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SMD code T4S 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.

1 part in SOT-23 is printed T4S

Not sure which one you have?

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

  • BSN20BKSOT-23N-channel MOSFET, 3 pins, NXPN-channel MOSFET3 pinsNXP
    What it is
    N-channel MOSFET
    Maker
    NXP
    Package
    SOT-23
    Pins
    3
    Source
    Published code list

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

  • 3 more parts have no package on record. Nothing rules them out, so they stay.
    • PJSD12ESD protection diode, PanjitESD protection diodeNot recordedPanjit
      What it is
      ESD protection diode
      Maker
      Panjit
      Package
      Not recorded
      Pins
      Not recorded
      Source
      Manufacturer datasheet

      Is it dead? The meter test is below: TVS or ESD protection diode.

      Datasheetfor PJSD12, opens in a new tab
    • TVD12WESD protection diode, Taitron ComponentsESD protection diodeNot recordedTaitron Components
      What it is
      ESD protection diode
      Maker
      Taitron Components
      Package
      Not recorded
      Pins
      Not recorded
      Details
      SMD TVS Arrays (Two Terminals)
      Source
      Manufacturer datasheet

      Is it dead? The meter test is below: TVS or ESD protection diode.

      Datasheetfor TVD12W, opens in a new tab
    • BFP640FESD4 pins, InfineonNot recorded4 pinsInfineon
      What it is
      Not recorded
      Maker
      Infineon
      Package
      Not recorded
      Pins
      4
      Source
      Published code list

      Is it dead? The meter test is below: This part.

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.

TVS or ESD protection diode

Diode range, from the protected line to ground, part lifted if you can.

Working, it reads

A one-way part reads about 0.6 to 0.8 V forward and open in reverse. A two-way part reads open both ways. Arrays with several lines read as the datasheet's diagram draws them.

Dead, it reads

  • From the line to ground, the same reading both ways, near 0 V with a continuous beep: shorted.
  • A reading both ways on a one-way part: leaky.
  • A one-way part open both ways: failed open.
On the board
, a line reading shorted to ground can be this part or anything else on that line. Lift it: if the short goes with it, it has failed.
Compare:
The same part on the next line or connector pin is the healthy reading to compare with.
Watch for:
A two-way part reads open both ways when it is good, exactly like one that has failed open. The meter cannot tell them apart; an identical part on the next line can.

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

This part

Diode range and ohms range, part lifted.

Working, it reads

Depends on what it is. The datasheet, or an identical part, says.

Dead, it reads

  • Between two pins, the same reading both ways, near 0 V with a continuous beep: shorted.
  • Open between every pair of pins: failed open, or a part that reads open when working.
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.

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 T4S

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 T4S

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

Did you find your part?

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