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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!
 

mr_ghz

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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
 

arturt134

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

lollobrigido

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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
 

mr_ghz

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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...
 

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