Laptop supply with linear voltage regulators

What if all your battery packs are worn out, the notebook itself has loose connections and missing keys, so there is no way you would pour money into it…

…but the diagnostics software for your car is installed (which was TIME CONSUMING) and now there is something to check, which can’t be done in your driveway?

Luckily I had plenty of old LM317s lying around. And old heat sinks. And two lead acid batteries. So why not regulate them to the PSU’s 18V and just connect them via barrel connector? Exactly.

Current consumption of the computer could be measured via lab power supply, so I knew that three LM317 paralleled would do the job – if I coud get rid of their heat losses. Some low-ohm resistors would separate the outputs just enough to keep them from working against each other and the regulators would share the feedback to avoid any tolerances there.


Easy enough to build on Stripboard, cuts made with a drill bit and bridged with SMD resistors where applicable:

DSCN5956 DSCN5957 DSCN5959 DSCN5952

So, did this work? Does it get rid of the heat?

Yes. 80 degree Celsius at the heatsink after 40 minutes of virus scanning are not a good value, but somewhat OK. And the voltage remained stable all the time. Data logging won’t be that much different.

DSCN6105 DSCN6106

(Original post:, July 20th 2011)

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