| 摘要 |
PROBLEM TO BE SOLVED: To use a coil of a power supply voltage circuit in common, which changes an output level depending on an output level of an output amplifier and to make the circuit efficiency high at a small output level. SOLUTION: The power supply voltage circuit 7 acts like a voltage step-down chopper circuit by turning off a switch S2 and switching a switch S1 when an output level of an output amplifier 5 is small. The power supply voltage circuit 7 outputs a voltage Vb of a battery as it is by turning on the switch S1 and turning off the switch S2 when the output level of the amplifier 5 is medium. The power supply voltage circuit 7 acts like a voltage step-up chopper circuit by turning on the witch S1 and switching the switch S2 when the output level of the output amplifier 5 is high.
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