I'm trying to use a portable power bank (5V/2.1A) and try to supply power to my DC/DC Converter which will then be used to power something else (probably a laptop or so). However, the issue is that with a load of 70W (in the case of a laptop), my input will need significantly higher current than just 2.1A (70W/5V=14A). Also, it seems like a 10W source from my port battery bank will not be able to supply enough wattage for a 70W load and hence my question.

However, the flexibility is that I do not need to supply a full load charge to the laptop and I just need to verify that this concept works and able to charge up a laptop even if it's a slow charge. On a side note, I need to feed the output of my DC/DC Converter to my laptop AC adapter. I'm using DC only because of SMPS-based adapters since rectification is the first stage.

Hence, I'm thinking if there are any current boosting techniques at the source side where I can use to amplify the 2.1A to a higher rating? I've heard of methods that is able to have a certain pulses of higher current (e.g. 5A) for an interval and a slightly lower current interval (e.g. 1A) and it averages it out to whatever the input can supply (e.g. 2.1A for my case). Not sure what is that called though. Anyone knows?

And what about darlington pair? Heard that transistors are used to obtain a higher current gain but not sure if this is applicable for my case as it seems to be used for small signal applications.

Any advice on this? Thanks!

  • \$\begingroup\$ Throw away the power bank and start again with a decent power source. The only way to "step up" current is to step DOWN voltage, which doesn't help. \$\endgroup\$ – Brian Drummond Sep 11 '17 at 16:30
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    \$\begingroup\$ You can certainly build your own power bank which can discharge at 70w but you can't magically go from 10W to 70W \$\endgroup\$ – sstobbe Sep 11 '17 at 16:32
  • \$\begingroup\$ You need "at least" 7 of those banks in parallel. \$\endgroup\$ – nvd Sep 11 '17 at 16:59
  • \$\begingroup\$ So am I right to say that a typical power bank that supplies through the USB port can only provide 10W at max? Assuming 5V/2.1A in my case. If I'm using a 12V lead acid battery (slightly bulky kind), will I still be bounded by the restriction of current drawn? \$\endgroup\$ – Morde Sep 14 '17 at 2:22

This would work if you could tell your laptop "hey, be nice, don't use more than 10W worth of power from the source..."

But your laptop has no such feature, when it is plugged into the charger, it is designed to charge as fast as possible, which means sucking in as much current as it can...

There is no way to do this, as the others said. The simplest is to get a spare battery for your laptop, by the way.


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