Increasing a DC-DC conv output from 5.00 to 5.25V

On a sunny day (Sun, 27 Oct 2013 19:29:00 +0000) it happened Peter wrote in :

cannot you put an extra turn on a switcher transformer somewhere?

---------------a diode k ----------------> + 5.25 | | ( extra turn[s] elco | | -----------------------------------------< +5

The smaller modules output a higher voltage at low loads. Changes are the output voltage is already suitable for your purpose.

Den søndag den 27. oktober 2013 20.29.00 UTC+1 skrev Peter:

how would you increase the output voltage with a diode drop?

unlesss you can get to the sense resistor inside I don't see how

maybe something like this:

-Lasse

In my opinion, no. BTW, I don't follow this paragraph from your original post. But diodes are temperature sensors, so I don't like the idea, even if I totally understood it.

To be honest, this sounds like a design flaw in the notebook. That is, the charger in the notebook need to take 5V +/- 5% and deliver 4.2V plus the burden of the current sense. This should be doable. I'm assuming the Lenovo doesn't have Lion batteries in series, otherwise I would find it hard to imagine a few tenths of a volt would matter if they are boosting the input voltage.

My opinion of Lenovo has dropped a notch, though their customers swear their notebooks are the best, mostly because of their keyboards. My opinion of Apple hasn't changed. Apple loves proprietary stuff. Basically f*ck the customer.

With a LM7805, you put it in the ground lead. Oobviously this is not going to work with a buck switcher.

Buy the Lenovo charger.

waste of time

Presumably, you want to tweek this existing box (part of the avionics package) and not create something entirely new? E.g., a separate "outboard" DC-DC converter (off of one of the voltages you have available already)?

Does whatever you do have to pass any sort of certification?

Is it that the tablet won't sense that it *should* charge? Or, that it *can't* charge with that low of a potential?

Learn to have lunch within DRIVING distance of your home -- instead of halfway across the Continent! ;-) ;-)

Can you *replace* a module? Or, are there mechanical issues involved? Can you gut a module, modify it and install that in its place?

Off the cuff, I'd just suggest something "stand-alone" that handled

Is there any other charging path into the tablet (e.g., 12VDC)

If this is your biggest problem, I'll assume life is treating you reasonably well! (living arrangement?)

Regards,

--don

He is in an airplane, probably there is no stock charger. However, a 28V to 12V step down plus a charger designed to work off of 12V might do the trick.

I'd use one of Ti's "Simple Switcher" chips. The low voltage output chips even have an integrated inductor so all you add is the feedback divider and filter capacitors. Overall you'll end up with a circuit board about the size of an SD card.

There are lots of variations but here is one to start with:

Don Y wrote

I have a 5V 2A DC-DC conv already in there and would like to "lift" its output by about 1/2 volt.

I don't have room in the box for one of the much bigger converters that have an adjustable output.

No - portable kit is OK. Plugs into a cigar lighter socket.

I don't know. It draws some current from 5.0V but not enough to charge while turned on.

Hohoho :)

Not enough room.

I am going that way, yes.

No, sadly, because in the same box I also have these handy outputs

Indeed :)

miso wrote

Yes - crap design.

I still think Thinkpad laptops are the best of them all. We use them at work and I have a few around the place myself.

I bought the Lenovo tablet because I needed a windoze platform to get DUN networking to talk to a satellite phone over RS232 and to run some apps which need windoze.

It's not clear to me the +5.5v requirement is proven. +5.0v should be more than enough, as you noted.

Given all the different, incompatible "cheats" to enable/request high current from the charger, it still seems possible that that's the problem.

Cheers, James Arthur

Lenovo has a bunch of different schemes for charging their PCs and Tablets, many of them are smart and communicate with the host or receive communicat ions from the host. The lowest tech but most reliable way of doing this is to obtain their stock charger and figure out the required DC/DC converter t o power it at an alternate input.

since the switch-mode DC-DC converter's input current will always be less than the output current, the net current through the diode will be below zero... "

No. That doesn't mean that. It all depends on where the reference is. Howev er if -20-1110 or whatever, the five pin jobs, adding a diode at the bottom will not work anyway, the reference and everything is inside.

If you can't get inside such a unit, you are up the creek and paddles are o n backorder.

the current is not very high, so really you could add a diode to the output s after a small inductor, and then throw in some AC from an oscillator or s omething. Umm, I guess I would recommend an oscillator over an or someting in this case. Just capacitively couple it. If you need to, post regulate, w ell wait, that is not what I mean. you HAVE inductance so PWN in your littl e gizwhicher would work fine. Damn shame to complicate it so much but that' s the breaks.