Reverse engineering/deciphering mystery buck boost circuit - Page 1
Forum section: electronics / projects

author: Hiemal
author_rank: Regular Contributor
timestamp: March 14, 2019, 02:29:56 am
content: Hi all!I bought thishttps://www.ebay.com/itm/173274739510module a few weeks ago and have been playing around with it, and decided to reverse engineer what I could...And I can't, for the life of me figure out how this is supposed to work. Is it a positive to negative buck boost? Is there some black magic stuff going on here?I double checked and triple checked all of the connections to make sure and I'm certain this is how it's hooked up. Any ideas or reference circuits that could show me how this is supposed to work? I can't figure out why the one mosfet has its gate tied to one side of the inductor...Additionally, the main controller IC has the top sanded off... so I can't look up whatever is controlling this thing unfortunately. The listing states it runs at 150 kHz. The inductor value is about 18 uH. It's a SOIC-16 package I believe.(note I did swap out the original FETs and diodes with ones I know are genuine and are much better rated parts)

author: wasyoungonce
author_rank: Frequent Contributor
timestamp: March 14, 2019, 03:39:28 am
content: https://m.aliexpress.com/item/32918425265.html?trace=wwwdetail2mobilesitedetail&productId=32918425265&productSubject=CIRMECH-Constant-voltage-constant-current-adjustable-automatic-lifting-and-lowering-power-supply-board-CV-CC-8AIt’s buck and boost CC and CV 8 A out 1.25v-30v out. Meaning it can operate as either buck or boost mode depends on input I think the drawing is missing something. The Chinese designer probably has many variants of this same cct just different capacities. I cannot find a cct but guess earlier or other variants operate on similar principle.

author: aiq25
author_rank: Regular Contributor
timestamp: March 14, 2019, 03:49:56 am
content: Looks like this configuration:https://upload.wikimedia.org/wikipedia/commons/e/e0/Basics_of_the_4-switch_buck-boost_converter.png

author: Hiemal
author_rank: Regular Contributor
timestamp: March 14, 2019, 03:53:04 am
content: Did some more digging and found this schematic for a similar module, that uses the same chip;Chip is labeled SH1215CS. Seems to be the same exact one used in my module, but I can't find any datasheet on it.This page (when google translated) suggests it's the same chip as a WD3002. Currently trying to find info on that chip as well.

author: Hiemal
author_rank: Regular Contributor
timestamp: March 14, 2019, 04:02:11 am
content: More digging;It's an LTC1625 that's had its marking scratched off. Checked over the datasheet and compared it to connections on the supplied schematic and it all lines up.Weird. So, the WD3002, and the SH1215CS are "rebranded" LTC1625 chips.Edit:Even found a reference design for this.

author: wasyoungonce
author_rank: Frequent Contributor
timestamp: March 14, 2019, 05:18:08 am
content: Quote from: Hiemal on March 14, 2019, 04:02:11 amHaha you mean a copied IC from China! Who’d have thought.In reality these devices are pretty nifty and efficient.

author: rick00
author_rank: Newbie
timestamp: July 05, 2023, 04:31:37 pm
content: Quote from: Hiemal on March 14, 2019, 03:53:04 amHello,please can you share the link to the schametic with me?I have bought an similar module with cloned LTC1625 chip on it.They used a shunt resistor in ground line which I have to eliminate for my purpose.I hope the schematic willl help me realize if I simply can shortcircuit it.Thanx

author: rick00
author_rank: Newbie
timestamp: July 07, 2023, 10:26:47 pm
content: I found the link by myself after digging the past days...unfortunately the schematic is only a low res picture:http://www.shenghan.net/keji/1693.html