茶馆 发表于 2011-6-10 09:55

电话机产品overvoltage M1 test

我们公司现在又一款电话机，客户在fuse 前设计了一段很细的PCB LAYOUT ，作用是在高温或高压情况下能够断开 保护后面的电路，其实作用跟fuse 相似。 现在我们做M1 ，600V,40A 时间1.5s 后。很细的那条PCB 断开，电话机的fuse 没有断开。 像这种情况是否可以判定PASS。我认为是可以的，大家也讨论一下。

安规007 发表于 2011-6-10 10:09

哪个标准的测试？提供一下标准让大家研究一下。

茶馆 发表于 2011-6-10 10:16

就是UL60950-1

安规007 发表于 2011-6-10 14:13

这个测试没做过，看了一下标准，其判断的依据在NAC.4 Compliance中有提到。
NAC.4 Compliance
In addition to the compliance criteria specified for the wire simulator and current probe,
compliance is checked by all of the following:
a) There shall be no ignition or charring of the cheesecloth indicator. Charring is
deemed to have occurred when threads have been reduced to char by a glowing or
flaming condition.
b) After the completion of each overvoltage test, the equipment under test shall
continue to comply with the requirements in 6.2.

NOTE In many cases, it will be obvious from the results of the tests that compliance with one or more of these clauses has not been
affected by the applied potentials. Where there is doubt or where continued compliance cannot be determined, the appropriate tests in
these clauses might need to be repeated.
做这个测试是不是需要盖一层棉布，棉布不能燃烧，不能碳化，纠结就出在碳化这里，因为这句话
Charring is deemed to have occurred when threads have been reduced to char by a glowing or
flaming condition. 不好理解，我的理解是，细线因为发热或燃烧变成碳就认为棉布碳化已经发生。不知道你板上那条很细的PCB断开情况是什么样的？

茶馆 发表于 2011-6-10 14:31

引用第3楼安规007于2011-06-10 14:13发表的:
这个测试没做过，看了一下标准，其判断的依据在NAC.4 Compliance中有提到。
NAC.4 Compliance
In addition to the compliance criteria specified for the wire simulator and current probe,
compliance is checked by all of the following:
a) There shall be no ignition or charring of the cheesecloth indicator. Charring is
.......

做完这个测试后符合NAC.4,棉布和产品的外面没有任何损伤。只是PCB trace 断开。现在的疑问就是：测试时间虽然是1.5s, 但是回路中的电流是由于pcb trace 断开而中止的。问题来了：这种设计是否可靠，能否被标准接受，PCB trace 可否像FUSE 那样能够具有可靠性。毕竟FUSE 是单独拿到UL认证的

安规007 发表于 2011-6-10 14:46

你这个算是次级电路, 在5.3.9.1 During the tests 中有这么一句话:
– if a trace in a secondary circuit is designed to intentionally open in a repeatable
manner, the test shall be conducted three times to determine if the circuit does open
repeatedly; and
– ENCLOSURES shall not deform in such a way as to cause non-compliance with 2.1.1,
2.6.1, 2.10.3 (or Annex G) and 4.4.1.
PCB trace 是可以这样设计的，只不过你要重复做三次测试，并且保证每次都要在同一个地方断开而已。

其实我觉得那个碳化的判断描述简直是扯淡，PCB trace 不发热碳化怎么可能断开，既然断开肯定是已经发热碳化了。

茶馆 发表于 2011-6-14 18:01

结论：第一步：重复三次，确保断开的是同一点（假设此点为M）。
      第二部：用第一步中的样机，用焊锡将M点短路，重复测试。看测试结果再做分析。

以上为UL 回复。给大家参考。
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