Help with current protection element ic (diode?) - Page 1
Forum section: electronics / beginners

author: algorithm
author_rank: Regular Contributor
timestamp: July 01, 2022, 10:36:11 am
content: So I now have 3 blown un10015's.1.5a 50vInternal resistance should be between 29-47mohmWhen I tested 2 before they went, I thought it was a transistor from the bottom cause 3 legs. It had .564 or so like a diode.Ive been testing transistors I have laying around but best Ive found on internal resistance forward is 5mohm.Anybody know how I can get the proper resistance there and a diode junction using another part?Or is there more to the internal circuit?Also thought about using a ptc thermistor? Wonder if that could work.

author: algorithm
author_rank: Regular Contributor
timestamp: July 03, 2022, 05:39:36 am
content: So theres the icp-n38. It is 50v 1.5a fusable or w/e, but internal resistance is 0.4 ohm or so. Not even k. So wouldnt that matter, if the internal resistance is so different?Had the idea to put a 39mohm resistor across externally. But doing it that way seemed to eliminate the internal resistance already there. Resistance across simply read the resistors value, omitting the diode.Btw I shelled out for unh1115s. But they were more than the psu is worth(or whole machine). At this point its personal or passion. Maybe just sentimentality.But I am curious if in a unobtainium pinch could be creative with what is easier/cheaper to get.

author: ebastler
author_rank: Super Contributor
timestamp: July 03, 2022, 06:55:09 am
content: You have not provided any context here. What are you trying to do? Where are these components meant to be used? What did you do to damage the UN10015? How do you know they are damaged?Also, you might be fundamentally misunderstanding what these components are and do. They act a bit like resettable fuses: Normally they have a very low resistance and let current pass through. Note that the UN10015 datasheet states 29 to 47milli-Ohm, that's 0.029 to 0.047 Ohm. But if the current exceeds a limit (which is defined by the design of the component, and stated in the datasheet), their resistance becomes high and they stop the current flow.These components have nothing to do with a diode or a transistor. While your UN10015 has three pins, the center one is not connected. ("n.c.", as stated in the datasheet you copied.) If you measure < 1 Ohm across the two active terminals, then the device is probably not damaged but just fine.As a general hint, you need to pay attention to capitalization here. "mOhm" means milli-Ohm, one thousandth of an Ohm. "MOhm" means Mega-Ohm, one million Ohm.

author: algorithm
author_rank: Regular Contributor
timestamp: July 04, 2022, 10:13:32 am
content: Thank you for helping me. Yeah I misunderstood. But that helps.Well I have 3 psus. Each was designed using the uhn1115 as pr1.I had tested them in diode mode. And then after last powering the last psu the diode test changed to a beep. Interesting because I dont know how I got a diode junction reading but fairly sure I saw that twice.The last psu I worked on reads 20k on un10015. Thats also the one that did have a diode junction of .564 or so across un10015.The other 2 are 0.2-0.3im pretty sure I tested diode mode on the first psu as well.Guess if the fuse "tripped" that might explain how I saw that. The diode junction was against the output iirc.As for the psus no schematic. Thats why I have 3 psus. Trying to manage to get 1 working at least. All if possible. Trying to make a schematic in my mind. Ive looked at it nearly enough.Thanks again. That helped a lot for me to get the picture in this scenario.Looks like I only have 1 bad protect element at least.