ruffrecords

+5V supply
« on: January 26, 2016, 02:21:10 PM »
I need a quick +5V supply to power a small micro controller project. I have a number of USB chargers lying around. Presumably I can plug a USB cable into one of these, snip the end of the cable and find the two wires that have +5V on them and use that as a power supply?

Cheers

Ian


ruffrecords

Re: +5V supply
« Reply #1 on: January 26, 2016, 02:29:03 PM »
I just tried it. There's +5V between the red and black wires. Interestingly the cable is screened with the screen also connected to 0V.

Cheers

Ian

Re: +5V supply
« Reply #2 on: February 15, 2016, 03:13:47 PM »
Yeah, i`m kinda interested in this topic. I have a bunch of those external hard-drive psu`s (line lumps) that seem to give plentiful 12v and 5v. But wondering how applicable these psu`s are to audio-usage.


ruffrecords

Re: +5V supply
« Reply #3 on: February 15, 2016, 03:17:12 PM »
Yeah, i`m kinda interested in this topic. I have a bunch of those external hard-drive psu`s (line lumps) that seem to give plentiful 12v and 5v. But wondering how applicable these psu`s are to audio-usage.

They will not have the low ripple you might expect or require for audio  but some additional smoothing ought to be able to take care of that.

Cheers

ian

Rochey

Re: +5V supply
« Reply #4 on: February 15, 2016, 03:56:31 PM »
i use them all the time for microcontroller projects.
Just don't forget that there's a fair bit of ground noise.
Expat Audio Home: http://www.expataudio.com

Whoops

Re: +5V supply
« Reply #5 on: October 29, 2016, 01:44:18 PM »
TheĀ“re normally very cheap switching PSU's  of 1amp max (2amps the ones for iPAD)

I really get annoyed with the 10Khz mechanical noise of  those USB chargers
« Last Edit: November 01, 2016, 04:03:30 PM by Whoops »

Re: +5V supply
« Reply #6 on: November 01, 2016, 05:41:07 AM »
While many of these cheapo switchers will produce a bunch of noise, if you're powering only logic circuitry, the blessing of 'noise immunity' from the logic family will allow you to ignore most or all of this noise.

One answer is to find a common mode choke, put that in series with both the +5V and GND terminals, and then put a shunt cap system after that. This will significantly reduce power supply noise, and add little ESR that could reduce your 'end of the day' supply voltage.

Barring that, most modern switchers only produce a couple dozen mV of noise, which is within the typical noise immunity range of logic. Proper shielding, grounding and bypassing will make that irrelevant.

Another idea is that a lot of logic these days runs on 3.3V, so with a 5V input, you can use a modern LDO regulator next to your logic to make a "nice" 3.3V rail, and hopefully ignore most of the noise from the raw supply. This is probably the highest performance, lowest cost and "smallest parts volume" answer, given the cost and bulk of passives like CM chokes and filter caps.

Whoops

Re: +5V supply
« Reply #7 on: November 01, 2016, 04:07:03 PM »
My router adapter and my iphone charger both make an awfull aprox 10Khz mechanical noise,
I can charge the iphone in my room, and I have to turn off the router during the night otherwise I cant sleep.

Really annoying.
A lot of people complain about being affected by Wifi , and wifi noise, they dont understand that the noise is not from the wifi but from the cheap switching Adapter that came with their wireless router

Re: +5V supply
« Reply #8 on: November 02, 2016, 01:03:58 PM »
One answer is to find a common mode choke, put that in series with both the +5V and GND terminals, and then put a shunt cap system after that. This will significantly reduce power supply noise, and add little ESR that could reduce your 'end of the day' supply voltage.

Agreed. This is key. A good size high mH common mode choke will make a huge difference in SMPS noise. Maybe if the SMPS is old or just poorly designed there might be some low frequency noise. But with a regulator after it, it will be difficult to see a difference with a linear supply.

Re: +5V supply
« Reply #9 on: November 02, 2016, 11:19:27 PM »
Agreed. This is key. A good size high mH common mode choke will make a huge difference in SMPS noise. Maybe if the SMPS is old or just poorly designed there might be some low frequency noise. But with a regulator after it, it will be difficult to see a difference with a linear supply.

Right. The only (possibly subtle) improvement is that the common mode choke will essentially prevent this hash and noise from leaving the noisy power supply. Even though this noise could be eaten up by a post-regulator, it may form a complex set of noise currents flowing in ground between the devices, and depending upon everything else, that may (or may not) become a problem.

I've never played with common mode chokes until recently, but they're pretty neat devices. They can have a _lot_ of common mode impedance at the same time as very little differential mode impedance. This can allow you to aggressively filter common mode noise (even from a signal) while only lightly affecting a true differential signal (or a low impedance switcher regulated power source).

Most of the CM chokes designed for power supplies also have very low DC resistance, and can handle a lot of current. TDK makes a bunch, as do other companies. Look on their websites and see the range available. And, because of the wide use of switch mode power supplies, they are readily available and cheap.


JohnRoberts

Re: +5V supply
« Reply #10 on: November 06, 2016, 08:31:23 AM »
I bought a cheap +5V supply to replace the one on my cheap 5.1 surround decoder. As I expected the new supply worked, the supply that came with the decoder would cause the processor to hang up when powered up. The processor would boot if hot plugged after the wall wart was stable.

I never bother to figure out why (life is short and other things to fix).

JR
John Roberts
http://circularscience.com
Tune it, or don't play it...