LM309:SUBSTITUIÇÃO DO CI OBSOLETO LM308

There are no difficult requirements on the opamp; even the LM358B should work.

Hi Rogerio,

I see two issues:

1. The transient response analysis shows that the OPAmp must not be too fast. The bandwidth of LM308 compensated with 200pF is about 200...300kHz. So I have chosen the OPA244 showing a bandwidth of 430kHz.

2. The scheme does not like pure capacitive loads without sufficient ESR. So I would recommend a standard 100µF electrolytic cap as a "snubber". These caps show an ESR of some 100mR. (A low ESR is not recommended here!) This 100µF electrolytic cap can be paralleled by a 100...470nF/X7R, of course (not shown below).

And see what happens with a capacitive load without sufficient ESR:

rogerio_lm317.TSC

I also wanted to simulate this circuit with a LM358, LM358B, TLV9302 and others. But the simulations either showed heavy ringing or were instable. My interpretation is that these OPAmp are too fast here.

Keep in mind, that with all such composite regulators (regulator ic plus OPAmp) a thorough testing with the actual load is necessary.

Kai

Hello Rogerio,

Linear regulators are heat generating power losses. I'd suggest using a switching buck regulator. We have many to from which to choose.