JPS6317551B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply circuit that detects the output supplied from a welding machine to a load, compares the detection signal with a preset reference signal, and controls the output using the difference signal. It is. More specifically, the present invention relates to a circuit for detecting the output.

FIG. 1 is a block diagram of a feedback control type constant current arc welding power supply circuit that detects current using an alternating current circuit.

In the figure, 1 is a transformer, 2 is a current detector such as a current transformer, 3 is a controllable semiconductor element such as a thyristor, and 4 is an arc load. Reference numeral 5 denotes a signal conversion circuit, and the output signal e ₁ and the reference voltage e ₀ from the current setting reference voltage circuit 6 are applied to an error amplifier 9, and the difference voltage therebetween is amplified. 8 is a phase control circuit whose firing signal changes depending on the input voltage, and 7 is a gate signal amplification circuit for the thyristor 3.

This circuit works so that the voltage difference between the output signal e ₀ and the reference voltage e ₁ is always constant even if the load 4 changes.
Constant current characteristics can be obtained.

FIG. 2 shows a conventional example of the current detector 2 and signal conversion circuit 5 shown in FIG.
11 is a current transformer (CT) that induces a current approximately proportional to the current flowing through the cable 10 in the secondary winding. A diode 12 forms a bridge rectifier circuit to rectify the detection signal. A resistor 13 produces a voltage drop _e1 proportional to the current of the current detection circuit.

FIG. 3 is a block diagram of a feedback control type constant current arc welding power supply circuit that detects current using a DC circuit.

In the figure, 14 is a current detector such as a shunt (shunt), and 15 is a signal conversion circuit, which in the case of the conventional example functions as an amplifier, so that the difference between the output e ₁ and the voltage e ₀ of the reference voltage 6 is constant. The other functions are the same as the circuit shown in FIG. 1, and constant current characteristics can be obtained.

FIG. 4A shows the relationship between the circuit current I and the detected voltage _e1 , which changes linearly.

Therefore, the relationship between the reference voltage e ₀ and the circuit current I is a straight line as shown in FIG. 4B, and the change in the circuit current with respect to the change in the reference voltage e ₀ does not change even in a small current range. For this reason, in a welding machine that can adjust the circuit current from 5A to 500A, for example, e ₀
When the current changes slightly, the current changes by 5A at around 500A.If the current changes by 5A at around 500A, the rate of change in the current in the small current range is large and it is difficult to adjust. Also, the same current value
Even a change of 5A is 1% compared to 500A, but 5A
This can be as high as 100% for the reference voltage, and when the ambient temperature or power supply voltage fluctuates, even a slight change in the reference voltage causes a large change in the small current range, making it difficult to improve accuracy in the small current range. .

In the above embodiment, a constant current circuit is shown, but the same thing can be implemented with a constant voltage circuit if the detection signal is the load voltage of the circuit. In other words, it has been difficult to improve accuracy in the small voltage range with conventional constant voltage circuits.

SUMMARY OF THE INVENTION An object of the present invention is to provide a feedback circuit that eliminates the drawbacks of the prior art described above and makes it easy to adjust the output even in a small output range.

In order to achieve the above object, the present invention provides a feedback amount detection circuit that increases the output at an inflection point where the rate of change of the detection signal with respect to the output (output current or output voltage) is larger at the time of small output than at the time of large output. The present invention is characterized in that it includes means for continuously changing the detection signal as the detection signal changes.

FIG. 5 shows an embodiment of the detection circuit according to the present invention, and shows a current detector and a signal conversion circuit that are improved from the feedback control constant current power supply circuit that detects current using the AC circuit of FIG. In FIG. 5, the same parts as in FIG. 2 are given the same reference numerals. The difference from the circuit shown in FIG. 2 is that a nonlinear element 16 such as a diode is connected in series with a resistor 13 between the output terminals of a rectifier circuit using a diode 12.

In this way, the secondary output voltage of the current transformer 11 overcomes the forward voltage drop of the diode 16, and as is known, the dynamic resistance of the diode 16 is large in the low output range where sufficient secondary current does not flow. As shown in FIG. 6A, the relationship between the circuit current I and the detected voltage e ₂ is such that the rate of change of the detected voltage e ₂ with respect to the circuit current I is larger than in the large output range. Therefore the reference voltage
The relationship between e ₀ and the circuit current I is as shown in FIG. 6B, and it is possible to reduce changes in the circuit current in a region where the reference voltage e ₀ is small. As a result, when e ₀ is slightly changed, for example, the circuit current I becomes 500A.
Even if it changes by 5A in the vicinity, it can be suppressed to about 1A at around 5A. Also, by connecting the low resistance 17 as shown by the broken line in FIG.
The slope of the characteristic shown in FIG. 6A can be varied.

FIG. 7 shows another embodiment of the present invention, and shows an example in which current is detected using the DC circuit shown in FIG. A shunt 14 generates a voltage proportional to the circuit current I. The signal conversion circuit 15 in FIG.
8, a DC amplifier circuit 19 in which the input voltage _e3 is proportional to the output current I as shown in FIG. .

In this case as well, the relationship between I and e ₄ is as shown in FIG. 8B, and e ₄ changes largely in the small current range of I.

As a result, as in FIG. 6B, the change in the circuit current I becomes small in the region where the reference voltage e ₀ is small.

In this embodiment, a constant current circuit has been described, but it is clear that the present invention can be similarly applied to a constant voltage circuit if the detection signal is the load voltage of the circuit. Further, although the signal conversion circuit 20 is shown as a broken line output having one inflection point, the number of inflection points is not limited to this and may be two or more.
It may also be a curve using, etc.

As described above, according to the present invention, it is possible to reduce the rate of change in output with respect to a change in reference voltage in a region where the output current or output voltage is small, and to adjust the current or voltage in the small output region where fine adjustment is required. is easy.

Even if the reference voltage changes due to changes in the power supply voltage or ambient temperature, the rate of change in the output with respect to the change in the reference voltage in the small output range is small, so the output change is small, and a welding machine with high precision output can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a feedback control type arc welding power supply circuit that detects current in an alternating current circuit, Fig. 2 is a circuit diagram showing a conventional example of the detection circuit of Fig. 1,
Figure 3 is a block diagram of a feedback control type arc welding wire circuit that detects current in a DC circuit.
The figure shows the relationship between the detection voltage, reference voltage, and circuit current in a conventional example, Figure 5 is a circuit diagram showing an embodiment of the present invention, and Figure 6 shows the detection voltage and reference voltage in the embodiment of Figure 5. , a diagram showing the relationship between the circuit current, FIG. 7 is a block diagram showing another embodiment of the present invention, and FIG. 8 is a diagram showing the relationship among the detection voltage, reference voltage, and circuit current of the embodiment of FIG. 7. be. 2... Current detector, 3... Thyristor, 4... Arc load, 5... Signal conversion circuit, 6... Reference voltage circuit, 8
...Phase control circuit, 9...Error amplifier, 13...Resistor,
14... Shunt, 15... Amplifier, 16... Nonlinear element such as diode, 17... Resistor, 18, 19...
amplifier.

Claims (1)

[Claims] 1 A transformer, a thyristor that controls the phase of the output from this transformer, a welding machine load supplied with the output of this thyristor, and a current detection body inserted between the transformer and the welding machine load. , a signal conversion circuit connected in parallel to this current detection body and including a series circuit of a resistor and a diode, a current setting reference voltage circuit that outputs a reference voltage to be compared with the output from this signal conversion circuit, and the signal an error amplifier that outputs a signal corresponding to the difference voltage between the terminal voltage of the series circuit of the conversion circuit and the reference voltage from the current setting reference voltage circuit; A welding power supply circuit comprising a phase control circuit that outputs a gate signal to be controlled.