AC product electrical certification requirements

I don't think they care what you do internally, as long as it meets UL creepage/clearance for the respective circumstances (wider for 'transient unlimited' voltages, like AC line connections; less for internal or protected (MOV/TVS) voltages). And that's more for industrial UL509 stuff.. I don't know what's applicable for consumer or whatever.

After all, CRT TVs have 10s of kV inside. Not on circuit boards of course, but obviously not an insurmountable restriction for consumer goods.

Tim

-- Seven Transistor Labs Electrical Engineering Consultation Website:

** No approval required, cos your box is safety isolated from the AC supply. It must still be safe to handle and use of course. ** AFAIK, Both would require agency testing for compliance.

... Phil

Any Voltage above 40v (?) will catch the eyes of UL. So it does not seem to matter which way you go. Using a UL opem frame PS is'nt such a big deal inside your box. But your 150v will need to meet creapage and clearance requirements so that the operator of the device is not injured.

lots of low voltage equipment makers opt for a UL wall wart to ease passing UL for obvious reasons. Less than 60watts or so UL does not care, it's not enough to cause an issue.

Don't forget Blue, Brown and Green/Yellow for the AC connections. And a single point chassis ground tie point.

Cheers

Since you talk about wall warts, I guess you are talking about quite low power levels 1-20 W ?

If you aim for the international market (not just US), the simplest thing would be to use a locally certified wall wart producing some extremely low voltage (PELV/SELV) below 50 Vac, 120 Vdc.

Each country may have quite strange requirements for mains connected devices, so you can just swap the wall wart and you do not have to (destructively) test your whole unit.

In EU, there are no testing requirements, but the manufacturer or importer into EU has to sign a Declaration of Conformity that the product fills the LVD (Low Voltage Directive) and EMC directive. Of course that requires a lot of standard reading before you can honestly sign that declaration.

For this case in particular, if you need a few watts at 150 V, these days I would use a switcher from some ELV instead of using an internal iron core transformer with 150 Vrms secondary.

ELV = Extra-low Voltage

That's correct, I'm only using about 15 watts on the low voltage side and a couple at 150. This is an audio effects product (for guitar, etc.) that will combine both solid state and vacuum tube processing. Some other products use an AC wall wart and step the voltage up internally using a cap diode voltage multiplier, but the voltage obtainable at any appreciable current with that topology is limited, so they often only boost their B+ supply to 48 volts or so. Such a low plate V isn't an option here.

I'm a little leery of having a boost switcher inside the box, but as the internal analog portion will be fully differential anyway I think with proper layout it may not be much of a problem.

This is good information, thanks.

--


----Android NewsGroup Reader---- 
http://usenet.sinaapp.com/

Thanks!

--


----Android NewsGroup Reader---- 
http://usenet.sinaapp.com/

You could also use an external iron-core wall wart with AC output (if the power consumption of this is allowed in your market countries), and step the voltage back up internally with another small iron-core transformer run backwards - which would not produce additional high frequency switching emissions. As long as you don't exceed the rated volts-per-turn you should be able to find one with the right turns ratio even if what you want is not quite a common mains voltage. I have done this in the past for leakage testing in a production test jig, where I didn't want any mains in the test jig once the lid was opened and I didn't want mains wiring to the door interlock switches.

In at least some countries, I don't think that you are excused from electrical safety compliance (and perhaps testing) just because you generate the hazardous voltages internally from a lower voltage. On the other hand, people may be less likely to expect or look for electrical hazards if your input power is supplied at Extra-Low Voltage, (so you might get away with non-compliance more easily). From your other posts it looks like you are incorporating a thermionic vacuum tube which will probably give the game away.

Chris

If the tube is going to be in a pedal, you better get the ruggedized version. What, from Russia instead of China ? I am not really sure.