Dear CW Lai,
Many thanks for your reply & useful information. I still have some queries and look forward to your further explanation. 1. Earth continuity test As the class 1 is due to the additional earthing plate, how can I ignore the earth continuity test? Without this earthing plate, the unit is in fact a class 2 construction. Thus, I am a bit confused with such construction and should I follow the required safety tests for class 1 or class 2. I have another thought that actually, the earthing plate and the DC output plug earthing are functional earthing, not safety earthing, so electrical continuity test using multitester is sufficient and earth continuity test using low voltage and 25A current is not applicable. 2. Hi-pot test The unit passes the hi-pot test at 3,000Vac if the grounding plate and the bridging capacitor are removed. If only the bridging capacitor is removed, the test voltage goes upto about 2,100Vac max. I note that there is breakdown around the grounding plate and the pcd side of mains female connector at the max. voltage. It seems once the production of the converter is completed, proper earth continuity test and hipot test are unable to be done at IQC of receiving warehouse. Any suggestion to do some extend of safety test without destruction of the finished goods is appreciated. Thanks and regards, Raymond Li OSA . ChengWee Lai <c...@netscreen.com> Sent by: owner-emc-p...@majordomo.ieee.org 25/10/03 02:03 AM Please respond to ChengWee Lai <c...@netscreen.com> To "'raymond...@omnisourceasia.com.hk'" <raymond...@omnisourceasia.com.hk>, EMC PSTC <emc-p...@ieee.org> cc Subject RE: Class 1 AC/DC adapter Raymond, In regards to your question, 1. I am guessing what you meant is a seperate PCB, about the size of the power supply main PCB, either on top or on the bottom side. Copper plate on one side only. If that is the case, it was designed to lower the emission. I am not sure how effective it is, but I see people doing it. As long as there are ground connection, it would considered as class I. The plate can't be view as one of the protection in your case. 2. Earth Continuity or ground bond testing with 25A or higher is not applicable with plastic case and not applicable at the DC output side. It was meant to check the earth protection continuity of a metal chassis. 3. I believe you will have to use 3000Vac or 4242Vdc between primary and secondary side, unless you have a failure, then there are steps to go through to isolate the failure. Here is a page I made during my years in power supply industry, it should answer to many of your question. Standard reference might be old, but principle is still the same. <http://www.phihong.com/html/safety_compliance.html> http://www.phihong.com/html/safety_compliance.html Take care, Chengwee Lai Netscreen Technologies, Inc Tel: +1-408-543-4126 email: c...@netscreen.com From: raymond...@omnisourceasia.com.hk mailto:raymond...@omnisourceasia.com.hk] Sent: Friday, October 24, 2003 10:05 AM To: EMC PSTC Subject: Class 1 AC/DC adapter I have seem a number of class 1 AC/DC switching power supply adapters for electronic apparatus. From outlook, it looks similar to class 2 adapter - plastic case. The obvious difference is that there is a grounding pcb containing a large area of copper track soldered on the solder side of master pcb. The side facing to the solder side has no copper track at all. The grounding pcb is connected to the earth terminal of the mains female connector on one end and to the earth of the DC output plug on the other end. I have following queries and seeking advice. 1. Function of the grounding plate The primary and the secondary is reinforced insulation and withstands over 3000Vac. Is this plate to change the whole safety protection system from class 2 to class 1? Or the plate is primarily for EMC suppression? 2. Earth continuity test After the unit is completely assembled, should we conduct the test between the earth terminal of the mains plug and the earth of DC output plug? 3. Hipot test As the unit is classified as class 1, 1,500 Vac is applied between the earth terminal of the mains female connector and the earth of the DC output plug. Actually, the primary and secondary can withstand 3000 Vac. Is it correct test voltage to apply after the unit is completely assembled? Thanks and regards, Raymond Li OSA