Input MOSFETS, a bit of theory

[Adenitz]

Hello guys,

I recently watched a new repair yt video from Sorin and in the comments there were a lot of discussion about whether or not he made a mistake of not checking the second input MOSFET (after DC IN).

I have found here, also a very interesting description of one repair where 2nd MOSFET was faulty.
Now the thing that interests me is the claim that bridging the first input MOSFET when actually second MOSFET is shorted is actually a dangrous practice, because this will create situation for battery to overcharge.

Can this be true? I mean if battery charging IC chip really prevents battery from overcharging by controling input MOSFETs. I believ not because, DC IN power would be cut down that way. I think that there must be some other protection method to prevent battery from overcharging like protection circuit on the battery itself.

Can you please explain this in a bit more details? I really wonder what stops battery to charging, when capacity is 100%?

Thanks!

P.S: I have alreday found and read on this forum about battery charging circuit and why 2nd MOSFET should be checked, but wonder how overcharging battery is prevented.

[ktmmotocross]

Re: Input MOSFETS, a bit of theory

1. Sorin is maybe worst repairman i know. injecting 19V, putting powered board on metal keyboard case and lots of other DOGGY shit stuff he do and say
2. if u have shorted second mosfet laptop will not charge battery
3. charging is controlled by charging ic with comunicating with SIO and battery IC.

[Sametbey]

Re: Input MOSFETS, a bit of theory

The notebook battery charge controller allows charging after receiving the AC_IN input (AC_OK signal). The charge control chip communicates with the battery via the SDA and SCL line. If there is a short circuit in the + B 19V line, 1 MOSFET circuit will not last. However, if you jamp 1 mosfet, it will cause bigger malfunction.

[Askic]

Re: Input MOSFETS, a bit of theory

2. if u have shorted second mosfet laptop will not charge battery
3. charging is controlled by charging ic with comunicating with SIO and battery IC.

That is understandable. In case 2nd Mosfet is shorted then ACP input of IC (positive leg of input current sensing resistor) will be either shorted to some other leg of the same chip or resistance will be changed between the legs and battery will not be charged.
When 2nd Mosfet is shorted, IC chip sense that and turns off input MOSFETs. That is why 1st Mosfet is switched off even if it is correct.

[Adenitz]

Re: Input MOSFETS, a bit of theory

Thank you for the replies, but still don‘t understand how ic stops battery charging when battery reaches 100 %. It does not shut down input mosfets for sure. I want to know how this works when everything is okay

[Sametbey]

Re: Input MOSFETS, a bit of theory

For example, an 11.8v battery goes up to a maximum of 13V. The charge controller stops charging when it reaches this value.

[piernov]

Re: Input MOSFETS, a bit of theory

As seen in the topologies described here: https://www.badcaps.net/forum/showthread.php?t=90356 , the battery is charged through a DC-DC converter (Buck or Buck-Boost), not directly after the DC-in MOSFETs. The DC-DC converter regulates the voltage going to the battery.
Additionally the battery itself has another set of MOSFETs as a protection to prevent any overvoltage to get across the cells.

[Adenitz]

Re: Input MOSFETS, a bit of theory

Thank you very much for the reply piernov. I was look at your guidelines and there is a schematic: https://www.badcaps.net/forum/attach...5&d=1605469300
This IC chip PU14 is actually IC (BQ247...) charging chip. I was confused because on the article I read that jumping first MOSFET can led to battery overcharge, but I don't see how that is possible based on this schematic.

If everything is OK, I guessthat BQBATDRV signal to gate of MOSFET PQ54 will stop charging the battery.

[jasko_jacker]

Re: Input MOSFETS, a bit of theory

I personally always recommend reading the component datasheet carefully and studying the recommended circuit. It is important not to underestimate: the host (depending on the circuit) could involve other components and the A_D_DOCK_IN line (on asus mainboard)

[ktmmotocross]

Re: Input MOSFETS, a bit of theory

For example, an 11.8v battery goes up to a maximum of 13V. The charge controller stops charging when it reaches this value.

it is not only about voltage. charging ic controls voltage and current. battery ic cut power to battery when something is not right too. like u have higher voltage by maybe 3V than actual battery voltage and if current is higher than max chaging current for battery. charging is difficult circuit because of many involved ic

[Mart202]

Re: Input MOSFETS, a bit of theory

1. Sorin is maybe worst repairman i know. injecting 19V, putting powered board on metal keyboard case and lots of other DOGGY shit stuff he do and say
2. if u have shorted second mosfet laptop will not charge battery
3. charging is controlled by charging ic with communicating with SIO and battery IC.

The man him self thinks the same check out this video where he mentions it:
https://youtu.be/YPBE8dXIzGc?t=3477

[ktmmotocross]

Re: Input MOSFETS, a bit of theory

The man him self thinks the same check out this video where he mentions it:
https://youtu.be/YPBE8dXIzGc?t=3477

So he make crap work because of no time?

i have one friend with me in shop. our shop works ok with good revenue without needing of crap work.

check northridgefix. HE make epic soldering work 10x faster than sorin with epic quality

[Oldi59]

Re: Input MOSFETS, a bit of theory

Sorin works at a totally different financial level that's called cheap and cheerful he probably charged sub £50 for that job and the owner gets a bit more use. The logic behind the repair is covered in several of his earlier videos. so basically speaking its horses for courses.

[Askic]

Re: Input MOSFETS, a bit of theory

Sorin works at a totally different financial level that's called cheap and cheerful he probably charged sub £50 for that job and the owner gets a bit more use. The logic behind the repair is covered in several of his earlier videos. so basically speaking its horses for courses.

Totally agree. In more than one occasion he mentioned that repair shop charges for motherboard repair about £50 or £60. The costs are the same for PC laptops and Macbooks. On the other end, "high level" repair specialists like Louis or Paul Daniels charge about 300 USD for macbook motherboard repair.

Therefore, I think that Sorin's work is the best you can get for such amount of money.

[piernov]

Re: Input MOSFETS, a bit of theory

Driving the whole market down with such practices does nothing good to anyone.
It is exactly why we have garbage laptops, TVs and even worse printers in the first place: they are built to extreme cost reduction because 1/ people expect to buy these products for pennies 2/ as a result the competition drives the prices down instead of driving the quality up.

Even worse here is when you spread this low quality work by making so-called "educational" videos that everyone takes as the one and only truth.
And yes, both the orator and the auditor are at fault here. One for spreading misinformation and bad practices, the other for not using critical sense and understanding the implications.

I fight everyday against this kind of practice in the hope of seeing less randomly reflowed BGAs, less randomly bridged MOSFETs and fuses, less randomly injected 19V that only help in increasing the number of non-repairable devices. Or just in general fight for some better quality work across the board.
As long as I'm here I'll personally not tolerate such practices.

Btw, I'm not saying that £50 or $300 is either cheap or expensive. The labor cost will vary depending on your location and situation. I'm saying that you should not sell yourself short and do garbage work as a result. You should take pride in your work and aim at doing the best for you and your customers.

[ktmmotocross]

Re: Input MOSFETS, a bit of theory

Totally agree. In more than one occasion he mentioned that repair shop charges for motherboard repair about £50 or £60. The costs are the same for PC laptops and Macbooks. On the other end, "high level" repair specialists like Louis or Paul Daniels charge about 300 USD for macbook motherboard repair.

Therefore, I think that Sorin's work is the best you can get for such amount of money.

In one video he "repair" poor wifi signal by switching antena cable to AUX connector and charge 90pounds. I think thats more like RIPoff. or "repair" bad solder ball by super light reheat and call it fixed.