Electronics > Beginners

TL431 linear power supply

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spec:

--- Quote from: xavier60 on December 14, 2018, 06:50:30 am ---
--- Quote from: mike_mike on December 13, 2018, 01:25:36 pm ---
And I want to be very stable and I want to NOT oscillate... this is the hardest thing for me.


--- End quote ---
The power supply circuit in your first post will work well  enough with compensation.

--- End quote ---
Can you show a circuit for this compensation using a TL431, especially one that you have built and tested successfully. Or perhaps know of such a PSU, that someone else has built and tested.

I am genuinely interested as stated before.

spec:

--- Quote from: not1xor1 on December 14, 2018, 08:11:59 am ---
--- Quote from: spec on December 14, 2018, 06:43:48 am ---
--- Quote from: not1xor1 on December 13, 2018, 07:58:37 am ---
--- Quote from: spec on December 12, 2018, 05:21:36 pm ---No probs :)

I will have a look for a suitable PSU, but I am quite busy at the moment. A number of members are experienced in PSUs, perhaps they could recommend some suitable designs as well.

But I can recommend a complete lab PSU that will do your job for around £47UK, including shipping (the transformer for a DIY PSU would cost more than that). The lab PSU provides 0V to 30V and 0A to 10A, with digital readouts for both voltage and current. There are controls for coarse and fine voltage output and the same for current. I have three of these and use them for electronics, battery charging, you name it.

https://www.ebay.co.uk/p/Adjustable-DC-Power-Supply-30v-10a-Variable-Precision-Digital-Lab-PSU-Clip-Cable/23025566378

You can probably get this generic lab PSU delivered to Romania.

--- End quote ---

From the pictures (if you look through the case aeration slots it looks empty inside) I guess it is a switching PSU.
The linear ones are better as they can be easily improved by replacing the electrolytic caps (they are low quality and too low voltage) and adding a proper TO3 heatsink (as minimal cure).

--- End quote ---
It is a linear PSU, with a very low level noise output of 3mV, why do any guessing. :-//

--- End quote ---

There are lots of chinese PSUs looking the same and with small or large differences inside (some with a huge heatsink on the back some with just a piece of aluminium inside).
I bought a similar one (30V 5A) for about 45€ including shipping.
It has a huge transformer.
The one you linked is 30V 10A. So it should have a 500VA transformer, but since they are coarsely overrated a 300VA one would be more likely.
But if you zoom the pictures and look at the last one, you can clearly see that the case is empty.
So unless it uses a low profile toroid it can be just a switching PSU.
OK ...I found a youtube video... it is definitely a switching PSU.
https://youtu.be/1_ZK68_c3Ok?t=145

--- End quote ---
Hell, you are right. I specifically ordered the linear type. My apologies.

spec:

--- Quote from: not1xor1 on December 14, 2018, 08:22:22 am ---
--- Quote from: spec on December 14, 2018, 07:11:32 am ---Hi mike-mike,

Attached below, is a schematic for your PSU as promised. Apologies for the delay, but it took longer to sort than expected, and other things got in the way too. >:(


--- End quote ---

you must be kidding  ;D
a 20V/µs opamp with a huge 1µF compensation capacitor...
and what would be the advantage versus a proven and foolproof design using the traditional LM723 ?

--- End quote ---
I said it was slugged. :)
I made no claim about any advantage over anything. Why didn't you post a suitable 723 circuit? You could have saved me a load of bother. >:D

not1xor1:

--- Quote from: mike_mike on December 13, 2018, 01:25:36 pm ---45Vdc means the voltage after rectifier and filtering.
I would still like to remain to LM358 since my electronic components vendor does not have this part number (the one with LT).
I just need something like a error amplifier controlling one or more transistors (npns), a ref voltage, a current limit (not variable). Also I want to have a output current of about max 5A and a voltage of about 3-25Vdc. A overload protection led should be very useful, but only if it is simple to implement.
I can use a 30vca 10A transformer or an 24vca, 6A transformer.
And I want to be very stable and I want to NOT oscillate... this is the hardest thing for me.

Could you please help me with such a schematic ?

--- End quote ---

With a 30VAC 10A transformer or even with the smaller 24VAC 6A transformer you are building more an expensive electric heater than a PSU  :)

You must first take into account that transformer are rated for resistive loads. If you put a rectifier bridge and a capacitor, you get narrow pulses of high value currents which increase power dissipation through the transformer winding, so according to the value of the capacitor you have to properly derate the transformer. For average values (around 2000-3000µF per ADC) 60% would work.
That means that a 30VAC 10A transformer is suitable for a 30VDC 6A PSU (with multiple electrolic capacitors in parallel for a total value of 12000-20000µF).
The 24VAC 6A transformer is suitable for a 30VDC 3.6A PSU (7000-10000µF).
And even with derating, in the worst cases you would need to dissipate approximately 200-220W or 100-110W. That is a lot of power.

It would be much better to just use a rectifier bridge and capacitors to get a DC voltage and then use one of those programmable switching modules to get a regulated output. That would save lot of wasted power and expensive heatsinks.

If you still want to build yourself such electronic heaters, given that you do not want current regulation, then the easiest solution is to just use the old LM723, even one of those datasheet circuits.

not1xor1:

--- Quote from: spec on December 14, 2018, 09:01:14 am ---
--- Quote from: not1xor1 on December 14, 2018, 08:22:22 am ---
--- Quote from: spec on December 14, 2018, 07:11:32 am ---Hi mike-mike,

Attached below, is a schematic for your PSU as promised. Apologies for the delay, but it took longer to sort than expected, and other things got in the way too. >:(


--- End quote ---

you must be kidding  ;D
a 20V/µs opamp with a huge 1µF compensation capacitor...
and what would be the advantage versus a proven and foolproof design using the traditional LM723 ?

--- End quote ---
I said it was slugged. :)
I made no claim about any advantage over anything. Why didn't you post a suitable 723 circuit? You could have saved me a load of bother. >:D

--- End quote ---

there are loads of 723 circuit diagrams/projects on the net, and lots of them even in the datasheets (ST, NSC, etc). So what would be advantage of yet another (in this case untested) design ?  :)

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