15A to 25A at the Overcurrent
Your sense resistor is too big (high Ohms) to allow 15A to flow.
Whan you say "Overcurrent", do you refer to the OC pin on the LT3805?
You do need a filter capacitor on that OC pin...like i have added on ther simulation.
You say some cards work and some dont.......maybe the working ones had the input capacitors already pre-charged.
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You seem to be hinting at "intermittent bad operation".
You seem to be saying that 95% of the PCBs with this power supply on work fine, but the others dont?
As far as i am concerned, your schem from the top post is poor in terms of not having capacitors on the OC pin, and on the Isense pin.
None of us here can really judge your schem though because you do not give the loading on each secondary.
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You seem to repeatedly say that the OC trip is whats bothering you.......you need to put a capacitor on the OC pin, as i have done in the sim....i have no idea if your OC trip point is set properly...and i cant work it out, because i dont know what is your loading?
Is it that you dont really know what the maximum load is?...
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Before designing such a power supply, it is always best to get a representative simulation of it working first, then go to the bench. Simulations aren’t that useful…but if you cant get some kind of representative simulation working first, then you will generally never get the real thing working.
There is the LTspice simulator which has a model for your LT3805, and so you should be able to get a very representative simulation working first.
I cannot do the simulation for you because I don’t know the loading on each of your secondarys.
I have requested from yourself the loading, but you do not tell it.....is this becausue this is someone else's power supply that you have had dumped upon yourself, and you dont know the spec?
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So anyway, it sounds like your OC pin is getting tripped, and this may be due to the lack of an OC pin capacitor. And/Or maybe there is too much capacitance on the secondaries and it cant start up without tripping OC…..only 5% fail because maybe there is a tolerance on OC trip point, or whatever, and those 5% fail that tolerance.
If you wanted to be really naughty, but cut to the chase, you could just ground the OC pin and see if it starts up then (the bad ones)