is conducting current or not a 34 high 34 level indicates current is flowing through the diode that is the diode is conducting and the switch is on otherwise the level is 34 low 34 and the switch is off and the diode is not conductive fig1 shows the resulting current vs time waveform for a portion of the load current waveform referring first to fig6 a in the first time period the switches s1 and s2 are turned on simultaneously to increase current to the load in the next period s2 turns off and the current is forced to flow through the antiparallel or flyback diode d3 across s3 during this time the load voltage is zero so the current decreases then switch s2 turns on again building up the current to the load again due to the positive dc bus voltage across the load then switch s1 turns off forcing the current to flow through the antiparallel diode d4 across s4 this switching sequence repeats with periods of both switches s1 and s2 on alternating with periods of time in which one or the other switch s1 and s2 is turned off and the load current flows through the opposite diode the load inductance is key to this operation since the inductance does not allow the load current to change instantaneously for example if s1 is turned off the current flows through the diode d4 across switch s4 this means that although switch s4 is turned off the current flows through s4 39 s antiparallel diode d4 anyway switches s3 and s4 are never.