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MOSFET recomendation for LTC4008 Li-ion Charger (5 cells pack)

Former Member — Mon, 04 Feb 2013 10:01:33 GMT

Hi,

I´m currently designing a 5 cell pack Li-ion charger with LTC4008 chip (discussion posted in Sep 2011 in this thread)

In page 15 of LTC4008 datasheet you can find the topic about the MOSFET selection.

I´m certainly lost in the proper selection. I know that logic-level MOSFETS must be used (gate voltage around (5.6V-6V), but is the first time for me designing with mosfets.

One important point is the output voltage of the carger, datasheet says that if Vout>20V then the RDSon should be little more high for reducing the ripple...

The charge voltage will be 20.5V and maximum Output Current 1.5A

I was thinking on use the mosfets that appear in the schematics of the datasheet, but has anyone any recommendation?, I mean, do I have to go deep in the mosfets area or can I use one recommended by anyone who has be involved in similar scenarios?

The only important thing in this design is the proper selection for minimum ripple current, at cost of something (as always). Efficiency for example is not a problem cause it´s a battery charger (I prefer to lost energy efficency if that means reduce ripple current in the output). I´m thinking to use a slightly high Inductor (around 40 microH) and two low ESR tantalum capacitors "surge robust" in parallel in the output of the mosfets.

Any comments are appreciated

PS: I need reference values. (What means high ... what means low... 0.001 - 0.01 ? (in mosfet parameters)

RE: MOSFET recomendation for LTC4008 Li-ion Charger (5 cells pack)

Pradipsinh — Fri, 24 Apr 2026 05:22:08 GMT

Which use mosfet

RE: MOSFET recomendation for LTC4008 Li-ion Charger (5 cells pack)

Pradipsinh — Fri, 24 Apr 2026 05:20:30 GMT

7.2 ah battery charger use Ltc4008 which mosfet runnig

RE: MOSFET recomendation for LTC4008 Li-ion Charger (5 cells pack)

Pradipsinh — Wed, 22 Apr 2026 05:02:04 GMT

Sir my name is pradipsinh pl suggestions accu nimh 7.2v 9Ah battery in side mosfet fire use ltc 4008 which mosfet use in side

RE: Safety of plugin solar?

beacon_dave — Mon, 05 Jan 2026 14:41:57 GMT

I think it was partly driven by another energy report that suggested something like 75% of around 380,000 homes in England were flats that had integral balconies, probably taken from here:

English Housing Survey: Floor Space in English Homes - technical report

and that plug-in solar appears to be marketed at such properties.

I suspect that it was more of a paper exercise.

Safety of plugin solar?

Workshopshed — Mon, 05 Jan 2026 07:36:14 GMT

Just seen a YouTube short from JerryRigEverything for a 4 panel solar system with roof top microinvertors.

The "interesting" feature is that it connects into a regular socket i.e. the power is provided through a plug.Jerry states this is only approved in Utah at the moment and is limited on the size of the system you can install.

For me this raises a couple of questions, firstly how it doesn't electrocute the person handling the plug? But how it doesn't back power the grid when there is a power outage?

I have a solar system at home and it is hard wired with a number of protective devices and isolators between the solar and mains.

Anyone know anything about these plugin systems?

RE: Safety of plugin solar?

michaelkellett — Mon, 05 Jan 2026 14:11:58 GMT

Doesn't look as if they are in much of a hurry.

Although solar panels in flats in most of the UK are not going to be a lot of use.

RE: Safety of plugin solar?

ralphjy — Mon, 05 Jan 2026 13:53:00 GMT

I have an older system with an SMA string inverter that has a disconnect that allows me to use the panels when the grid is down. Unfortunately, it is limited to 1.5 KW.

RE: Safety of plugin solar?

beacon_dave — Mon, 05 Jan 2026 13:52:38 GMT

It looks like plug-in solar is on the UK solar roadmap:

Solar roadmap: United Kingdom powered by solar

"...Plug-in solar can provide opportunities for households to adopt solar more cheaply, particularly for those in rented accommodation or flats. Currently, UK regulations do not allow plug-in solar to be used in the UK, but the government is working to explore its potential.

Action 2: Government will conduct a safety study this year with the aim of unlocking opportunities for plug-in solar over the next few years..."

RE: Safety of plugin solar?

Workshopshed — Mon, 05 Jan 2026 13:34:07 GMT

My solar and battery will go off if I lose mains. There was a disconnect option but that was a other £500 and we don't get a lot of power cuts around here.

RE: Safety of plugin solar?

obones — Mon, 05 Jan 2026 08:04:14 GMT

They are quite common in Europe and periodically tests for the presence of power coming into the wall socket to decide if it injects power into it.
Basically, if it "sees" 220V on its power line then the inverter will send its power, and it repeats that test at rapid frequency so as to stop immediately when "street power" goes out.

Note that it's the same with the solar panels I have here, that are fitted to the roof with their micro inverters connected to the main power panel. If there is no power coming from the utility provider, they don't generate anything either, so as to protect everyone in the street.

ATX power supply control interface with a PIC18F1220

Stuart_S — Wed, 22 Oct 2025 01:01:22 GMT

Here's a little circuit I've developed to operate an ATX PSU with a single push-button instead of a toggle or slide switch.

The heart of the circuit is a few components including a diode and a transistor. I'm wanting to power the MCU from the standby 5 volt line, can anyone here advise me what current this pin is normally able to source and is it usually held stable or does it power down periodically?

For those who'd like to understand more about the circuit I'm providing a link to my Wix project page: ATX power supply remote start with single push button. | Blokeystuff The key to the circuit is how D1 is reverse biased in both the states (while the PB is open) via the higher resistances to Vcc and the lower resistance paths to ground to counter the reverse biasing when the PB is pressed -and at the same time when the uC gets a low input on uCin_btnPSU it then runs an internal timer when it's in the ON state to decide when to release PS_HOLD. The push button does both ON and OFF control in the same way it's done on an IBM AT-X on the front panel. Ignore the NTC for the moment, I was using that to help regulate the PWM signal into a salvaged HP desktop PSU.

RE: ATX power supply control interface with a PIC18F1220

Stuart_S — Mon, 27 Oct 2025 16:23:57 GMT

Seems to work ok on the HP PSU, I had to do a bit more programming for that to drive the internal fan - reason why I have the NTC-thermistor there.

RE: ATX power supply control interface with a PIC18F1220

shabaz — Mon, 27 Oct 2025 16:05:29 GMT

I believe it works for you if you say it does, but just from general thoughts, will it always work for other ATX supplies too? The pull-down looks more borderline than it needs to be, especially with a diode drop.

However, I've never read an ATX spec so I'm only speculating. I too sometimes end up with elaborate or unusual configurations, but I would have thought the ATX interface probably doesn't need that, since standard power on configurations must have been in the minds of the designers of that spec.

I didn't understand the benefit of the momentary push-switch switch working without the microcontroller present, but I've never tried such a circuit, so it's likely there's ATX knowledge I'm missing.

RE: ATX power supply control interface with a PIC18F1220

Stuart_S — Mon, 27 Oct 2025 14:48:07 GMT

Your circuit appears much simpler than mine but it doesn't allow for push-button startup independent of the uC, I have updated the circuit to show the uC's I/O directions, hopefully someone can understand it now.

RE: ATX power supply control interface with a PIC18F1220

shabaz — Fri, 24 Oct 2025 14:56:50 GMT

Hi,

I'm not going to breadboard it; unfortunately, I don't have time for that.

If desired, you could simplify the circuit, as shown here. All microcontroller inputs are on the left, and all outputs are on the right side. This circuit puts the ATX supply power-on capability entirely under the control of the microcontroller, i.e. the power-on switch is now only wired to the microcontroller, so the code would need to control the supply based on that. It's a minimal circuit, you may want to add some extra parts, say to filter the standby supply a little bit, but it's a start. I'm not suggesting you scrap your circuit if it works, it's just a data-point about I would have gone about it, (and how I would have drawn the circuit, in this case without the need for buses) if you're looking for ideas. Also, just from habit, I've moved the thermistor so that one end is connected to 0V instead of the positive supply, that's just because I usually find that more convenient, obviously the code would change for that as a result too.

The symbol I'm using for the microcontroller has, as mentioned, the inputs and outputs on separate sides, that's possible with CAD software by making a copy of the current symbol and then editing it to move the pins.

RE: ATX power supply control interface with a PIC18F1220

Stuart_S — Thu, 23 Oct 2025 23:52:00 GMT

The circuit works, just add Vss to the COM line on the ATX pins. Did you take the time to breadboard it or try an example on say Multisim or Simetrix?

RE: ATX power supply control interface with a PIC18F1220

Stuart_S — Thu, 23 Oct 2025 00:51:54 GMT

Hi Shabaz, I've updated the site so hopefully now it can read a bit clearer for you This circuit is a snippet from a circuit I built to run a HP Desktop PSU (part no.702307-001 - slightly different to the standard ATX-PSU as it only has a main 12V output, a 5v standby and signal I/O's for PWM/Tacho for its internal fan usually operated by a chip on the HP motherboard.

RE: ATX power supply control interface with a PIC18F1220

koshkb — Wed, 22 Oct 2025 15:53:26 GMT

Usually the +5VSB pin is capable supply 2 amps os more, check the labet on the PSU.

RE: ATX power supply control interface with a PIC18F1220

shabaz — Wed, 22 Oct 2025 14:36:44 GMT

Hi,

The circuit can't work as it stands, because there's no ground (or 0V or Vss or whatever it's desired to be called) connection to the ATX connector. You've also got signals going into the bus with no labels, and some signals (such as RedLED and GrnLED) going into the bus with a label but unattached to anything.

Personally I don't understand the rest of the circuit (and the explanation was hard for me to follow) but if that is tested and working then I have no comment. The web page is silent on whether this is a tested and working project, or something in-progress and still to be tested.

On the schematic, it's worth restricting bus usage for grouping things with some type of similarity, otherwise it's very hard to follow. For instance, perhaps a bus for the port A signals (RA) and another bus for the port B signals (RB).

Regarding your 5V standby line question, I don't know the answer (I'd be surprised if google doesn't help here, since ATX supplies are so common), but it's going to be highly likely more than sufficient to power the PIC microcontroller.

RE: Is the "imminent" availability of sodium ion batteries affecting your decision of when to switch to an EV or solar house?

dougw — Fri, 12 Sep 2025 21:40:21 GMT

agreed

Is the "imminent" availability of sodium ion batteries affecting your decision of when to switch to an EV or solar house?

dougw — Tue, 09 Sep 2025 20:32:13 GMT

Sodium ion batteries seem to be pretty close to being available and lots of investment is being made into the technology. They promise very fast charging time, 10s of thousands of charge cycles and lower cost than Lithium.

[embed:33ecb077-39b7-4078-9b1e-dc3f977a690b:360f430a-7e43-4213-b677-cf7a73d6e05e:question=How%20will%20sodium%20ion%20battery%20technology%20affect%20your%20decisions%3F&description=%3Cp%3ESodium%20ion%20batteries%20are%20touted%20as%20the%20next%20big%20power%20source%20with%20rapid%20charge%20capability%20and%20large%20numbers%20of%20recharge%20cycles.%20Do%20you%20find%20this%20exciting%20and%20where%20do%20you%20see%20it%20affecting%20your%20life%20in%20the%20near%20future%3F%3C%2Fp%3E&pollOptions=%5B%7B%22OptionId%22%3A%220e902ec4-ac64-4209-bf2a-cece5fde6fed%22%2C%22Option%22%3A%22I%20will%20wait%20until%20sodium%20batteries%20are%20well%20established%20and%20proven%20value%20before%20making%20any%20decisions%22%2C%22Ordinal%22%3A0%7D%2C%7B%22OptionId%22%3A%223d9f0195-e5ae-48f5-89e4-2cb5c47e51d9%22%2C%22Option%22%3A%22I%20am%20not%20holding%20my%20breath%20waiting%20for%20promises%2C%20I%20will%20go%20electric%20with%20my%20next%20vehicle%22%2C%22Ordinal%22%3A1%7D%2C%7B%22OptionId%22%3A%225c699436-a081-42f5-ab3b-a5d0d9500841%22%2C%22Option%22%3A%22I%20expect%20to%20stay%20with%20IC%20engines%20for%20at%20least%20another%20decade%22%2C%22Ordinal%22%3A2%7D%2C%7B%22OptionId%22%3A%224eb645aa-c9bc-4667-9b8b-c32415a657c7%22%2C%22Option%22%3A%22I%20am%20keen%20to%20take%20advantage%20of%20advances%20in%20sodium%20batteries%20as%20soon%20as%20I%20can%20buy%20them%22%2C%22Ordinal%22%3A3%7D%2C%7B%22OptionId%22%3A%225add6f57-5f0f-4801-ab60-3b75a1328a7c%22%2C%22Option%22%3A%22I%20want%20to%20convert%20to%20solar%20as%20soon%20as%20sodium%20backup%20is%20available%22%2C%22Ordinal%22%3A4%7D%2C%7B%22OptionId%22%3A%22fe54a05a-d9e4-4439-88c2-9596efddd729%22%2C%22Option%22%3A%22I%20am%20on%20the%20fence%2C%20I%20want%20to%20see%20an%20element14%20road%20test%22%2C%22Ordinal%22%3A5%7D%2C%7B%22OptionId%22%3A%221fb14fd8-8330-4d6a-9742-4868c12e718c%22%2C%22Option%22%3A%22I%20don%27t%20believe%20sodium%20ion%20batteries%20will%20actually%20be%20a%20big%20thing%22%2C%22Ordinal%22%3A6%7D%2C%7B%22OptionId%22%3A%22d654627a-e35f-4921-9581-f1f6b5c12b2d%22%2C%22Option%22%3A%22Other%20-%20explain%20in%20the%20comments%20below%22%2C%22Ordinal%22%3A7%7D%5D&ShowResultsConfiguration=1%2C1]

Leave a comment to elaborate on your thinking.

RE: Is the "imminent" availability of sodium ion batteries affecting your decision of when to switch to an EV or solar house?

ntewinkel — Wed, 10 Sep 2025 18:02:25 GMT

Maybe if Canada were to drop the 100% tariff on Chinese EVs - then the average person could afford going electric. Seems the way things are set up, the people who need inexpensive transportation the most are specifically blocked from doing so in one way or another - EVs are cheap to run but too expensive to buy. We had some hope when city-speed electric cars were allowed and they only cost around $10k to buy, but then the government suddenly made them illegal again.

Electric scooters are generally not legal, electric bicycles are kinda pricey too. And also being right on the same road as giant trucks isn't safe or comfortable.

I'm all in favour of having quieter vehicles on the road that don't send fumes my way, but I feel the government is still being hypocritical in the way they block the biggest percentage of the population from having access to them.

RE: Is the "imminent" availability of sodium ion batteries affecting your decision of when to switch to an EV or solar house?

scottiebabe — Wed, 10 Sep 2025 13:08:05 GMT

EVs using 50% of their battery capacity to keep the car warm is a terrible design decision.

Ethanol (liquid firewood) is widely available, cheap, and carbon neutral. So dumb.

RE: Is the "imminent" availability of sodium ion batteries affecting your decision of when to switch to an EV or solar house?

michaelkellett — Wed, 10 Sep 2025 08:43:24 GMT

Complicated question - my response is no doubt affected by living in a very rural area (about 40 miles and 1hour from the nearest motorway)

Sodium batteries offer of fast charge is not much help with solar.

And much less than you might think with vehicles. Already in the UK there is a large premium charged on fast charge electricity and serious issues with grid capacity. Just because you car can be charged at 350kW doesn't mean that you will be reliably able to do so.

Right now I wouldn't buy an electric car - real world range is poor, especially at reasonable prices. My diesel powered car can do 400+ miles on a tankful and the "charge" time is about 5 minutes. The tank won't wear out in 200k miles of travel.

I noticed a motorway charging station (not that fast either) charging £0.78 per kwh.

EV's are marginally green, very expensive to buy and run (if you do long journeys) and super inconvenient -sodium batteries won't fix very much of that.

If you live in a big city you might feel differently.