Power Supply

[Nihkorb]

Hi guys,

I need your help to get my mind clear
I have a PCB that needs a 12V DC power supply and currently I'm using one power supply like this: http://www.vetco.net/catalog/images/SR-DC-12-10-21.jpg

The specs are: IN - 230v @50Hz
OUT - 12V 450mA

and I'd like to know if it's possible to use instead, one power supply like these one:
http://www.ebay.com/itm/S-SS-20-60W...c-Transformer-Spotlight-Adapter-/400666869782

There is any problem with that?
I'm a little bit confused because it says that is for lamps, but I think that can be for everything right? or it has some specific detail that I dont know?

Thanks and Best Regards

 

[BobK]

I think that second supply is intended to be used in a lighting fixture and might not be isolated, since they call it an "electronic transformer." If you use it like you would a transformer, your PCB might be at line potential, which is, of course, dangerous.

Bob

 

[Nihkorb]

Hum thank you Bob
And what kind of isolation do you think that the other power supply has? The one that I'm using now.

Best Regards

 

[(*steve*)]

And what kind of isolation do you think that the other power supply has? The one that I'm using now.

It almost certainly contains a transformer to isolate you from the mains.

 

[Nihkorb]

Hum ok. Thank you guys

 

[Merlin3189]

But notice it is 12V AC output, whereas your original is 12V DC. So you would need to add rectification.
Depending on your application you may need to add smoothing and regulation to both. Your first one has got a rectifier and probably a capacitor, but often that's all.
I'm a great fan of using these ready made power supplies for small projects, because you can often pick them up for very little money (and I've got a box full of ones left over from broken equipment) and someone else has taken care of the safety/isolation issues, so they're safe for use in projects for young people & inexperienced people. But I normally pop a diode (to protect against connection of wrong polarity psu), a regulator like a 78xx and a capacitor, just to make sure if I need a regulated supply.
Even with these you can often do the job for a pound or so - the socket to connect is often the most expensive bit!

 

[Nihkorb]

yes, I didn't notice that, you're absolutely right I'll try to see if the power supply that I'm talking about is also AC, but probably is..
And nice advices, mainly the diode, it will be useful

Btw, regarding to power supplies, it came to my mind another question: If the power supply is for 50/60Hz, how they filter the frequencies? with 2 pass band filter or one larger to capture both? or it's possible to encounter both approaches?

 

[Nihkorb]

Ok, I already search and read a lot of datasheets. For what I saw I assume that it's only one pass band filter, because all say that the range of frequencies are 47-63Hz. I was asking that because when I use a power supply that works for 50/60Hz it has more noise than when it's a power supply just for 50Hz. I don't have an oscilloscope to measure, however my sensors of that PCB don't work very well with the power supply for 50/60Hz.
I thought that difference should be the problem and that makes some sense, at least for me xD right?

 

[(*steve*)]

yes, I didn't notice that, you're absolutely right I'll try to see if the power supply that I'm talking about is also AC, but probably is..
And nice advices, mainly the diode, it will be useful

Note that rectifying and filtering 12VAC will give you a much higher DC output voltage (up to 17V).

Btw, regarding to power supplies, it came to my mind another question: If the power supply is for 50/60Hz, how they filter the frequencies? with 2 pass band filter or one larger to capture both? or it's possible to encounter both approaches?

This is just a rating designed to inform you that you can use the power supply on either 50Hz or 60Hz systems.

Many switchmode power supplies will be happy to run from anything from DC to maybe 400Hz. (I mention 400Hz because it's what you may find on an aircraft).

Out of interest I saw a piece of equipment that could be switched from 100V up to 250V (clearly it had a transformer) 50Hz or 60Hz, and actually mentioned that it should not be powered from a voltage source higher than 117V at 400 Hz.

 

[Nihkorb]

Note that rectifying and filtering 12VAC will give you a much higher DC output voltage (up to 17V).

Yes, you're right, I was forgetting that.

Many switchmode power supplies will be happy to run from anything from DC to maybe 400Hz. (I mention 400Hz because it's what you may find on an aircraft).

Out of interest I saw a piece of equipment that could be switched from 100V up to 250V (clearly it had a transformer) 50Hz or 60Hz, and actually mentioned that it should not be powered from a voltage source higher than 117V at 400 Hz.

Are you sure? I read that if you use one transformer with the wrong frequency, it can heat up and even burn.Or it depends on the type of power supply?

 

[(*steve*)]

YAre you sure?

Do you want a reference?

OK, it was 123V, not 117 -- but it was from memory.

edit: and yeah, it's a pretty expensive piece of kit and this forms part of the specification. It's designed for that.