| 摘要 |
There is provided a circuit for achieving a serial communication at the standard voltage defined in the RS-232 interface communication standard when the signal processing voltage of the host side circuit is 5 V and 3 V, for example, in which, when the DC input voltage Vin of the host side circuit is changed, this voltage level is detected to generate a stepped-up voltage having an appropriate step-up ratio by step-up circuits. This voltage level is detected to, regardless of the change of the power supply voltage, obtain the positive and negative DC output voltages Vdd, Vss matching with the RS-232 interface communication standard. To be specific, with the 5 V operation, a double stepped-up voltage within the DC/DC converter circuit and, during the 3 V operation, a three times stepped-up voltage are selectively generated to obtain the DC output voltage.
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