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Old 6th September 2005, 12:43 AM   #1
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Default 5v DC Quiet power supply

What should I be looking for in a 5v DC regulated power supply?

Are there any kits available? I only need around 2-3amps.
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Old 6th September 2005, 02:43 AM   #2
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What is your source? 12V? 120VAC? 240VAC? What is your load? How quiet do you want it? 50mV, 20mV, 10mV?

Switcher it linear?
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Old 6th September 2005, 05:24 AM   #3
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I want a linear regulated power supply. My source will be 24vAC (120 volts with a stepdown transformer, pretty much set on that.)

I don't know the answer to how quiet. I'd like it as quiet as possible while remaining withen a reasonable budget, and it will be powering a Slimdevices Squeezebox 2 which comes with a 5v 2amp DC switching power supply.
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Old 6th September 2005, 02:27 PM   #4
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Well, you can forget the 7805 or the LM317, as these will handle a maximum of 35V input, and are good for only 1.0 and 1.5A, respectively.

Additionally, your efficiency will only be about 25-30% because, at 2 Amps, with 24VAC input (~34VDC after rectifier and cap filter) you will lop off everything above 5V, for about 58W of heat dissipation. Is it possible to go with a lower secondary voltage transformer? If you use a 12VAC or even 98VAC secondary, you will drastically lower your heat dissipation and raise your efficiency.

If lower than 24VAC is strictly not an option, try rectifying and filtering it and going with an LM2596-5.0 SimpleSwitcher IC is good for 3.0A, switches at 150kHz, and can handle a maximum of 40VDC.

For the fixed 5V version, only one diode, one ciol and two caps (input & Output) are reqired for a complete step-down (buck) regulator. Your efficiency will be very good, and you will have very low noise. Adding an L-C filter to the output of the regulator will lower the noise even more.
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Old 6th September 2005, 03:25 PM   #5
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I was wondering, could I use a second smaller transformer? I ask this because I have a 24volt wall wart that is powering my headphone amp , and I want to build this power supply in the same box, so could I use a 4:1 step down transformer and have 6 volts?

The wallwart is rated at 1200ma @ 24 volts (although puts out 28 volts with no load).

If I put a 4:1 stepdown x-former would that be able to supply 2 amps after rectifying? (BTW 2 amps is the max I'd need. I am only measuring 1-1.5 amp draw on my SB2 currently)

Is there any power supply kit I could use to do this?
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