SU1542731A1 - Apparatus for limiting no-load voltage of welding transformer - Google Patents

Abstract

The invention relates to a welding technique, in particular, to devices for automatically reducing the no-load voltage of a welding transformer to a safe value. The purpose of the invention is to simplify the device and increase its reliability. The device consists of a welding transformer, a thyristor switch, a control unit, a pulse shaper, and a current sensor. The control unit of the thyristor switch is included in the primary winding of the welding transformer. The control unit is made in the form of a phase-shifting bridge consisting of the secondary windings of the control transformer, capacitance and transistor. The pulse shaper is made on the basis of a zener diode and an RC-chain. The output of the pulse former is connected to the control electrode of the thyristor switch. The base and the emitter of the transistor through a rectifier are connected to the output of a current sensor connected to the primary winding of the welding transformer. When the arc gap is open, there is a safe voltage of 12 V on the secondary winding of the welding transformer. The transistor through the current sensor is covered by a positive feedback on the load current of the welding transformer. Therefore, when the arc gap is closed, the thyristor switch will fully open, ensuring the flow of welding current. After the arc extinguishes, the circuit goes into the mode of limiting the no-load voltage of the welding transformer. 1 il.

Description

The invention relates to a welding technique, in particular, to devices for automatically reducing the no-load voltage of a welding transformer to a safe value.

The purpose of the invention is to simplify the device and increase its reliability.

The drawing shows a schematic diagram of the device.

The device for limiting the no-load voltage of the welding transformer contains a thyristor switch 1 included in the primary winding of the welding transformer 2, switch control unit 3, a pulse shaper 4, an RC circuit 5 to turn off, a current sensor 6 connected to the primary winding

welding transformer 2. The switch control unit 3 contains a control transformer 7, the secondary windings of which 8 and 9 together with the capacitor 10, the first diode bridge 11 and the transistor 12 constitute a phase-shifting bridge. The output of bridge 11 via a diode bridge 13 is connected to a shaper of 4 pulses, which consists of a zener diode 14 and an RC chain 15, 16. The output of the latter is connected to the control electrode of switch 1. The base and emitter of transistor 12 are through an RC chain (17, 18) to disconnect, the first Zener diode 19, the second diode bridge 20 is connected with the output of current sensor 6. The emitter and collector of the transistor 12 are connected to the capacitor 10 and the secondary winding 9 of the control transformer 7 via the first diode bridge 1 1.

ate

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WITH

The device works as follows.

In the initial state, a current flows through the gok sensor 6, the value of which does not exceed the value of the no-load current of the welding transformer 2. With the help of a variable resistor 18 a bias voltage is set at the base of transistor 12, at which the phase angle between the network voltage and the control voltage on switch 1 corresponds to switching on switch 1 at a time corresponding to the open-loop voltage on the secondary winding of the welding transformer 2 approximately 12 V. This voltage is set using a phase-shifting bridge, the transistor 12 of which is a variable active resistance, the value of which depends on the current through the base of the transistor 12. From the output of the phase-shifting bridge through the third diode bridge 13, the full-wave voltage is applied to the input of the imager 4 pulses, in which the zener diode 14, the capacitance 15, and the resistors 16 are formed, the control pointed pointed impulses, which are supplied to the control electrode of the switch 1. The transistor 12 through the sensor 6 gok covered by the positive In conjunction with the load current of the welding transformer 2. At the time of electrode closure, a current flows through the secondary winding of the welding transformer 2 to the product, and the current value increases in the primary winding of the welding transformer 2. Through the current sensor 6, the second diode bridge 20, resistor 18, capacitance 17, this increase | is transmitted to the base of transistor 12, transistor 12 opens slightly, this will reduce the phase shift between the network control voltage AND, the opening angle of switch 1 will shift upwards voltage on the secondary winding of the welding transformer 2. In turn, the secondary current will increase, an increase in the current in the secondary winding of the welding transformer 2 will lead to an increase in the current in its primary winding, and so this process runs like an avalanche different to full0

phase opening of switch 1 and maximizing the secondary current, an electric arc is ignited. This state of the circuit is maintained as long as the welding

arc. After the arc is extinguished due to the discharge of the capacitance 17, the thyristor switch 1 operates for some time in full-phase mode, then the process is reversed as described, and the circuit returns to its initial state.

Compared with the base object prototype, the use of this device allows to simplify the design and increase the reliability of its operation, while reducing power consumption and overall dimensions of the device.

Claims (1)

Invention Formula A device for limiting the no-load voltage of a welding transformer, comprising a thyristor switch included in the primary winding of the welding transformer, a switch switch control unit with a pulse driver, an A-C trip circuit, and a current sensor, 5 and improving reliability, the control unit is designed as a phase-shifting bridge, the two arms of which consist of the secondary windings of the control transformer and two arms from the capacitance, the first diode bridge and the transistor, the emitter of which is connected to 0 the output of the first diode bridge capacity / C-circuit to turn off, the first zener diode and the output of the second diode bridge, the collector of the transistor is connected to the output of the first diode bridge, the input of which is connected to the capacitance and the secondary winding 5 of the control transformer, the output of the phase-shifting bridge through the third diode bridge and the pulse shaper, made in the form of a second Zener diode and / C-chain, is connected to the control electrode of the switch, the base of the transistor is connected to the first Zener diode and / -C-chain to disconnect with the output of the second diode bridge, the input of which is connected to the output of the current sensor included in the primary winding of the welding transformer.