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I have a small SOT-23 (3 pins, transistor-like) device that burned out (shorted between 2 pins). I need to identify it so i can replace it, but i can't find the code at all. The code is: SE and a simbol like a horizontal "P". Like this image:

enter image description here

Here's a picture of the device, although i don't think it will help much:

enter image description here

I'm not sure if it's a transistor, FET or diode.. It belongs (apparently) to a driver circuit for a P-Channel Power Mosfet, but that's all i can share because the circuit is almost impossible to follow.

Looked the code up on many webpages and can't find anything but a "2SC4703" RF transistor, but it's definetly not one suited for the actual circuit.

Any help would be apreciated.

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  • \$\begingroup\$ A photo could help. \$\endgroup\$
    – Eugene Sh.
    Mar 21, 2017 at 17:29
  • \$\begingroup\$ Picture of the SOT-23 device would greatly help solve your issue. \$\endgroup\$
    – 12Lappie
    Mar 21, 2017 at 17:37
  • \$\begingroup\$ Well.. this photo is not very helpful :) We can't see what is written there.. \$\endgroup\$
    – Eugene Sh.
    Mar 21, 2017 at 17:58
  • \$\begingroup\$ @EugeneSh. Really... i'm telling you exactly what it says.. checked by 3 different people and with a microscope... If the only analisis here is wheter i'm blind or a liar it is not very helpfull \$\endgroup\$
    – ndelucca
    Mar 21, 2017 at 18:01
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    \$\begingroup\$ it's connected to the gate of a p channel mosfet \$\endgroup\$
    – ndelucca
    Mar 21, 2017 at 18:14

1 Answer 1

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It is most likely a Schottky barrier diode to accelerate the turn-on/turn-off speed of the gate of the PMOS. From the information given, it is hard to point on what consumer it is actually from. We would need more details for this. But what you could do is unsoldered the part and perform a few test to confirm my hypothesis.

Apply a small voltage (0.5V) and put a small load on either pin on the side with two pins. See if it conducts. Apply a larger voltage (2-5V) and look at the voltage drop of the diode (if it is indeed a diode).

You could also put the part on a curve tracer to see the characteristics like the breakdown voltage and the forward voltage. It is either two Schottky barrier diodes in parallel or a single one as shown below:

enter image description here enter image description here enter image description here

For a PMOS device, I would expect the diode to be arrange like the middle picture. Either single or double.

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  • \$\begingroup\$ If not for the following list i found, i would have marked this as the answer, but i must ask: I found this list from 2007 (of course, not a very reliable source: google): caxapa.ru/thumbs/588912/smd-codes.pdf, that leads to this device: infineon.com/dgdl/… . Is there a tipical p-mosfet drive circuit that would use a pnp transistor like the one on the list (the code in the list related to the SE marking on my original device) \$\endgroup\$
    – ndelucca
    Mar 22, 2017 at 14:09
  • \$\begingroup\$ the list apparently comes from turuta.md \$\endgroup\$
    – ndelucca
    Mar 22, 2017 at 14:21
  • \$\begingroup\$ @ndelucca Have you found what part it is? \$\endgroup\$
    – 12Lappie
    Mar 24, 2017 at 14:06
  • \$\begingroup\$ I wasn't sure this could be a diode, so i took another step. I looked everywhere on the board until i found another part with the same code...which i did!, so i took it out and tested it, it turned up to be a PNP diode, furthermore, it appears that this mosfet is being used to drop from 24Vdc to 8 - 9 Vdc, to power some buck converters.. I still don't know the specifications for the transistor, i seems to me that it's not a simplre 30mA transistor, i still dont know how to find this out.. \$\endgroup\$
    – ndelucca
    Mar 27, 2017 at 11:37
  • \$\begingroup\$ Alright, nice findings! Testing a PNP Mosfet can be done easily. Essentially, you could put your Mosfet through a sequence of tests to find out some of the main specifications such as Vt, Vds max, Id max, and so on. I would say begin by identifying the pinout of the package and then find the threshold for the gate voltage. After that, try establishing some type of Vd/Id characteristics curve with different Vg. \$\endgroup\$
    – 12Lappie
    Mar 27, 2017 at 12:14

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