SMPS power supply

[L'italiano]

Hi all! I need a power supply for a 5V 0.7A digital circuit and 9V 2.5A for a guitar pedalboard. Is an SMPS like a TRACOPOWER TXM 050-112 ok? Or might it output too much noise for audio application?

[vegaron]

Hi,

I use these SMPS a lot and I just love TracoPower for what they are doing. I build an application (at work), that is highly sensitive in the area around 30kHz and we had a) really, really good results and b) we have seen nothing in the signal that would come from any power supply (there are 3 on the board). So, I would say, you're save to use them for audio applications.

The TXM 050-112 is a 12V module, not 9V. Was that a typo? Would be bad, if not, because there are not nearly as many power supplies for 9V as for 12V. And they seems to be quite expensive.

What kind of 5V power supply do you need? AC/DC or would you consider connecting one to the 9V/12V power supply? That's what I usually do and makes things so much easier. Do you plan on making PCBs?


Cheers

[L'italiano]

Hi vegaron, thanks for the answer!
12V was not a typo. I have found some 9V SMPS but only 444mA.

9V and 5V are all derived from SMPS, that's why I indicate a 4.2A model. I thought using a 7805 to get 5V (probably cascaded from a 7809, or better a TSR 1-2450) and a few (actually 12) 7809 to avoid high temperature issues and get some separation (I assume) for each pedal.

I might build PCBs but I have an expert friend that will help, though I will design on my own.

Thanks in advance!

[vegaron]

I was once advised against cascading low dropout regulators. Generally I try to avoid using them altogether, because they do get warm and they have a bad efficiency. A 7805 behind a 7809 means that there is a permanent voltage drop of 4V which constantly produces heat. If you only use one of them for your digital part, it is not that bad, but using 12 7809's on a 12V source means 12*3V voltage drop. At least, that's how I understand them. I also understand, that they are a lot cheaper though. ^^

I guess you can not work at 12V, can you? 9V really limits your choices of electronic parts...

If money isn't you major concern, I've found two 9V-AC/DC-Converters (TracoPower again) which should be powerful enough to supply 12 devices and a 5V LDO.
ECE40US09-S -> 4,44A (~70€)
ECE60US09-S -> 6,67A (~90€)
That for me would be the most elegant solution...


Hope it helps

Peter

[L'italiano]

9V is the most common guitar pedals input voltage. Money is a major concern .

Of course cascading 7809 + 7805 is not the most elegant solution, it only spreads heat on regulators, but I will probably go with the TSR 1-2450 for no heat problems at all.

Powering all devices from 1 or 12 regulators should result to almost the same wasted power.
Suppose to supply 2 devices at 9V 50mA: if you have 1 regulator you have (12V-9V)*(50mA+50mA) = 300mW, instead if you use 2 regulators the power for each one is (12V-9V)*50mA = 150mW. So same power, the only difference is the small bias current around 4 or 5mA.

[vegaron]

My point about the one big single 9V source was, that you can connect all your single pedals directly to this source. So you wouldn't need any more LDOs or SMPS.

But a little question: Why don't you use several TSR 1-2490's? Their specifications go up to 1A. (I guess, one pedal doesn't need more) Since you have already planned to use 7809's, you seem to have something, that powers them in the range of their respective input voltage. Their switching frequency is about 500kHz, so I suspect, there will be no signals from it in the audio range.

And if you really have something, that powers the 9V-TSR (or the 7809), you don't have to chain the 7809 and 7805. You can simply put the TSR 1-2450 and the TSR 1-2490's to one single source.

[L'italiano]

Yeah, I have already redrawn schematics to use a TSR 1-2450 and few TSR 1-2490.
Thanks for all help!