RS232 Parasitic Power?

Gentlemen,

Can anyone tell me how much current I might be able to pull from a laptop serial port with this circuit please? The circuit appears to work well on my laptop running 9600 baud firmware on the PIC with 4.76v at the input to the LM2936 regulator and 3.3v at the output... I'm hoping I can pull about 2-3 ma total...

TIA... Regards, Mike

The only thing to do is measure it, laptops don't have very standard ports, and it's likely to vary considerably from model to model. Stick a suitable load resistor on the output of the regulator and measure the voltage out of it. I would also suggest measuring the voltage entering the regulator, both with and without the load, so you can see how much it drops.

You will certainly be able to draw a few mA's from the circuit; I have used a similar circuit to drive an IR led.

Just be aware that the input voltage can be as high as 12v on PC'c that implement a more correct RS232 interface - will your regulator cope with that input voltage and the resulting power dissipation?


{I just looked at the datasheet. It should be fine}

Mike.

What are the MBR0520L components in your schematic?

Are those diodes? Are there other diodes that will work
in the circuit?

Sorry in advance for my cluelessness.

Ilan

ilan1 said:

What are the MBR0520L components in your schematic?

Click to expand...

it's a schottky power rect: