In a circuit apparatus for transformerless conversion of an electric
direct voltage of a two-pole direct voltage source (1) connected to
ground having a first voltage pole (+) and a second voltage pole (-) into
an alternating voltage, hazardous capacitive leakage currents are avoided
by connecting the direct voltage source (1) to ground and the DC-AC
converter (400) is operated at a controlled intermediate circuit voltage,
a DC-DC converter stage (300) being connected between the direct voltage
source (1) and the DC-AC converter (400), said DC-DC converter stage
providing at its output a +/- voltage that is symmetrical with respect to
the grounding point, two series-connected capacitors (41, 42) having the
same polarity and being connected to ground at their connecting point (V)
and controlled are charged by two buck-boost choppers (100, 200)
connected one behind the other.