| 摘要 |
PROBLEM TO BE SOLVED: To improve user environment and ambient environment by reducing carrier sounds by changing the carrier frequency as required, also realize cost reduction by dispensing with the sound absorbing material and moreover provide sufficient output power without increase of capacity of a switching element. SOLUTION: A load is detected, and whether the load detected is a light load or a heavy load is determined. When the load is determined as being a light load, the carrier frequency is set to a higher frequency; and conversely when the load is determined as being a heavy load, the carrier frequency is set to a lower frequency.
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