[SOLVED] Voltage Follower For Max232 output

Hi all.
As you can see from the circuit schematic i try to send some data from PIC to PC(serial USB converter).


I used a max232. When i made the connection i saw that PIC-UART signal levels attenuate. So i decided to use a voltage follower after max 232 before serial-USB converter.
Although i tried many opamps i got the same result. Without load circuit behaves OK. I could get output what i gave from input of follower. But when i connect the serial USB converter (as a load) the output of voltage follower decays. Interesting thing is it can follow the negative side of the signal but cannot the positive side. BTW i supplied the opamp with +-14 volts (at my all trials).

This is my signal (from the board i designed) without load.


And this is what i got from output of follower after i connected the serial USB converter.
You can see the negative side OK but there is problem at following the positive side.


In order to see different opamp behaviours i used a signal generator and same simple voltage follower circuit.
LT1112. It is apparent that load affects both input(blue) and output(yellow).

opa07.


At all trials i got noise at positive side. Is there any thing you can suggest?

Is there any thing you can suggest?

Click to expand...

Abandon the useless OP buffers. All levels will be in required range without it.

It seems LT1112 is giving the best result but not enough. There must be something i am missing or doing wrong.

May be you are just shorting the output, e.g. using the wrong cable and connecting TX to TX? PC or USB-to-RS232 bridge has TX on pin 3, need a cross cable to connect to your circuit.

Thanx FvM for the reply. But TX pin; the one in the middle so it is unlikely to fool. But i checked it again:
T1OUT of max232 (pin14) ---> to the noninverting input of opamp. And output of opamp(also shorted to inverting input) --->to the 3rd pin(TX) of the DB9 connector. Besides the same abnormality happens in my demo circuit which i set on the breadboard. I am suspicious if USB-to-RS232 bridge is a complex load for the voltage follower. Or am i using totally wrong OA's for a voltage follower?

Edit: And once again edaboard saved my life thanks to FvM :-D After just a minute later sending the above reply i realized that TX of the sender and TX of the receiver is face to face :bang: