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Power supply design.


Well-known member
Nov 22, 2008
I have a set of laptop power supplies, both cheaply designed, both Chinese, and both failed or likely to fail (majorly overheating to the point of charred SMT remains in the one I opened up). I'm a cheapskate however, and I don't want to buy a pair of legit Dell chargers. I need a 19.5V regulated line capable of about 5A in one, and 7A in the other. My basic plan is to step down 230V mains to 23V, rectify with suitable bridge rectifier, then filter with a capacitor, and regulate with LM317s in parallel to source enough current. I was hoping to salvage some of the capacitors and possibly transformer too. My questions are:

What value capacitor would be suitable? (I presume the Chinese one would)
Would LM317s have any problem in parallel like this?
Is (23-19.5=3.5*7A=25W) into a chunky project-box style build going to cause problems?
Is there a way to do this tab-common to use a single large heat-sink?
Anything else I should watch out for?
Would a buck regulator be better (but more challenging for me to build)?

Or would I be better off in terms of price and reliability buying a legit charger?



New member
Oct 24, 2009
I have bought several laptop chargers threw ebay. they are all good but one. one got hot as a mother...
So i opened it up and put a nice large heatsink on it and then went to the shack and got a box and put it together and it works just fine now. its a bit bulky but it works.
It would be cheaper to buy the one you need and make it more robust.
I will never buy a dell or hp charger they suck. i always buy bigger psu than i need. they tend to least longer and preform better when you not pushing them to their max.