DC-DC Buck Converter Adjustable Step-Down LM2596S

[Kiriakos GR]

I just got 5 of those adjustable Step-Down LM2596S PCB and what I need is the confirmation that bellow the 3V as input voltage, this controller stops using the battery.

The plan is to use 18650 as source and power up small devices from a wall clock, and even other stuff which needs 6V, so to stop buying alkaline.

http://www.ebay.com/itm/200964338091...84.m1497.l2649

[budm]

Re: DC-DC Buck Converter Adjustable Step-Down LM2596S

The LM2596 has ON/OFF pin5 that you can use to shutdown using sensing circuit that monitor the input voltage and shutdown when the batteries voltage goes down to 3V (should make it adjustable), the circuit should latch into shutdown mode otherwise when it shutdown, the battery voltage will rise up due to no load which if the shutdown is not latch it will turn the IC back on again and keeps cycling on and off, or have the circuit with adjustable hysteresis. The one on EBAY does not have any info on how that ON/OFF pin is implemented.
https://cdn.badcaps-static.com/pdfs/...cd58db5a46.pdf

[Kiriakos GR]

Re: DC-DC Buck Converter Adjustable Step-Down LM2596S

The one on EBAY does not have any info on how that ON/OFF pin is implemented.
https://cdn.badcaps-static.com/pdfs/...cd58db5a46.pdf

I am looking those PCB for two hours, all the wiring instructions from those sellers advice to not use at all the volt sensing pin usually market by the letter T on those PCB.

Basically I do not mind about the possibility of this On/Off after been discharged.
As long the voltage does not get below 3V this translates that I do not need to spent additional money for Li-Ion 18650 battery protection controller.

About charging I will do it manually with professional power supply with current limiter.

[mariushm]

Re: DC-DC Buck Converter Adjustable Step-Down LM2596S

It would make more sense to just go with a more efficient buck-boost controller, that lm2596 isn't that efficient.

If you only need up to about 100mA output, try LT1307: https://cdn.badcaps-static.com/pdfs/...2b27d5d015.pdf (this one's also available in DIP so you could breadboard/veroboard/stripboard it)

If you need up to 1A, try LT1308: https://cdn.badcaps-static.com/pdfs/...c3bfd3cebc.pdf

Yeah, they're more expensive but you save up on inductors and capacitors and they're very efficient and you could also use them in SEPIC configuration (see lt1307 datasheet for application circuits, it's basically the small brother of lt1308 which has a more basic datasheet)

And they also have a low battery comparator/indicator and can design it to shut down at a threshold, and there's a pin that signals low battery to your circuits if you choose to use it.

ps. just be aware lt1308 accepts a maximum of 10v, while lt1307 supports up to 12v. I guess with 18650 batteries this won't be a problem.

ps2. LT1308 is more or less boost only, now that I double checked the datasheet. lt1307 works both ways, I've personally tested it. It's not clear from your original message, but I assumed you wanted a boost controller since you a 18650 battery is usually 3.7-4.2v and you said "even stuff which needs 6v" ....

Maybe see LT1610 as well but that one doesn't have battery indicator etc

[domas]

Re: DC-DC Buck Converter Adjustable Step-Down LM2596S

Just one more thing. If you’re planning to use 1 li-ion cell instead of 2 alkalines @ 1.5V nominal, this might be challenging as some of those converters have something called minimum voltage difference which is probably dropout voltage. That being said, if li-ion cell has 3.5V left, the maximum output might be as low as 2.5V

The ebay listing doesn't say anything about that.

[Kiriakos GR]

Re: DC-DC Buck Converter Adjustable Step-Down LM2596S

By the specifications of this controller.

1) Minimum input voltage: 3.2V

2) Minimum output voltage: 1.25V

Therefore by just one 18650, you can drive one wall clock at 1.5V until the battery to drop down to 3.2V from 3.8V as fully charged.

In one configuration with two 18650 in series, there is a problem there, its battery should have a protection circuitry, otherwise the DC-DC Buck Converter will bring them down to 1.5V its one.

[mariushm]

Re: DC-DC Buck Converter Adjustable Step-Down LM2596S

Well, like I said, if all you want to do is to power a clock, LM2596S sucks for that. poor efficiency at about 70-75%, high quiescent current (5mA typical, 10mA max, basically could be more than the clock actually uses)

LT1307 can work with as low as 1v, can output 1-5v with no problems, up to 80% efficiency depending on input voltage, 50uA quiescent current and you could set to shut down when voltage goes below a value you want and save the batteries.

A clock will probably have pulses of power as it moves the indicators on the face, and then it basically "sleeps" for the rest of each second, so you might want to keep that in mind.

[Kiriakos GR]

Re: DC-DC Buck Converter Adjustable Step-Down LM2596S

in order to avoid problems with low voltages, I just got two PCB for 7.2V packs, this will bring a better balance.
And it will drive stably the DC-DC Buck Converter.

http://www.ebay.com/itm/180674611172...84.m1497.l2649

[LLLlllou]

Re: DC-DC Buck Converter Adjustable Step-Down LM2596S

Well, like I said, if all you want to do is to power a clock, LM2596S sucks for that. poor efficiency at about 70-75%, high quiescent current (5mA typical, 10mA max, basically could be more than the clock actually uses)

LT1307 can work with as low as 1v, can output 1-5v with no problems, up to 80% efficiency depending on input voltage, 50uA quiescent current and you could set to shut down when voltage goes below a value you want and save the batteries.

A clock will probably have pulses of power as it moves the indicators on the face, and then it basically "sleeps" for the rest of each second, so you might want to keep that in mind.

I have, on occasion, soldered 10uf to 100uf caps across the standard alkaline D cells in clocks. Battery (cell) life almost doubles. Instead of pulling relatively large pulses of current through the ever increasing impedance of a discharging cell, the cap supplies most the current draw during the pulses.

I once did this with a cell that was too dead to power the clock. After the capacitor was added it ran for a few more months before it was finally too dead to work anymore.

[rhomanski]

Re: DC-DC Buck Converter Adjustable Step-Down LM2596S

Ding Ding Ding Ding. You get the skinflint award for today, Lou. Ha Ha.

[Kiriakos GR]

Re: DC-DC Buck Converter Adjustable Step-Down LM2596S

Ding Ding Ding Ding. You get the skinflint award for today, Lou. Ha Ha.

He gets an high imagination award for soldering a cap over an alkaline. LOL

Any way my two wall clocks are new with modern movement engines, they are silent and they do a constant rotation.


.

[ben7]

Re: DC-DC Buck Converter Adjustable Step-Down LM2596S

Ultimately you will want some battery management IC, most have built in DC-DC converters (some buck, some boost, some have both)...
This way it is easy to charge the battery too (unless you already have a charger)

[BlueBand]

Re: DC-DC Buck Converter Adjustable Step-Down LM2596S

[QUOTE=LLLlllou;389676] I have, on occasion, soldered 10uf to 100uf caps

I once did this with a cell that was too dead to power the clock. After the capacitor was added it ran for a few more months.

Hi all and a big Thank you to Lou, I have a Metamac Star burst 1970's, fitted a new battery Easter a few months later battery dead, So tonigh i decided on an 18650 conversion found your sugestion as I have about 500 Electolitics floating about so I though why not.

Well to tell the truth you said 10 - 100 uf all I could find (we moved house at Easter still not sorted) was a 47uf so I soldered the said cap accross the battery box terminals picked up the dead battery tested it on the battery setting/meter.

Low, tested it's twin (Bought at the same time in a twin pack) Good. Fitted the old battery and the clock stared working as for how long... Start time 00:05 time now GMT 01:37. Thank's Lou that was a quick Hack.

My thoughts on why it works and please correct me is 1/ a new movement will be in ace condition totaly free of dust/dirt etc. 2/ Cost, both time and componets. 3/ The clock was a fashion statement, in 7 years time it will be out of fashion so why make it last. Well at 42 years or so years old and still ticking, yes it needs a service but I was taught if it works leave well alone.

I have to say I had a Botox injection into my left eye and the keyboard is now in three dee (double vision) so sorry for the spelling as I can only just see also 2am need the sack pronto. By Guy's & Girl's Regards David