Quick Decision: Start Here

Step 1 — which side of the load? Low-side switching (load to ground) uses an N-channel. High-side switching (load from a positive rail) uses a P-channel, or an N-channel plus a bootstrap driver.

Step 2 — What does the rail actually do? Battery and 5V logic rails live in the 20V class; 12V/24V industrial and automotive rails need the 30V class.

48V, POE and telecom rails need the 100V class — where the NCE0102 and NCE0103Y live. The 60V P-ch (NCE2309) covers high-side positions above 30V on low-voltage industrial rails.

Step 3 — how much current, honestly? Under ~1A continuous with logic drive, stay in SOT-23. Above that, the power wall wins: a 2–5A real load belongs in SOP-8 or TO-252, no matter what the SOT-23 sticker says.

Why does every sticker oversell? Because the ratings are 25°C, single-pulse conditions — and your board is neither.

The SOT-23 MOSFET Family at a Glance

N-Channel, 20V class — battery and 5V logic rails:

N-Channel, 30V class — the logic-level mainstream for 12V rails:

N-Channel, 100V class — the 48V lane that SOT-23 rarely offers:

P-Channel — high-side and battery-rail switching:

How to Choose the Right SOT-23 MOSFET — Decision Tree

Read it in one pass: side of the load → rail voltage → honest current. The voltage class decides which family; the ~1A honesty gate decides whether SOT-23 is even the right package.

The SOT-23 power wall — sticker current vs the honest ~1A continuous line:

Bar length is the sticker — and the honest continuous line of all four is the same ~1A, because the package is the same. ~1–1.5W is all a SOT-23 can shed. The sticker sells pulse headroom and R_DS(on); choose on those, not on amps.

Family Deep Dives

The 20V N-ch class: battery and 5V-logic rails

SI2302DS, AP2302GN and NCE2302 cover loads on single-cell to 5V logic rails with margin for the ringing of hot-swapped connectors. For battery protection and load-switch duty at tens to hundreds of mA, this class is where BOM cost lives.

The 30V N-ch class: the logic-level mainstream

AO3400A defined the slot; NCE3400 answers it with R_DS(on) down to 22mΩ at 4.5V, and NCE3400X trades a little current for a lighter gate. On a 12V rail with a 5V or 3.3V logic gate, the 4.5V-guaranteed row is the spec that makes the part defensible.

The 100V N-ch class: the 48V lane

NCE0102 and NCE0103Y exist because 48V POE and telecom boards keep killing 60V and current-starved 100V small-signal parts. Same SOT-23 footprint, 100V rating, and honest continuous lines near ~1A — with the 0103Y adding a 20A pulse for inrush-heavy duty.

The P-ch lanes: high-side and battery paths

For high-side switching, the P-ch family carries the load above ground: SI2305DS at the exotic -8V end for 5V rails, the 20V and 30V lanes (SI2301DS, IRLML6402, NCE2305, AO3401A, AO3407) for battery paths, and NCE2309 at -60V for high-side positions above 30V rails — a rare voltage in SOT-23 P-ch.

The Most Common Mistakes When Selecting SOT-23 MOSFETs

Mistake 1: Choosing by the sticker current. A 3A SOT-23 sticker at 160mΩ burns 1.44W at its own rating — already 96% of the package's 1.5W wall. The honest continuous line of nearly every SOT-23 MOSFET lands near 1A, regardless of whether the sticker says 2A, 3A, or 5.8A.

Mistake 2: Ignoring the drive-voltage rows. If your gate comes from 3.3V logic, a part whose R_DS(on) is only guaranteed at 10V is a part running unguaranteed. Look for a 4.5V row — or drive at 10V — before you trust the resistance number.

Mistake 3: Assuming all SOT-23 MOSFETs share a pinout. The common order is 1-G/2-S/3-D, but it is not universal. A footprint library from one manufacturer and a part from another have shipped boards with the drain on ground — and the body diode then conducts forever.

Mistake 4: Forgetting the voltage class is a safety margin, not a suggestion. A 30V part on a 48V rail fails at the first transient. The 100V SOT-23 class exists precisely because of that gap.

Mistake 5: Buying the cheapest part without a test plan. In SOT-23, the counterfeit and re-mark problem is severe — fake parts pass visual inspection and fail the R_DS(on) bench check.

SOT-23 MOSFET Pricing Reality

Volume pricing for SOT-23 MOSFETs typically runs $0.02–$0.15 per unit depending on voltage class, R_DS(on) and brand — the 100V parts and the branded HEXFETs sit at the top of the band.

At these prices the BOM difference between a 20V and a 100V part is often cents; the board-rework difference is dollars.

Contact ICMASS for current pricing and availability on any model in this guide — volume pricing on the NCE family keeps the 100V lane in the same conversation as the 30V classics.

How to Spot Counterfeit SOT-23 MOSFETs

Test R_DS(on) at the datasheet condition and check the threshold band. Genuine parts hold their published max; fakes and re-marks scatter widely and run hot at a fraction of the rated current.

A $20 component tester catches most fakes in seconds — the R_DS(on) read across the actual pins is the whole game.

Buy from a source that tests lots, not from the cheapest reel. Marking alone is not evidence: SOT-23 markings are short codes that re-markers copy freely. The bench is the only honest referee.

Frequently Asked Questions

Q1: When is SOT-23 the right package for a MOSFET?

A: For switching, not for passing current. SOT-23 is right for low-side or high-side switching below ~1A continuous with logic-level drive — fans, relays, solenoids, load switches, signal-level switching. The package sheds roughly 1–1.5W; above that real line, SOP-8 or TO-252 earns its space.

Q2: What is the honest continuous current of a SOT-23 MOSFET?

A: Roughly 1A on a real board, whatever the sticker says. At 25°C, a 3A part at 160mΩ burns 1.44W against a 1.5W budget — 96% of the wall before ambient. Sticker currents are 25°C, pulse-class numbers; design the board against the power wall, not the sticker.

Q3: N-channel or P-channel — which should I use?

A: N-ch for low-side, P-ch for high-side — unless efficiency rules. N-ch parts have lower R_DS(on) per dollar and dominate low-side switching. High-side on a battery rail wants a P-ch for the simple gate drive; above a few amps continuous, an N-ch with a bootstrap driver beats the P-ch economics.

Q4: Why does the 4.5V drive row matter so much?

A: It is the guarantee your logic actually gets. A 4.5V row means R_DS(on) is specified at 4.5V — reachable from 5V logic. A 10V-only part conducts from 3.3V or 5V (thresholds are low) but its resistance is unguaranteed there. If the load is real, pick the guaranteed row.

Q5: Do I really need a 100V SOT-23 MOSFET?

A: Only if your rail or your ringing reaches it. On 48V POE, telecom and industrial rails, 100V is the honest class — 30V parts die at the first transient, and the 60V small-signal classics are current-starved. The NCE0102 and NCE0103Y fill exactly that gap in the SOT-23 footprint.

Q6: How does the 100V SOT-23 pair compare to the 2N7002 and BSS123 classics?

A: It outclasses both at 100V. The 2N7002 is 60V only. The BSS123 is 100V but carries ~170mA at several ohms. The NCE0102 is 100V with 2A and 229mΩ max — roughly ten times the current of a BSS123 in the same footprint — and the NCE0103Y adds a 20A pulse.

Q7: 20V or 30V class — how do I choose?

A: Match the class to the rail plus ringing margin. Battery and 5V logic rails sit safely in the 20V class. 12V and 24V rails need the 30V class for switching transients. When in doubt, the next class up costs cents and buys a lot of margin.

Q8: How do I verify a genuine SOT-23 MOSFET?

A: Bench-test R_DS(on) and threshold. Genuine parts hold their published max at the datasheet test condition and their threshold band. Counterfeits and re-marks scatter widely — sometimes 2–4× the resistance — and overheat under load. A component tester settles most parts in seconds.

Q9: What do I need for high-side P-ch gate drive?

A: The gate must reach the source rail — not logic ground. A P-ch turns on when V_GS goes negative; the pull-up or driver must reference the source (the rail), and a plain MCU pin needs a level-shift transistor. A 10k–100k pull-up to the source rail keeps the FET off during MCU reset.

Q10: NCE, AOS, Vishay or Infineon — which brand should I spec?

A: Spec the specs, then the supply chain. The voltage class, the 4.5V row, the R_DS(on) max and the gate charge are the real decision. NCE covers the same slots with tested lots and volume pricing; the branded parts carry their own test heritage and price. ICMASS stocks and tests the NCE family and cross-references the classics.

Internal Links — The Family on One Shelf

N-ch product pages: NCE0102 · NCE0103Y · NCE3400 · NCE3400X · NCE2302 · AO3400A · SI2300DS · SI2302DS · SI2304DS · AP2302GN · IRLML2803TRPBF

P-ch product pages: NCE2305 · NCE2305A · NCE2309 · AO3401A · AO3407 · SI2301DS · SI2305DS · IRLML6402TRPBF

Related guides: NCE0102 vs NCE0103Y vs NCE0110AK comparison · The Complete MOSFET Selection Guide (07-15) · NCE 100V TO-252 family pages