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PCB Ground

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ClickKlick

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I am making a 12Vac to adjustable DC supply. The 120Vac to 12Vac transformer I have does not utilize a ground. The bridge rectifier, capacitors, and ouput all need a ground. What do I connect to this GND of the PCB? The ouput is DC and is variable 1.5V-12V, but it needs a GND. Should I connect these to earth ground out of a wall socket?
 
You don't HAVE to. What, is it a wall-wart or something? The circuit will work fine without a path to earth ground, except for a few odd circuits like crappy TRF recievers, and even then you would want to use a better ground than a wall outlet. What are you building?
 
I am building the Variable DC output Supply. The bridge Rectifier needs a ground as well as the capacitors. I always thought that a DC circuit needed a ground source for the current to flow into/out of. Obviously all of the GND on the PCB are common to each other and connected, but shouldn't they be connected to some source, like an earth ground or case ground?
 
I am building the Variable DC output Supply. The bridge Rectifier needs a ground as well as the capacitors. I always thought that a DC circuit needed a ground source for the current to flow into/out of. Obviously all of the GND on the PCB are common to each other and connected, but shouldn't they be connected to some source, like an earth ground or case ground?

Could you provide me first with your schematic diagram? maybe I can help you.:)
 
If you use a full bridge rectifier the -pin of the rectifier is the reference for circuit ground.

Don't connect any part of the low voltage supply to PE (protective earth).

Use circuit ground for the connected load only!

If you use two way rectification (2 rectifier diodes at the outer taps of the transformer) the center tap of the transformer will be circuit ground.

The sample circuit shows a secondary two coil transformer. Connecting both it is a center tapped transformer.

The center connection on the primary side is not drawn.

Boncuk
 

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The ouput is DC and is variable 1.5V-12V, but it needs a GND. Should I connect these to earth ground out of a wall socket?
NO. Don't connect the DC ground (-) to chassis ground. Isolate it from the chassis ground entirely. This will make your power supply more versatile. ie: You'll be able to put it in series with another supply or use it as a negative voltage supply source.
By all means connect the AC ground lead to the metal case of the supply for safety reasons but float the DC - lead.
 
He doesn't have an AC ground lead. That was his question.
 
He doesn't have an AC ground lead. That was his question.

If he is pluging into an AC source, then he has ground lead. :)
 
Probably a wall wart. No ground.

I suppose your right. I never use those. I prefer using my own supplies. Just one of my quirks. Don't like wall warts...
 
They are handy for some things. A lot of the new ones are actually wall mount switching regulators, with controlled voltage.
 
My experience with wall warts is that they are made as cheap as can be, and quality control was not part of the design. I have had so many fail that I have little faith in them. It would be nice if a company would build a reliable unit that does not fail after a few months. Linksys wall warts are they worst...
 
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I suppose your right. I never use those. I prefer using my own supplies. Just one of my quirks. Don't like wall warts...

The biggest failure mechanism I've found with cheap0 wall warts is that the primary wiring size is such that it burns open as the only over current protection, turning it useless.

However I have seen very nice laptop switching power converters at thrift stores for give away prices. I recently found a HP 13vdc at 2.77 amps switching regulator pack that is the size volume of a pack of cigarettes and weights just a few ozs and cost me $2. I also found a nice cell phone switching regulated 5vdc @ 800ma wall wart for $1.

So wall warts can be useful but be careful about drawing too much current from them and be aware that the loaded to unloaded voltage variation of the unregulated variety can cause problems for certain applications.

Lefty
 
Radio Shack is selling switching wall-wart transformers. They're about $36. Might be worthwhile, have not used one of those yet...

...but I did use a switching wall-wart I stole from my camera. It had a rock-solid +5V that was good for an amp.
 
I bought some 5V/2A tiny switching power supplies that are the same as the $36 ones at RadioShack. I bought them from the same surplus store that RadioShack got them. I paid $1.25 each. The surplus store had thousands of them. Other stores in their chain also had thousands of them.
RadioShack is a rip-off joint.

I bought a video cable for $15 at RadioShack. Then I saw exactly the same one at The Dollar Store for $1. I bought it and returned it to RadioShack and got my $15 back.
 
Not all switching wall warts are regulated. I've seen plenty of mobile phone charger units which are completely open-loop and have absolutely no voltage regulation!

An unregulated switched mode wall wart is just a ferrite transformer normally driven blocking oscillator or Royer converter with a Schottky rectifier and on the output.

The cheapness is still there, they've just discovered it's now often cheaper to use a small ferrite transformer and oscillator than a huge leminate iron transformer.
 
Then I saw exactly the same one at The Dollar Store for $1.
I buy all my cables at the dollar store too. I remember buying a wired router at Futureshop for $25 and looking at 6ft Ethernet cables there for $20! Luckily, as I needed 3 of them, I already knew about the dollar store. The markup and rhetoric on cables in most electronics stores is huge.
 
I would use the term "insane" to describe audiophile rhetoric.
 
I am an audiophile but I have never believed the lies about very expensive Monster Cables and those spikes that speakers sit on.
Somebody was selling something to "damp resonances" in CDs.
 
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