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I’m trying to replicate something I got a few years ago for practical use and I found every component except for this one. It says WL BD on the package and measures 2.58x1.53mm (LxW) and around 1.3mm tall. It has a line towards the 100 ohm resistor leading me to believe it is a diode. I measured the voltage with the diode function on my meter and found it to be 0.352V. Any clue what component it could be?

Thanks!enter image description hereenter image description here

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It will be some form of diode.

Could be a Zener or TVS (transient suppression diode). The very low forward voltage suggests a Schottky diode, however your measurements could be skewed by the rest of the circuit, plus no idea what current your measurement is passing through the diode. Measuring the reverse voltage would be interesting, but that would be risky.

Zener is quite likely based on the circuit.

Based on the dimensions, you have a SOD123 package (typically 1.55mm x 2.65mm).


Decoding the marking is difficult without knowing more about the part. For example, BD could make it a 7.5V Zener diode (PDZ7.5BGW). Alternatively, WL could be a 15V Zener diode (BZT52C15).


A very likely candidate is a Diodes Inc. 18V Zener, specifically BZT52C18. From the datasheet it is marked as follows:

Complete Marking of BZT52C18

Notice the orientation of the markings.

First you have the bar as expected.

Then a two digit code. In your case "WL" which corresponds to 18V per the following excerpt from the full table:

Code Marking of BZT52C18

Then you have a two digit date code placed at a 90 degree angle. In your case BD which decodes as 2014 (B) December (D).

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  • \$\begingroup\$ Thank you for the information. It seems like the BZT52C18 looks the part. I will order this. I would've been searching for hours. Thanks so much \$\endgroup\$ – XxLogo Jan 26 at 0:40
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gate-to-source on a MOSFET, almost certaily a zener diode, nothing else makes sense in that location

http://static6.arrow.com/aropdfconversion/b99eb206e21a0aadd3b3bd94e3243174ac46775b/bzt52.pdf

perhaps BZT52B15, 15V

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    \$\begingroup\$ Think above person got it dead on the nail. However, I appreciate you taking the time out to reply. Can't wait to build this to see how it works \$\endgroup\$ – XxLogo Jan 26 at 0:49

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