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I have a Dell laptop charger, which claims to output 19V, 1.58A .

Is there any value in re-purposing this for hobby electronics?

I'm tempted to do something quite crude, such as feed an LM317 from it, and use that as a basic voltage source.

I'm aware that this will have various limitations, but what are they, exactly?

Are there risks involved in driving the laptop charger in this way?

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  • \$\begingroup\$ Bench power supplies typically have a current limiter. \$\endgroup\$
    – CL.
    Commented Nov 20, 2016 at 21:26
  • \$\begingroup\$ 19 to 5V for 1A means 14V drop *1A = 14W fried packaged without good heatsink. with a bit of work inside , you can modify the feedback to make it efficient and variable from 3V to 24V \$\endgroup\$ Commented Nov 20, 2016 at 21:36
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    \$\begingroup\$ The Laptop power supply will work great if you intend to put an LM317 on it's output. Laptop power supplies have internal current limiting and are short circuit proof and well isolated. These power supplies are constant voltage, and while many people call them chargers....they are not. The battery charging system is built inside the laptop and uses a fixed voltage input. \$\endgroup\$ Commented Nov 20, 2016 at 21:39

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First, there is nothing wrong with your idea. It will make a quite capable supply if you use it within its limitations. You can add an inexpensive panel meter to show you the output voltage (get the three-wire type that has a separate supply line).

In terms of limitations- your LM317 (+ heatsink) supply will only be adjustable from 1.25V to about 17V without adding more circuitry. In practice this is a very useful range. There will be no current limit other than the limiting inherent in the LM317 and the brick (probably around 1.5A to 2A). Bench supplies often have an adjustable current limit which is useful when you are gingerly powering something up for the first time, for example.

Ripple may be worse than a linear supply, especially at high frequencies, depending on whether you try to filter it well or not.

Power dissipation limiting will be by overtemperature cutout on the LM317 chip, which is pretty rough on it (it limits way above the absolute maximum listed temperature for operation), so you may have to be a bit more careful.

Many bench supplies are only optionally earthed, and have a jumper to allow earthing one side of the output. Your brick is probably permanently earthed on the minus side, so you cannot put supplies in series, for example. It would make damaging things that are already grounded such as USB ports more likely. Again, you can be careful.

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  • \$\begingroup\$ Many Laptop 'bricks' are not grounded, they are classified as double insulated. The majority do not even have a ground pin in the mains cable. Those that do have a ground pin typically have a large value resistance between input and output and not a direct earth connection. If you have an adapter with figure-8 2 pin power cable then it's double insulated. If you have a 3 pin IEC connector you should check with a multimeter. \$\endgroup\$ Commented Nov 21, 2016 at 4:45

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