Need help in identifying a diode like looking capacitor on a BEC board - Page 1
Forum section: electronics / repair

author: Ashwin619
author_rank: Regular Contributor
timestamp: August 23, 2023, 03:30:05 pm
content: Hello all,I could use some suggestions regarding a component that I am trying to identify,The PCB happens to be a single-channel Buck converter (BEC) that is used in drones and similar applications. It has a variable o/p (via switches) and can source up to 10A. The first component happens to be at the o/p along with filtering caps and has a designator that of a capacitor with a package similar to a diode (sod-123).The marking on it appears to be 1C (not 100% sure). After desoldering (probably got destroyed in this process) the component seems to have become an open circuit (resistance OL, no diode Vfd, and no capacitance).I am wondering if this is some kind of voltage suppression capacitor or something similar. Can't possibly be a tantalum due to the absence of any kind of polarity band.I would appreciate it if someone could shed some more light on the identity of this component.Regards,Ashwin619.

author: Ashwin619
author_rank: Regular Contributor
timestamp: August 25, 2023, 04:50:43 am
content: Hello all,I have moved this topic from Projects to repairs. Could really use some suggestion from you guys.Regards,Ashwin619.

author: fzabkar
author_rank: Super Contributor
timestamp: August 25, 2023, 05:04:22 am
content: D1 appears to be a TVS diode (Vishay / General Semiconductor).C10, by comparison, appears to be too small to be a protection device.I would expect that C6 and C7 provide the bulk of the low frequency filtering, C8 and C9 handle higher frequencies, and C10 handles the very high frequencies. That said, I have only ever encountered "two stage" filtering, not three. :-?

author: Ashwin619
author_rank: Regular Contributor
timestamp: August 25, 2023, 06:24:13 am
content: Hi,You are right w.r.t D1, it's a bidirectional TVS from Vishay (SMAJ75CA) with a Vbr somewhere near to 83.3V,The C10 is the one in question. The package seems quite unconventional for a capacitor. I wonder if such a capacitor is even needed for decoupling high frequency component. The MLCC's (~40uF each) next to it should probably be more than sufficient for such an application. There might be possibility that the designer must have messed up with the designator and this might be a bidirectional TVS. But then again, the small size doesn't really support this reason.Regards,Ashwin619.

author: fzabkar
author_rank: Super Contributor
timestamp: August 25, 2023, 06:52:26 am
content: Could it be something like this??? (I don't think so)Bidirectional ESD protection diode:https://www.vishay.com/docs/84137/vcut07b1hd1.pdf

author: gamalot
author_rank: Super Contributor
timestamp: August 25, 2023, 05:22:37 pm
content: Quote from: fzabkar on August 25, 2023, 06:52:26 amMaybe it's a CDSOD323-T18C, but I couldn't find any picture of it. I found the picture of CDSOD323-T03C, the marking on it is very similar to the one in the OP's picture.https://www.bourns.com/docs/Product-Datasheets/CDSOD323-TxxC.PDF

author: Ashwin619
author_rank: Regular Contributor
timestamp: August 28, 2023, 06:02:50 am
content: Quote from: fzabkar on August 25, 2023, 06:52:26 amI doubt whether this is the one. The package is slightly bigger than that (most probably a SOD-123 or something similar).

author: Ashwin619
author_rank: Regular Contributor
timestamp: August 28, 2023, 06:19:06 am
content: Quote from: gamalot on August 25, 2023, 05:22:37 pmHi,I believe you are correct; this is the one. The T18C one is a Bidirectional TVS with a Vbr of 20V (the board's max Vout is 16V) so it makes sense. The package also matches (my bad it was not SOD-123 rather its SOD-323). I wonder what requirements lead to the selection of such a miniscule package for a TVS. Maybe the transients expected on such rails will not be that long. Nevertheless, I'll go ahead with this one.Thanks @gamalot, @fzabkar for your suggestions.Regards,Ashwin619.

author: SimplyElectronics
author_rank: Contributor
timestamp: August 28, 2023, 03:37:13 pm
content: If you can get the dimensions and narrow down the package, you might find it in these results:https://www.repaircompanion.com/smd_code_search/1c?package=&pin_count=2SOD-123 isn't in the list if it is "1C". I don't see the marking being "IC".

author: fzabkar
author_rank: Super Contributor
timestamp: August 28, 2023, 04:45:45 pm
content: Quote from: Ashwin619 on August 28, 2023, 06:19:06 amMaybe the intention is to clamp incoming ESD rather than clamping overshoot/spikes (?) at the output.

author: Ashwin619
author_rank: Regular Contributor
timestamp: August 29, 2023, 06:49:02 am
content: Quote from: SimplyElectronics on August 28, 2023, 03:37:13 pmThis seems like quite a handy tool. Thanks for sharing !!!

author: Ashwin619
author_rank: Regular Contributor
timestamp: August 29, 2023, 06:56:28 am
content: Quote from: fzabkar on August 28, 2023, 04:45:45 pmThat may be the case.