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5) Drive circuit The STR-S5707 applies the proportional drive system in order to minimize turn-on and saturation loss, and storage time. In the conventional RCC system, turn-on loss and switching noise due to the surge current appearing when the power transistor turns on are high as because the transistor is driven by the drive current shown in FIg. 10-1. In addition, since is decreases linearly when the transistor turn off and a peak value of lB2 is not large, the storage time is long and the VCE(SAT) voltage is high, which results in large turn-off loss. The circuit and the waveforms of the proportional drive system which is applied to the STR-S5707 in order to reduce these switching loss and shorten the storage time are shown in Fig. 10-2 respectively.