Yuanjing 12DC power supply for LM3886 - diyAudio
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Old 16th May 2011, 12:20 AM   #1
hd220 is offline hd220  Canada
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Default Yuanjing 12DC power supply for LM3886

Has anyone seen the following product currently listed by several vendors on Ebay as:

"Switching boost Power Supply board DC12V to DC32V 180W" or similar.

The product description typically reads :

"Output Power: 180W
DC 12V to DC+_35V
Fit for auto audio transformation, Single 12V DC to dual +_32V DC, So that more power amplifier (such as LM3886,TDA7294) can be used in 12V DC car"

No more info on these listings, ie. current in and out, etc.

Would anyone use this as a cheap power supply solution, ie. no transformer, when coupled with a high current switching power supply such as the following?:

"- Input: 100-240V, 50/60Hz 1.5A.
- Output: 12V 5A .
- LED indication .
- Plug Size: 10mm x OD=5.5mm x ID=2.5mm .
- Size:110mm x 53mm x 37mm"

This doesn't seem right however, ie. 12V switchmode wallwart to power another switchmode converter supply.
. . . would there enough juice from the 5A wallwart to power the LM3886 at higher power, ie. volume levels?
Attached Images
File Type: jpg 12V-1.JPG (109.3 KB, 384 views)
File Type: jpg 12V-2.JPG (123.4 KB, 355 views)
File Type: jpg 12V-3.JPG (125.1 KB, 351 views)
File Type: jpg PS_12.JPG (78.2 KB, 350 views)
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Old 16th May 2011, 10:54 AM   #2
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Those seem to be separate things:

1) A DC-DC supply, which eventually could go on the box as an LM 3886 amp.

2) A walwart supply.

Why would you use a 12v DC ww supply to power a DC-DC supply? Certainly not a good idea.

An important part that is missing on the DC-DC supply is the heatsink, which should probably be quite large.
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Old 16th May 2011, 05:16 PM   #3
hd220 is offline hd220  Canada
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The heatsink is a given.

The DC-DC supply requires 12VDC, such as a car battery, so why couldn't the 12VDC (5A) walwart supply it? That was the question.

The DC - DC supply or converter takes a car battery 12VDC as the input and provide + and - 35 VDC rails.
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Old 16th May 2011, 08:42 PM   #4
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certainly not an elegant solution, but there is nothing against it.
At least for using an adapter to power a nother one.

One problem I can point out for You is that the wall wart You choosen has 5A current ability at 12 v. That is 60 VA at most. Probably less in real life.
The next adapter stage has its own losses, so i think You will end up with something less than 40 watt. So You will be able to take even less than that on the amplifier output.

So it will work, it will be just more than limited in power than You would think.
For the price of those things, why not just consider a more traditional approach of getting a regular transformator?
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Old 16th May 2011, 11:40 PM   #5
hd220 is offline hd220  Canada
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Arty Thanks,

Should have done the math (re 60VA / approx 40W). . . but if one isn't too concern about output power and doesn't crank up the volume (probably resulting in a much earlier clipping) then this solution, while not elegant, could keep the power issues simple, ie, not having to implement a transformer.

Another concern might be how clean the rails would be using this arrangement, with using 2 switching supplies. Switching noise? Likely not any or much ripple.

Anyway, not intending to use this method, just curious as I noticed for the first time from the "regular" Chinese DIY Ebay sellers this board and wondered if this unconventional approach is even worth considering.

Last edited by hd220; 16th May 2011 at 11:43 PM.
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Old 17th May 2011, 08:00 PM   #6
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well, hard to tell if it will be too noisy. Certainly not a fidelity freindly approach.
And allso account that filtering does stress powersuplys. Charge current of capacitors, Re of series inductors for example. Allso, You do not realy have a headroom with this powersupply so the rail voltage will be changing a lot. And both SMPS will work to avoid that, resulting is -probably, but not absolutely true, no one can be sure- more changes is supply voltage.
So in this case, as far as fidelity, i might just save my self the trouble, use the 12V wallwart adapter, and a TDA1557q or one of its relatives. It is comfortable with the 12 volt rail, driving a load of 8 ohm You canget something like 2x10 or maybe 2x12 watts, and it can happen it will be better quality than 2 smps after eatch other and the LM chip.
Less switching noise, still low cost (absolute less costs to be honest) and less issues.
That board would be usefull if You would make an LM amp for Your car. I suspect that was the original intention behind it.
And it may happen with quite ease that is is a good preformer there.
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Old 21st May 2011, 06:34 PM   #7
AndrewT is offline AndrewT  Scotland
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look for an AC to DC supply that suits your mains supply voltage and the amplifier rail voltage/s
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