I've seen the circuit diagram (found on the web) part of a Li Ion battery charger attached and from what I understand, the second LM317 (CC) serves a current limiter. I would like to ask for an explanation how it's done, since for all I know, the LM317 is a voltage regulator and if it can serve as as current regulator/limiter - what needs to be done in order to make it a variable current limiter and if it's possible to add a led indicating that it reached the set current?

 

I would like to ask for an explanation how it's done

The voltage between the output and adjust pins in nominally 1.25V, so the current limit would be 1.25V/R18.

what needs to be done in order to make it a variable current limiter

Adjust the resistance between the output and adjust pins.

 

The second regulator output through R18 tied to ground is a short circuit. Assuming you remove the short, the current would be around 600mA, not 600mAh. MAH is Milli Amps per Hour. Simple mistake. And I'm assuming 2R1W (the W confuses me) you mean 2R1Ω or 2.1Ω. At 2.1Ω current is 595mA. Close enough to 600 to not make a fuss about it. Or perhaps you mea 2Ω @ 1W. That case current is 625mA. Again, little to fuss over.

 

Adjust the resistance between the output and adjust pins.

Adjusting the resistance at high amperages means you need a high wattage variable resistor. 14V @ 600mA means 8.4 Watts. Would certainly not be a simple potentiometer.

 

Next question: Why the CV first and the CC second? If you want a more accurate CV reverse the two. What do you think. How accurate do you need the max cutoff voltage.

 

 

From crutschow
C1+Rs is the battery.

 

Why the CV first and the CC second?

Yes, that circuit obviously has the wrong order for the CC and CV sections.
The CV should be the last (connected to the battery) so the regulated voltage is delivered to the battery.
Otherwise the battery voltage will be 1-2V below the set regulated value.

 

The CC should be first because it will consume up to 3V in headroom / dropout. The remaining voltage is dropped by the CV.

Here's a example set to 5V @ 25mA. I included an extremely small 1pΩ load (short circuit) to show the current limiting in action.

 

Below is the LTspice sim of an LM317 with a limited current adjustment range as determined by pot U2:
The LED is ON when the circuit is limiting.

 

LEDs, 555s, Flashers, and Light Chasers
Current Limiting

 

I'm sorry, I guess that I wasn't clear enough. I don't need it as a Li Ion battery charger, I want to add a current limit circuit in order to make a lab power supply. my intention was to use a LM317 as a voltage regulator that will provide 0 to 30V and then to add current limit circuit - seems one like "crutschow" suggested, but with an additional power transistor, so that it will be able to provide 5A output current.

 

If you check my links you will see I posted did several types of current limiters,each has its own advantages and disadvantages. LDO ( low dropout) devices are best for this application. Also what is your maximum current you are wanting to go through this ? As well as the maximum voltage you expect out?

 

I would like to have an output of 0 to 30Volts at a current between 0 to 5Amps. how can I find your links?

 

That's roughly ~150-Watts,
placing You firmly into SMPS territory,
unless You intend to employ a huge Fan-Cooled-Heatsink for a Linear-Regulator.

It's not really worth it to build you own,
unless You are doing it for the education, or for entertainment.
.
.
.

 

I have always enjoyed building my own power supplies,as a starter I would recommend buying a SMPS from Amazon they are quite cheap. You can also buy an off the shelf one through Amazon for not a very large amount of money. But I do understand the DIY nature of what you wanna do. For example:


https://www.amazon.com/YIHUA-Regulated-Alligator-Precision-Electronic/dp/B08Y8VWDVG/ref=sxin_16_pa_sp_search_thematic_sspa?content-id=amzn1.sym.27b41115-b206-47c3-8621-713097e8442c:amzn1.sym.27b41115-b206-47c3-8621-713097e8442c&crid=2DOLLLYT6D4YW&cv_ct_cx=power+supply&keywords=power+supply&pd_rd_i=B08Y8VWDVG&pd_rd_r=0c118f0e-91e5-4aa2-a9da-7b4206f4e4ae&pd_rd_w=BGlok&pd_rd_wg=17lgW&pf_rd_p=27b41115-b206-47c3-8621-713097e8442c&pf_rd_r=1Z7QFTH2ZR0BPE0YEVK8&qid=1736111711&sbo=RZvfv//HxDF+O5021pAnSA==&sprefix=power+supply,aps,155&sr=1-2-6024b2a3-78e4-4fed-8fed-e1613be3bcce-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9zZWFyY2hfdGhlbWF0aWM&th=1


https://www.amazon.com/Adapter-Blue...736111975&sprefix=30V+6A+power,aps,153&sr=8-8

 

I would like to have an output of 0 to 30Volts at a current between 0 to 5Amps. how can I find your links?

Yes, my main purpose is to try learn. I'm well aware that a power supply can be purchased at a fair price on "Amazon" and even cheaper at "Aliexpress" but I would like to do it myself. I didn't knew, for example, that the LM317 can serve as a current limiter as well. as per your remark about the smps, I want to use a conventional transformer (it's secondary is 24V) with a bridge rectifier and the voltage will be regulated with a LM317.

 

MAH is Milli Amps per Hour. Simple mistake.

If you're going to correct someone, it's best to be correct in your assertion.

mAH (milli-amp hour) is a measurement of energy. If you charge a battery at 1000 mA for two hours, 2000mAH is the energy gain (i.e., the amount battery has been charged.

Current × time, not

Current/time.

 

Certainly J.C. is correct!! So I challenge the original source of that circuit shown in post #1 as being deficient in both competence and integrity! It IS a current regulated source, but it is in no way able to deliver only the correct charge to a battery. And worse yet, if it were applied to a 600 mAHour battery, it would be much more current charging than the battery was intended to have, and thus cause a serious problem, such as a fire.
There may be fast-charge batteries available, but they would certainly be identified as such.

 

If you're going to correct someone, it's best to be correct in your assertion.

mAH (milli-amp hour) is a measurement of energy. If you charge a battery at 1000 mA for two hours, 2000mAH is the energy gain (i.e., the amount battery has been charged.

Current × time, not

Current/time.

mAh is a unit of charge not energy. Specifically, it's the total amount of charge transferred per unit time.

1 ampere = 1 coulomb per second

1 amp-hour = 3600 coulomb per 3600 seconds

Without knowing the voltage we don't know how much work is done and don't know the energy.