Texas Instruments Incorporated
Switching time optimizer for soft switching of an isolated converter

Abstract:

An apparatus is disclosed for improving zero voltage switching ("ZVS") of a converter circuit such as an active clamp flyback converter. The apparatus includes a first timing circuit acting as the T.sub.D(L-H) optimizer, which uses the zero-crossing of the auxiliary winding voltage directly to adaptively vary the dead time. A second timing circuit acting as the T.sub.D(H-L) optimizer adaptively varies the dead time with a simple piece-wide linear function as an approximation of the complex optimal equation. A third timing circuit acting as the T.sub.DM optimizer contains a charge-pump circuit that adaptively adjusts the ON time of the clamp switch based on the zero-voltage detection of switching node voltage and feed-forwards the input voltage signal to enhance tuning speed so that the correct amount of negative magnetizing current is generated to improve zero voltage switching.