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Adding a current limiting feature to a LM317HVT based regulated power supply
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Zero999:
But the LM317 will have a much lower current limit, when the input-output differential is high. Pull the adjust pin down to near 0V and the current will be limited to a very low level, unless the input  voltage is also high. In this case the original poster is using a transformer with a 44VAC secondary, which would give an output voltage of 62V peak and is a little over the maximum voltage rating of the LM317HV, although it will drop under load and is unlikely to damage it.
David Hess:

--- Quote from: Zero999 on March 23, 2019, 05:27:35 pm ---But the LM317 will have a much lower current limit, when the input-output differential is high. Pull the adjust pin down to near 0V and the current will be limited to a very low level, unless the input  voltage is also high. In this case the original poster is using a transformer with a 44VAC secondary, which would give an output voltage of 62V peak and is a little over the maximum voltage rating of the LM317HV, although it will drop under load and is unlikely to damage it.
--- End quote ---

That is a different problem that I have not addressed; there are several ways to add high voltage capability to a 3 terminal regulator.  I would not rely on high differential voltage for current limiting.
David Hess:
I was looking for something else and found two applicable application circuits in the old LM317 datasheets.

The first one shows exactly what I described with a 1 x Vbe NPN current limit for a floating input.  I would add two diodes in series with the emitter to make it 3 x Vbe.

The second and third show two ways to safely parallel regulators.
not1xor1:

--- Quote from: vr6 on March 22, 2019, 10:10:37 am ---Hi,
some time ago I've built a power supply based on 3x LM317HVT IC's in parallel (circuit in the attachment) and now I'd like to add current limiting to it. I was looking for a circuit that would limit the output current to 3A (max 3.5A) but I couldn't find anything that would do that at any given voltage (1.25V - 52V). I'm using a transformer with 44V AC secondary. Can anyone help me with building such circuit?
Thanks in advance

--- End quote ---

Apart the other valid advices, I think nobody spotted the 1kΩ limited LED in the circuit...  :scared:

That's about 35mA in worst case (no load and a bit of AC overvoltage) (*) through a LED that I guess is just as an ON indicator.
Make that 10-22kΩ. Modern LEDs are bright and in any case (vintage or modern) would last much longer when fed with moderate current.

And if you want to get 5A out you'd better double the input capacitor. Make that 2 x 4700µF.
OK... now that I've read more carefully that is 3-3.5A... so make that 2x3300µF  :)

(*) the circuit diagram specifies 24V, but in the text you write 44V (so it would be even worse)...
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