Hi Everybody.

With my working LMC6482 spice model I went about and designed a power-supply with trannies and opamps, I wanted something retro, relative simple and rugged that could do about 0-30V at 5A.

But now I'm a bit concerned about C2 because 470uF was about the lowest I could go and still have 33V on the output (pout). But if I change C2 to e.g. 220uF the max output drops to about 21V, but why??

 

Not related to issue but sure looks like you are asking for trouble by C1
hung off OpAmp output, eg. phase margin.

And you are using real high valued feedback R's, which contributes
a pole with input C of OpAmp, again affecting phase margin.


Regards, Dana.

 

Not related to issue but sure looks like you are asking for trouble by C1
hung off OpAmp output, eg. phase margin.

And you are using real high valued feedback R's, which contributes
a pole with input C of OpAmp, again affecting phase margin.


Regards, Dana.

Hi Dana.

Thank you for your input. Is phase really something to take into consideration in this application? I mean it's more DC than RF?

Anyway I followed your advice and it seems it was related to my C2 worry somehow, because now I get full 33V output with C2 at 220uF, but again I can't go any lower than the 220uF before the output drops to about 21V and I don't know why?

Updated schematic:

 

Makes me wonder if you are seeing oscillation, do you
have a scope to look at output and OpAmp output ?

Phase and gain matter. Right down to almost DC.

http://www.ti.com/lit/an/sloa020a/sloa020a.pdf


Regards, Dana.

 

See

 

See
View attachment 178463

Hi Bordodynov, thank you for your input. As you indicated, it seems it is a better solution to use PNP plus a few other tips of yours, so I came up with this design, it seems to work very well, thank you.

 

Makes me wonder if you are seeing oscillation, do you
have a scope to look at output and OpAmp output ?

Phase and gain matter. Right down to almost DC.

http://www.ti.com/lit/an/sloa020a/sloa020a.pdf


Regards, Dana.

Hi Dana. Thank you for the application report, it looks exactly like what I need to educate myself on the subject.

Yes I had severe oscillation in the sim, but it's gone now with the new design.

I didn't build it yet, but I think now is the right time. And yes I do have a scope.

 

[QUOTE = "Sjöholm, publicación: 1397540, miembro: 551847"]
Hola a todos.

Con mi modelo de especias LMC6482 en funcionamiento, diseñé una fuente de alimentación con trannies y opamps, quería algo retro, relativamente simple y resistente que pudiera hacer alrededor de 0-30V a 5A.

Pero ahora estoy un poco preocupado por C2 porque 470uF era lo más bajo que podía llegar y todavía tenía 33V en la salida (puchero). Pero si cambio C2 a, por ejemplo, 220uF, la salida máxima cae a unos 21V, pero ¿por qué?

View attachment 178456
[/CITAR]
metrorias pasar el archivo .lib de lmc
6482

 

[QUOTE = "Sjöholm, publicación: 1397540, miembro: 551847"]
Hola a todos.

Con mi modelo de especias LMC6482 en funcionamiento, diseñé una fuente de alimentación con trannies y opamps, quería algo retro, relativamente simple y resistente que pudiera hacer alrededor de 0-30V a 5A.

Pero ahora estoy un poco preocupado por C2 porque 470uF era lo más bajo que podía llegar y todavía tenía 33V en la salida (puchero). Pero si cambio C2 a, por ejemplo, 220uF, la salida máxima cae a unos 21V, pero ¿por qué?

View attachment 178456
[/CITAR]
metrorias pasar el archivo .lib de lmc
6482

Diego:

Te sugiero dos cosas:
Que escribas en inglés, que es el idioma de este sitio.
Sé prolijo con lo que escribís. Nadie aprecia cosas descuidadas.


I suggest two things:

To write in English, which is the language of this site.

Try to post a tidy enough text. Nobody appreciate sloppiness.

 

Aren't R6 and R7 too high?

I am used to see dividers with much much lower values.

What about R3?