• posted
I wonder if anyone can help me with a simple power adapter query ?
(A) The preamble
I have a small piece of kit which, according to the rather inadequte
information on the pack (no instructions !), is rated at 50mW.
It's 30 years since I took physics in high school, so please bear with
me. IIRC, the relevant equation is as follows:
W = V x A
The kit runs off of a standard 9V battery, so to my simple brain, this
means that it draws a current of 5.56mA (0.05W / 9V = 0.0056mA).
Checking out the various power adapters in my local hardware store, I
can find ones which convert AC input to DC output at 9V with a range of
current values (from 300mA up to 1.0A).
(B) The question
Can I buy any adapter which outputs a current of at least 6mA at 9V and
be sure that my piece of kits is going to (1) work and (2) not get
fried ?
Nick
• posted
Yes, but make sure it is a regulated-output adapter. It will almost certainly supply enough current to meet your needs, whatever the make and model.
and
Buy a regulated supply. If you buy an unregulated one, its output voltage on this very light load will be far, far too high and your kit will fry.
• posted
Thanks - I'll check it out.
• posted
Palindr?me schrieb:
Hello,
but there are some regulated supplies which require a certain minimal load current.
Bye
• posted
Absolutely correct - but the only such supplies that I know of are intended for fitting internally into equipment. I have never come across a general purpose stand-alone SMPSU that needed a minimum (external) load to spabilise.
Not just SMPSU - a certain manufacturer that shall be nameless went in for shunt regulation rather than the normal series pass. And then put a fuse in the output line. So when and if the fuse blew, the shunt regulator dissipated more than it was "desgned" to do and really smoked (I don't recall one actually catching fire). Now what sort of idiot puts a fuse in the output side of a shunt regulator? I ask you..
But if you know of such units and could point me to a web page, it would be much appreciated.
• posted
He could also consider a 6 volt supply. The voltage at the light current draw is over 8 volts. John

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