INVERTER TYPE POWER SOURCES

For site welding and repair applications, a need was felt for long time to have light weight arc welding power source. Even though, a petrol driven rotary converter is portable, the weight is considerable and it produces lot of noise and smoke. Where power connection is available a simple rectifier type may do the job but not always. For example, for remote and elevated level welding, it is highly inconvenient to drag heavy welding cables and the cost of long welding cables is also high. Therefore to avoid these problems a new type of power source has been developed. This is called inverter type. A schematic is shown in Fig.

The weight and size reduction is achieved by using a HF step down transformer, to produce necessary arc voltage. Transformer size and weight are inversely related to the frequency of operation. A Normal 50 Hz step down welding transformer is bulky and heavy because the frequency is low. If the frequency is increased to say 5 to 10 kHZ, then the transformer (made of ferrite cores) size and weight are drastically reduced. This is the principle behind inverter type power sources. Input voltage is directly rectified and is fed to a inverter circuit. The inverter circuit may be made of either thyristors or transistors. The inverter circuit generates HF AC  (5 to 10 kHz) and the voltage is step down by a HF transformer. The transformer output is rect ified to give DC output . The inverter circuit can be easily controlled in a closed loop manner to give the desired output characteristics.