General > General Technical Chat
LDO current limiter
magic:
--- Quote from: --Oz-- on August 21, 2022, 06:24:28 pm ---only 50 cents each on Ali
--- End quote ---
That's not a lot of money to risk on Chinese roulette, but this is what it is when you buy from Ali.
It could be perfectly good and unused surplus parts, or recycled chips from scrap boards, or a Chinese clone which is maybe good enough, or some different LDO with fake markings which is maybe not good enough (think LM1117 designed for 0.8A), or LM317 with fake markings, or a transistor with fake markings, or hell knows what else. You may get anything.
LD1085 is cheap enough that it doesn't cost a lot to buy it locally from a legit IC distributor. Delivery is faster too.
magic:
Regarding capacitors, LD1085 datasheet suggests that the chip should be stable with infinite capacitance and 1.25Ω ESR.
This means that it may also prove stable with just a 1.25Ω resistor from OUT to ADJ, assuming that OUT-ADJ capacitance is good enough to stabilize it and there is no need for OUT-GND.
--Oz--:
--- Quote from: magic on August 21, 2022, 08:43:50 pm ---
--- Quote from: --Oz-- on August 21, 2022, 06:24:28 pm ---only 50 cents each on Ali
--- End quote ---
That's not a lot of money to risk on Chinese roulette, but this is what it is when you buy from Ali.
It could be perfectly good and unused surplus parts, or recycled chips from scrap boards, or a Chinese clone which is maybe good enough, or some different LDO with fake markings which is maybe not good enough (think LM1117 designed for 0.8A), or LM317 with fake markings, or a transistor with fake markings, or hell knows what else. You may get anything.
LD1085 is cheap enough that it doesn't cost a lot to buy it locally from a legit IC distributor. Delivery is faster too.
--- End quote ---
I have bought quite a lot of fets, IC's, leds, modules, etc from Ali (around 200 orders) and have only really got one fake fet that I can tell from my applications.
It was a IRFB4227 200V fet, but avalanched at 74V, I simply use a 10V ps connected to a inductor, then fet to ground, add a square wave to the gate and read the avalanche voltage, no questions on getting my money back.
My most risky purchase was a server Xeon E5-2678v3 12core/24thread cpu, MB, 32GB ram for $277, its been great for almost three years now.
--Oz--:
I found this interesting circuit to make this adjustable, buy has a few cons.
Too many parts and req negative supply.
https://electronics.stackexchange.com/questions/215418/smartest-way-to-use-current-limit-using-lm317
--Oz--:
--- Quote from: ledtester on August 20, 2022, 06:14:46 am ---You can use any linear regulator as a constant current source -- see this article:
https://www.maximintegrated.com/en/design/technical-documents/app-notes/4/4404.html
So then the challenge is to find one with:
- low dropout voltage
- low output voltage
- enough current capacity
- high enough Vin-GND voltage
Here's a list of some in-stock devices at Mouser which might work for you:
https://mou.sr/3dILUCS
--- End quote ---
Out of curiosity of your link info, I found some LDO's and they all have the Vfb reference to ground, connected them up as normal to verify they were was working (they are brand new).
Then tried the info in your link, none of them worked, I think its because the way most regulators Vref is tied to ground, where the lm317 and a few others are not.
I tried these three
MIC49150WR
MIC29152WU
MIC29502BU
They simplify would not regulate, tried 100mA and 1A shunt resistors, Thoughts?
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