And I want to be very stable and I want to NOT oscillate... this is the hardest thing for me.
The only reason I have not used the TL431 that way is why would I bother when better performing and easier to use operational amplifiers are plentiful? It is routine in isolated switching power supplies however.
The problem is a little like using the 723 or most switching regulator controllers where stabilizing feedback to the inverting input comes from the transconductance output instead of the low impedance buffered output. The TL431 has a transconductance output, despite what the datasheet specifications show, so gain varies considerably from device to device and with load. If you build a series regulator with it, then the variable biasing conditions are altering the transconductance unless steps are taken to prevent it so the frequency compensation becomes difficult to control.
A better question might be *why* the TL431 operates so benignly when used as a simple shunt regulator. It will normally have a relatively large load capacitance which rolls off the gain of its transconductance output for dominant pole compensation which is exactly how a transconductance amplifier is compensated. But in a circuit where it controls a series regulator, that cannot be done if fast response is desired and instead feedback from the squirrely output to the input implements the frequency compensation because people are used to working with voltage feedback amplifiers. It can work as the 723 shows but can also be hit or miss.
This brings up an alternate compensation scheme; place a series RC network from the TL431 output to ground.
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.
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).It is a linear PSU, with a very low level noise output of 3mV, why do any guessing.
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.
And I want to be very stable and I want to NOT oscillate... this is the hardest thing for me.The power supply circuit in your first post will work well enough with compensation.
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.
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).It is a linear PSU, with a very low level noise output of 3mV, why do any guessing.
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
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.
you must be kidding
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 ?
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 ?
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.
you must be kidding
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 ?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.
And I want to be very stable and I want to NOT oscillate... this is the hardest thing for me.The power supply circuit in your first post will work well enough with compensation.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.
And I want to be very stable and I want to NOT oscillate... this is the hardest thing for me.The power supply circuit in your first post will work well enough with compensation.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.The only times that I have used a TL431 as an active part of the regulation loop rather than as the voltage reference, are as low voltage control rail supplies. I used the same topology as the circuit in the first post, but with a medium power MOSFET or BJT acting as follower for the K voltage. Very easy to compensate with a capacitor between K and R.
Just like with the circuit you posted, even if the feedback capacitor is oversize, the op-amp or TL431 becomes a very slow Miller integrator.
Transient response remains reasonable because all that the op-amp or TL431 needs do is compensate for small changes in B-E voltage as load current changes.
Response can optimized by reducing the size of the capacitor and adding some series resistance.
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.
you must be kidding
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 ?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.
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 ?
you must be kidding a 20V/µs opamp with a huge 1µF compensation capacitor...
you must be kidding
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 ?
I take it then that you yourself or anyone that you know has built a successful TL431 PSU.
mike_mike,
Attached is a 723 PSU schematic which I found drifting around my laptop. This, is the kind of thing that not1xor1 and I were discussing.
Thank you.
But I cant see were is the current limit or the short circuit protection...
you must be kidding
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 ?
The compensation capacitor is way too large but a fast operational amplifier like that would be selected for lower noise. I have done the same thing many times using an LT1007 or OP27.