Dear CW Lai,
In addition, the existing earthing structure (PCB mounted mains female
connector -> soldered on master PCB->soldered on a earthing PCB->soldered to
the earth of secondary circuits, no earth symbol and preventive measure to
prevent accidental loosening the conductor) is acceptable or not if that is a
safety earthing.
Thanks and regards,
Raymond Li
OSA
Raymond Li/Omni
26/10/03 12:58 AM
To
ChengWee Lai <c...@netscreen.com>
cc
EMC PSTC <emc-p...@ieee.org>, owner-emc-p...@majordomo.ieee.org
Subject
RE: Class 1 AC/DC adapter Link <Notes:/
/482569EB005BA074/DABA975B9FB113EB85256
B5001283EA/A49E0A2444B8F4E548256DC90063F196>
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
