GB2301495A

GB2301495A - Power supply for electrical welding apparatus

Info

Publication number: GB2301495A
Application number: GB9607354A
Authority: GB
Inventors: Kevin Kirk
Original assignee: Countertone Ltd
Current assignee: Countertone Ltd
Priority date: 1995-04-05
Filing date: 1996-04-09
Publication date: 1996-12-04
Also published as: GB9607354D0

Abstract

The power supply has a transformer T, with a secondary winding connected to welding electrodes 14 and a primary winding connected in series with a transistor power switch 10 (such as an IGBT) across a DC supply 12, and a control circuit 16 which applies a train of pulses to the control electrode of the transistor 10. The pulse train may have a repetition frequency in the range 1 KHz to 100 KHz. The pulse repetition frequency and width may be independently controlled by manual means. Alternatively or additionally, pulse frequency and/or width may be controlled by a feed back circuit responsive to the welding activity, eg. responsive to the light output from the weld, the electrical resistance across the welding electrodes, or the transformer primary current. The DC supply 12 may be provided by a 12 volt battery or by a rectified mains AC source. The apparatus may be in the form of a hand-held welding tool.

Description

ELECTRICAL WELDING APPARATUS The present invention relates to electrical welding apparatus.

Electrical welding apparatus are generally of complex arrangement and relatively large and heavy. Typically such apparatus are powered from the mains and include transformers having special steels to step the voltage down. Commonly the apparatus is powered from a d.c. source via an inverter circuit, which is controlled to vary either the repetition frequency or width of pulses applied to the transformer primary.

We have now devised an electrical welding apparatus which is of relatively simple arrangement.

In accordance with the present invention, there is provided a welding apparatus which comprises a transformer having primary and secondary windings, the primary winding being connected in series with a transistor power switch across a d.c. supply means, and a pair of welding electrodes being connected across the secondary winding, and control means for applying a train of pulses to a control electrode of the transistor power switch.

The d.c. supply means may comprise a battery.

Alternatively, the apparatus may be powered from mains a.c. and include a rectifier for providing d.c. from the mains.

Preferably the repetition frequency of the train of pulses provided by the control means is greater than 1 kHz: preferably the repetition frequency is in the range of 1 kHz to 100 kHz. In any event, preferably both the repetition frequency and width of the pulses are independently variable for example, by manual control of the control means: in this way, the repetition frequency and pulse width can be selected to suit each inaividual use of the apparatus. Alternatively or in addition, the repetition frequency and/or width of the pulses may be varied by a feedback circuit which responds to the welding activity, e.g. in accordance with the light output from the weld, the electrical resistance measured across the welding electrodes or the current passing through the primary winding of the transformer.

The relatively high frequency at which the transformer is driven enables the transformer to be formed of relatively light material and of relatively small size, preferably of ferrite or other high frequency material.

Preferably the drive circuit for the transformer primary comprises a single said power switch (although it may include additional components of passive type).

Preferably the unrectified output of the secondary winding is applied across the pair of welding electrodes.

It will be appreciated that the welding apparatus of the present invention is of relatively simple arrangement, with few components compared with conventional welding apparatus. The apparatus can thus be made of relatively small size and weight and reduced costs: in turn, the apparatus may be formed as a portable e.g. hand-held welding tool.

An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawing, the single Figure of which is a schematic diagram of the electrical circuit of a welding apparatus.

Referring to the drawing, there is shown the electrical circuit of a welding apparatus, comprising a transistor power switch 10 in series with the primary winding of a transformer T, across a d.c. power supply 12. A pair of welding electrodes 14 are connected across the secondary winding of the transformer T. A control circuit 16 supplies a train of pulses to the control electrode or gate of the power switch 10: this train of pulses has a high repetition frequency (above 1 kHz), but both the repetition frequency and width of the pulses are independently variable, by manual control of the circuit 16.

Additionally or instead, the repetition frequency and/or width of the pulses may be controlled by a feedback circuit, as mentioned above. The transistor power switch 10 may comprise an insulated gate bipolar transistor (or IGBT). It will be appreciated that the switch 10 is rendered conductive for the duration of each pulse of the train.

Because of the high frequency at which the transformer T is driven, this enables the core of the transformer T to be formed of high frequency magnetic material (such as ferrite) instead of iron, thus saving weight and size.

The d.c. power supply may comprise a battery, e.g. a 12 volt battery. Alternatively, the apparatus may be mains powered, in which case the power supply comprises means for rectifying mains a.c. to provide a d.c. supply across which the power switch and transformer primary are connected.

It will be appreciated that the drawing is schematic and in practice the circuit will include additional components, but of subsidiary purpose. In any event, it will be noted that the apparatus which has been described is of a simple arrangement with relatively few components, and of relatively small size and weight.

Claims

1. A welding apparatus which comprises a transformer having primary and secondary windings, the primary winding being connected in series with a transistor power switch across a d.c. supply means, and a pair of welding electrodes being connected across the secondary winding, and control means for applying a train of pulses to a control electrode of the transistor power switch.

2. A welding apparatus as claimed in claim 1, in which said d.c. supply means comprises a battery.

3. A welding apparatus as claimed in claim 1, in which said d.c. supply means comprises a rectifier for rectifying a mains a.c. supply.

4. A welding apparatus as claimed in any preceding claim, in which the control means is arranged to provide a said train of pulses at a repetition frequency greater than 1 kHz.

5. A welding apparatus as claimed in claim 4, in which the control means is arranged to provide a said train of pulses at a repetition frequency in the range of 1 kHz to 100 kHz.

6. A welding apparatus as claimed in claim 4 or 5, in which the core of said transformer is formed of ferrite.

7. A welding apparatus as claimed in any preceding claim, in which said control means is controlled or controllable to vary the repetition frequency and/or width of the pulses of said train.

8. A welding apparatus substantially as herein described with reference to the accompanying drawings.