DE1277999B - Protective device for a switching arrangement for generating current pulses - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY GERMAN 4mtW ^ PATENTAMT Int. α .:

H02h

EDITORIAL

German KI .: 21d3-2

Number: 1277 999

File number: P 12 77 999.6-32 (A 40480)

Filing date: June 19, 1962

Opening day: September 19, 1968

The invention relates to a protective device for a switching arrangement for generating Current pulses with a direct current source, at least one transistor, which has two of its ! Electrodes is connected between the direct current source and a consumer circuit, and with a device for controlling the transistor by applying a control voltage to a transformer.

Protective devices of this type, in which by modulating a transistor the exceeding a given current is prevented, are in the most varied of more or less complicated Embodiments known. For example, there is a circuit for interrupting the power supply Occurrence of overcurrents is known, in which a semiconductor resistance when the nominal value is exceeded blocks the circuit. This known circuit works like a circuit breaker and requires at least two transistors, which together form a bistable circuit, around a once started Power interruption to accelerate relatively strongly. This known circuit is not very reliable. It is already a protective device against overloading power converter systems known, in which a voltage derived from the current to be monitored creates a circuit feeds that via the control path of a transistor and in the reverse direction via a Zener diode runs whose Zener voltage corresponds in terms of value to the upper limit current setpoint at which the Protective device should respond. A second circuit is also provided here, which is via the emitter-collector path of the transistor and a voltage for supplying an electrical timing circuit supplies, which controls the protective device of the system after a predetermined sequence. This known circuit is also very complicated and expensive in structure. The same applies to Another known short-circuit protection circuit in which a flip-flop circuit is used which is connected to a stabilization transistor via a diode. This known circuit must be returned to its original position after the short circuit has been eliminated, including a Push-button switch is used, with the help of which the base of an additional transistor is opposite the emitter positive voltage pulse is supplied, so that an auxiliary transistor is non-conductive and another transistor becomes conductive. This known short-circuit protection circuit is also not very reliable.

The object of the invention is to create a protective device of the type mentioned in the introduction, which is used in the protective device for a switching arrangement
for generating current pulses

Applicant:

Ateliers des Charmilles S. A., Geneva (Switzerland)

Representative:

Dr.-Ing. F. Wuesthoff, Dipl.-Ing. G. Pulse
and Dr. E. v. Pechmann, patent attorneys,
8000 Munich 90, Schweigerstr. 2

Named as inventor:

Jean Pfau,

Heinz Rhyner, Geneva (Switzerland)

Claimed priority:

Switzerland of June 23, 1961 (7371)

Structure is very simple and yet very reliable and especially for spark erosion serving pulse generator is suitable.

Based on a protective circuit of the type mentioned at the outset, this object is achieved according to the invention solved in that a primary winding of the transformer in series with an auxiliary DC power source and a rectifier is connected in parallel with the transistor that the voltage of the auxiliary DC power source is less than the voltage of the direct current source, but greater than the voltage drop on the conductive semiconductor switching element that the forward direction of the rectifier is selected is that when the transistor is conductive, the current from the auxiliary DC power source through the winding of the Transformer flows while it blocks the current from the DC source, and that through saturation of the transformer or an excessively high voltage drop across the transistor blocking voltage is induced in the secondary winding of the transformer.

A major advantage of the protective device according to the invention is that the transistor The current flowing through is not only interrupted when this current has an unusual effect

809 617/228

3 4

reaches high value or the transistor itself over- the voltage between its collectors and emit-

is loaded, but also after a predetermined tern is smaller than the voltage of the source S ₂ .

Pulse duration is automatically interrupted, the assumption that the Zener voltage of the diode 9 is

is correct by the time it takes to saturate the 4 volts, that of the diode 10 8 volts and the span transformer. 5 voltage of the auxiliary DC power source S ₂ 3 volts. To the

Advantageous developments of the transistors Q ₁ ... Q _n according to the invention in the conductive state

If the protective device results from the accommodation, a pulse is generated via the transformer 8

address. The invention is sent below to such that on its secondary winding

Hand schematic drawings on execution- a voltage of 10 volts is created. The sign is explained in more detail. io of this tension is such that the bases of the tran-

F i g. 1 shows a protective device according to the invention Q ₁ ... Q _n negative with respect to its emitter

tion in use in an electrical discharge machine, and since this voltage is greater than the

tung; Zener voltage of the diode 10 can be a base current

F i g. 2 shows a further exemplary embodiment of a flow, since the diode 9 is also in the forward direction protective device according to the invention; 15 is traversed by the current.

F i g. 3 shows the application of an inventive method. In non-conductive transistors, no current can be used

ßen protective device with a feed circuit for through the primary winding 3 of the transformer 2

an electric motor; flow because the potential difference between collector

F i g. 4 shows the application to an oscillator; and emitter equal to the voltage of the direct current

F i g. 5 shows a further embodiment of an ao source S ₁ from z. B. 40 volts and thus greater than

protective device according to the invention. the voltage of the auxiliary DC power source S ₂ . These

F i g. 1 shows a pulse generator to the metal - the latter can therefore no current through the

machining by spark erosion. It includes a circle send, likewise no stream of

Direct current source S ₁ , the negative pole of which ßen via one of the direct current _{source S 1} through the winding 3 flow-variable resistor R with an electrode E and 35, since the diode 11 blocks the current,

whose positive pole via PNP transistors Q ₁ ... Q _n When the transistors Q ₁ .. _n .Q by the ignition

pulse connected to the workpiece P to be machined can be brought into the conductive state,

is. All of these transistors are connected in parallel, the potential difference between the collectors is

and serve to practically zero the direct current source S ₁ and the emitters, and from the supplied current in approximately rectangular current pulses 30 a current flows through the _{auxiliary direct current source S 3}

to chop up. Winding 3. This current causes a progressive

The collectors C ₁ ... C _{n of} the transistors tend to increase the magnetic flux in the trans-

Via a diode 14 with the negative pole, the emitter 2, as long as its core is not saturated.

ter E ₁ .. .E _n with the positive pole of the direct current during this increase in flux is connected in the secondary source S ₁ . In parallel with the direct current source 35 winding 4, a voltage of about 2 volts is induced

An electrolytic capacitor 15 is connected to S _1. Here- (loss in the primary circle), which is now related to the bases

overvoltages between the collector and the emitter are negatively polarized and thus the

and emitter when switching off the transistors keeps transistors in their conductive state,

avoided. The diodes 9 and 10 are for a voltage below

The circuit according to the invention comprises an auxiliary 40 4 volt non-conductive, and thus the secondary winding _{current source S 2} , formed by a potentiometer 12, development 4 is not short-circuited by these diodes, which is traversed by a direct current and des- When the transformer is saturated, take the sen sliding contact on the one hand via a capacitor bases the potential of the emitter, so that the Tran-12 α with the collectors of the transistors Q ₁ ... Q _n begin to block and between the KoI and on the other hand via a diode 11 and the Primary 45 lectors and the emitter a potential difference winding 3 of the transformer 2, which approximately arises, which has a rectangular magnetization characteristic of the current through the primary winding 3, of the transformer 2 counteracts. This decrease is associated with the emitters of these transistors. of the primary current causes a reversal of the in

The transformation ratio between the primary and the secondary winding 4 induced voltage,

winding 3 and the secondary winding 4 of the Trans- 50 caused by the bias current in

formator 2 is 1: 1. The winding direction of the windings of the winding 13, and this tension tensions the

is indicated by a point. Bases positive and causes an even more intense one

The secondary winding 4 is on the one hand via the blocking of the transistors.

Secondary winding of a pulse transformer 8 with The transistors can also be connected to emitters E ₁ .. .E _n before grounding and, on the other hand, to the fields of saturation of the transformer in the sen of the transistors. In addition, it is brought into a non-conductive state as soon as the two oppositely connected Zener diodes 9 and 10 bridges the current flowing through the transistors Q ₁ ... Q _n. exceeds a maximum value. An increased

A winding 13 is for the bias current, z. B. provided as a result of a short circuit between the transformer 2. The transmissive 60 electrode E and the workpiece P, causes from one direction of the rectifier 11 is selected so that the specific value a considerable increase in the span current from the auxiliary _{power source S 2} flow unhindered between the emitter and collector, which is connected to the ßen can, the current of the DC voltage source S ₁ kink in the voltage-current characteristic is blocked together, however, while the transistors are connected.

O ₁ ... Q _{n are} in the non-conductive state. This 65 As soon as this voltage drop becomes greater than that

Current can be in the collectors and emitters of the voltage of the auxiliary DC power source S ₂ , the

Transistors Q ₁ ... Q _n containing circuit only flow current in the primary winding 3 no longer flow,

ßen, provided the latter are in the conductive state and and in the secondary winding 4 is a voltage

induced, which biases the bases positively and thus brings the transistors into the blocking state. These Voltage is limited to 8 volts by the zener diode 10, preventing the transistors from overvoltage are protected and at the same time a rapid demagnetization of the transformer 2 is effected. This Zener diode 10 can also be replaced by a resistor.

Assuming that the resistor R has such a value that it causes a voltage drop of 15 volts for the machining current, that the voltage of the direct current source S _{1 continues to be} 40VoIt and the voltage between the electrode and the workpiece is 25VoIt, it can be seen that in the case In the event of a short circuit, the entire source voltage appears at the resistor R and that the current then assumes 2.7 times the value. With the known circuits it is possible to give a new current pulse by means of the transistors, even if the electrode and the workpiece are short-circuited. Therefore, the transistors must be dimensioned so that they are able to carry the short-circuit current, which is much greater than the operating current. However, if you want to reduce the number of transistors connected in parallel, you can also increase the resistance R so that the voltage drop z. B. is 25 volts. Since the voltage between the electrode and the workpiece is 25 volts, the direct voltage must be 50 volts. In this case, the short-circuit current is only twice as large as the working current, but much more energy is destroyed in the resistor R , which reduces the efficiency of the system.

With the protective circuit according to the invention, however, it is not possible to bring the transistors into the conductive state when the electrode is short-circuited with the workpiece, because in the event of a short-circuit with the supply of an ignition pulse through the pulse transformer 8, the voltage drop across the transistors is greater than the voltage of the Auxiliary direct _{current source S 2} , so that this source cannot send any current through the winding 3 of the transformer 2, and the transistors cannot be kept in the conductive state in order to deliver a current pulse of a certain duration to the electrode short-circuited with the workpiece. In this case, the transistors only have to be able to carry a current that is hardly greater than the maximum operating current. The potentiometer 12 can be used to set the value of the current at which the automatic locking should start, e.g. B. to 10 to 15% above the normal working current.

In the circuit arrangement described, the amplitude of the current pulses is adjusted by changing the value of the resistor R. The sliding contact of the potentiometer 12, which represents one pole of the auxiliary direct current source S ₂ , is coupled to the sliding contact of the resistor R in such a way that the voltage output by the auxiliary direct current source S ₂ increases when the value of the resistor R decreases. In this way, the voltage which feeds the bases during the pulse duration is high when working with pulses of great intensity, which prevents the transistors from blocking even when there is no short circuit. In the event of a short circuit, the transistors block automatically.

The current pulse, which is controlled by the transistors Q ₁ ... Q _n , can be interrupted from the outside at any time by a certain time after the ignition of the transistors by the transformer 8, a quenching pulse is fed in such that it is positive with respect to the bases on the emitter and whose voltage is greater than 4VoIt. This makes the combination of the diodes 9 and 10 conductive, because the diode 10 is switched in the forward direction, and the voltage mentioned is higher than the Zener voltage of the diode 9. The transition from

ίο conductive to the non-conductive state of the transistors Q ₁ ... Q _n therefore takes place very quickly, especially since, as soon as the blocking has started, the current in the primary winding 3, which comes from the source S ₂ , stops flowing, which in the secondary winding 4 induces a positive voltage, which still supports the locking process. By varying the frequency of the ignition pulses and the timing of the extinguishing pulses, the pulse repetition frequency and the pulse duration of the working pulses can be varied

ao can be regulated at will.

Instead of the diodes 9 and 10, a resistor in parallel with one of the windings of the Transformer switched to the beginning of the transition of the transistors in the non-conductive State any positive overvoltages at the bases.

The transition from the conductive to the non-conductive state and vice versa is somewhat slower. This disadvantage can be eliminated by connecting this resistor in parallel with the secondary winding 4. The auxiliary direct current source S ₂ could also be used to supply the polarization current of the transformer 2.

In the embodiment according to FIG. 2, the ignition pulses are fed in parallel to the base control circuit of a transistor Q ₁ and the extinguishing pulses in series with the primary winding of the transformer 2. In the base control circuit of the transistor Q ₁ is a pole of

Auxiliary DC power source S _{2 is} connected to the emitter via the secondary winding of the pulse transformer 8. The same pole of this auxiliary direct current source S ₂ is also connected to the base of the transistor via a diode and a resistor 16. This arrangement allows the ignition pulses to be fed directly into the base, but does not allow the positive extinguishing pulses originating from the pulse transformer 8 to be fed in directly, since the diode 15 blocks these pulses. The extinguishing pulses are fed in series with the primary winding 3 of the transformer 2 and counteract the self-holding current of the auxiliary direct current source S ₂ . The diode 15 could also be replaced by a Zener diode, which would allow erasing pulses from the transformer 8 to be fed directly into the base, provided that the voltage of these pulses is greater than the Zener voltage of the diode used. A resistor 14 is connected in parallel with the primary winding 3 in order to limit the overvoltage occurring on the base during the transition from the conductive to the non-conductive state.

The resistor 16 allows the base current to be metered for the duration of the ignition pulse, so that the transistor does not remain in its conductive state after the ignition pulse has disappeared, provided that the load 1 is less than a certain value. By adjusting the resistor 16, the minimum resistance between electrode and workpiece,

in which an operating current pulse is emitted and a voltage source with adjustable span, can be chosen at will. Tests have an average value that is proportional to the ratio give that it is possible to remove the electrodes from the time during which the transistors conducts, to reduce wear considerably without, however, the and the ignition period duration, d. H. the time between Working current and thus the working speed 5 is two ignition pulses, and therefore the function to decrease significantly. the voltage of the variable auxiliary direct current

The diode 15 could also be made up of two opposing sources S ₂ .

other connected Zener diodes are replaced. In the case of the circuit acting as an oscillator

In this case, the blocking of the transistor by the F i g. 4, a resistor 42 connects the auxiliary DC primary winding and the secondary winding of the io power source S ₂ with the winding 4 of the transformer 2 initiated simultaneously. tor 2, such that a negative voltage is applied to the

When the feed circuit for the armature 24 a base is applied. In addition, the secondary winding DC shunt motor is shown in FIG. 3 is the development 4 via a Zener diode 43, which is connected in such a way, direct current _{source S 1} with rectifiers together that the current, which flows in the forward direction in the three-phase transformer and the 15 base, makes the transistor conductive, with the transistor Q ₁ is connected to a fixed frequency from the emitter of transistor Q ₁ , driven twelve times the mains frequency, as a result of the negative voltage generated by the auxiliary

Via a pulse transformer 31 with a post-DC _{source S 2 connected} to the base of the transistor, rectifier bridge 32. As soon as it reaches the base of the transistor, the transistor begins to conduct and carries out the directed pulses from the DC source S _{1 to the base of the NPN-20} Load 1 flowing transistor Q ₁ via a further PNP transistor Q _a . Current. The auxiliary _{direct current source S 2} then drives the control of the transistor Q ₁ again a current through the winding 3 and the diode 11, via a transformer 2, which in turn has no front magnetization winding in the winding 4 of the transformer 2, but one induces a current at the base with respect to the air gap acting equally. The primary winding 25 the emitter also produces a negative voltage 3 of this transformer 2 is on the one hand directly calling. The current can flow unhindered because the Zemit the collector of the transistor Q ₁ and on the other hand nerdiode 43 the current in this direction through the auxiliary DC power source S ₀ in series with the circuit, formed from this diode, the emitter, rectifier bridge 32 - the one here the same roll of the base and the winding 4 flows. As soon as the diode 11 plays - with the emitter of 30 the transformer 2 saturates, the transistor Q _{1 is} connected. Base less negative, since the current in the secondary

The secondary winding 4 of the transformer 2 is winding 4 decreases, which a decrease in the tran one hand with the emitter of the transistor Q _a and sistorstromes and thus also the current in the other hand via a Zener diode 33, the Zener winding 3 results.

voltage is 10 volts, with the emitter of 35 In the winding 4, a voltage is induced, transistor Q _{1 is} connected. which biases the base strongly and positively. This span in this embodiment is that of the seconds is limited by the resistor 14 and the winding 4 of the transformer 2 in the base of the should be greater than the breakdown voltage of the transistor Q ₁ fed in regardless of the Zener diode 43. The transistor controlled the voltage of this secondary winding, since the tran- 40 current pulse is thus interrupted, and it versistor Q ₂ acts as a current limiter. The maximum value of the goes a certain time until the base is no longer positive-limited current is given by the potential tively biased and then via the resistance difference between the base and emitter of the transistor 42 and the Zener diode 43 back to a negative Q _a , the terminals 34 and 35 are applied. Potential is brought. The time that elapses from the end of one In this embodiment, the transistor Q ₁ 45 pulse to the beginning of the next depends on each of the rectifier bridge 32, essentially on the value of the resistor 14, brought into the conductive state by the next pulse. The saturation flux of the transformer 2 and the current flowing in the blocking of the transistor between the ignition pulses polarization winding 13 from. is caused by saturation of the transformer 2, which is so in the circuit arrangement described last

is designed so that the time to saturation is less than 50 it is not necessary to use a transformer as the time between two ignition pulses. supply of control pulses is to be provided, but if the voltage of the auxiliary direct current source S, this happens without further ado in the same way as changes, then the time to saturation also changes in the arrangements described above. In particular, and thus also the period of time during which the transponder can conduct the ignition pulse applied to the transistor in the conductive transistor Q ₁ after each control pulse that brings the state to that of the bridge circuit 32 55. the oscillator with a different frequency

To synchronize the source between the base and emitter of the transistor Q _a.

applied voltage sets the value of the base current according to F i g. 5 are the ignition and extinguishing pulses

of the transistor Q ₁ and consequently determines the maximum value of the collector current for the transistor Q ₁ via two transistors Q _b and also the maximum value of the collector current that is supplied to the 60 Q _{c of} small power. The secondary winding of the transistor Q _{1 is able} to lead without the development 4 of the transformer 2, which here an air gap to trigger automatic locking as soon as the auxiliary has, the primary winding of the transistor _{is directly connected to the emitter and the base DC power source S 2} Q ₁ connected. The primary winding 3 formator 2 is no longer able to feed. The is in series with the auxiliary _{direct current source S 2} , the switching arrangement shown thus corresponds to a transistor Q _b and a diode 11. The second tran current source with limitation of the maximum current, sistor Q _c sets, when it conducts, the auxiliary direct current, this value is selected by choice the voltage at the source S _{2 is set} directly to the primary winding 3 of the trans terminals 34 and 35 of the transistor Q _a , transformer 2.

The emitters of the transistors Q ₆ (PNP) and Q _c (NPN) are directly connected to one another. The bases of these two transistors are connected to the negative pole of a polarization voltage source 39 via the resistors 37 and 38, respectively. Positive ignition or extinguishing pulses for the transistor Q ₁ are fed into the bases of the transistors Q _b and Q _c via the capacitors 40 and 41. If the ignition or extinguishing pulses are missing, the transistor Q _{6 is} in the conductive state and the transistor Q _c in the non-conductive state.

Claims (8)

Patent claims: 1. Protection device for a switching arrangement for generating current pulses with a direct current source, at least one transistor which is connected via two of its electrodes between the direct current source and a consumer circuit, and with a device for controlling the transistor by applying a control voltage of a transformer, characterized in that, that a primary winding (3) of the transformer (2) is connected in series with an auxiliary direct current source (S ₂ ) and a rectifier (11) in parallel with the transistor (Q ₁ ), that the voltage of the auxiliary direct current source (S ₂ ) is lower than that Voltage of the direct current source (S ₁ ), but greater than the voltage drop across the conductive transistor (O ₁ ), so that the direction of the rectifier (11) is selected so that when the transistor (Q ₁ ) is conductive, the current from the auxiliary direct current source (S ₂ ) flows through the winding (3) of the transformer while it receives the current from the direct current source (S ₁ ) blocks, and that due to the saturation of the transformer or an excessively high voltage drop across the transistor, a voltage blocking the transistor is induced in the secondary winding of the transformer. 2. Protection device according to claim 1, characterized in that the transformer (2) has a Bias winding (13) for direct current carries, and that the core of the transformer one has approximately rectangular magnetization curve. 3. lowering device according to claim 1 or 2, characterized in that the secondary winding (4) of the supplying the control voltages Transformer (2) bridged by Zener diodes (9 and 10) connected in series against one another is. 4. Protection device according to claim 1, characterized by a second transistor (Q ₆ ) which is connected in series with a winding (3) of the transformer (2) supplying the control voltages, and a third transistor (Q _c ) which is connected in this way that the voltage of the auxiliary direct current source (S ₂ ) can be applied directly to the primary winding (3) of the transformer (2), even if the transistor (Q ₁ ) is non-conductive (FIG. 5). 5. Protection device according to claim 1 to 3, characterized in that the transformer (2) Has a third winding for short switch-on and switch-off control pulses for the transistor. 6. Protection device according to claim 1, characterized by a further transistor (Q _a ) which is connected in series as a controllable current limiter with the secondary winding (4) of the transformer (2) (FIG. 3). 7. Protection device according to claim 1, characterized in that the secondary winding (4) of the transformer (2) via a Zener diode (43) is connected to the emitter of the transistor (Q ₁ ), while a resistor (42) is the auxiliary direct current source (S ₂ ) connects to one end of the secondary winding (Fig. 4). 8. Protection device according to claim 1, characterized in that the secondary winding (4) of the transformer (2) is connected in series with a Zener diode to the emitter and to the base of the transistor (Q ₁ ), that the Zener diode in the direction of the current, which comes from this winding and keeps the transistor in the current-conducting state, is permeable and that a current source, which generates short-term pulses with always the same polarity, is connected in parallel to the overall arrangement. Considered publications:
German Auslegeschrift No. 1050 877,
069 760, 1 072 714, 1 074 133, 1102 837,
084 820. 1 sheet of drawings 809 617/228 9. 68 © Bundesdruckerei Berlin