| 摘要 |
PURPOSE:To simplify and miniaturize the constitution of a power source part by fetching the voltage of a telephone circuit as a power source voltage via a DC/DC converter connected to the telephone circuit. CONSTITUTION:The polarity of DC 48V supplied from the terminals L1, L2 of a telephone circuit 14 is held by a rectifier DB in one direction. And an AC voltage is oscillated by a bias resistor R1, a transformer T2, oscillating transistor Tr2, a resistor R2, and a capacitor C2. This AC voltage is deformed by the transformer T2, then rectified and smoothed respectively by a rectifying diode D2 and a smoothing capacitor C4, and made a power source voltage Vc to be supplied to various circuits. Therefore, separate power sources are not necessary, and the constitution of the power source part can be simplified and miniaturized.
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