transformerless power supplies - green?
transformerless power supplies - green?
(OP)
In the near future, it would appear the sale of the traditional wal-warts will be a thing of the past in California, and probably followed on by other states.
So, do new devices that are to be sold in California that might use a simple transformer type supply embedded, subject to the same restrictions? Just curious....
New design looking for a very compact non-isolated AC-DC supply. The circuit will be attached directly the AC line, and isolated by the plastic case, with all the standard NRTL safety considerations of course. But thats another issue.
The circuit is going to only need maybe 150mA total current (if that) at 5V, so I was looking at using a capacative type supply that uses just two diodes, two caps and a power resistor. Anyone built one of these for a product...what kind of issues did you run into if so?
Or if there is a better suggestion, open to that as well.
So, do new devices that are to be sold in California that might use a simple transformer type supply embedded, subject to the same restrictions? Just curious....
New design looking for a very compact non-isolated AC-DC supply. The circuit will be attached directly the AC line, and isolated by the plastic case, with all the standard NRTL safety considerations of course. But thats another issue.
The circuit is going to only need maybe 150mA total current (if that) at 5V, so I was looking at using a capacative type supply that uses just two diodes, two caps and a power resistor. Anyone built one of these for a product...what kind of issues did you run into if so?
Or if there is a better suggestion, open to that as well.





RE: transformerless power supplies - green?
Check www.maxim-ic.com they had some non-isolated regulators. Not sure they will go to 150mA but take a look.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: transformerless power supplies - green?
You must ensure that the circuit always draws power from the supply. A zener shunt regulator is the easiest method. You could also use a bridge rectifer - smaller smoothing cap, and the smallest bridges don't take up much more space than a pair of 1N4001's. Costwise there is probably little in it.
The circuits are not good for keeping mains-borne noise out. The series capacitor is effectively a short at HF. If your circuit is noise-sensitive you might be better off with a purpose-made switchmode module from one of the numerous vendors, rather than fighting a losing battle trying to keep mains-borne noise at bay. The cheap & cheerful solution might end up more expensive if it has to be heavily filtered.
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I don't suffer from insanity. I enjoy it...
RE: transformerless power supplies - green?
RE: transformerless power supplies - green?
What about something like http://www.onsemi.com/pub/Collateral/NCP1200-D.PDF
According to EDN the magnetics are available from a couple of suppliers:
http:/
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I don't suffer from insanity. I enjoy it...
RE: transformerless power supplies - green?
Thanks very much!!
RE: transformerless power supplies - green?
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I don't suffer from insanity. I enjoy it...
RE: transformerless power supplies - green?
http://datasheet.astrodyne.com/PWB.pdf
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: transformerless power supplies - green?
"I was looking at using a capacative type supply that uses just two diodes, two caps and a power resistor."
These supplies, as said before, need something to limit the voltage and that will consume power. Unless you switch the AX nains and have a load that is always the same current, you will consume more power overall than a wall wart. This defeats the intent of the law. Without isolation, the entire powered device will have to be built to code.
X2 capacitors are the simple way to go. You can achieve the same results by placing two to three lower priced capacitors in series. This is internally what X2 capacitors are. A capacitors AC rating is not proportional to the DC rating. Under AC fields tiny air gaps in the insulation wrap cause corona and "light up" eventually destroying the capacitor. I've used garden variety capacitors in this way for 480V UL line operated equipment.
RE: transformerless power supplies - green?
Basic circuit is an X2 capacitor feeding a bridge rectifier (4 x 1N4007 or a ready-made bridge). On the DC side of the bridge a smoothing capacitor in parallel with an appropriate Zener, the smoothed DC being fed to an LDO (low dropout voltage regulator) of the desired voltage.
1: remember to place a high-voltage capable resistor across the X2 capacitor, value 200...500 kohms. This is to bleed off charge when you unplug the supply, so you don't get a shock from the capacitor when touching the plug pins. Vishay VR37 types are a good choice.
2: remember to place a current limiting resistor in series with the X2 cap. This is to limit the surge when plugging the power supply in, as you otherwise would probably blow the Zener or the smoothing cap. Select a resistor with an appropriate Ws capability, I've used Vitrohm BW234 and BW235 types (wirewound). Value 50...200 ohms depending on how much current you need.
That's it. The main input current of this type of supply is reactive (leading), so it shouldn't give a lot of problems with power loss. It might even improve the situation in an environment where most loads are lagging.
Benta.
RE: transformerless power supplies - green?
RE: transformerless power supplies - green?
Question not understood. What leakage current?
Benta.
RE: transformerless power supplies - green?
RE: transformerless power supplies - green?
by a static/lightning etc.
If you connect cap's in series, it is not a bad idea to
add a R parallel with each to control/balance the leakage
currents.
Plesae read FAQ240-1032
My WEB: <http://geocities.com/nbucska/>
RE: transformerless power supplies - green?
RE: transformerless power supplies - green?
Agency approval will be required anyway, for the entire design so as long as I do the layout properly, shouldnt be a big issue. I've been thru NRTL before. Client pays for it as well.
RE: transformerless power supplies - green?
May your design go well.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: transformerless power supplies - green?
RE: transformerless power supplies - green?
But there are some alternaives:
Most of the integrated switching power supplies circcuits (from PowerIntegrations, ST (Viper) or Infineon (Coolset)) can also be confiured to work just with an inductor if no isolation is required. Check for ANs on that.
There are alos some circuits on the market using a different approach. See:
http://www.supertex.com/feature_sr03x.html
I have not used the Supertex circuits, but I have designed cicuits using the same approach with discrete parts long time ago and it worked well.