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how to get current from rs232?

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xworld2008

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I am designing rs232 circuit,i want to like mouse to get current from
rs232,use which ic to do it? thx!
 

Hi xworld2008

the problem is, that you cannot draw much current out of an rs-232 port.
You have to take an unused handshake-line like DTR, and set it to
digital '0'-pegel. This pegel will be converted to +9V at the output of the
rs-232 (inverted logic!). This line can be loaded with max. 10mA
(depending on type of PC, a notebook can't drive as much).
Now you can regulate this voltage with a low drop linear regulator, which
should have a low quiescent current (e.g. LM2931).

Greets
 

Also, you can use second handshake line (RTS) parallel with DTR (connected by diodes). Then your max current doubles.
 

you can use data wires too, by rectify it and filtrate. For a good example for this method you can look at Ludi*i*o board (PIC programmer).

(*=p)

Lollo
 

The increasing of the maximal current by using two or more lines can work
or not, it depends on the internal structure of your PC.

Mostly an RS-232 Transceiver with integrated charge-pump is used. In
low-power devices, the max. available current of this charge-pump is
about 10-20mA. This current can be drawn also from 1 line.

So the use of two lines will bring you no more current...
 

You find Information and Schematic
 

Look at page 9 and 10 in this datasheet from Maxim: **broken link removed**
 

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