JPH026068A - Dc welding power source - Google Patents

Abstract

PURPOSE:To prevent deflected magnetization of a secondary winding so as to improve the utilizing efficiency of a transformer by providing a voltage detection circuit which detects a reverse voltage produced in the primary winding of a DC welding power source and a switching circuit which is conducted by the detect signal of the voltage detection circuit and suppresses the reverse voltage. CONSTITUTION:A reverse current produced in the primary winding L1 of a transformer 3' when a semiconductor switching element 4 is turned off is detected by a voltage detection circuit provided with a constant-voltage diode 22. An FET 21 connected in parallel with the primary winding L1 of the transformer 3' is conducted by the detect signal of the circuit. Therefore, occurrence of such a state that the reverse voltage exceeds a constant-voltage value decided by the diode 22 can be prevented and deflected magnetization of the secondary winding L3 of the transformer 3' can also become possible. Moreover, when the constant voltage value is set higher than the output value of a DC power source, the conducting rate of the FET 21 can be improved to >=50% and, as a result, the utilizing efficiency of the transformer can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a DC welding power source for a high frequency inverter welding machine,
In particular, the present invention relates to a DC welding power source that can reduce the number of windings in a transformer.

[Conventional technology]

Figure 3 shows the main circuit of a conventional DC welding power supply. In the figure, (1) is a DC power supply with three-phase AC input; (2)
is a capacitor that is connected in parallel to the output side of this DC power supply (1) to smooth the output of the DC power supply (1), and (3) is a transformer that has three windings, L1%, L2, and L3. The winding polarities of lines L1, L2, and L3 are shown without markings. The number of turns of the winding and L2 are the same, and the positive output of the DC power supply (1) is connected to the connection point thereof. (4)
is a semiconductor switching element (hereinafter referred to as a transistor) composed of, for example, a transistor, whose collector is 7
, is connected to the remaining side of the winding Ll of the transformer (3), and its emitter is connected to the negative output of the DC power supply (1). (5) is a diode I, whose cathode side is connected to the remaining side of the winding L2 of the transformer (3), and whose anode side is connected to the negative output of the DC power supply (1). (6) is the welding machine control circuit,
Its output is input to the base of the transistor (4).

(7) is a diode 11 whose anode is connected to the unmarked end of the winding L3 of the transformer (3).
(8) is a DC reactor, and the diode ■! (7)
connected in series to the cathode side of the (9) is a diode III whose cathode is the diode II above.
(7) is connected to the cathode side, and the anode is connected to the remaining side of the winding L3 of the transformer (3). (10) is a current detector, and the above DC reactor (
8) in series, and its detection output is input to the welding machine control circuit (6).

A conventional DC welding power source is configured as described above, and the output of the DC power source (1) with three-phase AC input is connected to a capacitor (
2) is smoothed. The output of this smoothed DC power supply (1) causes current to flow through the winding of the transformer (3) by switching on the transistor (4) which is operated by the command signal of the welding machine control circuit (6). become. The current at this time is a so-called current proportional to the welding current that flows from the winding of the transformer (3) to the diode n (7), the DC reactor (8), and the current detector (10) to the welding part. , and the excitation current for exciting the transformer (3). At the same time, transformer (
The direction of the voltage induced in each of the windings 3, L2, and L3 in 3) is such that the positive side of the windings L+, L2, and L3 in the figure is positive. Therefore, the induced voltage in the winding L2 puts the diode I(5) in a blocking state, and no current flows. Next, when the transistor (4) is switched off by a command signal from the welding machine control circuit (6), a voltage generated by the excitation inductance and leakage inductance is applied across the winding of the transformer (3). It occurs in the direction opposite to the induced direction when the switch is turned on (4). At this time, the winding L of the transformer (3)
2. A voltage in the opposite direction is similarly induced in L3. The reverse voltage applied to winding L3 puts diode II (7) into a blocking state. As a result, no current flows through the winding L3. In this case, the welding current is generated without interruption by passing the electromagnetic energy stored in the DC reactor (8) through the external load (welding part) and making the diode (9) conductive to circulate it. Although the flow will gradually decrease, the welding current is constantly detected by the current detector (10) and the welding machine control circuit (6)
In the welding machine control circuit (6), it is compared with the set target value and outputs a switch-on command and a switch-off command to the transistor (4) to operate the transistor (4) as much as possible to reach the target value. By doing so, it is possible to obtain an arbitrary target welding current.

On the other hand, as mentioned above, the transistor (4)
When it turns off and a voltage in the opposite direction is induced in the winding L2,
While this voltage exceeds the smoothed output voltage of the DC power supply (1), the forward voltage of the diode I (5) is applied, and the diode I (5) becomes conductive. A charging current will flow to the capacitor (2).

As a result, the reverse voltage generated in the winding L2 does not exceed the smoothed output voltage value of the DC power supply (1).

That is, the same applies to the reverse voltage generated in the winding L1. Therefore, the voltage applied to the collector of the transistor (4) is 2 times the output voltage value of the smoothed DC power supply (1).
The breakdown voltage of transistor (4) is
You can set it slightly higher than this value. In addition, in this way, the same voltage with the same peak in the positive and negative directions is always applied to the winding L1 of the transformer (3).
So that the product of each voltage value and each application time is constant,
As long as this main circuit is used, the iron core of the transformer (3) will not be biased and magnetic saturation will not occur due to the eccentric magnetization of the iron core, so overcurrent damage to the transistor (4) can be prevented. Here, as mentioned above, the product of the positive and negative voltage values and each applied voltage can be made constant by the transformer.
(3) The conduction rate to the winding L1 [(conduction period/(conduction period + non-conduction period)) x 100) is up to 50%, and it is sufficient to use it below this value.

[Problem to be solved by the invention]

In the conventional DC welding power source as mentioned above, a transformer (3
), three windings Ll, L2, and L3 are required for the transformer (
Since the transformer (3) can only be used when its conductivity is less than 50%, there was a problem in that the usage efficiency of the transformer (3) decreased.

This invention was made to solve the above problems, and is a DC welding power source that can reduce the number of windings of a transformer to reduce weight, volume, and price, and improve the conductivity of the transformer. The purpose is to obtain.

[Means for Solving the Problems] A DC welding power source according to the present invention is a transformer in which a series body of a primary winding of a transformer and a semiconductor switching circuit is connected to the output side of a DC power source that inputs AC power. The transformer is configured to allow current to flow in only one direction, and the secondary output of the transformer is
A DC welding power source used as a welding output after rectification includes a voltage detection circuit having a constant voltage diode for detecting a reverse voltage generated in the primary winding when the semiconductor switching element is switched off; A switching circuit connected in parallel and made conductive by a detection signal from the voltage detection circuit to suppress the reverse voltage below a set value is provided.

[Effect]

In this invention, the reverse voltage generated in the primary winding of the transformer when the semiconductor switching element is switched off is
It is detected by a voltage detection circuit having a constant voltage diode, and this detection signal causes a switching circuit connected in parallel to the primary winding of the transformer to conduct. Therefore, it is possible to prevent the reverse voltage from exceeding the constant voltage value determined by the constant voltage diode, and it is possible to prevent biased magnetization even with the secondary winding as a transformer. Further, by setting the constant voltage value higher than the output value of the DC power supply, it is possible to increase the conductivity to 50% or more and improve the usage efficiency of the transformer.

〔Example〕

FIG. 1 shows an embodiment of the present invention.
The same reference numerals as in the figures indicate the same or corresponding parts. A transformer (3') has a two-winding structure with a winding L1 on the primary side and a winding L3 on the secondary side. These windings, L
The windability of No. 3 is indicated by a black mark in the figure. Further, the application side of the winding is connected to the positive output of the DC power supply (1), and the other side is connected to the collector of the transistor (4).

(21) is an FET whose drain is connected to the above transformer (3).
It is connected to the winding L1 of the transistor (4) on the side connected to the collector of the transistor (4), and the source is connected to the output side of the winding L1. (22) is a constant voltage diode, the cathode of which is connected to the drain of F ET (21), and the anode of which is connected to the gate of F ET (21). (23) is a diode (2), the cathode of which is connected to the source of the F ET (21). (24) is a resistor I, one end of which is connected to the anode of the diode IV (23), and the other end of which is connected to the anode of the diode IV (23).
It is connected to the gate of E T (21) and the anode of the constant voltage diode (22).

In the DC welding power source configured as above, the output of the DC power source (1) with three-phase AC input is the capacitor.
Smoothed in (2). The output of this smoothed DC power source (1) is applied to the winding of the transformer (3') by switching on the transistor (4) operated by the command signal of the welding machine control circuit (6).

A current will be passed through. The current at this time is the transformer (
A current proportional to the so-called welding current flows from the winding L3 of the coil L3 through the diode n (7), the DC reactor (8), and the current detector (lO) to the welding area, and excites the transformer (3'). This is the combined value with the excitation current for At this time, each winding Ll, L3 of the transformer (3')
It goes without saying that the direction of the voltage induced in both the windings and L is such that the side marked with black in the figure is positive. Next, when the transistor (4) is switched off by the command signal of the welding machine control circuit (6), a voltage is generated across the winding L1 of the transformer (3') due to its excitation inductance and leakage inductance. It occurs in the opposite direction to the induced direction when the transistor (4) is switched on. At this time, winding L3 of transformer (3')
Similarly, a voltage in the opposite direction will be induced. The reverse voltage applied to winding L3 is applied to diode TI
Let (7) be in the blocking state. As a result, no current flows through the winding L3. In this case, the welding current passes the electromagnetic energy stored in the DC reactor (8) due to current energization through the external load (welding part) and the diode ++
r (9), the welding current flows without interruption and gradually decreases, but the welding current is constantly detected by the current detector (10) and the welding machine control circuit (6) It is input to the welding machine control circuit (6
), a switch-on command and a switch-off command are output to the transistor (4) so that the target value is compared with the set target value, and an arbitrary target welding current is obtained by operating the transistor (4). It is possible to do so. On the other hand, when the transistor (4) is switched off as described above and a reverse voltage is generated across the winding, this voltage is applied to the forward direction of the diode IV (23) and the resistor I.
(24) to the constant voltage diode (22), and while a voltage that attempts to exceed this constant voltage characteristic is applied, the constant voltage diode (22) is ON.
Show characteristics. As a result, voltage is supplied to the gate of F E T (21), and F E T (21)
is switched on.

As a result, the reverse voltage generated across the winding of the transformer (3') is prevented from exceeding a certain value determined by the constant voltage diode (22). At this time, if the constant voltage value of the constant voltage diode (22) is made approximately equal to the smoothed output voltage value of the DC power supply (1), the windings of 1 to lance (3') can be adjusted. The generated voltage is always a voltage with approximately the same value of peak with positive and negative directions, and as long as this main circuit is used so that the product of each voltage value and each application time is constant, the transformer ( Since the iron core (4) is not biased and magnetic saturation accompanying the biased magnetization of the iron core does not occur, overcurrent damage to the transistor (4) can be prevented. Also, at this time, the voltage applied to the collector of the transistor (4) does not exceed approximately twice the output voltage value of the smoothed DC power supply (1), and the withstand voltage of the transistor (4) is lower than this value. Just make it a little higher. Here, the product of the positive and negative voltage values and each applied voltage as described above can be kept constant only when the conductivity to the winding L1 of the transformer (3') is up to 50%, and it must be used below this. It's a good thing. On the other hand, when trying to increase the conductivity to 50% or more and improve the usage efficiency of the transformer (3'), the constant voltage value determined by the constant voltage diode (22) is changed to the smoothed DC power supply. It is sufficient to raise it above the output value of (1). However, this constant voltage value needs to be smaller than the voltage value obtained by subtracting the output voltage value of the DC power supply (1) from the withstand voltage value of the transistor (4).

Therefore, by suppressing the reverse voltage of the winding L1 of the transformer (3') below a certain value, the two-winding transformer (3')
It becomes possible to do this.

In addition, in the above embodiment, one constant voltage diode (22
), the case where the reverse voltage of the winding L1 is detected is shown.
It is also possible to obtain arbitrary constant voltage characteristics by connecting a plurality of constant voltage diodes in series.

Moreover, as shown in FIG. 2, the drain I! of F E T (21)! (25) may be connected in series to form a switching circuit to reduce loss at FET (21).

Furthermore, the switching circuit may be configured using so-called bipolar transistors instead of using FET (21).

〔Effect of the invention〕

As explained above, this invention connects a switching circuit in parallel to the primary winding of a transformer, detects the reverse voltage of the primary winding with a voltage detection circuit having a constant voltage diode,
Since the switching circuit is operated so that this reverse voltage does not exceed a certain value, it is possible to prevent unbalanced magnetization even in the secondary winding as a transformer, reducing weight, volume, and cost. This has the effect of increasing the conductivity and improving the usage efficiency of the transformer.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main circuit of a DC welding power source showing one embodiment of the present invention, FIG. 2 is a partial circuit diagram showing another embodiment of the invention, and FIG. 3 is a main circuit diagram of a conventional DC welding power source. FIG. 2 is a configuration diagram showing a circuit. 1)...DC power supply, 3')...Transformer, 4)...Transistor, 21...FET. 22... Constant voltage diode, 23... Diode [V. 24)...Resistance I, 25...Resistance TI. In each figure, it is shown. The same symbols indicate the same or equivalent parts.

Claims (1)

[Claims] A series body consisting of the primary winding of a transformer and a semiconductor switching element is connected to the output side of a DC power source that receives AC power as input, so that current flows in only one direction through the transformer,
In a DC welding power source that uses the secondary output of this transformer as a welding output after rectifying it, a voltage detection circuit has a constant voltage diode that detects the reverse voltage generated in the primary winding when the semiconductor switching element is switched off. and a switching circuit that is connected in parallel to the primary winding and is turned on by a detection signal from the voltage detection circuit to suppress the reverse voltage below a set value.