, the point P4 immediately assuming a negative potential determined by the voltage divider resistors 172, 173. The resulting ^ negative bias of the ignition electrode

prevents thyristor misfiring due to interference. the The next triggering of the thyristor can only take place after the supply of the next voltage pulse (FIG. 8a) through the conductor 133.

The circuit of the ignition angle sensor described has, inter alia, the advantage that the (generally large) manufacturing tolerances of the transistors do not affect the ignition angle. The charging process of the capacitor 154 depends only on the capacitance of the capacitor 15 ^ and the resistances of the charging resistors 155, 156, 157. As a result of the unavoidable tolerances, these variables cannot be assumed to be the same in the three ignition angle sensors will. By setting a single element per ignition angle sensor, namely the resistor 155, one achieves but without further ado a time constant that is the same for all ignition angle sensors and thus also identical charging processes. the The steepness of the charging curve 176 is sufficient to keep one sharp to result in defined intersection with the horizontal line 177, which is the output from the operational amplifier 121 Control signal corresponds.

309844/0475

Claims (9)

- 58 -. Patent claims: 1. Power source for manual welding with a rapidly decreasing voltage-current characteristic, consisting of a three-phase transformer with low magnetic scatter (low reactance), a three-phase rectifier connected to its secondary winding with controlled valves, an ignition angle sensor to generate ignition pulses that control the valves and their phase position the magnitude of a control signal supplied to the ignition angle sensor, consisting of a direct current or a direct voltage, is determined is, and a control signal generating the control signal generator, which means for producing a constant, means an adjustment member adjustable first component (basic component) of the control signal and means including one Link for the acceptance of the welding current actual value, for the production contains a second component of the control signal which acts against the basic component and which multiplies the welding current mit.einem first proportionality factor is equal, characterized in that the control signal transmitter also means (17, 11, Fig. 1; 44, 48, 43, 35, Fig. 3; 98, 99, 103, 105, 106, 107, Fig. 5) for introducing a third component of the control signal, which is multiplied by the actual value of the welding voltage is equal to a second proportionality factor, and a member (17a, Fig. 1; 42, Fig. 3; 105a, 105, Fig. 5) for setting the Ratio between the second and the first proportionality factor, which link with the link (13a, Fig. 1; 39, Fig. 3; 115, Fig. 5) is coupled for setting the basic component, so that between the current determined by the basic component 309844/0475 strength setting and the slope of the (static) characteristic the current source a certain correlation is automatically maintained. 2. Power source according to claim 1, characterized in that the coupling causes a decrease in the steepness of the characteristic curve increasing current setting causes at least within the lower half of the setting range of the power source will. 3. Current source according to claim 1, characterized in that the correlation given by the coupling between the current setting and the slope of the characteristic is matched so that the ratio between the (static) short-circuit current and the arc amperage remains substantially constant throughout the current setting range. 4. Power source according to claim 3, characterized in that the ratio between the short-circuit current strength and the arc current strength lies between the limits 1.1 and 1.2. 5. Power source according to one of claims 1 to 4, characterized in that that the two adjusting members (13a, 17a, Pig. I; 39 »^ 2, Fig. 3) are mechanically coupled. 6. Power source according to one of claims 1 to 4, characterized in that that a control circuit (116, 105a, Fig. 5) is provided for setting the second proportionality factor, 309844/0475 to which a current proportional to the basic component is supplied will. 7. Power source for manual welding with a rapidly decreasing voltage-current characteristic, consisting of a three-phase transformer with low magnetic scattering (low reactance), a three-phase DC connected to its secondary winding Richter with controlled valves, an ignition angle sensor to generate ignition pulses that control the valves and their phase position by the size of a control signal supplied to the ignition angle sensor and consisting of a direct current or a direct voltage is determined, and a control signal generating the control signal, which means for producing a constant, by means of an adjustment element adjustable first component (basic component) of the control signal and means including one element for taking the actual welding current value, for producing a second element that acts against the basic component Contains component of the control signal, which equals the welding current multiplied by a first proportionality factor is, characterized in that the control signal generator also the includes the following means: a. Means (17, 11, Fig. 1; 44, 48, 43, 35, Fig. 3; 98, 99, 1-3, 105, 106, 107, Fig. 5) for introducing a third component of the control signal, which is the actual value of the welding voltage multiplied by a second proportionality factor is equal to; b. a series connection of a capacitor (20, Flg. 1; 50, 309844/0475 Pig. 3; HO, Pig. 5) and a resistor (21, Pig. 1; lower part of resistor 48, Fig. 3; lower part of the resistor 103, Fig. 5), which series connection the Welding voltage or a voltage reflecting the changes in welding voltage is applied; c. Means (19, 10, Fig. 1; 43, 35, Fig. 3; 105, 106, 107, Fig. 5) for producing a fourth component of the control signal, which component occurs between the ends of the resistor Voltage multiplied by a third proportionality factor is the same and which is the same when the capacitor discharges interacts with the basic component; and d. a member (19a, Fig. 1; 42, Fig. 3; 105a, 105, Fig. 5) for adjusting the relationship between the third and the first proportionality factor, which link with the link (13a, Fig. 1; 39, Fig. 3; 115, Fig. 5) for setting the Basic component is coupled so between the current setting determined by the basic component and the Slope of the dynamic characteristic curve of the power source a certain correlation is automatically maintained. 8. Power source according to claim 7, characterized in that a member (17 a, Fig. 1) for adjusting the ratio between the second and the first proportionality factor provided and with the member (13a, Fig. 1) for setting the basic component is coupled so that the slope of the static characteristic has a certain correlation with the current setting. 309844/0475 9. Power source according to claim 7, characterized in that the third and fourth components of the control signal have a common Taken from the circuit and through a common member (42, Fig. 3; 105a, 105, Fig. 5). 30984 4/04 L e r s e i t e