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LDO current limiter
magic:
If you just want an LM317 with lower dropout, there are LM1117 or LM1085/LD1085 for higher currents. Both are 1~1.5V dropout, depending on load conditions and die temperature.
Beware that they may require some output capacitance for stability, perhaps also in CC mode. I think you may get away with a capacitor in parallel with the current sense resistor rather than one going from OUT to ground, which would compromise CC dynamic performance.
fourfathom:
--- Quote from: --Oz-- on August 20, 2022, 04:10:49 am ---
--- Quote from: fourfathom on August 20, 2022, 01:36:21 am ---How precise and stable do you need? A simple two-transistor, two-resistor current limiter can have a sub-1V dropout, but the limiting will be soft and the tempco and precision may be found wanting.
--- End quote ---
Good question. I am thinking of +/-25mA of the 1A C.C. mode.
Do you have a link to that circuit?
--- End quote ---
I was thinking of a two-NPN circuit, but it either has a larger voltage burden or it draws more quiescent current that i would prefer. So here's a similar topology using a PMOS pass transistor and a PNP sense transistor. The current-limit depends on VBE of the PNP transistor so that variation will be about 2mV per degree C (giving about 3.3mA per deg C), and the initial value will vary a little. So it sounds like you need more stability.
But the voltage burden (dropout) is quite good, under 0.6V until the current hits that 1A limit.
But if you can find an IC solution with the specs you need that's probably a better choice.
BTW, I just chose the first reasonable FET I could find in the LTSpice library.
SiliconWizard:
--- Quote from: --Oz-- on August 20, 2022, 04:11:34 am ---
--- Quote from: SiliconWizard on August 20, 2022, 02:09:17 am ---https://www.onsemi.com/products/power-management/linear-regulators-ldo/ncp692
--- End quote ---
Looking at the DS, it has current limiting, not really a C.C. mode. I looked for applications for the chip and there is none, just typical C.V. circuit.
And, I plan on this to be dissipating the heat, so a little qfn package is not ideal, plus needs a circuit board, I was thinking through hole and something like to-220 so i can burn some watts (at least 5W or more), I will add to my 1st post. Thanks for the reply.
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I didn't suggest it for its internal current limiting (which is not configurable anyway), but for its very low drop-out voltage @1A.
--Oz--:
--- Quote from: magic on August 20, 2022, 08:52:28 am ---If you just want an LM317 with lower dropout, there are LM1117 or LM1085/LD1085 for higher currents. Both are 1~1.5V dropout, depending on load conditions and die temperature.
Beware that they may require some output capacitance for stability, perhaps also in CC mode. I think you may get away with a capacitor in parallel with the current sense resistor rather than one going from OUT to ground, which would compromise CC dynamic performance.
--- End quote ---
You the man! haha, looking at the datasheet, LDO 3A to-220 and has a full 1 volt less dropout voltage than the LM317, has the CC mode mentioned in the DS, only 50 cents each on Ali, ticks all the boxes, this is a perfect part for my application. Thank you!
And thanks for everybody's replies!
mariush:
Yeah, though make sure they're not counterfeit or renamed chips.
Another IC you may want to check is LM2941 ... should have around 0.5v dropout voltage up to 1A of current, for normal temperature ranges (may go up to 1v in extreme temperatures)
Also LM2940.
Though just like 1117 regulators, it can be picky about output capacitors and their ESR - a capacitor with ESR between 0.1 ohm ... 1 ohm is recommended.
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