I'm trying to figure out how a PCB works (that I took out of something). I'm going through and looking at the different components, and I've identified a handful of parts, but I'm totally stuck on this one. It is near a few capacitors, but it has no uF written on the side, and the packaging doesn't look like a capacitor, although the general shape is the same, so I don't think it is a capacitor, though it could be. The outside has a rubbery texture to it.

Photo #1 of unknown component

In the photo above, it says "E487" (the seven is on the corner - I'm pretty sure it is a seven, but perhaps not)

Photo #2 of unknown component

The underside of the PCB. I've outlined in red where I think the component is connected (not totally sure, though)

Underside of PCB

Sadly, searching for "e487 datasheet" didn't yield anything helpful. What is this strange component?

  • 2
    \$\begingroup\$ reference designation code: 'L' is for inductors. 'Q' for transistors. 'M' sometimes used for MOSFETs (a type of transistor). 'R' for resistor. 'C' for capacitor. 'U' for any type of integrated circuit, whether an op-amp or a fancy CPU on a laptop or cell phone. 'J' and 'P' for jacks and plugs and headers (kind of used interchangeably). 'Y' for crystal oscillators or similar. 'F' for fuses. Transformers may be 'T' or 'TR'. An SCR may be 'SCR'. And diodes, whether light emitting or other are usually just 'D'. \$\endgroup\$
    – user57037
    Mar 24, 2022 at 3:43

1 Answer 1


It's an unshielded (drum type) inductor with shrink-wrap tubing around it to protect the winding.

Hence the designator "L2". Part of a switching regulator.


The PN8016 switching regulator chip here is a non-isolated DC-DC converter, so the output is not galvanically isolated from the mains. It is potentially lethal if you come into contact with the low voltage output or "GND" (or pretty much any other part of the circuit).

enter image description here

In this case, the DC input is several hundred volts.

  • \$\begingroup\$ Any ideas what it does? The circuit takes AC 120v and (I think) uses low voltage DC internally (probobly either 5, 12, or 3.3 - I haven't figured that out yet). Could that inductor convert the AC to DC? I know the basic components, but I'm not familiar with inductors. Also... is there some list of the different "designators", like L2, so I know what that designator means? Thank you! \$\endgroup\$
    – cocomac
    Mar 24, 2022 at 3:37
  • 1
    \$\begingroup\$ Typically takes one voltage (eg. 12V) and produces a lower voltage (eg. 5V) as is marked on the PCB. Check out the Wikipedia entry for "reference designator". \$\endgroup\$ Mar 24, 2022 at 3:42
  • \$\begingroup\$ The ic shown looks like a power supply chip. The 120VAC will go through a bridge rectifier and capacitor before getting to that chip. The inductor is part of the power supply. Show the whole board so we can assist more. \$\endgroup\$
    – Kartman
    Mar 24, 2022 at 7:27
  • \$\begingroup\$ @Kartman Spehro Pefhany mentioned that the board is potentially lethal if I touch it. I was hoping to be able to modify the board to take low-voltage directly (i.e., 5v), as opposed to having to rely on the AC power supply. Here are the photos of the PCB: note that the two thick red wires went to a non-polarized AC plug (120v) ibb.co/album/JqpYzG \$\endgroup\$
    – cocomac
    Mar 24, 2022 at 16:17

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