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how does blackdog's PSU work?
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blackdog:
Hi EXE,


If its only a "normal" hobby supply, you can trow a few extra windings on the power transformer.
But wat is your problem with a extra small transformer for the reference section?

Its also possible to build de Circuits Online power supply, maybe with my modifications?
https://www.circuitsonline.net/forum/view/131554
Google translation time again  :-DD

This is a link for a more up to date schematic, it is not a complete schematic, i removed the "difficult" components.
But to make Tim more happy with me, (i mean this friendly) i changed al the diodes who are of a Schottky type and the last MOSfet i dit forget.



Analog Devices has a new opamp, interesting for fast lineair power supply's.
Its the ADA4625-1, minimum 5V en Max. 36V power supply.
Fast, 48V/uSec, low noise, low bias current and relativ good DC specs.
But what is really special, is the phase margin, which is 88 degrees, normaly it is around 65 Degrees for opamps.

If its realy this good (i have to do some test) than i can choose for a lower value electrolitic capacitor on the output or better dynamic performance.
We shall see what the tests will tell me.

Kind regards,
Bram

PS
I started with a TL431 Reference for this power supply, look a the link below, the pictures tells enough if you cant read Dutch.
https://www.circuitsonline.net/forum/view/116156
 
Jwillis:
Most definitely an interesting design.I will have to give this one a try sometime.I'd like to shake your hand for all the hard work you put into it and would very much like to see the finished design.Bravo!
exe:

--- Quote from: Cerebus on March 19, 2018, 07:44:40 pm ---So, the question is: What is a reasonable slew rate for an applied step load when testing PSU regulation recovery times? Are there industry standards? (I couldn't find evidence of any.) Or do people just test with whatever slew rate the electronic loads available to them support?

--- End quote ---

What I often see in specs is something like "50us recovery time". As I understand, this reads as "in 50us or less the output level gets back to normal (or settles within 5-10%) under any step load". But 50us is waay to slow, imho.

So, what is a good recovery time? My benchmark is LT3080 which I consider a fast regulator (there are some faster, but not as versatile). It has recovery time around a few us (the datasheet has a few pictures). I also check overshooting and, uhm, undershooting at step load. If it's below 100mV  (at 3.3V) for step load 0.1A => 1A, then it's a good power supply. (Of course, slew rate of step load affects results)

So, everything close-enough to LT3080 I consider a good PSU. I assembled my variation of blackdog's PSU, it was good. If I find oscilloscope screenshots, I'll share.

BTW, there are many things affect performance. Like, pass transistor. My 2STA1943 (from ST) showed better performance than 2TA1943 from Toshiba. But I measure the transistor alone, not in the circuit. So, I don't know what would be real impact. Also dropout voltage affects performance a lot. BJTs don't like to work near saturation voltage (imho).

My two eurocents, I'm no expert  :D
Cerebus:

--- Quote from: exe on March 20, 2018, 10:39:22 am ---
--- Quote from: Cerebus on March 19, 2018, 07:44:40 pm ---So, the question is: What is a reasonable slew rate for an applied step load when testing PSU regulation recovery times? Are there industry standards? (I couldn't find evidence of any.) Or do people just test with whatever slew rate the electronic loads available to them support?

--- End quote ---

What I often see in specs is something like "50us recovery time". As I understand, this reads as "in 50us or less the output level gets back to normal (or settles within 5-10%) under any step load". But 50us is waay to slow, imho.


--- End quote ---

You misunderstand, what we're talking about is the slew rate of the current step waveform of the load that is used to test the PSU load effect recovery time. We're not talking about the load effect recovery time itself.

As it is, we already have an answer, one that convinces me anyway, which is 5 times faster than the rise time of the supply.
blackdog:
Hi EXE,  :)

Measuring the performance of a fast linear power supply is not easy.
And if you are say above the 2-Ampere output current, you will also have to take the EM field of the all wires  with these current into account.

I already showd a picture of my setup and the BNC connector has a 90 degree angle to the current wiring.
Even de sense wires i try to give them a 90 degrees angel.

The measuring point for performance measurements are the points where the sense wires soldered to the current wires.
That is on the back of the 4mm banana sockets, every mm extra wire give a extra L and R.
I want to measure the performance of the electronics ande not the wiring during testing  :)

And i explaned already that i also do testing with one of my Dummy Loads for more practical testing.
If you connect your device under test with 1M cables to te Power supply, and most users do not twist the cables, all those nice specs are out of the window  :-DD

My standard measuring puls from one of my generators used with my Dummy Loads.



This is a picture of how my 200-Watt Dummy Load is performing in one of my tests of this dummy load afther building him.



To see how a power supply is reacting on realy fast pulses, i use my Jim Williams dummy load.

Kind regards,
Bram





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