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SMD code 357 in SOT-23

Marking codes are not standardised, and the same code is reused by unrelated makers for unrelated parts. Below is every part in our tables printed with it, and any printed with a code that is easy to misread as it, from the manufacturers' own marking tables and published code lists.

3 parts in SOT-23 are printed 357

Not sure which one you have?

Answer up to 4 quick questions and these 3 parts are ranked, with a meter test that settles it. It works on a dead part too.

all SOT-23, 3 pins. What differs:

  • FDN357NSOT-23N-channel MOSFET, onsemiN-channel MOSFETonsemi
    What it is
    N-channel MOSFET
    Maker
    onsemi
    Package
    SOT-23
    Pins
    3
    Details
    MOSFET - N-Channel, Logic Level, Enhancement Mode
    Source
    Manufacturer datasheet

    Is it dead? The meter test is below: N-channel MOSFET.

    Datasheetfor FDN357N, opens in a new tab
  • MMBT357-CSOT-23Transistor, SeCoSTransistorSeCoS
    What it is
    Transistor
    Maker
    SeCoS
    Package
    SOT-23
    Pins
    3
    Details
    Bipolar transistor
    Source
    Manufacturer datasheet

    Is it dead? The meter test is below: Bipolar transistor.

    Datasheetfor MMBT357-C, opens in a new tab
  • NDS357NSOT-23onsemiNot recordedonsemi
    What it is
    Not recorded
    Maker
    onsemi
    Package
    SOT-23
    Pins
    3
    Details
    n-ch mosfet 2.5Apk 30V
    Source
    Published code list

    Is it dead? The meter test is below: N-channel MOSFET.

Is it dead? One meter test per kind

Parts of the same kind are tested the same way, so each test is here once. Each part above points to its own.

N-channel MOSFET

Diode range, part lifted. Test drain to source first, then short gate to source and test again.

Working, it reads

Red probe on the source, black on the drain: about 0.4 to 0.9 V, the body diode. Open the other way. The gate reads open to both other pins, both ways.

Dead, it reads

  • Drain to source the same both ways, near 0 V with a continuous beep, and still so after shorting gate to source: shorted. The classic failure.
  • The gate reads low to source or drain: gate shorted. Often all three pins end up shorted together.
  • No body diode at all: failed open.
On the board
the gate usually has a resistor to the source, so gate to source reads that resistor, which is not a fault. A drain short can be the load. Lift a leg to be sure.
Compare:
If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.
Watch for:
The diode range can charge the gate enough to turn the part on, and then drain to source reads near 0 both ways on a good part. Short gate to source and test again before you condemn it.

A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.

Bipolar transistor

Diode range, part lifted or its base leg off the pad.

Working, it reads

From the base, one probe colour reads about 0.6 to 0.75 V to the emitter and to the collector, and open the other way round. Collector to emitter reads open both ways.

Dead, it reads

  • Collector to emitter the same both ways, near 0 V with a continuous beep: shorted. The commonest failure.
  • The base the same both ways to another pin, near 0 V or a middling value: a shorted junction.
  • Only one junction reads, or none: a junction has failed open. It then looks like a diode.
  • A reading the wrong way round, where it should be open: leaky.
On the board
this is a first look only: the meter reads every path between those pins, and a short can be a neighbour. Lift one leg before you condemn it.
Compare:
If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.
Watch for:
A pair of diodes with a common pin reads just like a transistor, and some transistors carry a built-in diode or resistor. The datasheet says which.

A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.

Printed with a code easy to misread as 357

One character differs, and it is one that is easy to confuse under a lamp. Each code has a page of its own.

Codes that begin with 357

For a marking with its end worn or burnt off. Each code has a page of its own.

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