How good is a typical laptop power brick?

Discussion in 'General Electronics Chat' started by wayneh, Mar 30, 2016.

  1. wayneh

    Thread Starter Expert

    Sep 9, 2010
    Just curious what the output looks like at, say, 80% of rated load.

    I suppose the DC voltage may vary a little with load. I can measure that easily with a meter. But I'm wondering more about the higher frequency noise, which I cannot measure since I don't have an oscilloscope. Is it DC with a small ripple? Big ripple?

    I'm planning a project using a spent brick as my DC power supply and I'm wondering if there is any concern with cleaning it up. I'll use a regulator to supply my control circuit (a 555 etc.), but will pulse the DC power directly into a transformer to get the voltage up (a wall wart in reverse, as an inverter). Can a brick handle that kind of loading?
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    I'd guess its 100% dependent on the manufacturer,etc..
    Same with current rating,etc..
    I've had some "cheap" power supplies go dead in under a year while a "name brand" will usually last forever (powering the same load)..
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    If your brick is rated at 5 amps, it will probably give out that current, maybe more, it maybe easier to alter the output of the brick, they can go upto 25v. What voltage range do you need?
  4. wayneh

    Thread Starter Expert

    Sep 9, 2010
    The ~20V out of the brick will be fine for my needs. I'm just wondering 1) What the noise looks like and 2) If a brick can handle an inductive load being switched at 100Hz-2kHz. I may add a series diode, with a "big" capacitor to ground on the load side.
  5. tcmtech

    Well-Known Member

    Nov 4, 2013
    I've used many laptop power bricks for other applications.

    They are just like any other SMPS in that if they are cheap they work like cheap units. Output noise wise they are usually filtered pretty good though being the electronics in a laptop are far fussier about power line noise than a 555 timer is.

    That said put a good sized capacitor in your circuit and see what happens.
  6. #12


    Nov 30, 2010
    I can only remember dropping one such brick in the trash bin, so they're probably pretty good.
  7. wayneh

    Thread Starter Expert

    Sep 9, 2010
    I guess as long as it's a spare that I don't care about destroying, my test protocol will be to hook it up and see what happens. :eek:
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
    If it is pre-2008, the main toroidal core is likely iron power (Micrometals type core) and is subject to aging - the iron powder oxidizes over time - even in the epoxy binder. After that time, switching frequencies went way up and ferrite cores have been used - much less aging. Ferrite cores were used before 2008 but almost none after 2008.

    The aged iron power cores saturate at lower currents and run hotter.

    Note - the iron power core power supplies generally run under 200kHz switching frequency. 1MHz+ for ferrite cores.
    Last edited: Mar 30, 2016
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