The simplest method to control the primary side transistor switches is to operate them directly out of phase, which results in a hard-switching realization with high switching losses. Some reduction in switching losses is possible by the soft-switching operation, which is achieved with an implementation in the TESLAconverter as shown below.
Note that the timing of the switches is such that there are two “dead-time” transition intervals in each switching cycle, during which the two input switches are both turned OFF. During these dead-time intervals, the charge stored on parasitic capacitances of input switches is partially re-circulated resulting in some switching loss reduction.
However, the full benefit is obtained by implementing the new Lossless Switching Method as illustrated in the above figure. Note that the output diode CR1 is replaced by a controllable transistor switch S2, whose timing during the second transition interval is essential for the elimination of the switching losses.
The comparison of two switching methods reveals that the soft-switching operation mode only partially reduces the voltage of the input switch while in the Lossless Switching operation, the input switch voltage is reduced to zero, hence resulting in complete elimination of switching losses.
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