LM338 Regulated Power Supply Diagram: 1.25V-30V, 0-3A - Resistor Selection & Adjustment Help

Question

Hello.
I want to enrich my workshop with a regulated power supply. I found a pattern and did a little bit of it. could anyone check if i made it correctly and help in choosing resistors?
The power supply is to have parameters 1.25V-30V and 0-3A, I also care about coarse and accurate adjustment of these parameters. I am beginner, that's why I count on your help. If this is a bad department, please move.
Regards.

zasila..PNG Download (56.95 kB)

_jta_ · Accepted Answer

It will not be regulated from 0 and from about 0.66A; current limitation will not work at low voltage (below about 1.4V). I don't know if the fan has a chance to work sensibly ... And what's the deal with BC557 and BD136? Maybe look for something better, because it will be nothing but trouble.

_jta_ · Accepted Answer

This negative voltage enables: (1) current regulation also working at low output voltages; and (2) output voltage adjustment from 0.

Anonymous · Accepted Answer

You can. Only then will there be no voltage regulation from zero.

Freddy · Accepted Answer

In the LT1083 catalog card you have on page 13 a very nice and cool system with a pre-regulator. It's a little complicated, but it's worth doing.

Anonymous · Accepted Answer

Yes, it serves it.

_jta_ · Accepted Answer

You can give 2k2 in parallel, connecting the ends of both potentiometers with each other, but then the sliders of both need to be connected to the ADJ pin through resistors, e.g. the one from the R2 potentiometer = 150R through the 100R resistor, and the one from 2k2 through 2k. I considered another option, the 2k2 potentiometer in parallel to the 120R resistor (only then it can replace it with a larger one, the 150R would be just right), from a slider through a 2k resistor connection to ADJ, and the ADJ would not be connected directly to ground, but via a 100R resistor - but in this version, precise regulation at high current would have a small range (at maximum zero), which makes little sense.

DamianRTV · Answer

Hello, wouldn't it be easier to buy? e.g. this: Regards - my respect.

Daniel.1990 · Answer

Thanks for the advice. I will look for a different pattern and present it here so that someone with more experience can analyze it. As for this layout with BD557. It was supposed to be an electronic fuse but after analyzing I gave up this idea and apparently forgot to remove it from the schematic.

As for buying a ready power supply, I'd rather avoid it. And there is always the satisfaction of doing something yourself.

Daniel.1990 · Answer

Hello.

I would ask you to check this pattern for correctness. I also want to ask more experienced colleagues what I need to change in it to achieve current regulation from 0A and how to make the current limitation work from about 0V?
The next question is how to add short-circuit protection to this scheme and signaling a possible short circuit with an LED.
As for controlling the fan with an NTC thermistor, the system was tested by me and works decently. I hope for a quick response.

ZASILACZ S..MAT.PNG Download (55.79 kB)
Regards!
daniel

_jta_ · Answer

what do I need to change in it to achieve current regulation from 0A and how to make the current limitation work from about 0V? On the LM338K it is difficult - the matter was discussed for the LM317, read about the charger on the LM317. The next question is how to add short-circuit protection to this scheme and signaling a possible short circuit with an LED. I have the impression that LM338 (like LM317 and many others) has such protection built in.

Anonymous · Answer

Yes, but it does not work in the case of a system with an external transistor. In this forum, nothing will change and the same topics will be rolled out; stomach contents come to the throat about subsequent inquiries with various three-tip integrated stabilizers. And it is enough for 40 years known L200 and you can let your imagination run wild with the design of the power supply. This age-old bone offers everything at a cost of only 2 feet more than the LM117 mutations

_jta_ · Answer

The protection does not work (or rather, it works not quite as you would like: it protects the LM338, but the transistor does not) in a system with an external power transistor, and it is not here.

Anonymous · Answer

And I am surprised by these four potentiometers in the voltage control circuit. I would already understand two, coarse and fine regulation, but four?

Daniel.1990 · Answer

As for four potentiometers. These two are for adjustment Current and two to voltage. At least, that was the result of the original pattern. And back to the pattern. Will this meet my expectations? Zasilacz_2...878742.png Download (166.38 kB)

Anonymous · Answer

Yes, of course it will, because as you can see, you like a lot of overclocked circuits. By the way, this power supply is very dangerous for powered systems, due to the auxiliary negative voltage power supply.

Daniel.1990 · Answer

I just don't trust simple systems. I prefer to use it as more recombined but be sure that it makes sense. One more question, can I remove this negative guide somehow? Is it needed for the proper functioning of this power supply

Daniel.1990 · Answer

One thing remains. R2 150 is a potentiometer with which we adjust the current value? Is my reasoning wrong?

Daniel.1990 · Answer

How can I add a second potentiometer to the R2 2.2k potentiometer to get a coarse and fine adjustment? In the case of R2 150 I don't have such a problem. Regards daniel

Anonymous · Answer

You need to add it in series, from experience it is enough that the value of the fine adjustment potentiometer is 10% of the value of the basic (coarse) adjustment potentiometer.

[Solved] LM338 Regulated Power Supply Diagram: 1.25V-30V, 0-3A - Resistor Selection & Adjustment Help

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