Is an old laptop power brick a good starting point for a bench power supply? - Page 1
Forum section: electronics / projects

author: technix
author_rank: Super Contributor
timestamp: September 03, 2017, 11:51:12 am
content: I have an old Dell laptop power brick. It can no longer be used with the laptop, as the identification chip in the power brick died (evidently a common issue on those power supplies, damn you DRM) but otherwise perfectly useable as a generic 19.5V 65W power supply. Is it a good starting point for building my own bench power supply?

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: September 03, 2017, 01:16:42 pm
content: Yeah why not.it take more than a fixed voltage source to make a bench supply. But yeah you can start with one.years back, i used DVD player and satellite dish receiver power supply, those thing are multi-rail 3.3V 5V 12V 24V and 32V. and a Chinese one cost around 5$, was perfect for low power small circuits in my home lab.

author: rstofer
author_rank: Super Contributor
timestamp: September 03, 2017, 02:32:14 pm
content: Maybe...The 19.5V output is pretty high for running into a 7805 regulator.What voltages do you expect to need? I commonly use 5V and 3.3V and, if I am playing with op amps, +- 15V. I bought a Rigol bench supply after many years of using wall warts, primarily for the +- 15V. In the end, regulated wall warts are still in use on my bench. I highly recommend them!The brick may be quite useful if you want to use it with a 7812 regulator. Still a little high but workable.One thing a bench supply will often provide is current limiting. I tend to set mine fairly low so as not to let the magic smoke pour out of my latest project. It's nice to be able to set the current at, say, 100 mA and, so long as the output voltage hasn't folded back, know that there is some chance I don't have a short circuit somewhere.There are pretty cool:http://store.digilentinc.com/powerbricks-breadboardable-dual-output-usb-power-supplies/

author: tooki
author_rank: Super Contributor
timestamp: September 03, 2017, 03:13:25 pm
content: Quote from: technix on September 03, 2017, 11:51:12 amI'd say it's not a great starting point. But you could use it to power one of these buck-boost lab power supply modules:https://www.banggood.com/DPH3205-160W-Buck-boost-Converter-Constant-Voltage-Current-Programmable-Digital-Control-p-1105294.htmlOf course you'll be limited to the 65W of the laptop brick, but for most purposes that's far more than enough.

author: Fungus
author_rank: Super Contributor
timestamp: September 03, 2017, 04:07:08 pm
content: Quote from: technix on September 03, 2017, 11:51:12 amI'd say "no".The parts/effort needed to make it work will cost more then the power brick is worth. It's much better to find an old PC and pull the power supply out of it.

author: Gyro
author_rank: Super Contributor
timestamp: September 03, 2017, 05:02:27 pm
content: If you want to make a variable linear supply then I'd put it above a PC supply - higher output voltage and more self-contained and compact (not to mention safer if the PC supply isn't built into an enclosure).You have more chance on implementing sensible current limiting too. If you use the 3.3V and 5V outputs of a PC supply then you're really limited to PTCs or fuses if you want to maintain their regulated output voltages. Either that or external regulators on the 12V output.I'd say that all in all it's a pretty good starting point if you want to build something that doesn't involve mains wiring. Hopefully it has a 3 pin mains connector with grounded output.P.S. I wouldn't be as confident with an ebay replacement adaptor as I would with a genuine Dell one.

author: DaJMasta
author_rank: Super Contributor
timestamp: September 03, 2017, 05:09:53 pm
content: Reasonable place to start, but of course it's not without its limitations. If you aren't looking for higher voltages or split rail, it will certainly do, but it's not necessarily a big leg up over other commercial starting places. A simple linear supply or something would be fine off it (though maybe the voltage is a bit high for a linear supply down to logic levels - just lots of power dissipation), and a switcher would give you better efficiency and power output, but is it better to use a laptop supply over a computer PSU or even a LED string PSU or something.... probably not.If you just want a project and don't have the money for a different starting point.... why not!

author: b_force
author_rank: Super Contributor
timestamp: September 03, 2017, 05:22:40 pm
content: If you can live with the noise coming out of it.Or at least take enough thought into lowering it as much as possible.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: September 04, 2017, 01:37:46 am
content: If you have need of a semi portable soldering iron these power supplies could be used for a Haako t12 controller kit or ts100 handle both easily available on Taobao.

author: Rbastler
author_rank: Frequent Contributor
timestamp: September 04, 2017, 08:11:52 am
content: Quote from: chickenHeadKnob on September 04, 2017, 01:37:46 amI agree. Use my TS100 with a old 16V laptop PSU at home. Works great Sent from my A0001 using Tapatalk

author: Zero999
author_rank: Super Contributor
timestamp: September 04, 2017, 10:56:46 am
content: Does it have a three pin power lead? If so, it's very likely the negative of the power supply, is referenced to earth, which is not good for a bench power supply. Check for continuity between both sides of the power supply (positive and negative) and the earth pin of the mains connector. If there's continuity, then you know not to connect your oscilloscope or signal generator's chassis to the non-0V side of the supply.

author: Gyro
author_rank: Super Contributor
timestamp: September 04, 2017, 11:38:45 am
content: There's a toss-up there between earthed PSU output negative terminal and Y-cap leakage. Both could have their own issues. You could of course run a separate ground lead to an output earth terminal but physically, things start to get more messy. Personally, I'd want to loose the leakage.

author: buck converter
author_rank: Regular Contributor
timestamp: September 04, 2017, 02:11:31 pm
content: Quote from: Hero999 on September 04, 2017, 10:56:46 amThere are compatible chinese chargers available that do not have the third power lead.

author: technix
author_rank: Super Contributor
timestamp: September 04, 2017, 05:26:08 pm
content: What I expect to get out of this thing is a 15V 3A adjustable CV/CC rail and two fixed 5.3V/2.1A rails, all with common ground. I don't need the negative rail and I actually prefer some kind of earthing on the GND line. For the 5.3V outputs I can accept some slight switch mode noise (just two USB charging ports, the connected devices are expected to handle the slight over-voltage and the ripple anyway.)