I am designing a preamp that has transformer in. I am wondering if I should
a)put ground plane everywhere including under transformer in
b) put no ground plane on trafo in and start it after rectifier
c) put no ground plane under trafo in or rectifier out and just put it where the PS voltage has been "cleaned"
Thanks!
a)put ground plane everywhere including under transformer in
b) put no ground plane on trafo in and start it after rectifier
c) put no ground plane under trafo in or rectifier out and just put it where the PS voltage has been "cleaned"
Thanks!
It occurs to me that if I put a cap right after the rectifier the voltage seen after the rectifier (before the cap) will be the same as that after the cap. So starting it at the rectifier might be the thing to do. Opinions?
Is it a audio transformer or a mains transformer ?
You will need to be careful about creep-age distances if its a mains transformer and you put power plane around transformers mains side.
You will need to be careful about creep-age distances if its a mains transformer and you put power plane around transformers mains side.
It is a mains transformer. By being careful about creepage do you mean keep some distance between the transformer (pre-rectifier) traces and power/ground planes?
Hi Vladimir,
Check with the electrical code. Creepage is a safety thing where the primary circuits must be a minimum distance away from anything a person can come into contact with. That includes the power transformer secondary windings and case. Normally the case of the transformer (if it's an EI type) would be grounded to the chassis. The power transformer must be UL listed I think. ULC is better.
You can look this stuff up on the internet. Just make certain you are reading the rules instead of someone's opinion on this subject. There can be insurance implications if you don't follow the electrical code. Best to just make sure you comply, even if you are only ever making one for your own use.
-Chris
Check with the electrical code. Creepage is a safety thing where the primary circuits must be a minimum distance away from anything a person can come into contact with. That includes the power transformer secondary windings and case. Normally the case of the transformer (if it's an EI type) would be grounded to the chassis. The power transformer must be UL listed I think. ULC is better.
You can look this stuff up on the internet. Just make certain you are reading the rules instead of someone's opinion on this subject. There can be insurance implications if you don't follow the electrical code. Best to just make sure you comply, even if you are only ever making one for your own use.
-Chris
Typically 5 to 7mm clearance between the AC input primary side and ground plane or any signal the user may contact.
Hi Mike,
I want him to look it up and confirm first hand. Knowing where and what to look for is valuable. I know you are trying to help, you could always post the link in that case.
-Chris
I want him to look it up and confirm first hand. Knowing where and what to look for is valuable. I know you are trying to help, you could always post the link in that case.
-Chris
Hi Chris,
By far, the best way to learn is to answer your own questions, researching and focusing until you have a solution. Extremely fulfilling also. My only link would be to IEC 60950-1:2005, the design standards to which I adhere. Unfortunately IEC charges 800USD+ and if I distribute the publication, IEC nails me for copyright infringement (their primary job description). Here is the link https://webstore.iec.ch/publication/4024
Best Regards,
Mike
By far, the best way to learn is to answer your own questions, researching and focusing until you have a solution. Extremely fulfilling also. My only link would be to IEC 60950-1:2005, the design standards to which I adhere. Unfortunately IEC charges 800USD+ and if I distribute the publication, IEC nails me for copyright infringement (their primary job description). Here is the link https://webstore.iec.ch/publication/4024
Best Regards,
Mike
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Hi Mike,
I completely agree with you. You're also dead right about distributing copy write materials. I would never suggest that you do. However, I'm sure there must be this information out on the web somewhere.
The other suggestion would be to examine some commercial goods that are approved. You can be pretty sure that the minimum distances you find in the bunch would be the spec. Then go a little larger for safety.
Correct me if I'm wrong, but isn't that distance listed on data sheets for PCB mounted transformers, switches and power entry modules? The PCB mounted kinds that is. There are all kinds of places where a person can find this information. These would be North American data sheets of course.
Please don't get me wrong, I really appreciate that you are helping someone out. I'm much the same, but with a different skill set.
Best, Chris
I completely agree with you. You're also dead right about distributing copy write materials. I would never suggest that you do. However, I'm sure there must be this information out on the web somewhere.
The other suggestion would be to examine some commercial goods that are approved. You can be pretty sure that the minimum distances you find in the bunch would be the spec. Then go a little larger for safety.
Correct me if I'm wrong, but isn't that distance listed on data sheets for PCB mounted transformers, switches and power entry modules? The PCB mounted kinds that is. There are all kinds of places where a person can find this information. These would be North American data sheets of course.
Please don't get me wrong, I really appreciate that you are helping someone out. I'm much the same, but with a different skill set.
Best, Chris
It is good education to look at boards from large and competent companies like Marantz. You will see PCBs with cut outs so that the transformer is actually bolted to the case, no planes near the mains side and good separation of the mains side from everything else, to meet the safety codes of multiple countries
As you are in the USA also look for:
UL840
UL508A
UL608C
UL-60950
Recent discussion here...
https://www.linkedin.com/grp/post/2155931-6047987923599572994
Seems UL testing and accreditation can be interpreted differently by different inspectors (uncounted this a few times in the past).
UL840
UL508A
UL608C
UL-60950
Recent discussion here...
https://www.linkedin.com/grp/post/2155931-6047987923599572994
Seems UL testing and accreditation can be interpreted differently by different inspectors (uncounted this a few times in the past).
Now for your design, I would route all the mains stuff up to the main smoothing caps as broadside coupled traces to mimic planar bus bars, this will help noise etc. From the other side of the smoothing caps run a wide thick trace to your ground plane for the rest of the circuitry., as this is best for low level analogue.
How many layers are you using...
Got anymore info...
And if you don't understand any of the above give us a shout and I'll dig out examples or try and describe it in more detail.....
On creepage and clearance, always play safe... Personally I prefer to hide as much as possible on inner layers so that there is minimum bare metal exposed that could be at dangerous voltages.....
How many layers are you using...
Got anymore info...
And if you don't understand any of the above give us a shout and I'll dig out examples or try and describe it in more detail.....
On creepage and clearance, always play safe... Personally I prefer to hide as much as possible on inner layers so that there is minimum bare metal exposed that could be at dangerous voltages.....
Often stricter for imported goods than made in the USA 🙄
Silicone rubber insulation boots were a good example when I had to deal with this, in an imported product these were considered flammable
It is a good move to mark the safety barrier on the pcb with silkscreen hatching. It helps an inspector measure the correct gap
Having had to get the UR accreditation I can agree on that, the designs were picked to pieces and some failed on minor things, that passed CE (we did have them checked even though CE is self regulating, the MD didn't fancy 6 months in jail). It did teach me a lot and now ALL designs get the same pedantic attention to detail for creapage and clearance and high current areas.
I prefer to leave any gaps between high voltage side and SELV clear so they can shine a light through it and really see the gap...🙂
I prefer to leave any gaps between high voltage side and SELV clear so they can shine a light through it and really see the gap...🙂
That is almost essential, otherwise you descend into the pit as they start querying the thickness of each pre-preg sheet and looking very hard at your pcb source. A simple gap, with nothing assumed to be a better insulator than air and the only thing bridging it are transformers and qualified to death optoisolators is the easy path
If by 'ground plane' you actually mean a ground plane then this is often a bad idea for audio because you lose control of where the ground currents go. Better to use a ground bus.
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