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Serial stealing from three-wire RS232 port to the power circuit

Published on Oct 28 2010 // Micrcontroller circuits

Serial stealing -from three-wire RS232 port to the power

The circuit in Figure 1 gives RS-232 ports from a semi-regulated 5V output produced.
PC power supply or rely on the mouse and modem
control signals DTR and RTS can be different from the comparison circuit,
the circuit uses 3-wire port (GND, Rx and Tx) work, and only from the Tx line to obtain power.
(Unless the high duty cycle, Tx line, RCV-232 were still in the delivery of power available.) Output current of about 8mA,
of CMOS low-power microcontrollers and other circuitry is sufficient.
IC1 is a switched capacitor charge pump voltage converter, It can reverse the input voltage,
the input voltage can be doubled. The figure providing doubler circuit connection configuration,
the input voltage polarity reversal: positive input voltage is generally connected between GND and OUT,
but the circuit is connected between the OUT and GND a negative input voltage. IC to Vin in a positive double negative,
producing a positive output with Vin equal (at Vdd side.)
Zener diode D1 as a shunt regulator, so Vin "semi-regulated" to-5V (the actual as-4.7V).
Figure of 33uF capacitor’s capacitance value than bigger,
which in the worst transfer mode (all zero) to support the output voltage. For example, 9600 baud,
the zero-down feature allows the output voltage of about 0.2V. The lower baud rate,
you need to replace a larger capacitor C1.