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how does blackdog's PSU work?
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Kleinstein:
It depends on the application on how fast the current limit should engage. Sometimes you want a very fast current limit, essentially limited by the output capacitor and sometimes one wants a current limit that is a bit slow and can deliver more current for a few ms. In the slow case one can usually tolerate more capacitance at the output.

The simple single pole loop results in a constant output inductance for the regulator. However this inductance can be close to ideal and thus cause ringing together with a low loss load capacitor. For small caps a high loss output capacitor (e.g. the extra series resistors) helps to dampen the possible resonance, but this does not work anymore with large caps. It's only the lead resistance that can save the day. With external sense wires one may loose this resistance - so adding external sense wires can get tricky.

For the sense wires one should also consider the case of the load wires interrupted and thus delivering power over the protective diodes / resistors.

For very low output capacitance a push pull output stage with some standing current helps as this essentially the only way to provide a low output impedance even with low load current. At low current one way output stages often get slow and thus might get unstable there.

exe:

--- Quote from: technogeeky on March 23, 2018, 03:42:13 pm --- In practice, I've measured  times as low as 5 to 10 microseconds for a 1000% change in load.

--- End quote ---

To me, that's just a matter of pre-loading :). Like, the "useful" load changes from 1mA to 1000mA. So, it's like 1000x change, right? But if I put an internal load sinking 200mA, the actual change for the PSU would be just 5x. So, this let's getting away with slower power supply. At least that's what I get in a simulator.

Of course this wastes power, that's why I want this current to be settable.

But this also opens another big question to me: how PSU behavior changes with the load. I think this should also affect stability.
blackdog:
Hi exe,

You can use my design and scale it down is you only need say 1,5 Ampere.
The output capacitor can then be scaled down also, so the peak current wil also scale down, the power supply is fast enough.

But maybe a nother design is better for you, one moment...
Look at this, it is a first setup...


The original schematic you wil find in app note 16 from LT, is uses en LT118 and a LT1010.
My version is absolute not finished!
It need extensive testing and probably the zobel network can be smaller.
The first tests look promising, verry fast acting current limiting.
The easy way for more current in the orriginal design is to use say 5x LT1010 TO220.
It is easy to parallel them, the have a internal 7 Ohm output resistor and that maks them perfect for capacitiv loads.
Read the datasheet and app notes on the LT1010.

Do not use a high voltage power supply if your requirements for only 12V output voltage.
This wil keeps the dissipation down and easyer to build.

Kind regards,
Bram
Kleinstein:
With a simple output stage the load current can effect stability. Usually the transistors get slow at low current. There is an additional change with the Sizlaki stage. With MOSFETs the effect could also be quite significant.

So coss-over to instability usually either starts at low current because the output stage gets to slow or at high current because the output stage is fastest there.  An internal constant current load is only a partial solution, as there can be times when this current is used to discharge an output capacitor when recovering from overshoot.

There is also a difference between power supplies with a more current controlled output stage and those with an emitter-follower type. The emitter-follower type can be more sensitive to changing current. To get away from the low current problem, a push pull output stage can help.
Zero999:

--- Quote from: blackdog on March 22, 2018, 12:54:25 pm ---Hi Hero999,

Thanks for the warning :)
But i already now that, i dril out the holes around the 230V powerline connections before i do the real testing, this is only the reference section build.
--- End quote ---
Then please make that clear in future, especially as this is the beginners section.
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