| 摘要 |
PURPOSE:To reduce cost by detecting respectively the presence of a power supply to a converter by other tuner and its own tuner so as to select a changeover switch thereby simplifying the configuration. CONSTITUTION:When power is already supplied from other tuner to a converter, after a converter power supply voltage is inputted from an IF signal input terminal 11, a transistor(TR) 42 is turned on to set a collector of the TR 42 to a low level. Thus, a voltage applied to a control terminal of a changeover switch 44 goes to a low level, the switch 44 remains turned off to stop the supply of power to the converer. On the other hand, when the power from the other tuner to the converter is not supplied, the TR 42 is turned off to set the collector of the TR 42 to a high level. Thus, the switch 44 is turned on to supply power to the converter. When power is supplied to the converter, the switch 44 remains ON and power supply is continued.
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