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Electronics => Repair => Topic started by: Garywoo on August 23, 2018, 01:49:17 am

Title: SMD Component Identification Assistance
Post by: Garywoo on August 23, 2018, 01:49:17 am
Hi everyone,

I've never had to decipher an SMD code before, so I thought I'd run my thoughts past you bunch of helpful folks to make sure I'm on the right track.

I've identified a failed SMD transistor (shorted) on an LED light strip controller PCB. The transistor outputs directly to the LED strip. There are 5 on the board, one for each colour channel (one removed in photo for testing).
The board runs on 24v from a CV 0.83A 20W power supply.

I'm pretty sure the component is a SOT-23 package. Length and width seem about right.
The markings on the component are WKC 72. I'm not quite sure which part of the marking is significant. I used this codebook (http://www.marsport.org.uk/smd/mainframe.htm) as a reference. Initially I thought the WKC was the important part. This lead me to BCR119
(https://i.imgur.com/nO3nTSy.png)

However I'm not sure if this is right. If the 72 is the important part, then it could be 2N7002
(https://i.imgur.com/mIN7KER.png)

The silkscreen designates the component with an M. MOSFET? I'm thinking the 2N7002 is most likely correct. Am I correct in my assumption?
Looking at octopart (https://octopart.com/search?q=2N7002&start=0&specs2.2.values=SOT-23), they come in a variety of continuous drain currents. What would be a safe choice for my application?

(https://i.imgur.com/N5o7CCp.jpg)

Thanks for any help or advice ;D
Title: Re: SMD Component Identification Assistance
Post by: SMdude on August 23, 2018, 07:39:48 am
I think you nailed it with bcr119.
Check page 10 of the datasheet, it has a breakdown of the smd code..
https://www.infineon.com/dgdl/Infineon-BCR119SERIES-DS-v01_01-en.pdf?fileId=db3a30431428a37301143f643b380286 (https://www.infineon.com/dgdl/Infineon-BCR119SERIES-DS-v01_01-en.pdf?fileId=db3a30431428a37301143f643b380286)

Cheers
Title: Re: SMD Component Identification Assistance
Post by: Garywoo on August 23, 2018, 08:07:16 am
Nice find SMdude!

I was a little unsure about the max collector current of 100mA with the bcr119, as that seemed a little low to me, so I was leaning towards the 2N7002 which comes in variants from 115mA to 1.4A.
Title: Re: SMD Component Identification Assistance
Post by: SMdude on August 23, 2018, 10:48:03 am
If you're ever unsure, pop an ammeter in and see what current the load draws, then it will be easier to sleep at night!
Title: Re: SMD Component Identification Assistance
Post by: Garywoo on August 24, 2018, 01:07:50 am
I tested the current between one channel of the LEDs and the transistor, and read 315mA at full brightness.
As I mentioned, the BCR119 has a max collector current of 100mA. It's looking unlikely that it's a BCR119.

Does anyone else concur that it could be a 2N7002?
Title: Re: SMD Component Identification Assistance
Post by: amyk on August 24, 2018, 01:57:23 am
Not BCR119, nor 2N7002. If you Google pictures of those you will see why.

The former has literally "WKs", like this one (http://www.eric1688.com/product.aspx?id=355509) where you can just make out the marking "WKs". Not WKC.

The latter does not have the "72" at vertical, and their mark is "12W". You can see themhere (https://detail.1688.com/offer/565491237719.html).

Now Google "WKC sot23" and you find... this (https://www.aliexpress.com/item/20PCS-LOT-PMV20ENR-SOT-23-MOSFET-N-CH-30V-SOT23-WKC-KC/32861711149.html). PMV20ENR (https://assets.nexperia.com/documents/data_sheet/PMV20EN.pdf). You will also find some other people asking what this part is, on the same LED strip as yours (a Philips Hue lightstrip, I presume?) with the same conclusion:

https://www.mikrocontroller.net/topic/443091 (https://www.mikrocontroller.net/topic/443091)
http://elektronikforumet.com/forum/viewtopic.php?f=8&t=91868 (http://elektronikforumet.com/forum/viewtopic.php?f=8&t=91868)

Philips/NXP/Nexperia are known to use the 3-letters + vertical date/batch code scheme. Here's a previous repair thread with a board full of them. (https://www.eevblog.com/forum/repair/repair-of-seat-occupancy-sensor/)
Title: Re: SMD Component Identification Assistance
Post by: Garywoo on August 24, 2018, 01:38:52 pm
Fantastic info, thanks so much amyk!
You are right about it being from a Philips Hue Lightstrip.

PMV20ENR looks to be a good match.
In that second forum link. I saw a suggestion of IRFML8244TRPbF (https://datasheet.octopart.com/IRFML8244TRPBF-Infineon-datasheet-10898597.pdf) as an alternative. They are a little cheaper, and since I have a number of PCBs to repair, and require ~50, it's a decent saving. Is this a sensible alternative?
Title: Re: SMD Component Identification Assistance
Post by: Garywoo on August 30, 2018, 10:56:40 am
Ended up purchasing the PMV20ENR's. They worked perfectly.

Thanks again for the help!