Dear Andy Thank you for you help. As I know, the voltage of multimeter is about 12V. If I want to measure the correct dc resistance between the power and ground, should I adjust the voltage of the multimeter to that of measured power net? In another word, the power net is of 1.5V. When I measure the dcresistance, I should adjust the voltage to 1.5V. Therefore, I will get the correct dc resistance. According to my experience, it is because item 3 that I didnot get the correct result. However, I could not understand that, if there is SRC-like circuit, the dc resistance should also be very large. Best Regards Zhangkun 2005.12.1 ****************************************************************************************** This email and its attachments contain confidential information from HUAWEI, which is intended only for the person or entity whose address is listed above. Any use of the information contained herein in any way (including, but not limited to, total or partial disclosure, reproduction, or dissemination) by persons other than the intended recipient(s) is prohibited. If you receive this e-mail in error, please notify the sender by phone or email immediately and delete it! ***************************************************************************************** ----- Original Message ----- From: Andrew Ingraham <a.ingraham@xxxxxxxx> Date: Wednesday, November 30, 2005 11:29 pm Subject: [SI-LIST] Re: DC resistance of the Power Supply on PCB > > I measure the dc resistance between Power and Ground. Normally, the > > resistance is about dozens of ohms. > > At least three things can make the measured resistance less than > "normal": > (1) If you've connected the meter leads so that the applied DC > voltage is > opposite normal, it can forward-bias junctions that are normally > reverse-biased. Often this doesn't make much difference > (depending on the > meter and the selected range, often the voltage is less than a > diode drop), > but sometimes it can. Some electrolytic capacitors also behave > like diodes. > > (2) If there are large electrolytic capacitors that take a long > time to > charge up, given the low ohmmeter currents from the multimeter, > and you > didn't wait that long. > > (3) Active circuits can behave in unexpected ways in the absence > of normal > voltages; sometimes there are parasitic devices and SCR-like > structures that > turn on. Abnormal currents should be expected when supply > voltages aren't > in the normal range. > > Regards, > Andy > > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > List FAQ wiki page is located at: > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > List technical documents are available at: > http://www.si-list.org > > List archives are viewable at: > //www.freelists.org/archives/si-list > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu