U.S. Patent No. 3,808,545 - 04/30/1974 - Gerald Stanley
Comments Concerning the Patent Gerald Stanley 03/03/2003: "Bipolar Junction Transistors (BJTs) are severely limited in high voltage safe operating area (SOA) and the classic totem-pole output stage exposes the transistors to twice the voltage that the load is ever subjected to.  By being able to float and control a full-bridge output stage it is possible to ground one of the full-bridge output terminals and retain an amplifier's two-channel bridging capability. The result is that four times the power is now available from a given channel for a given output semiconductor's SOA capability and when in bridge mode, the output voltage is twice the voltage that any transistor is exposed to. This is Crown's old technology (invented in 1971) but it represents the pinnacle of our competitor's now that the patent has expired."