High frequency self-oscillating welding apparatus

Claim 1

Welding apparatus which comprises first and second switching elements in series, third and fourth switching elements in series, the first and second switching elements, and the third and fourth switching elements, being respectively connected in parallel to a power supply in a circuit for operating in a load dependent self-oscillatory manner under the full supply voltage without voltage doubling effect, a transformer, the transformer having a primary winding, and a secondary winding from which welding current is drawn, the primary winding being connected between the connection points of the first and second switching elements, and the third and fourth switching elements, respectively, and self-oscillatory switching means arranged in the circuit for operating in such load dependent manner and which includes means coupled to the primary winding for turning the switching elements on, and first, second, third and fourth sensing means associated respectively with the first, second, third and fourth switching elements, each sensing means sensig the voltage across at least part of the respective switching element while it is on, and including voltage regulator means and electronic switch means initiating the switching off of the said switching element if the voltage is above a predetermined level, whereby the first and fourth switching elements, and the second and third switching elements, are alternately turned on, thereby to cause current from the power supply to flow alternately in opposite directions through the primary winding without voltage doubling effect, and further including energy storage means which is connected across the primary winding and which establishes a circulating current in the primary winding and the energy storing means, and which thereafter returns energy to the power supply when the first and second switching elements, and the third and fourth switching elements, respectively, are turned off.