[sdiy] power woes

[Barry Klein]

Hi Dan,
This may depend on your product design...
What is your spec for output voltage regulation?  What's your worstcase 
load?
I have seen some real crappy adapters - especially in these low output 
ranges you seem to be focusing on.
The output voltages can be all over the map.
Take your adapter, get a variable load, and test them to see what the no 
load voltage is and what it goes to
as the load increases.  You don't want to see anything outside of say a +/- 
5% range.
You want to be sure the supply has short recovery.
If you plan to ship offshore you need to test at 240V or so too and make 
sure you have sourced
a supply that has appropriate certs and plugs.  You probably get under the 
radar due to low volume sales here
but if volumes increase it will be a hellish experience for you to manage 
appropriately.
If the supply passes the load tests ok, power your circuit and look at the
noise level on the supply output.  Maybe you need input capacitors and/or 
ferrite/toriod input components.
If you can't add those try 2 wraps around a ferrite clamp of the DC cable. 
But try at both the product
side and supply side to see which is better.
You might think about going to 12V and higher current; adding regulation 
components to your design.
There are many 12V adapters out there for external hard drives that are 
good.
Our WD store sell them quantity one for 15 bucks.
Or try here: http://www.surplustraders.net/a/0298.shtml
Looks like some 9V ones are for doorbell circuits and probably have poor 
regulation...

Barry

----- Original Message ----- 
From: "dan snazelle" <subjectivity at hotmail.com>
To: "synth diy" <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, March 06, 2010 7:15 AM
Subject: [sdiy] power woes


> Ok
>
> I am sitting here with a pile of DC adapters. (trying to find one to 
> bundle with my products)
>
> half of them cause HUM, half of them cause a whine (switching)
>
> Only 2 out of the pile don't cause ANY noise
>
>
> One is a DUNLOP class 2, 60hz 7w, 9vdc 200ma adapter which is made in 
> china and has a chinese model number of
>
> ad-0920
>
>
> i can find these online for $12-15 dollars a piece
>
>
>
> the other is one of the new BOSS switching adapters.
>
> (it costs 30 bucks!)
>
>
> one of the odd things is that some of the switching adapters or class 2 
> adapters have
> seemingly the same SPECS but cause different problems or noise
>
>
> SO...my question is whether anyone has any advice on DC adapters
>
>
> i might be able to get a bunch from dunlop but it still doesnt answer WHY 
> some cause noise and some dont
>
>
> thanks so much!
>
>
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