A passive reduced rating output rectifier snubber for plasma cutting power supply

Abstract

R-C snubber circuits are used to absorb the reverse recovery energy of a rectifier diode and limit the associated voltage spike across it as presented by MacMurray (1972). This circuit, while being simple and reliable is unsuitable for applications with power levels above 10 kW due to its high power dissipation. Existing alternatives efficiently recycle the diode reverse recovery energy into the load. However, these suffer from drawbacks such as excessive diode voltage stress or circuit complexity. This paper proposes a reduced rating diode snubber that limits the diode voltage stress over the entire load operating range while keeping the snubber power dissipation to a minimum. A simple circuit model is simulated to evaluate its operation over the entire power supply operating range. It is first experimentally verified with a proof-of-concept 7 kW prototype. Experimental results show a 60 % reduction in power dissipation in addition to a 30 % reduction in diode voltage overshoot when compared with the conventional R-C snubber under nominal operating conditions. Further experimentation with a 100 A, 150 V plasma cutting power supply shows that the output rectifier voltage stress is kept within reasonable limits over a wide load operating range verifying the robustness of the proposed circuit.