A power converter apparatus includes a primary bridge having a plurality of diagonally opposed primary power elements, and a secondary bridge having a plurality of diagonally opposed secondary power elements. The pattern may comprise two or three contiguous left frames followed by contiguous black frames followed by two or three contiguous right frames followed by contiguous black frames. Once welded the apertures can be sealed by preferably placing a battery label over the apertures. The tissue stabilizer may be configured for use in surgical procedures, such as performing coronary artery bypass grafting on a warm, beating heart. The current generator includes an adjustable compliance voltage source connected to the power supply terminal. 0Conditional\u2062\u2062Expression\u2062\u20621where f is an overall focal distance of an optical system and f4 is a focal distance of the fourth lens.