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TL431 linear power supply
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not1xor1:

--- Quote from: mike_mike on December 12, 2018, 05:12:51 pm ---Thanks for the reply.
Please recommend a good power supply schematic.
I need the following performance
1. min 5A output
2. 3-25V output voltage
3. to not oscillate
4. to have a simple schematic

--- End quote ---

It would be better to use at least a center tapped transformer, switching the secondary winding appropriately to halve the power dissipation.
Do you already have a transformer?

It would be possible to modify the 431 psu, and run a few simulation to get a coarse idea of the compensation network, but IMHO a classical 2 opamp circuit, with fixed feedback network and variable references and both voltage and current regulation, is much better.
If you feel audacious I can provide you with a proper 2 opamps circuit, but just tested it in LTspice as my lab is not available at the moment.

Here is a proof of concept schematic, just to get a rough idea.
If you like it I can provide you with a complete and real world usable circuit diagram.

BTW what do you plan to use the PSU for?
mike_mike:
Currently I am waiting for a response from @spec. The current limiting led is not necessary. If you will use an operational amplifier, then please use a common operational amplifier for example LM358 (I have many of them). The input of the supply will be maximum 45Vdc, so there needs to be made something in order to power the op amp.
I need the power supply to power leds, Arduino, motors, relays etc.
not1xor1:

--- Quote from: mike_mike on December 13, 2018, 09:27:46 am ---Currently I am waiting for a response from @spec. The current limiting led is not necessary. If you will use an operational amplifier, then please use a common operational amplifier for example LM358 (I have many of them). The input of the supply will be maximum 45Vdc, so there needs to be made something in order to power the op amp.
I need the power supply to power leds, Arduino, motors, relays etc.

--- End quote ---

What does it mean 45VDC?
i.e. is that just transformer secondary rmsV * sqrt(2) or an AC/DC switching module?

LM358 might still work up to 24-25 VDC out with a single transformer. But you should use a 24VAC (or better 12+12VAC) 8+8A transformer to get a regulated 24-25V 5A DC output.

The best opamp IMHO is LT1013 due to a high supply voltage, limited cost and wide IO range (and much better features than LM358). A cheaper alternative is MC33171/2/4
Better opamps are more expensive and harder to find.

Another solution is a voltage boost stage (common base or common emitter) at the expense of higher chances of self-oscillations.
The Harrison topology would be better (i.e. floating control circuit) requiring just a further small power (few VAs) transformer and is usually more stable.
mike_mike:
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 ?
spec:

--- 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 ---

UPDATE #1  2018_12_14  not1xor1 is correct, my PSUs are in fact switching- I just had the covers off
[/quote] It is a linear PSU, with a very low level noise output of 3mV, why do any guessing.

Although these PSUs work well as is, there are a few things that you can do to enhance them.
[1] Check the quality of solder joints and general workmanship (my three are fine, but the quality can vary according to some reviewers)
(2) Fit an output rail on/off switch
(3) Fit better quality potentiometers, say ten turn for the fine controls.

Incidentally these power supplies, at the price, can just be bought for the parts. The transformer itself would cost you over £50, and then there is the chassis, voltage and current meters, 2N3055s, heatsinks, fan, knobs, caps, resistors, diodes ...

I am thinking of converting one into a precision current source.
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