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offline regulator

 
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jharvey
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Joined: 15 Mar 2009
Posts: 362
Location: Maine USA

PostPosted: Sun Dec 27, 2009 7:10 pm    Post subject: offline regulator Reply with quote

I've been looking into offline regulators. I'm curious if anyone has a recommendation for a circuit. I'm sure that there's better than this.

http://www.discovercircuits.com/DJ-Circuits/images/offline5v.jpg

I'm sure a high side driver could be used as a buck circuit. But I havne't found a PWM drive chip that I'm happy with.

Any suggestions?
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Cliff



Joined: 23 Jan 2007
Posts: 150
Location: Saratoga, CA

PostPosted: Sun Dec 27, 2009 8:42 pm    Post subject: Reply with quote

Hi Jared,

Take seriously, the warning on that schematic - the +5V and circuit ground are at dangerous voltages relative to earth ground, along with the rest of the circuit. The only place that this type of supply can be used safely is inside a earth grounded box with no connections going outside of the box.

For general purpose use, you need to look for isolated power supply designs, which usually involve using a transformer for isolation. The best design solution is going to depend on your supply requirements. There are a lot of trade-offs involved. (Size, cost, efficiency, etc.)

Cliff
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jharvey
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Joined: 15 Mar 2009
Posts: 362
Location: Maine USA

PostPosted: Sun Dec 27, 2009 10:08 pm    Post subject: Reply with quote

Agreed, the isolation is quite handy. A switching supply should be able to produce significant power with a min sized transformer. Min size correlates to min cost. I suspect it can be done with a minimal increase in cost. I suspect this type of regulator can be build in a couple bucks catagory, I just haven't found the right chip to allow it.

About the earth ground enclosure, I'd agree with that a good second level of protection. However, if it's a plastic case, that's also a good barrier to the potentail of a faulty hot.
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jharvey
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Joined: 15 Mar 2009
Posts: 362
Location: Maine USA

PostPosted: Wed Dec 30, 2009 9:43 pm    Post subject: Reply with quote

I found this one that seems to have some potential, but I'd really like a device with more current capability.

http://www.supertex.com/pdf/misc/LR8K4PSS.pdf
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