Power from Serial Port

[JaMe]

I'd like to get supply +3.8v from serial port. It will be used to power MAX3237, a RS-232 transceiver. Pin 4 and 7 at serial port is connected with 2 diodes 1N4148, and mixed together. Then, cathode of the diode is used to supply LM317(TO-227 package).
The problem is, once I connect LM317, the voltage at cathode comes from 10V down to 3V. Anyone help ?

 

[emanuelcsm]

JaMe,

LM317 require more current than serial port can provide, and MAX3237 need current too... PC Serial port can provide 50mA only, you need to review your design and put a external power suply....


Emanuel Cassimiro da Silva
C++ Expert code writer...

I'd like to get supply +3.8v from serial port. It will be used to power MAX3237, a RS-232 transceiver. Pin 4 and 7 at serial port is connected with 2 diodes 1N4148, and mixed together. Then, cathode of the diode is used to supply LM317(TO-227 package).
The problem is, once I connect LM317, the voltage at cathode comes from 10V down to 3V. Anyone help ?

 

[jhbbunch]

When you think aabout it, using one serial port chip to power another serial port chip is really dumb. They are rated to handle the current they need and that is all. You throw a load like that on it and run it through signal level diodes to boot, not good design practice.

 

[JaMe]

Yes, both of you are correct. I decided to use external power supply to power the MAX.

 

[hcet]

I'd like to get supply +3.8v from serial port. It will be used to power MAX3237, a RS-232 transceiver.

Maybe this **broken link removed** will give you a hint.

ep20k