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| Current limiter IC needed |
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| exe:
--- Quote from: ogden on July 18, 2019, 03:39:25 pm ---Those also are just adjustable circuit breakers which are not suitable for battery charging. --- End quote --- That's exactly the opposite datasheets say. E.g. http://www.ti.com/lit/ds/slvse42a/slvse42a.pdf: --- Quote ---When the current-limit threshold is hit, a closed loop activates immediately. The output current is clamped at the set value, and a fault is reported out. The device heats up due to the high power dissipation on the power FET. If thermal shutdown occurs, the current limit is set to IILIM(TSD) to reduce the power dissipation on the power FET. --- End quote --- I never used one myself, even though I have a similar part in my parts bin. So, don't know if it is suitable or not. But if it is for charging batteries, then I wouldn't use it because limits are most of the time not precise. At least calibration is needed. I'd buy a charger, or charging ic controller. But chances are such controllers are already built-in in the "handheld devices" (whatever they are). Esp. if they use lipo batteries. My guess current limit is needed for protection. |
| bdunham7:
--- Quote from: Teun on July 17, 2019, 11:46:17 am ---Hi all, I'm working on a project which has 5 parallel outputs for charging handheld devices. I need to limit the current of every channel to +/-3.5A at 5V. Or 2A at 9V (roughly 18W). Can anyone recommend a good IC for this? Preferrably with little other components needed. I tend to get a bit confused searching for these things. Do I need a "load switch" or "current limiter" or any other name these things might have? --- End quote --- What do you want it to do if the device being charged draws more than it's allotment? Shut off, shut off temporarily and reset, limit the current to exactly the specified amount or foldback? Why the different voltage specs--are these phones or what? What will be the input voltage from the power supply? If you don't know the answer to those questions, can you tell us exactly what type of handheld devices you will be charging? |
| MagicSmoker:
^^^Above asks good questions. It's certainly possible to design a circuit to limit current to 3A when the input is 5V, or 2A when Vin is 9V, but it will either require a bunch of components (op-amp based control loop) or drop a good deal of voltage (~1V or so) even when current is just under the maximum permitted (e.g. - the classic two-BJT current limiter circuit). A foldback current limiter would likely be a better choice here, but the OP didn't specifically say why current needs to be limited, or what the downstream load actually is - presumably a battery charger, and not a battery itself, because there aren't any batteries that will be happy having either 5V or 9V applied to them. Given that, it makes more sense to use an efuse rather than try to turn a voltage source into a current source, especially at 2-3A, as that could result in 15-20W of dissipation per channel in the event of a hard and persistent short. |
| wraper:
--- Quote from: Teun on July 18, 2019, 10:11:18 am ---There is a big 90W power supply which will be divided in to 5 channels. So this is more of a distribution board. Preferably I would like it to work in CC mode. But a disconnection with some sort of auto reset after a few seconds would be ok as well. --- End quote --- Such approach is simply wrong. Half-decent charger will have individual buck converter for each channel. |
| ogden:
--- Quote from: wraper on July 18, 2019, 08:09:39 pm --- --- Quote from: Teun on July 18, 2019, 10:11:18 am ---Preferably I would like it to work in CC mode. But a disconnection with some sort of auto reset after a few seconds would be ok as well. --- End quote --- Such approach is simply wrong. Half-decent charger will have individual buck converter for each channel. --- End quote --- Right. You usually do not build 3.5A chargers using linear components, not to mention smart fuse ICs. "Disconnection with some sort of auto reset after a few seconds" means circuit breaker. Do you need circuit breaker (fuse) or battery charger? If battery chargers are built-in (into handheld devices) then obviously fuse is all you need and mentioned chip is good enough: http://www.ti.com/lit/ds/slvse42a/slvse42a.pdf |
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