Now that I am just finishing my SMPS, I would like to know a bit more about what the clearances should be between mains - connected points and chassis, as well as between different hv nodes, such as the outputs of the mains rectifier, etc.
Any references?
Thanks!
Any references?
Thanks!
You should leave at least 5mm between each mains node and each secondary side node, or any other part that the user may eventually touch like the chassis.
You should use at least three layers of mylar tape between mains side and secondary side windings in SMPS transformers. Also, you should try to keep at least 3mm clearance between magnet wires of mains side and secondary side (5mm is better but not so practical). In practice, that implies leaving 2mm or so of margin between the windings and the edges of the coil former, and using the pins of one side for mains connections and the pins of the other side for secondary winding connection. I usually employ thick paper or insulating tape to fill that 2mm gap in order to prevent turns of other winding layers from moving and falling into the gap.
You should also pay attention to insulation between heatsink and power devices, including the voltage rating of the mica or silicone-based pads (3KV or better is recommended). Fastening the mains side power devices with screws to the heatsink is not recommended, except maybe for large TO-247 cases that come well insulated by a thick resin layer. For TO-220 use clip mounting or some form of sandwitching.
You should use at least three layers of mylar tape between mains side and secondary side windings in SMPS transformers. Also, you should try to keep at least 3mm clearance between magnet wires of mains side and secondary side (5mm is better but not so practical). In practice, that implies leaving 2mm or so of margin between the windings and the edges of the coil former, and using the pins of one side for mains connections and the pins of the other side for secondary winding connection. I usually employ thick paper or insulating tape to fill that 2mm gap in order to prevent turns of other winding layers from moving and falling into the gap.
You should also pay attention to insulation between heatsink and power devices, including the voltage rating of the mica or silicone-based pads (3KV or better is recommended). Fastening the mains side power devices with screws to the heatsink is not recommended, except maybe for large TO-247 cases that come well insulated by a thick resin layer. For TO-220 use clip mounting or some form of sandwitching.
Hi
Shouldn't you need to know this before starting a SMPS design rather than just finishing? You need this for transformer and PCB design among others. If I remember correctly from TUV/VDE requirements.
Primary to Secondary creep distances = 8mm
Primary to safety ground and chassis = 4 mm
Pri to Pri = 3mm (line to line)
google TUV / VDE
Shouldn't you need to know this before starting a SMPS design rather than just finishing? You need this for transformer and PCB design among others. If I remember correctly from TUV/VDE requirements.
Primary to Secondary creep distances = 8mm
Primary to safety ground and chassis = 4 mm
Pri to Pri = 3mm (line to line)
google TUV / VDE
Hi EVA,
you said " I usually employ thick paper or insulating tape to fill that 2mm gap in order to prevent turns of other winding layers from moving and falling into the gap."
If I understand you correctly that would be only 2+2 = 4 mm creep distance between interleaved windings on a bobbin. I always used 4mm corrugated kraft paper as edge guides for each layer to get the 8mm requirement between Pri to Sec. I always hated that.
you said " I usually employ thick paper or insulating tape to fill that 2mm gap in order to prevent turns of other winding layers from moving and falling into the gap."
If I understand you correctly that would be only 2+2 = 4 mm creep distance between interleaved windings on a bobbin. I always used 4mm corrugated kraft paper as edge guides for each layer to get the 8mm requirement between Pri to Sec. I always hated that.
I'm fed up of dissasembling commecial SMPS and no one mets that 8mm criteria. Good quality stuff coming from Germany and the like uses 2.5mm + 2.5mm. Chinese, Taiwanese, Korean and the like stuff does not use any spacing.
That topic has been already gently discussed, and I posted several pictures demonstrating the absence of magnet wire spacing in commercial products that we use everyday, specially computer-related. You will find all that information if you give a try to the forum search engine.
That topic has been already gently discussed, and I posted several pictures demonstrating the absence of magnet wire spacing in commercial products that we use everyday, specially computer-related. You will find all that information if you give a try to the forum search engine.
Apparently no meets the 8mm TUV/VDE requirement. Then that begs the question. I always wondered why my transformers were oversized. Those days have passed by for me I was just curious. Eva no simple answer to the question it appears.
I would take Eva´s comment with a grain of salt. Most(over 90%) chinese/whatever cheapo products also fullfills safety standards.infinia said:
8mm is a good rule of thumb but its not always required:
http://focus.ti.com/lit/ml/slup227/slup227.pdf
- Status
- Not open for further replies.