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Author Topic: Good (and cheap) power supply with low noise  (Read 2755 times)
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I'm amplifying some small signals so need a reasonably smooth power supply. Probably around 60 watts for everything as I have an amp and speakers, I need 12v and 5v. What's the best option for something fairly smooth. An ATX PC supply? These seem pretty cheap for the power and give both voltages but are they clean? Or do I go for a 12v brick and add a 7805 (or something better?) for the 5v. I've never really considered noise before so I'm a bit stuck.
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Computer power supplies are in general pretty noisy - you have to filter out the noise before passing it to sensitive analog circuitry.  A linear regulator can do this nicely, but this only works if the analog circuitry is using a lower voltage than the main output.  Filtering with an RFC (radio-frequency-choke) can help.  Using analog circuitry with a good power-supply-rejection-ratio can help.

You need to work out what level of noise you can tolerate.  If your analog side can run off 10V or less then a linear regulator from the 12V will be a simple approach.   You also need to consider power losses if the load is significant.
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Probably the best short term very low noise power supply is a 12 volt sealed-lead-acid (SLA) battery

60watts = 5 amps  s if the load is required for say 1 hour then you will extract 5AH so something in the order of 17AH will suit.

After use a recharge will get it ready for your next requirement.
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I use ATX supplies.. Remember they are clean enough to run a computer, they are probably going to be clean enough for your projects.  One caveat.. Some ATX designs require a load to regulate properly, usually a couple of watts on the 5v side.. I haven't seen this, but the usual solution is to add a 10w ten ohm resistor across the 5v output to ground.  Ground the green "PS ON" line, and you have a nice high output power supply (I recommend a fuse, these can provide a LOT of current...)

You can always add a big ole filter cap...

They are great at feeding big bunches of LED's.. granted it's not lab stable, but it generally is clean enough to handle servos on the 12v side while running an Arduino via 5v pin directly driven from a 5v line, or with a couple hundred uF cap for smoothing out the bumps..

If you go looking around for a reasonably stable 12v power supply capable of 10 amps or more, you just can't beat scavenging up an ATX P/S...
« Last Edit: June 14, 2012, 11:51:59 pm by focalist » Logged

When the testing is complete there will be... cake.

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