Electronic voltage reducing partic. rectifying device for arc welding - has two thyristors triggered by a control portion having a RC circuit a diac and a triac

摘要

The voltage reducing device has a voltage-reducing portion and a controlling portion. The voltage-reducing portion comprises two thyristors, opt. a number of diodes (for rectifying purposes in d.c. welding equipment) and other electronic parts such as resistors and capacitors, in electrical connection to allow positive pulses of the a.c. input to pass through one of the thyristors and the negative pulses to pass through the other thyristor under control of the controlling portion. The controlling portion comprises a RC circuit with changeable resistance a diac, and a triac in electrical conne-tion with the voltage-reducing portion so that thea.c. input can first charge the capacitor of the RC circuit to a potential sufficient to trigger the diac, then the diac triggers the triac, and the triac in turn effects alternate switch-on and switch-off of the thyristors. Bulky coil-type transformers are dispensed with, a highly stable d.c. or a.c. output is obtd. irrespective of transient current peaks and power is not consumed between welding operations. Thus, the device has only one-eighth of the wt. and only one-tenth of the vol. of conventional devices, and has a power factor of as high as 95% compared with 45% for conventional equipment so that the 15-30V output can do as much work as a 30-60V output. (Provisional Basic previously advised in Week E21).