I am having hard time in finding what this component is . It has 8 pins and a marking on it says 500. It has 2 pins on bottom on each side and two on each top side.

On the board 2 pins on left bottom are as inputs and two on the right are used as outputs.

I searched for it on SMD codeBook as well as this site but couldn't find anything.

I hope some one can help here. It is part of a rs485 circuitry on a board. There is another Sot23 marked W216j I couldn't find this also. This is how they are connected. Please ignore the pin names on SOT23/IC1

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I have got the product and its the exact one by help provided by @Tom and @jp314 This is the product that was marked 500, The SOT package is quite lear but still I couldn't get the exact one.

  • 1
    \$\begingroup\$ The SMD codebooks I know of only contain info about components that happen to have a datasheet in English. There's however a fairly vast swath of components that have datasheets only in Chinese these days... if they are public at all. Sometimes it's easier to figure out what such a component does from the circuit. \$\endgroup\$ Commented Nov 28, 2015 at 17:58

2 Answers 2


I'm going to post this as an answer as I've seen the same type of question come up multiple times, and for each I've basically commented the same thing:

It's pretty much impossible to identify this sort of component unless you either have a BOM of the circuit, schematic, or already know what they are.

If you have some rough idea of the function they perform and it is something more complex than say a discreet transistor, then you may be able to identify them by searching for parts with that functionality on manufacturer websites and comparing marking codes from datasheets. But really this is a shot in the dark.

Having said that, based on your description, the SOT23 package device is almost certainly some sort of TVS device - used for ESD and Transient (EFT) protection on inputs. These are quite common on RS485 devices as per this TI application note. There are components like this specifically for RS485 in the same package like this one. Doesn't have the same marking code, but will like have the same function.

The other package as pointed out by @jp314 in the comments is likely some kind of line filter. As you have found WE has some in a similar package with similar markings, so this is quite clearly what it is. In fact looking at the datasheets from that link, this part has a marking of 500 and looks identical to your picture.

For both of these parts, it could be inferred from the circuit what the parts do. Finding a datasheet for the exact part is the hard bit.

  • \$\begingroup\$ Is it a common-mode filter ? Can you measure the resistance between the 2 top pins (one one each side) ? Between the two lower ones ? If it appears low (< 10 ohm), then it's probably a choke (inductor). \$\endgroup\$
    – jp314
    Commented Nov 26, 2015 at 22:10
  • \$\begingroup\$ @jp314 the resistance is somewhat 1 Ohm \$\endgroup\$
    – dmSherazi
    Commented Nov 27, 2015 at 14:32
  • \$\begingroup\$ @jp314 katalog.we-online.de/de/pbs/WE-SLM \$\endgroup\$
    – dmSherazi
    Commented Nov 27, 2015 at 15:06
  • \$\begingroup\$ @dmSherazi something like that, yeah. \$\endgroup\$ Commented Nov 27, 2015 at 15:25
  • \$\begingroup\$ @dmSherazi in fact the datasheet is likely this - says in it that the marking is 500. \$\endgroup\$ Commented Nov 27, 2015 at 15:29

There are 2 windings on the toroidal transformer. The top connections are 1 coil, the bottom are the other. For signals that pass through differentially, the windings 'cancel'; for common-mode signals, the windings 'add' and tend to limit the currents.


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