JPH0215315B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an electric welder.

an inverter with an output frequency above the audio frequency range, and a primary winding with a center tap connected to the inverter and an electrode and an output terminal for electrical connection to the workpiece to be welded. It has been proposed by the applicant to construct a welding device including a transformer with a secondary winding.

This welding machine is the applicant's South African Patent No. 81/
Forming the issue of issue 2611.

During operation of this type of welding machine, a voltage twice the supply voltage is applied to its primary winding. If the supply voltage is obtained from a rectified three-phase alternating current voltage of, for example, 380V, the primary winding during operation will have a voltage of approximately 1000V. Transistorized switching devices capable of handling this voltage at operating currents are difficult and expensive to make.

The patent literature discloses many welding circuit arrangements. Related patent specifications known to the applicant include British Patent No. 2046537, British Patent No. 2019135, British Patent No. 1591185, British Patent No. 1570614, British Patent No. 1541068,
Same No. 1530906, Same No. 1431379, Same No. 1420319,
Same No. 1362163, No. 130869 and No. 722494
No.: U.S. Patent No. 4201906, U.S. Patent No. 4159409, U.S. Patent No.
No. 4117303, No. 4048468, No. 4047096, No. 4038515, No. 4004209, No. 3973165,
Same No. 3818177, Same No. 3728516, Same No. 3518401,
Same No. 3304485, Same No. 3231711, Same No. 3211953
and German Patent No. 2325793.

The circuits in many such patents suffer from the disadvantages mentioned above.

The specification of GB 2046537 discloses a different scheme using two controlled bridge-type thyristor inverters, each connected to a primary winding and operated together in parallel. The inverter there does not exhibit voltage multiplication. However, because the inverters are externally controlled, they function or are switched at a rate that is independent of the load. This is undesirable for the components of the circuit, and if an overload were to occur, the thyristor there could burn out unless additional precautions were taken.

The object of the invention is to provide a high-frequency welding device which can operate at frequencies above the audio frequency range, is load dependent and does not exhibit voltage doubling effects.

The present invention includes first and second switching elements 12 and 14 connected in series, and third and fourth switching elements 16 and 18 connected in series, wherein the first and second switching elements 12, 14 and the third and fourth switching elements 16, 18 are connected to the power supply V in a circuit which operates by load-dependent self-oscillation under sufficient supply voltage without voltage doubling operation. and a connection point 60 between the first and second switching elements 12, 14 and the third and fourth switching elements 16, 18, respectively.
a transformer 10 having a primary winding 24 connected between 62 and a secondary winding 26 from which the welding current is drawn, and self-excited switching means 20 arranged in a circuit operating dependent on said load; ,22,
28, the self-excited switching means includes a primary winding 2 for turning on the switching element.
means 34 coupled to the first to fourth switching elements 12 to 18;
first to fourth detection means 22 respectively interlocked with the switching elements, each of which detects the voltage between the terminals of at least a portion of the switching element while each switching element is in the on state; If the switching element is above the above level, the switching element starts switching off, thereby turning on the first and fourth switching elements 12, 18 and the second and third switching elements 14, 16 alternately;
voltage regulating means and electronic switching means 42 for causing current from said power supply V to flow alternately in opposite directions through said primary winding 24 without voltage doubling; energy storage means 28 connected to produce a circulating current in the primary winding and the energy storage means, after which the first and second switching elements and the third and fourth switching elements are respectively turned off; When providing a high frequency welding device, the device includes: a device that returns energy to a power source;

The switching means control the operating frequency of the transformer, preferably in the audio range or above, such that the core volume of the transformer is reduced.

Since the switching means is of the self-oscillating type, it means that during operation of the welding device, the circuit of the welding device is essentially of the free-running bridge type, and the operation of the circuit is determined by the load itself, resulting in Automatically act to protect itself. For example, during overload or fault conditions, the circuit stops vibrating and damage to the components is thereby forestalled.

The switching means is respectively interlocked with the first, second, third and fourth switching means, and when the switching means is on, detects the voltage across at least a portion of each switching element;
It includes first, second, third and fourth sensing means for initiating a shutdown of the device if the voltage is above a predetermined level. Each of the sensing means simultaneously initiates the shutoff of other switching elements that are on.

The switching means are turned on by means preferably inductively connected to said primary winding.

Each switching element includes one or more transistors.

The voltage sensing means herein utilizes electronic switches, preferably including field effect transistors, for connecting the base of each transistor to a predetermined voltage.

The device includes energy storage means, preferably constituted by a single capacitor and connected in parallel to the primary winding.

The output of the secondary winding of the transformer is rectified to provide a DC welding current, which welding current is controlled by a variable inductor in the output lead of the secondary winding.

The present invention exhibits the following effects with the above-described configuration.

While each switching element is in the on state, the terminal voltage of at least a portion of the switching element, here the collector-emitter voltage of the transistor, is detected, and if that voltage is above a predetermined level, the switching element is switched off. This causes the first and fourth switching elements 12, 18 and the second and third switching elements 14, 16 to alternately turn on, allowing the current from the power source to flow without voltage doubling. alternately in opposite directions through the primary winding, creating a circulating current in the primary winding and the energy storage means, after which the first and second switching elements and the third and fourth switching elements are turned off, respectively. It returns energy to the power supply when it is used.

For this purpose, the four switching elements are used to control the current flowing alternately in opposite directions through the primary winding, with means for turning on the switching elements (bias circuit) and sensing means helping to turn on each switching element. By applying an appropriate voltage and monitoring the collector-emitter voltage of each switching element, the switching element can be turned off when the voltage is greater than a predetermined voltage value.

Therefore, the maximum rate of change in the collector-emitter voltage of any switching element is controlled by the capacitor 28, which is the energy storage means.
This capacitor provides a path for the load current at the correct moment and can ensure that the correct collector-emitter voltage changes at a controlled rate during switching.

The invention also protects the components of the circuit, since in the event of an overload or faulty operation, the oscillatory operation due to self-excited oscillation is stopped or the current drawn from the circuit is limited as much as possible.

Furthermore, the present invention provides that the maximum voltage applied alternately between the primary windings with opposite polarity is equal to the power supply voltage;
Since there is no voltage multiplication operation, switching elements can be chosen with voltage ratings equal to the supply voltage.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in detail with reference to the accompanying drawings, which show circuits of a welding device according to preferred embodiments thereof.

The drawing shows a welding transformer 10, four transistor switches 12, 14, 16 and 18;
A bias circuit 20 and a detection circuit 22 provided corresponding to each of circuits 16 and 18 are illustrated.

Welding transformer 10 includes a primary winding 24 and a secondary winding 26. The primary winding 24 is shunted by a capacitor 28 and the secondary winding 26 is
It is connected to four rectifiers in a bridge configuration, also indicated collectively by the reference numeral 30. The bridge configuration rectifier 30 has output terminals 32 and 33 which, in use, are connected to a welding electrode and to the workpiece to be welded.

The bias circuit 20 has the same configuration as the detection circuit 22, but the transistor switch 1
2, 14, 16, and 18, respectively. Thus, in the following the configuration of only one bias circuit 20 and only one sensing circuit 22 will be described.

The bias circuit 20 is connected to the primary winding 24 of the welding transformer.
It includes a winding 34 that is inductively coupled to. The winding is shunted by a capacitor 36 and a diode 38 in series and connected by a diode 40 to the base of an interlocking transistor switch. Although each transistor switch 12, 14, 16, 18 in a real case would consist of a number of transistors connected in parallel, here for convenience each transistor switch 12, 14, 16, 18 is constructed from one transistor. Treated as consisting of transistors.

Sensing circuit 22 includes a field effect transistor 42 with a zener diode 44 and a winding 46 connected in parallel between the gate and source of field effect transistor 42 . The gate is connected to the collector of the coupled transistor switch through a second zener diode 48 and an RC network.

The winding 34 of the biasing circuit 20, which is coupled to the transistors 12 and 18, respectively, is connected in one sense to the primary winding 24, but in the other two, which is coupled to the transistors 14 and 16.
The windings 34 of the two bias circuits 20 are otherwise coupled to the primary winding 24. Additionally, windings 46 of sensing circuit 22 that are associated with transistors 12 and 18 are inductively coupled to each other, while windings 46 of sensing circuit 22 that are associated with transistors 14 and 16 are inductively coupled to each other. is connected to.

Each of transistors 12, 14, 16, 18 has a free transistor connected between its collector and emitter.
shunted by wheel diodes 52, 54, 56, and 58, respectively.

Transistor 12,1 in bridge configuration
4, 16, 18 are connected between ground and a supply voltage V, drawn for example from a rectified three-phase source.

During operation of the welding device, transistor pairs 12 and 18 and 14 and 16, respectively, are alternately turned on so that the power source is connected to its primary winding 24.
connected in opposite polarity to. The alternating magnetic flux induces a voltage in the secondary winding 26, which is used to supply welding current to the welding electrode.

The operation of the circuit is as follows. Initially, transistor pair 12 and 18 are turned on by a pulse applied to the bases of the two transistors 12, 18 by means not shown. Therefore, the current flows from the power supply V to the transistor 1
2, flows through primary winding 24 and transistor 18 to ground. The transistors 12, 18 are then driven into further saturation by the base current drawn from the winding 34 coupled to the primary winding 24.

Since transistors 12 and 18 remain on, the full voltage V is applied to primary winding 24 and the magnetic flux in the ferrite core of the transformer increases linearly. When the magnetic flux is saturated, the magnetizing current drawn by the primary winding 24 is
The collector current flowing through the two transistors 12 and 18 increases rapidly until the total current drawn by its primary winding 24 is equal to the product of the current gain and the base current. When the collector current exceeds this value, the two transistors 12, 18 tend to come out of saturation and power dissipation increases.

As transistors 12 and 18 move out of saturation, their collector-emitter voltage increases. Since the current gains of transistors 12 and 18 are not the same, the result is that one of transistors 12 and 18 reaches its maximum collector current before the other. Thus, the collector-emitter voltage of the associated transistor increases more rapidly than that of other transistors. As an example, assume here that this preceding transistor is transistor 12. The collector-emitter voltage of this transistor 12 is continuously monitored by the respective sensing circuit 22, and when that voltage exceeds the zener voltage of the zener diode 48, the field effect transistor 42 is turned on, thereby The base of transistor 12 is connected via diode 38 to a negatively charged capacitor 36 . The charged base region of transistor 12 is thereby discharged and transistor 12 is turned off with a fairly short collector current fall time.

Since transistor 18 is still on, capacitor 28 begins to discharge. Since the right side of capacitor 28 is clamped to ground via transistor 18, a circulating current is established in that capacitor and in primary winding 24. At this point, there is no current flow from or to the power supply V. As capacitor 28 begins to change polarity, i.e. as its left side becomes negative,
Diode 54 turns on provided transistor 18 is still on. Current then flows through transistor 18 to ground, and from ground through diode 54 to the capacitor. If, on the other hand, transistor 18 were to be turned off by the action of the respective cross-coupled winding 46, the potential between the two terminals of capacitor 28 would float. If the voltage across capacitor 28 is completely reversed in polarity and exceeds the supply voltage V, diode 5
4 and 56 are turned on at the same time, and the excess energy is returned from that transformer to the power supply.

After the stored magnetic energy is returned to the power source,
Transistors 14 and 16 beginning to conduct
is turned on by the voltage across base winding 34. Therefore, current from the power source V flows through the primary winding 24 in the opposite direction. In this manner, the above process is repeated to establish alternating magnetic flux fields within the transformer core.

The voltage induced in the secondary winding 26 is rectified in a bridge rectifier 30 and supplied to terminals 32 and 33 for welding. The welding current drawn is controlled by a variable inductor 64 connected to the output lead of the secondary winding.

The circuit configuration described has the configuration of a self-excited bridge circuit. 4 transistors 12,1
4, 16 and 18 are used to control the current flowing in opposite directions and alternately through the primary winding 24. The bias circuit 20 consists of a suitable pair of transistors.
2,18 and 14,16 are used to turn on. This bias circuit 20 also
Respective transistors 12, 14, 16, 18
Apply appropriate voltage to help turn on. The detection circuit 22 includes each transistor 12,1
monitor the collector-emitter voltages of transistors 4, 16, and 18 and turn on each transistor pair 12, 18 and 14, 16 when the collector-emitter voltage of one of that transistor reaches a predetermined value. -Used to turn off. The maximum rate of change of the collector-to-emitter voltage of any transistor is such that it provides a path for the load current at the correct instant, and
Capacitor 28 that ensures that the emitter voltage changes at a controlled rate during switching
controlled by. Therefore, this self-oscillating circuit is load dependent. The design is such that in the event of overload or fault operation, the oscillatory operation is stopped or the current drawn from the circuit is limited as much as possible. This is an important advantage in that the components of the circuit are completely protected.

In the configuration of the present invention, the maximum voltage applied between the primary windings 24, alternately with opposite polarity, is equal to the power supply voltage. Therefore, since there is no voltage multiplication operation, the transistors used as switching elements can be chosen with a voltage rating equal to the supply voltage. A single capacitor used for buffering is substantially less expensive and much simpler than an equivalent regeneration network for transistor protection, yet equally effective.

In a welding machine constructed according to the principles of the present invention, the average output current was 200A, continuously adjustable from 0 to 200A, and the short circuit current was 300A. The open circuit voltage was 80V and the weight of the welding machine was 6Kg. The welding machine was operated with either a 380V, 50Hz three-phase power supply or a 220V, 50Hz single-phase power supply, and its output frequency was 15-20KHz.

Note that to the extent that the circuit of the present invention is self-excited, the exact operating frequency is determined by operating conditions. However, when it comes to circuit design,
Care has been taken to ensure that the operating frequency is sufficiently high in order to reduce the iron core size. On the other hand, the frequency must not be so high that electrical losses in the core become significant.

[Brief explanation of drawings]

The only accompanying drawing is a schematic diagram of a preferred embodiment constructed in accordance with the principles of the invention. 10: Transformer, 12, 14, 16, 18: Transistor switch, 20: Bias circuit, 2
2: Detection circuit, 24: Primary winding of transformer 10, 2
6: Secondary winding of transformer 10, 28: Capacitor,
30: Rectifier block, 34: Winding, 36: Capacitor, 38, 40: Diode, 42: Field effect transistor, 44: Diode, 46: Winding, 48: Zener diode, 52-58: Free wheel diode , 66, 62: Connection point, 64: Variable inductor.

Claims (1)

[Scope of Claims] 1. A switching element including first and second switching elements 12, 14 connected in series, and third and fourth switching elements 16, 18 connected in series; 2 switching element 1
2, 14, and the third and fourth switching elements 16, 18 are connected to the power supply V in a circuit that operates by load-dependent self-oscillation under a sufficient supply voltage without voltage doubling operation. a primary winding connected in parallel between the first and second switching elements 12, 14 and between the connection points 60, 62 of the third and fourth switching elements 16, 18; A transformer 10 having a wire 24 and a secondary winding 26 from which the welding current is drawn.
and self-excited switching means 20, 22, 28 arranged in a circuit operating in dependence on said load, said self-excited switching means being coupled to a primary winding 24 for turning on the switching element. means 34 and first to fourth switching elements 12 to 18
first to fourth detection means 22 respectively interlocked with the switching elements, each of which detects the voltage between the terminals of at least a portion of the switching element while each switching element is in the on state; If the switching element is above the above level, the switching element starts switching off, thereby turning on the first and fourth switching elements 12, 18 and the second and third switching elements 14, 16 alternately;
voltage regulating means and electronic switching means 42 connected in parallel to said primary winding 24 for causing current from said power source V to flow alternately in opposite directions through said primary winding 24 without voltage doubling; energy storage means 28 which generates a circulating current in the primary winding and the energy storage means, after which the first and second switching elements and the third and fourth switching elements are respectively turned off; A high-frequency welding device comprising: a device that returns energy to a power source; and a device that returns energy to a power source. 2 Each switching element 12 to 18 has at least one
each sensing means 22 includes a voltage regulating means and an electronic switching means 4.
2, arranged so that when switching off of each switching element is initiated, respective corresponding electronic switching means are operated to apply a predetermined voltage to the base of each switching element transistor. A high frequency welding device according to claim 1, characterized in that: 3. characterized in that each electronic switching means 42 comprises a field effect transistor having a gate coupled to the emitter of a corresponding switching element transistor and connected in series with a corresponding voltage regulating means coupled to the collector of said switching element transistor. A high frequency welding device according to claim 2. 4 The means coupled to the first and fourth sensing means 22 and the means coupled to the second and third sensing means 22 cause switching off of one of the first and fourth switching elements 12, 18. When initiated, the switching off of the other of the first and fourth switching elements is initiated substantially simultaneously and the switching off of the other of the first and fourth switching elements 1
When the switching off of one of the switching elements 4 and 16 is started, the switching off of the other switching element of the second and third switching elements is started substantially simultaneously. The high-frequency welding device according to any one of items 1 to 3.