a fourth switching element disposed between a control terminal of {TAIL ~ the first switching element} and a control terminal of {HEAD ~ the third switching element} 
a fourth switching element disposed between a control terminal of { TAIL ~ the first switching element } and a control terminal of { HEAD ~ the third switching element }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD