12V input

Question about power
Posts: 1462
Joined: Fri Oct 19, 2012 5:11 am

Re: 12V input

Post by YahooArchive »

Never use cheap Wall-Warts, they are inaccurate and unreliable and wasteful
of power even if they actually work as they should, you usually need extra
circuitry to "tame" a cheap wall-wart and make it useful....

Make sure you are always using a power supply that is a Switched Mode type,
some Wall-Warts are made using Switched Mode designs, but usually cost a
little bit more. Some mobile phone chargers are SMPSs (all the ones I have
ever looked at were, but that is not that many!) and need not be thrown away
if still serviceable and provided they supply a voltage suitable for further
use. Some Nokia units are of a high quality but are only 3.7 volts for
example. That could be a useful value still for some people though!

A careful check of any Power Supply after purchase/before use with various
loads to check that the voltage is stable over the required current range,
as well as looking at the output with an Oscilloscope for noise levels are
all things a "good" user does to stop any nasty surprises...(If you don't
have access to a 'Scope, a quick and dirty method of measuring noise on a
DC power supply is to switch the multimeter to the lowest value of AC
voltage, usually 200mv or so..this is certainly not a perfect method, but it
does give a relative indication, better than NONE at any rate!!

I personally usually make my own supplies (I believe I have mentioned this
before, so I will only mention a few details, but anyone needing better
info's please just ask) using LT1074 chips (see below for the LT1074 data
sheet) for up to 5 amps output at anything between 2.5 and 50 volts (input
up to 60 volts, a higher voltage version is also available).

It is actually not a completely true SMPS, it's a type of power supply
called a Step-Down Switching Regulator Power Supply which is technically
similar (because it uses a step down transformer), which is far less
dangerous to the builder (the mains is only on the input to the transformer
and not all over the circuitry) than a true SMPS, but almost as efficient
(around 85%).

A version using two of these chips (I have the .pdf if anyone wants it) from
Elektor in 2003, will supply up to 10 amps from anywhere from 2.5 to 50
volts with the recalculation and replacement of just two resistors....

Check out this data sheet for further info's.

http://www.datasheetcatalog.org/datashe ... 1074fd.pdf



Post Reply