| 摘要 |
PURPOSE:To prevent generation of surge by connecting a buffer capacitor between a gate and a drain of an MOSFET driving an inductive load so as to soften the switching operation and to decrease the delay time. CONSTITUTION:When a switch SW1 is turned on and a switch SW2 is turned off, a gate-(G)-source-(S) voltage VGS rises toward a voltage V1 in a time constant decided by a resistor R1 and a stray capacitance CGS, and when the voltage reaches a threshold voltage VTH, the voltage VHS is in the resident state because of the effect by the capacitance CGS and the buffer capacitor C0. Thus, the rate of rise of a drain current ID and the rate of fall of a drain- source voltage VDS are decreased attended therewith and a recovery current IR is decreased. Then the voltage VGS keeps the resident state due to the increase in the internal capacitance of the FET and then the voltage VGS rises up to the voltage V1. In operating conversely and switches SW1, SW2, the opera tion is made converse and the resident state of the voltage VGS is kept longer by the effect of the buffer capacitor C0 also in this case. Thus, the rate of change in the ID and VDS is decreased and the generation of a surge voltage at the drive of the inductive load 3 is prevented.
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