| 摘要 |
PROBLEM TO BE SOLVED: To decrease the stand-by time by a simple construction when an ultrasonic oscillator E is driven by switching from a first voltage VH to a lower, second voltage VL. SOLUTION: A transistor Tr is controlled so that a discharge current Ih, which is not a second current Il adjusted to the second voltage VL and is larger than the second current Il, is caused to flow within a specified timeτjust after switching from the first voltage VH to the second voltage VL. Thus, the stand-by time in driving an ultrasonic oscillator by switching from a first voltage to a lower, second voltage can be decreased, and the real time properties (frame rate) can be improved. A simple construction requiring no specific discharge circuit can be adopted, reducing cost.
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