JPH0349801Y2 - - Google Patents

Description

[Detailed explanation of the invention] (a) Technical field This invention relates to a power supply circuit used in an arc welding machine that can perform both TIG welding and manual welding, and in particular improves the arc start.
Regarding the power supply circuit for TIG and manual arc welding machines.

(b) Prior art and its drawbacks In recent years, switching control type power supplies for TIG and manual arc welding machines have become popular in place of the conventionally used SCR control type. This switching control type power supply device rectifies the power supply voltage, then switches it and supplies it to the load.It also detects the magnitude of the load current as a voltage level, and performs switching according to the magnitude of the error between the voltage level and the reference level. The load current is set to a predetermined value while varying the frequency and switching pulse width. This switching control type power supply device can make the switching frequency extremely high, so the response speed of the control system is extremely fast.
Therefore, responsiveness to transient changes can be extremely improved.

However, this switching control type power supply
When applied to TIG and manual arc welding machines, it is extremely suitable for TIG welding, where the electrode used is thin and wears out if overcurrent continues for a long time, but the diameter of the electrode is large and the electrode itself is Manual welding, which involves melting, results in a defective state at the time of arc start. In other words, in the latter case, because the set current is reached in a short period of time during a short circuit, the electrode rod sticks to the electrode, making it difficult to start the arc.

(c) Purpose of the invention The purpose of this invention is to eliminate the above-mentioned drawbacks and shorten the hot current time at arc start by utilizing the fast response, which is the original characteristic of the switching control type, in the case of TIG welding. However, in the case of manual welding, the hot current time at arc start is increased by reducing the response, and TIG and manual welding can be used for both manual welding and to ensure a good arc start in either type of welding. Our objective is to provide a power supply circuit for arc welding machines.

(d) Structure and effects of the invention Figure 1 is a block diagram of the current circuit according to this invention. In the figure, terminals a, b, and c are input terminals of a three-phase power supply, 2 is a rectifier circuit, 3 is a smoothing capacitor, and 4 is a switching circuit composed of a switching transistor. The switching output is supplied to the primary side of the inverter transformer 5, and the secondary output is rectified by diodes 6 and 7, smoothed by a reactor 8, and then supplied to a load. The load current is detected by a current detector 9, and a voltage at a level corresponding to the load current is output. The output of this current detector 9 is led to an error amplifier 10, which compares it with a reference voltage E0 and outputs the error to a switching control circuit 11. Switching control circuit 1
1 varies the switching frequency or switching pulse width of the switching circuit 4 depending on the magnitude of the error. By feeding back the secondary side output to the primary side in this manner, the load current on the secondary side can be stabilized.

The output of the current detector 9 is led to an error amplifier 10 and also to a first voltage forming circuit 13 and a second voltage forming circuit 12. Voltage forming circuit 12 includes TIG and manual welding selection switch SW
It receives voltage +B through the contacts. switch
When the SW is on, the voltage +B as shown in the diagram.
is supplied to the second voltage forming circuit 12.
In this state, the manual welding mode is selected. When the switch SW is off, the voltage is +
B is supplied to the first voltage formation 13. switch
When SW is off, TIG welding mode is selected. That is, when the switch SW is turned on and the manual welding mode is selected, the second voltage forming circuit 12 is set to operate effectively, and when the switch SW is turned off and the TIG welding mode is selected, the second voltage forming circuit 12 is set to operate effectively. 1 voltage forming circuit 13
is set to operate effectively. These voltage forming circuits 12 and 13 are further connected to the current detector 9.
The operating state is restricted based on the output of In the second voltage forming circuit 12, when the switch SW is turned on and the manual welding mode is selected, a certain period of time elapses after the current detector 9 detects that the load current starts flowing after the power is turned on. It works until. In addition, when the switch SW is turned off and the TIG welding mode is selected, the first voltage forming circuit 13 operates only for a period after the power is turned on until the current detector 9 detects that the load current flows. . The capacitor 14 is used to measure a certain period of time after the current detector 9 detects the load current.

15 is a load current control voltage forming circuit for setting the load current to a desired magnitude after arc starting. This circuit has a variable resistor and the voltage +B
is divided by the variable resistor, and the divided voltage is output to the error amplifier 10. The voltage formed by the first and second voltage forming circuits 13 and 12 is TIG
It is added to the output voltage of the load current control voltage forming circuit 15 through the welding voltage input circuit 17 and the manual welding voltage input circuit 16, and is output to the error amplifier 10. Therefore, the switching control circuit 11 adjusts the switching frequency or switching pulse width so that the error between the two voltages becomes zero.

Next, the operation of the above power supply circuit will be explained. First, a case where the welding mode is set to TIG welding mode will be explained. For TIG welding mode, switch SW
is off. Therefore, when the power is turned on, the voltage +B is immediately supplied to the first voltage forming circuit 13. Also, voltage +B is load current control voltage forming circuit 1
5 will also be supplied immediately. When the power is turned on, the input voltage to the error amplifier 10 immediately after that becomes equal to the sum of the output voltage VI of the load current control voltage forming circuit 15 and the voltage VT formed by the first voltage forming circuit 13. As a result, the error detected by the error amplifier 10 becomes larger than the error between the reference voltage E0 and the voltage VI, and a switching operation is performed to make the load current larger than the set current. When a certain period of time passes and a load current flows through the secondary side of the inverter transformer 5, the current detector 9 detects this state. Then, the operation of the first voltage forming circuit 13 is stopped and the voltage VT is set to zero. At this time, the input voltage of the error amplifier 10 is the load current control voltage forming circuit 15.
The switching control circuit 11 immediately performs switching control corresponding to the error between the voltage VI and the reference voltage E0. As a result, the waveform of the load current at arc start becomes as shown in FIG. 2A, which is a hot start waveform suitable for TIG welding.

When the welding mode is manual welding mode, the operation is as follows. When the power is turned on, the voltage +B is immediately supplied to the second voltage forming circuit 12 and the load current control voltage forming circuit 15. In this case, the second voltage forming circuit 12 also charges the capacitor 14 with voltage. Immediately after the power is turned on, the input voltage to the error amplifier 10 is the voltage VI as in the TIG welding mode.
and the voltage VM formed by the second voltage forming circuit 12
The size is the sum of . Therefore, the load current becomes larger than the current value set by the load current control voltage forming circuit 15. When a certain amount of time passes after the power is turned on and a load current flows through the secondary side of the inverter transformer 5, the current detector 9 detects this state. Then, as in the case of a TIG welder, the second voltage forming circuit 12 detects this state, but the capacitor 1
Even after the load current starts to flow due to the charging voltage to 4, the voltage VM is outputted to the error amplifier 10 while being gradually lowered for a certain period of time. Therefore, the voltage input to the error amplifier 10 is large immediately after the power is turned on, and after the load current flows, it gradually becomes smaller. Then, after a certain period of time, the voltage VM becomes 0
From then on, the error between voltage VI and reference voltage E0 is 0.
Switching is controlled so that Second
Figure B shows the load current waveform at hot start in this manual welding mode. In this way, in the manual welding mode, unlike in the TIG welding mode, the fall of the current during hot start is slow, and the hot start current can be made suitable for manual welding.

As described above, according to the present invention, a hot start current suitable for TIG welding can be obtained by taking advantage of the inherent response performance of the switching control circuit during TIG welding, and the response performance can be automatically adjusted during manual welding. This makes it possible to obtain a hot start current suitable for manual welding.

(e) Embodiment FIG. 3 is a diagram showing a specific circuit example of the main part of the power supply circuit. The switch SW for switching the voltage forming circuit corresponds to the switch SW'. 1st
The voltage forming circuit 13 is composed of a transistor TR1, a resistor R2, a resistor R3, and a switch circuit SW1. The switch circuit SW1 turns off when receiving the output from the current detector 9. Second voltage forming circuit 12
is composed of a transistor TR2, a resistor R4, a capacitor R5 14, and a switch circuit SW2.
The switch circuit SW2 turns off when it receives the output from the current detector 9, similar to the switch circuit SW1. The TIG welding voltage input circuit 17 includes a resistor R6 and a diode D1. The manual welding voltage input circuit 16 is composed of a resistor R7 and a diode D2. Further, the load current control voltage forming circuit 15 is composed of a variable resistor RS, and the reference voltage E0 is set by a resistor R1.
The voltage across both ends is set to 1.

In the above configuration, when the switch SW' is set to the terminal d, the first voltage forming circuit 13 is selected, and when the switch SW' is set to the terminal e, the second voltage forming circuit 13 is selected.
The voltage forming circuit 12 is selected. switch
When SW' is set to the terminal d, the switch circuit SW1 is turned on immediately after the power is turned on, so the transistor TR1 is turned on. Therefore, resistances R2 and R3
A divided voltage VT is formed. When the load current flows and the current detector 9 detects this state, the switch circuit SW1 turns off, so the above voltage
VT becomes 0. On the other hand, when switch SW' is set to terminal e and manual welding mode is selected, when the power is turned on, transistor TR2 is turned on, so voltage VM divided by resistors R4 and R5 is formed, and the capacitor 14 is started. Note that it takes some time for the voltage VM to be established because of the capacitor 14, but the capacitance of the capacitor 14 is determined so that it can be almost ignored. When the load current flows and the current detector 9 detects this state, the switch circuit SW 2 is turned off, and the transistor TR2 is turned off. Therefore, no voltage is supplied to the resistor R4. However, from that moment on, the charging voltage of the capacitor 14 is discharged via the resistor R5. For this reason, the switch circuit
Even if SW2 is turned off, the voltage VM does not become zero immediately but gradually decreases.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a power supply circuit according to this invention. Figures 2A and 2B are waveform diagrams of hot start current during TIG welding and manual welding, respectively. FIG. 3 is a diagram showing a specific example of the main parts of the power supply circuit. 4... Switching circuit, 10... Error amplifier, 12... Second voltage forming circuit, 13... First
16... Voltage input circuit during manual welding, 17... Voltage input circuit during TIG welding.

Claims (1)

[Claims for Utility Model Registration] A primary side rectifier circuit that rectifies the power supply voltage, a switching circuit that switches the output of the primary side rectifier circuit and inputs it to the transformer, and a secondary side that rectifies and smoothes the secondary output of the transformer. A rectifier circuit, an error amplifier that detects the magnitude of the load current as a voltage level and amplifies the error between that voltage level and a reference level, and adjusts the switching frequency and switching pulse width of the switching circuit according to the magnitude of the error. In the power supply circuit of a TIG or manual arc welding machine equipped with a variable switching control circuit, when TIG welding is selected, the first voltage forming circuit operates for a period after the power is turned on until the load current flows to form a predetermined voltage. a TIG welding voltage input circuit that inputs the voltage formed by the first voltage forming circuit to the error amplifier so that the error with respect to the reference level becomes large; and when manual welding is selected, the load current after power-on is a second voltage forming circuit that operates to form a predetermined voltage until a certain period of time has elapsed since the start of the flow of voltage; A power supply circuit for a TIG and manual arc welding machine, comprising: a manual welding voltage input circuit that inputs the voltage to the error amplifier so as to reduce the error.