5V Supply Derives Power From 3-Wire RS-232 Port

The circuit of Figure 1 produces a semi-regulated 5V output from an RS-232 port. Unlike a PC-mouse supply or comparable circuits that rely on the modem-control signals DTR and RTS, this one operates with a 3-wire port (GND, Rx, and Tx), and obtains power only from the Tx line. (Except at high duty cycles, the Tx line, RCV-232, remains operational while supplying power.) The output current-about 8mA-is sufficient for CMOS microcontrollers and other low-power circuits.

Operating in voltage-doubler mode on a reversed-polarity input voltage, this switched-capacitor voltage converter produces a semi-regulated 5V at 8mA from the Tx line of an RS-232 port.

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5V_RS232/5V_RS232.htm
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5V Supply Derives Power From 3-Wire RS-232 Port