POE pcb not standards compliant- how to fix? - Page 1
Forum section: electronics / beginners

author: Purduephotog
author_rank: Regular Contributor
timestamp: January 26, 2020, 08:23:53 pm
content: I've been assembling a POE camera and the typical POE pcb from aliexpress has worked fine- for everything except one switch. That switch puts out -53.6V, as opposed to the -48V on nearly all the others I own.The cheap Ali board (of which I've only ever found this type) apparently can't handle it. I've just finished probing it and it produces 16.8 or 17.0V when powered at -54V. So my gear isn't working. Other equipment that is POE compliant works fine in that switch, so it's obviously a defect in the design that it isn't handling the regulation properly.I've managed to track down the circuit from the manufacturer-http://www.silan.com.cn/UploadPic/20190620161725883.pngThe POE pcb-https://www.aliexpress.com/item/32874259693.htmlI can't read the language, however I see some places that might have an impact- there's a 3.0V listed (of which I haven't found yet by probing) and there are a pair of resistors to feed an op-amp.Looking at the circuit (I'll try to put up photos), the pin 7 goes to ground via a capacitor, which matches the block diagram. However without the language I fear I'm not going to be able to decipher much.Seeing FB as 'feedback', there is a resistor bank of approximately 7.9K connected to pin 3 (as well as a capacitor I can't measure in circuit).Were I to hit this with a scope, what would be a good place to start? Am I understanding the diagram the right way?Thank you

author: amyk
author_rank: Super Contributor
timestamp: January 27, 2020, 03:08:50 am
content: What's the actual part number of that IC?

author: Purduephotog
author_rank: Regular Contributor
timestamp: January 27, 2020, 09:52:42 pm
content: SD4932B - that's the sad part. That's the PN of the DC/DC transformer AND the IC chip. The only place I've found the documentation is that PNG, which was a surprising post on a forum on Bao.

author: shuum
author_rank: Newbie
timestamp: February 19, 2021, 08:18:56 am
content: Quote from: Purduephotog on January 26, 2020, 08:23:53 pmPlease renew circuit picture link please

author: LateLesley
author_rank: Frequent Contributor
timestamp: February 19, 2021, 09:40:47 am
content: Well I had a wee look for the SD4932B, and I did find a pic of the circuit for it.So I dunno if that will be of help? Looks like it's meant to be good to 57V.

author: shuum
author_rank: Newbie
timestamp: February 19, 2021, 09:48:06 am
content: Great thnx!!!Unfortunately, this is not a diagram from the modulehttps://www.aliexpress.com/item/32874259693.htmlfrom the post above, I'm looking for it.

author: Purduephotog
author_rank: Regular Contributor
timestamp: March 17, 2021, 11:43:24 am
content: Quote from: shuum on February 19, 2021, 09:48:06 amSadly I never had the circuit for the POE board; I was specifically referencing the chip on that board (if memory serves).

author: cjheath
author_rank: Contributor
timestamp: October 10, 2021, 06:16:43 am
content: I came across this thread while exploring other PoE splitters. I don't know if this info is too late to be helpful.The SD4932 is made by Silan. The English webpage for it is here and by submitting your email you can get the datasheet:http://www.silan.com.cn/en/product/details/2893.htmlThe same part number is on the transformer, but that's clearly wrong. Typical transformers used with this chip are PM3812R, as seen here:https://www.aliexpress.com/item/1005002768318128.html