Linear vs. Switching DC Power Supply in electronic repair troubleshoot - Page 1
Forum section: electronics / testgear

author: Wattiman
author_rank: Newbie
timestamp: February 10, 2018, 10:53:16 pm
content: Hi all,I am fairly new to electronics, so try to bear with me if this question is silly or if my understanding is totally wrong. I have tried to use search and look for the answer, but probably because of my low knowledge on the matter, I have not yet found the answer in the threads I read.I have started to learn about motherboard repair and my goal is hopefully some day to even fix laptop and mobile phone motherboards.I just got a old switching DC power supply (Amrel PPS-1326) as a freebie from my neighbour. I would like to use it to power up and troubleshoot the motherboards. I don´t mind spending the 100€ to a new linear power supply, but of course if I can make use of the old beautiful unit I definitely will.If I understand correctly the noise is the main reason why people don´t want to use the switching power supply´s to power up delicate electronics as computer motherboards?The old power supply I got (Amrel PPS-1326), seems that it has been expensive one back in the day and it is very well built. I have tried to look the specs on the manual and if I understand them right the noise is not that bad compared to a cheap Chinese linear power supply that would be my other option budget wise.Have I got the whole thing wrong and what am I missing or is there any (other) reason that I should not or cant´t use it in those applications I mentioned?Here is the manual for the Amrel PPS-1326 (on the bottom at page 40 has the noise levels, that are well beyond my understanding):http://programmablepower.com/products/amrel/PPS/PPS-Manual.pdfAny help of understanding the subject or just telling me I should ditch the nineties tank Amrel and move on would be much appreciated!If I really need a linear power supply, then so be it and no worries. Just don´t want to waste a good piece of equipment if I can.Thanks in advance!

author: bitseeker
author_rank: Super Contributor
timestamp: February 11, 2018, 07:04:26 am
content: Hi Wattiman,Welcome to the forum!The Amrel PPS power supplies are linear, hence the low noise and high weight. So, go forth and enjoy your electronics repair, etc. You got a good power supply for a great price (i.e., free).If you still have doubts, take a look at the first paragraph of the specifications page in the manual:Quote

author: Wattiman
author_rank: Newbie
timestamp: February 11, 2018, 09:20:28 am
content: Hi bitseeker!Haha, well this is embarrassing…Thank you for clearing that up and for the warm welcome.I should have probably look at the manual a bit better... Just went straight to the noise levels and wondered the low noise with my limited knowledge.In my defence, the guy who gave me the unit is an electric engineer and said that it is a switching PS and I did not question him.Excuses aside, thank you again for the information! The PS feels very well built and I am really happy with it, at least now.Just need to learn to use it properly with the button interface, but that is a another thread. And this time I am going to read the manual thoroughly before posting.So that some other noob like me might have still some use of my silly thread, can you confirm that the noise is the main issue when comparing Switching power supply vs. Linear in delicate electronic´s use?

author: alm
author_rank: Super Contributor
timestamp: February 11, 2018, 10:40:26 am
content: Other disadvantages of a switching power supply compared to linear are often a slower transient response (response to a quickly changing load, like a transmitter that quickly turns on and off) and for the cheap ones immunity to RF. I could see transient response being an issue for cell phones that are designed to work with a very low impedance lithium battery as power source.

author: bitseeker
author_rank: Super Contributor
timestamp: February 12, 2018, 03:49:07 am
content: A floating switch mode power supply could have high leakage voltage that, although very low in current, could be problematic for sensitive circuits.For working on PCs, switch mode power supplies are generally OK, which is why they've been using them for as long as I remember.

author: Wattiman
author_rank: Newbie
timestamp: February 25, 2018, 08:59:23 am
content: Thanks for your answers, good information there!I will go on and start to learn to troubleshoot stuff with my "new" Amrel.Hopefully this thread has some use to other noobs like me.