EN 60950-1: Safety in SMPS

[electronZ]

Hello all,

Long time since I have been here. Feels good to post again :-D

I want to sketch a design of a SMPS for audio applications. It has to operate with universal input and it outputs 400 Wrms @ +/- 60 V.
Please see the block diagram below.


The transformer in the PFC Converter will provide the safety isolation. I am trying to find out what the minimum creepage and clearance distances between primary and secondary side of the transformer.

I have been reading around in 60950-1 2006, and here is what I got:
1. Pollution degree 2
2. Reinforced insulation
3. Overvoltage Category II: 2500 Vpk @ AC Mains Supply 300 Vrms (Table 2J)
4. Minimum clearance for insulation in primary circuits and between primary and secondary circuits/side of the transformer is 4 mm for reinforced insulation at peak voltage of 420 V (Table 2K)
5. Minimum creepage distance on Printed boards, material Group IIIb, Basic insulation 0.75 mm and for Reinforced insulation it is 2x0.75 mm having RMS working voltage of 320. But since it is less than the clearance distance, the value of minimum CLEARANCE shall be applied as the minimum creepage distance (Section 2.10.4.3 Minimum creepage distances)

How does the above sound? Am I missing somthing?

 

[treez]

If you are doing SMPS, application note 18 by Power integrations is what you need to see.
Is that a single stage PFC and PWM converter?.....so its a PFC'd flyback or something?
You know PFC stages have a fair bit of 100 hz ripple on there output..thats not bad for your amp?

pri to sec is 6mm clearance... you must use 3mm margin tape each side of bobbin or Triple insulated wire in transformer.
The mains hipot test is 3500vac for one minute I think, because mains transients can be that big (or bigger)
Guitar amps seem to just use cheap mains transformers even for 400w...since as you know audio is a peaky load, not 400w all the time, and mains transformers can overload without breaking.
We were told that you dnt need pfc for guitar amp below about 600w....AND ONE OF THE GUITAR AMP SMPS (sorry caps) companies told us pfc is not needed for guitar amp below 8 x 75W (600W). tHE GUITAR AMP SMPS COMPANY FROM HOLLAND TOLD US THIS (im giving up on my keyboard, sorry about caps)

 

[electronZ]

If you are doing SMPS, application note 18 by Power integrations is what you need to see.
Is that a single stage PFC and PWM converter?.....so its a PFC'd flyback or something?
You know PFC stages have a fair bit of 100 hz ripple on there output..thats not bad for your amp?

pri to sec is 6mm clearance... you must use 3mm margin tape each side of bobbin or Triple insulated wire in transformer.
The mains hipot test is 3500vac for one minute I think, because mains transients can be that big (or bigger)
Guitar amps seem to just use cheap mains transformers even for 400w...since as you know audio is a peaky load, not 400w all the time, and mains transformers can overload without breaking.
We were told that you dnt need pfc for guitar amp below about 600w....AND ONE OF THE GUITAR AMP SMPS (sorry caps) companies told us pfc is not needed for guitar amp below 8 x 75W (600W). tHE GUITAR AMP SMPS COMPANY FROM HOLLAND TOLD US THIS (im giving up on my keyboard, sorry about caps)

Hey,

Haha... I think I need more than that application note, to design this SMPS. Thanks for the tip, nice application note.
Yes, the plan is to design a flyback operating in DCM. The topology has its disadvantages, and I am willing to look into them one by one. This is not my concern atm.

I just want to extract the necessary safety distances from the standards, in this case EN 60950-1, based on the voltage levels am dealing with in the design :smile: